Textiles- History, Properties and Performance and Application 2014

CHEMISTRY RESEARCH AND APPLICATIONS

TEXTILES HISTORY, PROPERTIES AND PERFORMANCE AND APPLICATIONS

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CHEMISTRY RESEARCH AND APPLICATIONS

TEXTILES HISTORY, PROPERTIES AND PERFORMANCE AND APPLICATIONS

MD. IBRAHIM H. MONDAL EDITOR

New York

Copyright © 2014 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

Library of Congress Cataloging-in-Publication Data ISBN: (eBook)

Published by Nova Science Publishers, Inc. † New York

CONTENTS Preface

vii

Contributor Contact Details Andrej Javoršek, Cesar Pulgarin, Eva Bou-Belda, Gordana S. Ušćumlić, Ignacio Montava, Jaime Gisbert and Sami Rtimi

ix

Chapter 1

An Exploration of Vintage Fashion Retailing Julie McColl, Catherine Canning, Louise McBride, Karina Nobbs and Linda Shearer

1

Chapter 2

Developing Sustainable Design on Denim Ready-Made Apparels by Stone and Enzymatic Washing Md. Ibrahim H. Mondal and Md. Mashiur Rahman Khan

Chapter 3

Digital Textile Printing Using Color Management Dejana Javoršek, Primož Weingerl and Marica Starešinič

Chapter 4

Inkjet Printed Photo-Responsive Textiles for Conventional and High-Tech Applications Shah M. Reduwan Billah

Chapter 5

Synthesis and Grafting of Cellulose Derivatives from Cellulosic Wastes of the Textile Industry Md. Ibrahim H. Mondal and A. B. M. Fakrul Alam

Chapter 6

History, Synthesis and Properties of Azo Pyridone Dyes Dušan Ž. Mijin, Gordana S. Ušćumlić and Nataša V. Valentić

Chapter 7

Smart Textiles and the Effective Uses of Photochromic, Thermochromic, Ionochromic and Electrochromic Molecular Switches Shah M. Reduwan Billah

19 53

81

123 157

187

Chapter 8

Smart Textiles Ali Akbar Merati

239

Chapter 9

Overview of Textiles Excavated in Greece Christina Margariti, Stavroula Moraitou and Maria Retsa

259

vi Chapter 10

Contents Innovative Ag-Textiles Prepared by Colloidal, Conventional Sputtering and HIPIMS Including Fast Bacterial Inactivation: Critical Issues Sami Rtimi, Cesar Pulgarin, Rosendo Sanjines and John Kiwi

277

Chapter 11

Fungal Deterioration of Aged Textiles Katja Kavkler, Nina Gunde-Cimerman, Polona Zalar and Andrej Demšar

315

Chapter 12

Durability of Functionalized Textiles by Microcapsules Lucia Capablanca, Pablo Monllor, Pablo Díaz and Maria Ángeles Bonet

343

Chapter 13

New Approaches and Applications on Cellulosic Fabric Crosslinking Eva Bou-Belda, Maria Ángeles Bonet, Pablo Monllor, Pablo Díaz, Ignacio Montava and Jaime Gisbert

Chapter 14

Wrinkle Resistant and Comfort Finishing of Cotton Textiles Vahid Ameri Dehabadi and Hans-Jürgen Buschmann

Chapter 15

Evaluation of Physical and Thermal Comfort Properties of Copper/Alginate Treated Wool Fabrics by Using Ultrasonic Energy Muhammet Uzun

355

367

383

Chapter 16

Hemp Fibers: Old Fibers - New Applications Mirjana Kostic, Marija Vukcevic, Biljana Pejic and Ana Kalijadis

399

Chapter 17

Textiles Using Electronic Applications Marica Starešinič, Andrej Javoršek and Dejana Javoršek

447

Chapter 18

Textiles for Cardiac Care Narayanan Gokarneshan, Palaniappan P. Gopalakrishnan, Venkatachalam Rajendran and Dharmarajan Anita Rachel

465

Chapter 19

Effect of Clothing Materials on Thermoregulatory Responses of the Human Body P. Kandha Vadivu

483

Designing of Jute–Based Thermal Insulating Materials and Their Properties Sanjoy Debnath

499

Effects of Ring Flange Type, Traveler Weight and Coating on Cotton Yarn Properties Muhammet Uzun and Ismail Usta

519

Chapter 20

Chapter 21

Chapter 22 Index

Optical Fiber Examination by Confocal Laser Scanning Microscopy Andrea Ehrmann

531 547

PREFACE This book reveals the expanding opportunity of textiles in a wide range of industrial applications. No longer limited to apparels and home furnishings, textiles are being used in many sciences and technologies, such as clothing and fashionable materials, smart textiles, technical textiles, medical textiles, agro-textiles, geo-textiles, electronics, photonics, intelligent sensors, etc. This book is intended for all those who are interested and engaged in the latest developments in the field of textiles, especially chemists, engineers, technologists, application technicians and colorists of the textile industry, technical colleges and universities. Textiles are essential and one of the most important classes of materials used by all people since ancient time. Despite textiles having been around and in use for so long, advances and improvements continue to be made. This book contains 22 invited contributions written by leading experts in the field of textiles. Each contribution presents an updated science and technological advances that have happened during this period and are fully discussed. The first chapter discusses the present and future prospects of vintage fashion clothing, i.e., an old fashion clothing and its retailing. Chapter 2 searches for the dynamic best method for producing specific washing effects and designs on denim ready-made apparels. The chapters 3 and 4 present a discussion on color management application in the field of digital printing onto textile substrates, and inject printed photo-responsive textiles used in fashion and design, self indicating security alert systems, anti-counterfeit and brand protection. In chapter 5 and 6, an attempt has been made to cover the most up-to-date information regarding synthesis, and application of cellulose derivatives and azo dyes on textiles. Smart textiles incorporated with different functionalities have many uses in a variety of fields, some of them are widely used in the fields of biomedical or healthcare applications. The smart textiles and its multi-disciplinary applications have been well discussed in chapters 7 and 8. In chapters 9, 10 and 11, preservation of textile objects in different environments like home, stores, museums etc. have been discussed. These chapters also discussed how to protect textiles from bacterial and fungal deterioration. An elaborative discussion has been made in Chapters 12, 13, 14, 15 and 16 on the new applications of textile materials through modification by physico-chemical methods. The modification has been done to obtain durable, comfort, sustainable and environment friendly finished products using various organic and inorganic chemicals for much better performance. Use of micro-capsulation techniques to modify textiles offers extra-properties, e.g., durable fragrances, skin softeners to textiles. Electronic applications of textiles have been discussed in chapter 17. Textiles, from

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Md. Ibrahim H. Mondal

fibers to fabric, with integrated special electronics are more and more used as special materials in newly developed smart clothing. The chapter 18 specifically focuses on the technological advances with regard to development of textiles for cardiology purpose, i.e., cardiac care. The thermoregulatory process of human body, the thermal comfort properties of fabrics and the effect of clothing material on the thermoregulatory process of human body in different weather conditions has been discussed in Chapter 19. In chapter 20, effort has been made on diversification of jute specifically, development of jute-based materials for thermal insulating applications. The main aim of chapter 21 is to utilize the ring flanges and travellers of ring spinning, which is the most effective staple yarn production process, for the yarn quality in terms of hairiness, twist, breaking strength and irregularity. The last chapter 22 gives an introduction into the techniques of confocal laser spinning microscopy, and depicts optical differences between several textile fibers, enabling a non-destructive examination of natural and chemical fibers. I am very much grateful to all the specialized contributing authors of this book. My special appreciation is also extended to Ms. Carra Feagaiga of Nova Science Publishers, Inc., for her good collaboration, support and numerous discussions throughout the project for this book. I wish thank to my colleagues Professor C. M. Mustafa, Professor F. I. Farouqui, and Professor M. A. Sayeed for their constant support and encouragement. I also thank my graduate students, Dr. Md. Mashiur Rahman Khan, Md. Raihan Sharif, Md. Saifur Rahman and Md. Tariqul Islam for their help during editing this book. Lastly I am thankful to Khadijatul Qubra and Ishrat Rafia for their constant encouragement, understanding and support. Any constructive suggestions and comments are therefore welcome for future revisions and corrections.

Department of Applied Chemistry & Chemical Engineering, Rajshahi University, Bangladesh November 2013 Professor Md. Ibrahim H. Mondal

CONTRIBUTOR CONTACT DETAILS A. B. M. Fakrul Alam Polymer and Textiles Research Lab, Department of Applied Chemistry and Chemical Engineering, University of Rajshahi, Bangladesh

Ali Akbar Merati Advanced Textile Materials and Technology Research Institute (ATMT), Amirkabir University of Technology, Tehran, Iran E-mail: [email protected] Ana Kalijadis Laboratory of Physics, Vinca Institute of Nuclear Sciences, University of Belgrade, Mike Petrovica Alasa 12-14, 11000 Belgrade, Serbia Andrea Ehrmann Niederrhein University of Applied Sciences, Faculty of Textile and Clothing Technology, Webschulstr. 31, 41065 Moenchengladbach, Germany E-mail: [email protected] Andrej Demšar Faculty of Natural Sciences and Engineering, University of Ljubljana, Ljubljana, Slovenia Andrej Javoršek University of Ljubljana, Faculty of Natural Sciences and Engineering, Snežniška 5,1000 Ljubljana, Slovenia

x

Md. Ibrahim H. Mondal Biljana Pejic Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia Catherine Canning Department of Fashion, Marketing and Retailing, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4OBA, Scotland Cesar Pulgarin EPFL-SB-ISIC-GPAO, Ecole Polytechnique Fédérale de Lausanne, Station 6, CH-1015, Lausanne, Switzerland. Christina Margariti Textile conservator, Directorate of Conservation of Ancient and Modern Monuments / Hellenic Ministry of Culture, 81 Peiraios Avenue, 10553 Athens, Greece E-mail: [email protected] Dejana Javoršek University of Ljubljana, Faculty of Natural Sciences and Engineering, Snežniška 5, 1000 Ljubljana, Slovenia E-mail: [email protected] Dharmarajan Anita Rachel NIFT TEA College of knitwear fashion, Tiruppur 641 606, India E-mail: [email protected] Dušan Ž. Mijin Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia E-mail: [email protected] Eva Bou-Belda Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Plaza Ferrandiz y Carbonell s/n, 03801 Alcoy, Spain Gordana S. Ušćumlić Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia

Contributor Contact Details

xi

Hans-Jürgen Buschmann Deutsches Textilforschungszentrum Nord-West gGmbH, Universität Duisburg-Essen, NETZ / DTNW gGmbH, Carl-Benz-Straße 199, D-47057, Duisburg, Germany Ignacio Montava Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Plaza Ferrandiz y Carbonell s/n, 03801 Alcoy, Spain Ismail Usta Department of Textile Engineering, Faculty of Technology, Marmara University, Goztepe, Istanbul 34722, Turkey Jaime Gisbert Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Plaza Ferrandiz y Carbonell s/n, 03801 Alcoy, Spain John Kiwi EPFL-SB-ISIC-LPI, Ecole Polytechnique Fédérale de Lausanne, Bâtiment Chimie, Station 6, CH-1015, Lausanne, Switzerland

Julie McColl Department of Fashion, Marketing and Retailing, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4OBA, Scotland E-mail: [email protected]

Karina Nobbs London College of Fashion, 272 Holborn, London WCIV 7CY, UK

Katja Kavkler Restoration Centre, Institute for the Protection of Cultural Heritage of Slovenia, Ljubljana, Slovenia E-mail: [email protected]

Linda Shearer Department of Fashion, Marketing and Retailing, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4OBA, Scotland

xii

Md. Ibrahim H. Mondal Louise McBride Department of Fashion, Marketing and Retailing, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4OBA, Scotland

Lucia Capablanca Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Plaza Ferrandiz y Carbonell s/n, 03801 Alcoy, Spain

Maria Bonet Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Plaza Ferrandiz y Carbonell s/n, 03801 Alcoy, Spain E-mail: [email protected]

Maria Retsa Textile conservator, Directorate of Conservation of Ancient and Modern Monuments / Hellenic Ministry of Culture, 81 Peiraios Avenue, 10553 Athens, Greece Marica Starešinič University of Ljubljana, Faculty of Natural Sciences and Engineering, Snežniška 5, 1000 Ljubljana, Slovenia E-mail: [email protected]

Marija Vukcevic Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia E-mail: [email protected]

Mashiur Rahman Khan Polymer and Textile Research Lab., Department of Applied Chemistry and Chemical Engineering, Rajshahi University, Rajshahi- 6205, Bangladesh and Department of Apparel Manufacturing Engineering, Bangladesh University of Textiles, Tejgaon, Dhaka-1208, Bangladesh

Md. Ibrahim H. Mondal Polymer and Textiles Research Lab, Department of Applied Chemistry and Chemical Engineering, University of Rajshahi, Bangladesh E-mail: [email protected]

Contributor Contact Details

xiii

Mirjana Kostic Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia

Muhammet Uzun Institute for Materials Research and Innovation, University of Bolton, Deane Road, Bolton, BL3 5AB, UK, and Department of Textile Engineering, Faculty of Technology, Marmara University, Goztepe, Istanbul 34722, Turkey E-mail: [email protected]

Narayanan Gokarneshan NIFT TEA College of knitwear fashion, Tiruppur 641 606, India E-mail: [email protected]

Nataša V. Valentić Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia

Nina Gunde-Cimerman Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia, and Centre of Excellence for Integrated Approaches in Chemistry and Biology of Proteins (CIPKeBiP), Jamova 39, SI-1000, Ljubljana, Slovenia

P. Kandha Vadivu Department of Fashion Technology, PSG College of Technology, Coimbatore 641004, India E-mail: [email protected]

Pablo Díaz Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Plaza Ferrandiz y Carbonell s/n, 03801 Alcoy, Spain

Pablo Monllor Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Plaza Ferrandiz y Carbonell s/n, 03801 Alcoy, Spain

xiv

Md. Ibrahim H. Mondal Palaniappan P. Gopalakrishnan NIFT TEA College of knitwear fashion, Tiruppur 641 606, India

Polona Zalar Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia

Primož Weingerl University of Ljubljana, Faculty of Natural Sciences and Engineering, Snežniška 5,1000 Ljubljana, Slovenia

Rosendo Sanjines EPFL-SB-IPMC-LNNME Ecole Polytechnique Fédérale de Lausanne, Bat PH, Station 3, CH-1015, Lausanne, Switzerland

Sami Rtimi EPFL-SB-ISIC-GPAO, Ecole Polytechnique Fédérale de Lausanne, Station 6, CH-1015, Lausanne, Switzerland. E-mail: [email protected]

Sanjoy Debnath National Institute of Research on Jute & Allied Fibre Technology, Indian Council of Agricultural Research 12, Regent Park, Kolkata – 700 040, West Bengal, India E-mail: [email protected]; [email protected]

Shah M. Reduwan Billah Department of Chemistry, Durham University, Durham DH1 3LE, UK and The School of Textiles and Design, Heriot-Watt University, Galashiels TD1 3HF, UK E-mail: [email protected] or [email protected]

Stavroula Moraitou Textile conservator, Directorate of Conservation of Ancient and Modern Monuments / Hellenic Ministry of Culture, 81 Peiraios Avenue, 10553 Athens, Greece Vahid Ameri Dehabadi Deutsches Textilforschungszentrum Nord-West gGmbH, Universität Duisburg-Essen, NETZ / DTNW gGmbH, Carl-Benz-Straße 199, D-47057, Duisburg, Germany E-mail: [email protected]

Contributor Contact Details Venkatachalam Rajendran NIFT TEA College of knitwear fashion, Tiruppur 641 606, India E-mail: [email protected]

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In: Textiles: History, Properties and Performance … Editor: Md. Ibrahim H. Mondal

ISBN: 978-1-63117-262-5 © 2014 Nova Science Publishers, Inc.

Chapter 1

AN EXPLORATION OF VINTAGE FASHION RETAILING Julie McColl1,, Catherine Canning1, Louise McBride1, Karina Nobbs2 and Linda Shearer1 1

Department of Business Management, Glasgow Caledonian University, Glasgow, Scotland 2 London College of Fashion, London, UK

ABSTRACT The purpose of this research is to offer a definition of vintage fashion and consider the characteristics of the vintage fashion consumer and the positioning of the vintage fashion store from the perspective of fifteen vintage fashion retailers. The research indicates that vintage fashion retailers position themselves on the basis of their uniqueness, based upon their experience, knowledge and skills.

Keywords: Vintage, fashion, definition, customer characteristics, positioning

INTRODUCTION Over the past decade there has been an increasing trend for vintage fashion clothing [1]. Indeed, McMeekin [2] and Wilson and Thorpe [3] have identified that vintage fashion is a multimillion pound industry. Previously, second-hand clothing was purchased by low income groups, economically disadvantaged in terms of mainstream fashion. More recently, however, vintage clothing has become an alternative or an additional choice to high street fashion [4, 5]. Tolkien [6] has proposed that vintage stores and markets have become a desirable source for acquiring fashion items. This may be the result of increasing societal acceptance of an aesthetic shift, with vintage fashion being intended as a means of self-expression and differentiation [4, 7, 8]. 

Corresponding author: Julie McColl. Department of Business Management, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4OBA, Scotland. E-mail: [email protected].

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Julie McColl, Catherine Canning, Louise McBride et al.

The acceptance of second hand clothing as an alternative to high street fashion is partly due to the resurgence of fashion styles from the 1960s, 1970s and the 1980s [9], and the influence of celebrity culture [4, 10]. Consumers are increasingly aware of unethical practices in the fashion industry [10-12], and have become less tolerant towards disposable fashion and more suspicious of the behavior of global brands [8, 13]. The move of vintage from niche sub-culture to mainstream may be evidenced by the increased vintage offerings by high street, luxury and online retailers and by the plethora of guides on selecting and assembling vintage clothing outfits [4, 14, 15, 8, 16]. This apparent increase in vintage offerings has broadened the opportunities for the consumption of vintage clothing. The term vintage is widely used yet has never been clearly defined [4, 7], in terms of the parameters, characteristics and the positioning of the vintage fashion retail store. The literature on the retailer positioning strategies is clearly established [17-26], however, there is little published research on vintage fashion retailing, and developments in the market and their implications for vintage fashion retailers has not been addressed. This exploratory study defines the concept of vintage fashion and the vintage fashion consumer. It evaluates the positioning strategies of vintage fashion retailers, explores how they differentiate themselves in the face of increased competition and considers the implications of the more recent vintage trend for traditional vintage retailers.

LITERATURE REVIEW Definition of Vintage It is difficult to define the concept of vintage, partly due to the lack of agreement regarding the specific time periods of ‘vintage’, ‘antique’ and ‘retro’ but also due to differences in opinion about the constituents of such clothing items. According to De Long [7, p. 23] “in clothing, vintage usually involves the recognition of a special type or model, and knowing and appreciating such specifics as year or period when produced or worn”. Furthermore, they suggest that vintage clothing is concerned with a specific time period or setting and is distinguished from “antique, historical, consignment, reused or second-hand”. Palmer and Clark [4, p. 175], define the term more broadly proposing that it is “used to cover a huge spectrum of clothes that are not newly designed”. Tungate [8, p. 221] offers a more focused definition which highlights the evolution and complexity of the term, identifying that “any one particular item may change through time and usage by the fashion media, so that second hand becomes known as retro then in turn as vintage”. The increase in availability of vintage and the growth of on-line availability of vintage clothing has added confusion to the array of vintage definitions [4]. From the customer view point, Tungate [8], proposes that vintage is an intangible concept which is more about attitude than style of dress. Similarly Palmer [4], characterises vintage fashion as a symbol of individuality and originality. A primary aim of this research was to define vintage from the perspective of the vintage fashion retailer.

An Exploration of Vintage Fashion Retailing

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Characteristics of the Vintage Consumer Traditionally the buying of second-hand apparel has been subject to negative meanings as a mark of poverty [27, 28]. Tseëlon [29] acknowledged that this type of social judgment has been discounted by the vintage consumer in their quest for non-conformity to fashion trends. Silverman [30], recognized increased demand for vintage goods amongst the young consumer and the middle class consumer. Crewe and Forster [31], agree with this explanation, adding that these groups acquire vintage fashion for excitement and as a means of displaying themselves in public. Hansen [32], segments the vintage consumers into young professionals who want good quality apparel at modest prices, or young people keen on retro subculture looks like Punk, Rave or Mod styles. In addition, Woodward’s [16] study explored younger consumer’s affection for vintage clothing and recognized that the incentive for consumption was to achieve a level of differentiation from their peers. Additionally, a substantial consumer group has been acknowledged as taste-makers: stylists, designers and image makers who use it as a means of inspiration and creativity [33-35]. The ownership, or the wearing of vintage items along with high street clothes, has become anindication of how fashionable the wearer is, with an increasing prominence on how the items are sourced, and not just on how the person looks [16]. The increase in mass market vintage has possibly weakened the authentic charm of vintage among ‘fashion’ orientated consumers, i.e., those more concerned with how things look and being individual in style, than having a deferential concern with the historic and representative links of these sometimes uncommon items which the vintage connoisseur and retail experts so value [7, 36, 38].

History and Key Drivers Vintage as mainstream fashion emerged as a trend in the 1980’s [38]. Tolkien [6] has identified vintage as stemming from the New York social fashion elite, influenced by sentimental pictures of 1940’s couture. In addition, celebrities fueled demand and popularity of the style by wearing luxury vintage gowns to major award ceremonies and fashion shows. Others credit Barbra Streisand as the first vintage-couture advocate [39]. In turn, this encouraged designers such as Marc Jacobs, in the 1990s to create the ‘nouveau vintage’ look by reinventing older styles [40]. This trend also occurred in the UK and Europe with designers and celebrities such as Stella McCartney and Kate Moss inspiring mainstream adoption of vintage fashion [41, 42]. The appreciation of vintage aesthetics which grew in the 1990s helped to decrease the stigma of wearing second hand clothing, and permitted them to develop in to acceptable sources of fashion. This resulted in a differentiation both in-store and in the consumer’s mind, between vintage and clothing purchased from charity stores [1, 4, 6, 43]. The media has endorsed vintage fashion as a means of conveying connoisseurship and uniqueness, more recently extended by the juxtaposition of vintage and contemporary in one ensemble [4, 8]. Jackson and Shaw [44] highlight an important driver in the vintage movement is media attention on the unethical practices which exist in the fashion industry, resulting in a consumer backlash against disposable fashion and the beginnings of a ‘slow fashion’ movement, who emphasize the importance of quality as opposed to quantity [45].

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An additional driver acknowledged by Tungate [8] is customer defiance of expensive, branded products and trends promoted through marketing communications. In recent years, the economic downturn has witnessed ‘upcycled’ fashion items becoming a mainstream phenomenon; this is the re-working of old clothes into more modern-day, higher value pieces [46, 47]. The influential ‘retail guru’, author and broadcaster Mary Portas, successfully developed a media campaign in 2009 called ‘Living and Giving’ which improved the image of charity shops and further increased demand in vintage clothing [48]. More recently, in a study of street style Woodward [16], indicated that the trend for vintage has reached maturity and might now be perceived as commonplace or omnipresent. In the case of both the retailer and the consumer alike, the uptake of the vintage trend in the ‘noughties’ has caused a reduction in the availability of interesting and unusual items, affecting the market in two ways. Firstly key pieces have increased in value and vintage fashion has grown to be an investment prospectrivaling the collection of artwork [49-50]. Agins [51] has identified that this is as a result of the widely broadcast view that the couture industry is declining, with prices accelerating and skilled workmanship growing scarcer. Secondly it means that traditional vintage consumers are being forced to search extensively and even globally to source the desired article [52]. In total there are three key drivers of vintage fashion trends. Firstly, the trickle down feature from celebrities and designers, secondly, the ethical aspect of the fashion industry and finally the need for individual uniqueness and authenticity. Palmer [4, p. 197) proposes that “vintage has now shifted from subculture to mass culture because of the disappointing fact that, regardless of price, fashion today is rarely exclusive”.

Market Structure and Vintage Retail Formats Mhango and Niehm [53] suggest that vintage clothing retailers are focused within the small business sector, and are characteristically independently owned. These include secondhand stores for example thrift or charity shops, estate sales, garage sales, flea markets and auctions, usually the province of commercially-mediated lateral recycling [31, 54]. Nevertheless, vintage clothing retailers have now developed to comprise multifaceted retail support functions such as sourcing, supply chain management and visual merchandising [55]. Moreover many charity stores in Great Britain have re-invented themselves as ‘vintage’ to increase their apparent brand value and to distinguish themselves from others in the sector [12]. Mainstream high street retailers such as Top Shop and Urban Outfitters have successfully sold vintage clothing ranges for a number of years [15]. Tolkien [6] ascertains that the internet as a significant channel in the distribution of vintage clothing, however this phenomenon requires an alternative research approach and can be addressed in future studies.

Retail Positioning Porter's [56, 57] theory of positioning theory has had an lasting impact on the marketing literature [58-65], and practice [66, 67], as one of the most significant concepts and fundamental principles of marketing [63, 64], central to strategic marketing success [68].


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The positioning strategy implemented by any company is grounded in the needs of the customer, the behaviour of the competition, and is ultimately how companies can achieve competitive advantage [69-73]. It is commonly acknowledged that although there are a number of positioning typologies developed within the marketing planning framework [59, 73-74], there is a lack of empirical research testing these typologies [61, 64]. Yip [75] has proposed that a number of the positioning approaches suggested within the literature, are incomplete and may be confusing. Table 1 offers a summary of positioning typologies. The concepts of these positioning typologies are considered by the authors as the central means by which the organisation can attain differentiation, increase competitive advantage and therefore position themselves within the market [64]. Table 1. Summary of positioning typologies Author

Aaker and Shansby [59]; Berry [78]; Buskirk [76]; Brown and Sims [77]; Crawford [79]; Hooley, et al. [63]; Wind [73]

Ries and Trout [66]

Easingwood and Mahajan [80]

Arnott [61, 58]

Kalafatis, et al. [72]

Positioning constructs i.e., concepts Features and Benefits Features, price, advertising, distribution, problem solved, usage situation, users, competitors, value, time efficiency, high contact, sensory, benefits, product class dissociation, attributes, price, quality, use or application, product/service user, product/service class, competition, direct/indirect, surrogates: nonpareil, parentage (brand, company, person), manufacture, target, rank, endorsements, experience, predecessor, innovation-imitation, superior service-limited service, differentiated benefitsundifferentiated features, tailored offering-standard offering. Strategic positioning Market leader, follower, reposition the competition, use the name, line extension (use of house name). Reputation/capabilities of organisation: expertise, reliability, innovativeness, performance, augmentation of product offering: product augmentation, extra service, people advantage, more attractive package offering, a superior product through technology, accessibility, extra attention given to individual requirements through customisation, satisfaction of more user needs within the sector through offering a complete product line. Empathy, solvency, promotions, administrative time, helpfulness, reliability, attentiveness, staff competence, flexible products, access to people, reputation, customisation, incentives, social awareness, security, technology. Easy to do business, personal contact, product performance, range of offerings, presence, safety, leadership, distinct identity, status, country identity, differentiation, attractiveness.

Source: Adapted from Blankson and Kalafatis [64].

Blankson and Kalafatis [64], however, consider existing studies to be descriptive, difficult to put into practice and based on limited empirical testing, principally in terms of their representation within consumer marketplaces, their propensity being to represent the

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views of management. They propose that the literature lacks an empirically based consumer/ customer derived typology, which can measure the effectiveness of positioning strategies employed. Having carried out extensive empirical research, they have proposed a positioning typology based on customer opinions, which they advise is suitable for both product and service markets and recommend that managers develop their positioning based on consumer perceptions of prestige, service, reliability, attractiveness, country of origin and brand name. These, they propose, are the key differentiating features within the marketplace and can be successfully deployed in marketing communication. In the retailing literature, Cook and Walters [19] suggest that a company’s market position is its reaction to its understanding of the needs, desires and behavioural characteristics of its target customer profile. Retail positioning is defined by Wortzel [81, p. 47] who proposes: “For a retailer, strategic positioning involves providing unique value. Strategic positioning involves selecting and then bringing to bear an integrated set of tools and communication techniques that identify and explain the store to the customer.”

Walters [18] offers a model of positioning developed as the consequence of wide-ranging empirical research within the retail sector. The fundamentals of the positioning strategy in retailing, he suggests, are a visible response to the needs and wants of the identified target market. The key decision areas for retailers in evolving their marketing strategy are those of trading format, merchandise strategy, customer service and customer communications strategy. These decision areas define the retailer positioning strategy, and position them in terms of what the customer anticipates and customer satisfaction, creating a point of distinction which separates retailers from their competitors and represents the retail brand [82, 26]. While established as a theoretical model, the strategic elements of Walters’s [18] value added positioning statement are still recognised in the retail marketing literature as the means by which retailers should position themselves in the market [17-26]. Therefore it forms the basis of a number of empirical studies on retailer brand positioning [20, 26, 81, 83-88, 89, 90], which stress the possible benefits of developing a clear and distinctive positioning statement using the elements of the retailing mix. Consequently it was thought to be the most suitable framework for application within this study. However, although there are a number of positioning typologies developed in the marketing and retailing planning context [59, 73-74], there is still a lack of empirical research testing these typologies [61, 64]. The literature suggests that small retailers, like those addressed within this study, are different from larger companies in terms of management systems and resources, and that planning, control and strategy are a result of the personal objectives and personality of the owner manager [91-93]. However, within the vintage retail sector, this proposition has not been tested. This research serves to help address this issue.


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METHODOLOGY Small companies are dominant within the vintage retail sector and generally evolve from the entrepreneurs who are enthusiastic about vintage themselves [12, 14]. The decision to focus on small scale companies is also supported by evidence provided in the vintage retailing literature, as existing research focuses on small companies [53, 54]. To be selected for this study the vintage retailers had to meet some or all of the specifications within the literature. They had to have high levels of experience in both buying and merchandising and so had to have been in business for at least two years. The participants of the study therefore had between two and twenty three years experience of running a vintage retailing company. To ensure consistency of trading practices, participants were required to trade as bricks and mortar businesses. Therefore, participants would provide credible information as to the concept, positioning and differentiation of small vintage fashion retailers. Thirty nine vintage fashion retailers from Scottish towns and cities were identified from The Yellow Pages, trade journals and company websites. Of these, twenty seven were found to have been in business for over two years, however one was found to sell only on an online basis. A letter was sent to these twenty six vintage fashion retailers from the population sample of thirty nine in September of 2009. A follow up phone call was made a week later. Sixteen retailers responded that they were willing to participate in the study, however, one potential participant remained unavailable. Therefore fifteen interviews were carried out with owner/managers of vintage retail stores. All participants had direct experience in the areas of buying and merchandising within the vintage retail sector. The owner managers were between twenty three and fifty eight years old. The interviews took place within the retail premises and were approximately two hours long. Confidentiality was assured. The interviews were taped, transcribed and retained as Microsoft Word documents. Analysis was carried out by one member of the research team to ensure consistency. First of all the transcripts were analysed to identify common characteristics and emerging themes and issues. At this stage, a “cluster” approach was adopted and a framework for theoretical development began to emerge [94]. These clusters were selected on the basis of significance, mutual exclusivity and ability to stand by themselves [95]. Yin [95] suggests that data analysis consists of examining, categorising, tabulating, and testing the content to address the initial propositions of the research. Interviews were analysed one at a time individually and then on a cross interview analysis. Patton [96] suggests that the analysis involves the application of the existing theoretical framework, developed from the literature, and the subsequent analysis of the interviews to allow for an examination of emerging patterns. According to the theories and concepts extracted from the literature, the interviewees were asked open-ended questions about their definition of vintage, the vintage customer, merchandising and the positioning of the vintage store. The results and discussion section is therefore divided into three sections. Firstly, the research seeks to define vintage fashion and investigate the vintage fashion movement, secondly, the research explores the characteristics of the vintage fashion consumer from the perspective of the store owner/managers, and finally it explores positioning in relation to the retail vintage fashion sector.

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RESULTS Defining Vintage Fashion There was no unified or clear definition of vintage with each vintage retailer offering differing opinions and suggestions. However, three dimensions emerged. Firstly the age of the apparel, secondly the style, (a piece of clothing which sums up the era), and finally the quality of the vintage clothing. The majority stated that fashion which predates the 1990s would be considered to be vintage. To a number of interviewees ‘vintage’ could be categorised as anything up until the 1950s, with anything that pre dates 1980 being classified as ‘retro’, and anything before the 1920s being considered as ‘antique’. “Probably not the 1990s but anything before that, especially the 1980s at the moment. Only the fashion forward are looking for 1990’s articles”

Some items of clothing were seen to represent the zeitgeist of bygone eras and these were particularly important to vintage consumers. Examples included a 1950’s prom dress or Dior’s ‘New Look’ full skirt. In 1960, ‘Twiggy-style’ 1960’s mini dress, in the 1970’s platform shoes and bell bottom trousers and 1980’s pedal pusher short trousers and frilled shirts from the New Romantic movement. All participants agreed that, in order to satisfy customers, articles have to be of good quality. Almost all the participants agreed that vintage fashion was second hand, however, a few retailers sold old clothing manufactured in the past which was unworn. One retailer was selling unworn “Brutus” and “Lee” denim jeans from the 1970s which had been discovered in a warehouse. The most desirable items were those which had been bought in a past era but had rarely or never been worn, for example items which have been kept for special occasions and were in pristine condition. Examples included evening dresses, a wedding dress or a formal suit. One participant summed up the general opinion stating: Vintage fashion isn’t something that is just old. If a ‘50’s dress is an ugly hideous rag- that is what it is, an ugly hideous rag. Vintage is the very, very best of its type.

Characteristics of the Vintage Consumer Retailers were invited to define the vintage consumer from their own viewpoint. Participants stated that many of their customers were “fashion conscious” and “young” consumers, with an average age of between eighteen and twenty (many of them students), however all participants stated that the age range of their consumers was very diverse. It was found that he 18-25 year old consumers are most likely to be influenced by fashion trends. It was recognised that this particular segment had adopted the ongoing vintage trend which had positively increased demand for vintage clothing overall. These younger consumers were seen to be setting the trend for current trickle up fashion looks such the “nerd college look”, and “geek chic” (spectacles, drainpipe trousers or retro skirts with blouses and tank tops). The interviewees proposed that these trends had also extended to celebrities and were linked to sub-culture music trends.


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Young consumers were seen to purchase for originality and enjoyment, to display aspects of their own individual style, and in many cases, price. Participants stressed their ability to offer uniqueness which people see as a method of individual self expression. There was a certain status provided by the originality of rare clothing. One proposed: You always feel quite smug when you say ‘Oh its Vintage’ there’s no way the person can go out and copy you

The next most important group of consumers identified were older customers (aged 3070) who tended to purchase on price and nostalgia rather than trend. This segment were likely to invest more time, money and effort in their purchases and were generally more motivated about the authenticity of the product. For example, a number of participants discussed the importance to the customer of the story behind the garment; what one termed as “vintage magic.” Consumers were buying ‘more than a skirt or shirt,’ they were buying a piece of history, and often enjoyed hearing a story behind an item or ‘a treasure.’ Additionally, participants highlighted an increase in the number of ethical consumers, conscious of environmental issues and recycling. This customer group was diverse in age and nature. Finally, a small proportion of customers were collectors and business customers, for example television, film and theatre wardrobe designers and stylists for fashion magazines.

Vintage Retailer Positioning Merchandising Strategy The main concern by the retailers in sourcing garments was the authenticity of vintage fashion. Most considered vintage fashion to be authentic by the perceived age and its level of originality. They particularly sought garments which had been handmade and were therefore exclusive. Exclusivity is of particular importance as it allows premium pricing and provides differentiation for the store. Older designer clothing from fashion brands such as Chanel and Biba are becoming rare and difficult to source. Some of these older garments particularly with brand names are highly sought after. Products that are mass produced (even older clothing from the 1980s for example) are less likely to be perceived as authentic and are therefore less desirable. One retailer stated: Authentic vintage is an original garment and not a vintage label from a high street store. They are obviously complete one offs and that in my mind is worth a lot more than some dress that’s been churned out by Marks and Spencer. Back in the ‘40s, ‘50s and ‘60s people were making their own clothes, which are highly desirable now.

Participants explained that they were able to verify the authenticity of garments through their personal expertise, gained through experience of sourcing and buying. Many retailers considered themselves to have expert technical knowledge, and could determine garment authenticity by the stitching, (e.g., of hand sewn products rather than machine produced) the fabric quality, and the smell of the garments. Because of the increasing difficulty in sourcing good quality vintage items some retailers had decided to sell more modern items that had been manufactured more recently but were made to an appropriate vintage design.

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They understood that the authenticity of these garments was debatable; however they agreed that consumers wanted to purchase this type of ‘pseudo-vintage’ product due to the desire to follow the vintage trend. Retailers sourced second hand merchandise from a wide variety of second hand stores and markets both at home and abroad, charity and second hand clothing stores, car boot sales, recycling plants and many garments are donated by customers or other shoppers who wish to recycle. Vintage retailers will also recycle clothing back to recycling plants or ‘rag yards’ if they are unable to sell the garments. Merchandise was both bought in bulk ‘by the sack’ or ‘large load’, or handpicked. Retailers occasionally sourced more exclusive merchandise from private individuals who perhaps were collectors themselves and chose to trade their personal vintage garments to be enjoyed by other enthusiasts or vintage collectors. Some store representatives discussed of more recent emerging markets in Eastern Europe which offer opportunities for trade and sourcing of vintage clothing, offering alternatives to what is still available in the UK market. Participants also highlighted France and the US as fruitful sources. One stated that the US was particularly good for 1920’s dresses. One retailer observed: I am sure there is a totally untapped market in Russia. I would like to visit there and raid some wardrobes. Russia is so large and many people don’t know the value of vintage garments yet.

Retailers selected merchandise according to ‘gut feel’ and intuition and was therefore a very personal issue. Participants sourced according to their personal expertise of the market, their customers and their personal knowledge of fashion history. The research found therefore that this personal expertise was highlighted by all participants as their main point of differentiation and competitive advantage. In many cases they proposed that a synergy existed between themselves, their knowledge of style and their customers. In most cases retailers explained that they understood their regular customers’ needs and wants and were able to buy accordingly. The most popular brands were found to be Biba, Bus Stop, Mary Quant, Burberry, Dior and Chanel. Unlike high street fast fashion models, stock was not ‘turned around’ in weeks however, there is a seasonal approach to vintage merchandise. During the spring and summer, female consumers were looking for summer dresses, 1950’s style dirndl skirts (full skirt gathered at the waist), miniskirts and more recently in line with changing fashion trends, maxi dresses. During the winter, the demand was for heavier outerwear and coats, hats, gloves and scarves. Retailers explained that as a result of catwalk trends, there is still demand for real fur coats. Participants explained that consumers believed that the wearing of old, second hand fur coats was acceptable to many of their customers because these items were manufactured prior to increased ethical awareness of animal rights issues. Older fur therefore was perceived as glamorous and stylish despite the recent concerns surrounding new fur products. ‘Occasion’ dresses from any vintage era were always in demand and at Christmas, customers were looking for appropriate glamorous party wear. A table of the most popular items is outlined in Table 2 below. Selection of these items was based on more than half of the sample highlighting these product categories:


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Table 2. Most popular vintage items for men and women Ladies vintage items 1950s prom dresses 1960s shift dresses, 1970s maxi dresses Evening wear – glamorous gowns, sequined and embroidered dresses Real and fake fur coats and jackets Cashmere jumpers and cardigans Jewellery and watches Handbags, scarves and belts High heels and flat boots for ladies from the 1960s, 1970s and 1980s

Men’s vintage items Formal wear Evening suits Suits from the 1950s and 1960s Traditional dress (Kilts) Retro Adidas tracksuit tops from the 1970s Levis jeans and denim jackets Cowboy boots Military dress Leather briefcases Ties

One of the key challenges that participants highlighted was the procurement of appropriate, second hand stock which is in good condition. Due to the popularity of the trend, there is an increasing scarcity of stock as older garments become more worn and therefore less appealing due to reduced quality. This was seen to be an enduring problem which has heightened competition in the vintage sector. There was a level of preparation required for all second hand garments. All the vintage retailers washed or dry cleaned items before sale. Some items required repairs such as sewing on buttons or zips, or making alterations such as altering hem lines. However, normally alterations were minimal so that the authenticity of the garments was not compromised. In some cases however, participants created new garments by combining two pieces together. If a part of a garment was too ‘worn out’ to be sold, sections of garments and fabrics could be ‘rescued’. One participant proposed: We buy dresses that are full length and we cut them to mini dresses. We actually have a tailor next door who does all that for us. We have bought blazers and put accessories on them to make them look more interesting

Customer Service Personal service was found to be essential to the success of most of the retailers. Most employees were owner/managers, assisted by partners, friends or family members who had a vested interest in the success of the store. All retailers explained that they know a high proportion of their customers very well, considering individual customer tastes, needs and style when sourcing garments. Some participants would store items for particular customers. In addition, customers frequently request the sourcing of specific items. Therefore, the basis of much of the customer service for vintage retailers was the building of relationships. Additionally, all had a loyal and regular customer base. Many proposed that the development of these relationships allowed retailers to offer a personalised service. A number of retailers offered an alteration service for their customers. Therefore differentiation was possible for these retailers due to the relationships and customer service they developed with their consumers.

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Most proposed that they themselves personally were the differentiation through their passion for the vintage concept, their choice of merchandise, their expert knowledge and expertise. One participant stated: It’s me. The company is built around my personality, personal style and taste. My customers like that and they trust my judgement.

Communications Store image elements were the most important methods of communication for vintage stores. That is, the window display and the store interior. The window display was seen as vitally important to generate interest and curiosity from passersby and the unique store interior and merchandise communicated a distinctive brand image. In terms of traditional communications, most of the retailers did not use print advertising often due to expense and due to limited success using this method in the past. A few advertised in local directories and the Yellow Pages. Many participants explained that local press editorial had proved to be very effective in increasing awareness and enhancing business profile. The main type of communication reported that was thought to be essential by all interviewees is word of mouth (WoM) marketing due to the high levels of personal service outlined above. Positive customer experiences were thought to be vitally important for promotion and generating custom. The group was divided in relation to e-marketing. Only half of the participants operated a website. However, several participants interacted with social media platforms (at varying levels) in order to connect with the vintage fashion community, to increase brand awareness and generate enquires and consumer awareness. Store Trading Format All the participants in the study were small-scale retailers who were independently owned. Typically, most stores were single units which were 700-1100sq.ft. in size. Many were located in secondary geographical locations with a ‘neighbourhood feel.’ All of the retailers included in this research described themselves as traditional ‘bricks and mortar’ boutique-style shops. Of those that operated websites, most were non transactional, and two of the stores had their own on-line stores. The majority of sales were traditional, meaning in store retailer to consumer business. Interestingly, a few retailers had evolved their stores from market stalls and indicated that a proportion of vintage trade still took place on that basis. All proprietors explained that the store image was essential to vintage retailing. Many participants stated that the window styling, store layout and product display was important to create the atmosphere of “a bygone era” and many described the stores as “quirky” and “individual”. Each store represented the personality of the owner, with one retailer explaining that he wanted to “create the right kind of vibe” with music from a previous era and choosing items carefully to represent his sense of taste and style. Many displayed interesting pieces that were collectors’ items or were appropriate to present the vintage image. Old gramophones, old bicycles, wallpaper from the 1970s and 1980s, old pictures and pieces of art and various other pieces of memorabilia were displayed according to the proprietors’ preference. The product display varied from store to store. Most displayed clothing in racks similar to new modern high street retailing and many had containers such as baskets and boxes and shelves of mixed accessories and jewellery that consumers enjoyed “sifting through” and “hunting for a treasure or a bargain.”


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CONCLUSION The vintage movement was mainly something of a “fad” that was followed by a small group of innovators such as art school and fashion students. However more recently it would appear to be an enduring trend, increasing in popularity, growing into a mainstream fashion phenomenon. This is evidenced by its diverse customer base, adopted by young, fashion conscious consumers and maintaining a group of diverse traditional vintage customers of a variety of age groups. The movement has also gained interest due to more recent concerns over ethical issues such as recycling and sustainability. This study discovered two main groups of consumers; young and fashion conscious, interested in current trends and mix and matching from various styles, high street and vintage and also an older customer with a greater focus on price and interest in nostalgia. An emerging issue for many customers were their ethical concerns. This research explores the retailer perspective of the vintage fashion trend. Future research is necessary, to investigate consumer motivation buying vintage fashion of these different groups. This research set out to define the concept of vintage fashion within its current context. Therefore, vintage fashion can be defined as: Garments and accessories which are more than twenty years old, which represent a particular fashion era, and which are valued for their uniqueness and authenticity.

Positioning strategies of vintage fashion retailers was also explored. Table 3 highlights the key areas of positioning within vintage retailing. The research therefore revealed that vintage retailers position themselves through their distinctive retailing mix. Vintage proprietors explained they could source items that were totally individual and unique. As one store owner stated, You are buying a piece of history… a treasure. This was the main difference between other independent stores. Table 3. Vintage Retailer Positioning Elements Customer communication

Trading format

Individual retail brand image, quirky and constantly evolving, distinctive store environment, window and interior displays, retro props, localised PR, word of mouth, growing importance of social media

Small scale, independent, single site, secondary geographical location, multichannel participation, boutique style, unique store image which represents the personality of the owner

Source: adapted from Walters [22].

Merchandise strategy Sourcing: personal, diverse, intuitive, expert and historical knowledge, global Product: authentic, original, exclusive, rare brands, preowned, handpicked, limited supply of merchandise

Customer service Personal, individual, relationship based, long term, synergy between business owner and customer, availability of adjustments and alterations, employee passion for the vintage concept

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Sourcing therefore was an extensive challenging and time consuming process which reflected the personality and expertise of the proprietors. The “quirkiness” of the store interior and environment was also of importance and word of mouth communication was also found to be very important in terms of promotions. Vintage retailers are often small scale, ownermanaged businesses, and are because of this, closer to their customers and able to form individual relationships through merchandise supply and customer service. The influence of the owner/manager, their style and personality is consequently reflected and embedded in the positioning of the company, offering differentiation of their individual stores in the market. There remains a gap in the literature in terms of analysis of the vintage customer. The positioning model above could, in future studies, be used to establish consumer responses to vintage retailer strategy.

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[88] Warnaby, G. (1993). Laura Ashley - An international retail brand. Management Decision 32(3), 42-48. [89] Birtwistle, G., Clarke, I., Freathy, P. (1999). Store image in the UK fashion sector: consumerversus retailer perceptions. The International Review of Retail, Distribution and Consumer Research 9(1), 1-16. [90] Morschett, D., Swoboda, B., et al. (2006). Competitive strategies in retailing-an investigation of the applicability of Porter's framework for food retailers. Journal of Retailing and Consumer Services 13, 275-287. [91] Shuman, J. C., Seeger, J. A. (1986). The theory and practice of strategic management in smaller rapid growth firms. American Journal of Small Business 11, 7-18. [92] McAuley, A. (2001). International Marketing. Wiley, Chichester. [93] Hutchinson, K., Quinn, B. (2011). Identifying the characteristics of small specialist international retailers. European Business Review 23(3), 314-327. [94] Guba, E. G., Lincoln, Y. S. (1994). Competing Paradigms in Qualitative Research. In: Handbook of Qualitative Research. Denzin, N. K., Lincoln, Y. S., Thousand Oaks, CA., 105-117. [95] Yin, R. K. (2003). Case Study Research. Thousand Oakes, SAGE Publications. [96] Patton, M. Q. (2002). Qualitative Research and Evaluation Methods. Thousand Oakes, SAGE Publications.



Chapter 2

DEVELOPING SUSTAINABLE DESIGN ON DENIM READY-MADE APPARELS BY STONE AND ENZYMATIC WASHING Md. Ibrahim H. Mondal1, and Md. Mashiur Rahman Khan1,2,† 1

Polymer and Textile Research Lab., Department of Applied Chemistry and Chemical Engineering, Rajshahi University, Rajshahi, Bangladesh 2 Department of Apparel Manufacturing Engineering, Bangladesh University of Textiles, Tejgaon, Dhaka, Bangladesh

ABSTRACT Denim is the most preferable apparel of today’s youth. Washing is one of the fundamental chemical processing steps prior to finishing fresh-assembled denim readymade apparels and has the largest effect on outlook appearance and other physicomechanical properties of finished denim apparel. The fresh denim trousers, twill 3/1 weave and composition 100% cotton, have been processed by enzyme washing and pumice stone-enzyme washing technique using various parameters namely concentrations of pumice stone (10 to 70%) (owg), concentration of cellulase enzyme (0.5 to 3.5%) (owg), washing temperatures (40 to 65oC) and treatment times (20 to 60 min) with fixed pH (4.8) in fiber to liquor ratio of 1:10 in an industrial sample washing machine. In order to evaluate the influence of these washing parameters on the properties of denim apparel like tensile strength, fabric weight, color change, stiffness and water absorption has been determined. Fabric surface was also examined by scanning electron microscope (SEM) and fluorescence microscope (FM). The washing parameters has a great influences on the properties of denim. Stone washing increased the softness (by reducing stiffness) and flexibility (in terms of bending length) of denim apparels and gave a used look appearance on denim apparel distinctly. The properties of denim apparels are varied depending on the amount of pumice stone used. 

Md. Ibrahim H. Mondal: Polymer and Textile Research Lab., Department of Applied Chemistry and Chemical Engineering, Rajshahi University, Rajshahi- 6205, Bangladesh. E-mail: [email protected]. † Md. Mashiur Rahman Khan: Polymer and Textile Research Lab., Department of Applied Chemistry and Chemical Engineering, Rajshahi University, Rajshahi- 6205, Bangladesh. Department of Apparel Manufacturing Engineering, Bangladesh University of Textiles, Tejgaon, Dhaka-1208, Bangladesh.

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Md. Ibrahim H. Mondal and Mashiur Rahman Khan The results indicate that for producing sustainable denim apparel the optimized washing condition for the best value is 30% pumice stone with 2.0% cellulase enzyme at 55 oC for 40 min.

Keywords: Denim apparel, cotton, cellulase enzyme, pumice stone, tensile strength, washing, color fading

1. INTRODUCTION The increasing demand of denim apparel in the world market has imposed extreme pressures on the textile industries. The use of chemicals in the textile industry has been known and applied commercially for many years. In particular, textile washing industries are using various chemicals in processing denim ready-made apparels for producing specific washing effects and designs. The research attempts to examine different washing techniques for the modification of denim apparels and searches for the dynamic best method for producing sustainable denim apparel designs. Understandably, this concern motivates many efforts to modify denim apparels with new designs in order to face the challenges of fastchanging fashion trends. Although denim apparel has been popular since the early1980’s, the term “sustainable denim” is a relatively new concept to the apparel industry. Sustainable denim has become to be a dominating factor in the apparel industry. Now-a-days, there is awareness on environmental concern among the customers and buyers. In this respect, present work has been undertaken to fulfill the current demand of customers using environment friendly chemicals for denim washing. Therefore, the study investigated evaluative specifications used by designers and buyers for producing denim apparel with sustainability. Bangladesh is a textile industry based developing country. At present, Bangladesh earns about 80% foreign currency from the textile and RMG sectors. Bangladesh started RMG export in 1977-78 and continues export under quota to the US till 2004. In January 2005, the RMG sector of Bangladesh faced new challenges due to the withdrawn of quota by US government. From that time, the US market is open for all and highly competitive. Currently there are about 5600 ready-made garment industries in Bangladesh and from these RMG industries Bangladesh earns about 21.51 billion US dollar [1]. To sustain the RMG sector of Bangladesh in the competitive world market, it is essential to produce new design and fashion apparel with sustainability. Denim apparel is produced from very strong and stiff denim fabric and its popularity is increasing day by day in the world market. Without washing/finishing treatment denim apparel is uncomfortable to wear, hence it can be modified by washing and introduces new look and fashion. There have been many attempts to use chemicals in various washing techniques like bleach wash, enzyme wash, stone wash, etc. The washing of denim apparel by enzymatic process, specially cellulases that would degrade the color of denim and improve the handle and drape, dimensional stability and surface characteristics reported by Kawamura and Wakida [2], Tyndall [3], Kumar et al. [4], Duran and Marcela [5], Gubitz and Cavaco-Paulo [6] and Cortez et al. [7]. Cellulases are introduced to replace aggressive chlorine bleach in denim washing [8] but the enzymatic attack of cellulase is not only limited to the surfaces, act synergistically in hydrolysing cellulose to glucose [9], causing unacceptable weight and strength loss to the fibers.

Developing Sustainable Design on Denim Ready-Made Apparels …

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It is believed that if the denim apparels are chemically washed with enzyme and stoneenzyme separately in order to decrease their minimum strength and weight for producing specific washing effects and designs, their chemical attack would be restricted only to the surface of the fabric, which is the main purpose of this research work. Thus, the work proposes the use of bio-degradable cellulase enzyme and stone-enzyme in place of harmful chemicals and attempts to optimize the process parameters, such as, concentrations of chemicals, concentrations of pumice stone, temperatures, and times with high wear performance like durability and longevity (with minimum strength losses) of apparel in producing sustainable denim apparel.

1.1. Denim Apparel Washing The washing of apparel generally means cleaning of dirty apparels with soap or detergent. But industrial apparel washing is a technology which is used to modify the appearance, outlook, comfort ability and fashion of the apparels. With the changes of time, human choices, demands, and apparel’s design and fashion changing very quickly. To meet the present demand of consumers, apparel manufacturers are adapting new technology and processes in washing. The washing technology needs various types of chemicals for washing apparels. Denim washing is the aesthetic finishing process given to the denim apparel to enhance the fabric properties and provides fashion effects. Various chemicals are used in various washing processes, e.g., bleaches are used in bleach washing process, enzymes are used in enzyme washing process, pumice stones are used in stone washing process etc.

1.2. Denim Denim is a yarn-dyed cotton twill fabric, basically warp yarns are dyed with indigo and weft yarns are white [10]. Indigo is insoluble dye and diffused on yarn surface [11]. Indigo dye is popular for denim because it washes down easily and clear bright blue shades are achieved by washing [12]. Today denim has various washing aspects for designs, it can be stone washed, bleach washed or enzyme washed. The word denim is derived from the French word ‘Nimes’, the Nimes was the French city where the denim was first produced. The fabric which was produced in Nimes was called ‘Serge’ in French. Resultant it was called ‘Serge De Nimes’ means ‘fabric of Nimes,’ later the name was shortened to DENIM.

1.3. Sustainable Design Sustainability is a vital topic within the design world. Sustainable practices are now growing in the apparel industry. In the past, apparel designers and merchandisers have emphasized a product’s functional, aesthetic, and economic aspects during the design process [13]. With increased consumer interest in the environmental implications of apparel production, many companies have introduced sustainable practices [14, 15]. Consumers are also interested to get fashion products [16] which are a challenge to sustainable practices in the apparel industry.

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Md. Ibrahim H. Mondal and Mashiur Rahman Khan

Figure 1.1. Flow chart of denim manufacturing.

Designers seek to practice environmental responsibility and discover solutions for current problems [17]. Literature suggests that sustainable practices in the textile and apparel industries include the use of renewable and non-harmful materials [18-20], applying lowimpact processes [21, 22], the re-cycling of waste materials [23], the eco-friendly, green and environmental friendly process [24], and fashion product which is one of the biggest barriers encountered in the apparel industry [25]. Along with increasing global awareness of environmental problems, consumers’ awareness of sustainability has risen and consumers are seeking environmentally friendly clothing, and producers are exploring ways to meet these demands while processing clothing. Sustainable design includes production processes also. In producing sustainable design, the designers determine the properties of the products with sustainability [26]. Sustainability requires a delicate balance of choices. Therefore, sustainable denim designs represent an apparel product which is fashion oriented, performance based; and environmental friendly. Therefore, sustainable denim apparel refers to eco-friendly, fashionable, aesthetic, durable and high wear performance apparel, based on customers’ choice. Sustainable practices are growing in the apparel washing industry. In denim washing industry, bleaches are commonly used with other chemicals. Most of the cases, textile and apparel manufacturers are using traditional hydrogen peroxides and hypochlorite bleaches in processing textile and denim apparels, which has more or less negative-impact in the environment. Enzymatic washing and stone-enzyme washing processes are now popular and increasing its use in textile and apparel washing industry, because it is eco-friendly, support the green chemistry and safe for the environment.


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In the textile and apparel industries, the concepts of sustainable washing for denim apparel explore to the enzymatic washing and stone-enzyme washing processes which can be used to develop sustainable denim designs.

1.4. Literature Review In the last few years, the popularity of denim apparel washing has been increased and many researchers have investigated the effect of the washing for denim apparels. Some important works of various washes on denim apparels are presented below.

Enzymatic Treatment in Denim Apparel Washing The study of enzymatic washing on denim apparel is important for physical, aesthetical and environmental point of view. Denim apparel manufactures have washed their apparels for many years with chemicals to achieve a soft-hand as well as desirable washing effects. Indigo-dyed denim apparel is the most popular for youth [27]. Therefore, the properties of denim apparels have been widely studied due to its fundamental importance and its many applications in current fashion trends. The existing literature in this domain has focused considerable attention with enzymatic washing for denim apparels. The use of environmentally friendly, nontoxic, fully biodegradable enzymes have been using in the modern textile wet process industries for decades. Enzymes are produced by living organism and one kind of protein that is obtained from fermentations method from naturally existing bacteria and fungi and attack to a specific molecular group. Structurally, enzyme is a biological polymer. Cellulases are enzymes and commonly used in textile industry. According to their amino acid sequences, it consists of either a catalytic domain (CD), or a cellulose-binding domain (CBD) or both domains [28]. Most of the cellulases used in the denim washing are fungal (with a CBD of family I, cellulose-binding domain) [29]. CavacoPaulo et al. [30] reported that the cellulases used in the denim washing industry have CBDs from family I (30-36 amino acids, i.e., fungal cellulases from Trichoderma ressei and Humicola insolens), whereas CBDs of cellumonas fimi bacteria belong to family II (103-146 amino acids). Commercially, there are mainly two kinds of cellulase being used for denim washing, namely acid cellulose and neutral cellulase. Acid cellulases are more aggressive on cotton [31]. Cellulase hydrolyses the cellulose, yielding long chain cellulose polymer to a short-chain polysaccharides and glucose. The enzymatic action also loosens the indigo dye, which is more easily removed by the mechanical abrasion of rotating cylinder washing machine. Cellulases are inducible enzymes synthesized only in the presence of cellulosic materials or other appropriate inducers [32-36]. Today approximately 80% denim apparels are treated with cellulase enzymes [37]. Cavaco-Paulo [38] reported that desizing with amylases was the first applications of enzymes in textile industry [38]. Enzymatic treatment with amylase enzymes has replaced the harsh processes since the beginning of the last century [39]. Many commercial α-amylases are available now and it is estimated that approximately 15% of all commercial textile enzymes are used in desizing processes [40]. In order to prevent the yarn breaking during weaving, warp yarns are sized with starch and its derivatives. The starch is a natural, biodegradable, and a mixture of two polysaccharides, amylase and amylopectin consisting mainly of α-1, 4-linked glucose units [41].

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Cavaco-Paulo et al. [30, 42] carried out a series of studies to investigate the washing effects of denim garments by cellulase treatment. From their studies reported that cellulases are most successful in producing the stone-washed look denim apparels with modified appearance. Aged/old looked denim with cellulase is the non-homogeneous removal of dye, giving the fashionable contrast of various blue shades. Cavaco-Paulo [43] reported that cellulases are always applied in washing processes where strong mechanical action on the fabric is provided. As a result, the weight and strength loss increased. Nevell [44] reported that, the primary wall of cotton contains waxes, proteins, lipids, pectins, organic acids and noncellulosic polysaccharides constituting up to 10% of the total fiber weight and by washing the fiber loss weight mostly. The secondary wall contains a mature fiber and consists almost entirely of fibrils of cellulose arranged spirally around the fiber axis [45] and by enzymatic washing the fibrils of cellulose in secondary wall is slightly disoriented and partly damaged and strength is lost and softens apparels are produced. Cavaco-Paulo et al. [30] explained that the slow kinetics of enzymatic degradation of crystalline cellulose improves fabric and fiber properties (remove fuzz fibers) without excessive damage. Mori et al. [46] showed that cellulase treatment improves the handle of cotton fabric. They found that the primary wall of the cotton fiber is eliminated in the initial step of hydrolysis; as a result a reduction in the fineness of the cotton fibers takes place. They also suggested that enzymatic hydrolysis occurs in the secondary wall of the cotton fibers, even during the initial step of hydrolysis so that cotton fabric becomes soft and loses strength. Also, Walker and Wilson [47], Pedersen et al. [48], Duran and Marcela [5] studied cellulase on cotton and found that cellulase improves fabric hand and enhance aesthetic properties. Similar, many studies of cellulase applications on textiles and the properties of cotton fabrics were reported by Buschle-Diller et al. [49] and Radhakrishnaiah et al. [50]. Heikinheimo et al. [8] reported that cellulases are introduced to replace aggressive chlorine bleach in textile industry.

Pumice Stone in Denim Apparel Washing The fundamental problem of enzyme in denim wash has received considerable attention from researchers. Such a problem is usually overcome by stone wash. A few but some important studies of the stone washes are given below. Pumice stone is generally used on the denim apparel to achieve a soft handle as well as a desirable bleached-out character. In denim washing, pumice stones are mixed with enzymatic processes to obtain irregular, nice stone-wash look effects. The surface of pumice stone is rough, irregular, light weight and perforated and floats on water during washing in machine. The use of stone makes brushing action on the apparel surface; as a result irregular color fading effect is produced rapidly. But stone wash causes processing and equipment problems. The main disadvantages of stone washing are the difficulty of removing residual pumice from processed clothing items and the damage to the equipment by the overload of tumbling stones [51]. In spite of these disadvantages, pumice stone is still used in denim washing industries and researchers using certain researches with pumice stones [52]. Pumice stones combined with cellulases cause the desired fading and softening of the apparel [53]. They concluded that mechanical action by pumice stone opens the outermost layers in secondary cell of cellulosic crystals, thus increasing the part of the cellulose accessible to enzymes and enhancing enzymatic removal of the dye in presence of pumice stone. Again, pumice stone with cellulases reduces time in washing process [54].


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High levels of mechanical friction with pumice stone will produce strong mechanical abrasion of yarn surfaces, releasing the indigo dye quickly and produced the stone-wash effect [30, 42]. Feki et al. [55] examined the effect of stone-washing on denim garments and evaluated compressibility, bending rigidity, shear rigidity and breaking work, but they did not worked on the other properties like water absorption, elongation at break, tensile strength and color fading.

1.5. Motivation From the literature review it is clear that very little investigational study have been carried out on the effect of chemicals in denim apparel washing. The study of denim apparel washing with sustainable designs is important for the apparel designers and manufacturers and is the new challenge in the fast changing current trends. The consumer’s has interest now in eco-fashion. To apply a system as an effective wash method for denim with chemicals is important. Thus to produce specific washing effect, considering sustainability, the analysis of the effect of parameters in denim washing is necessary. Previously, majority of the studies on denim apparels were carried out with dry processes. Thus, so far, none have conducted studies involving the effect of chemical wash for producing sustainable denim apparels, although denim is very popular apparel. Therefore, from the buyer’s point of view, consumers are concern now on sustainable denim designs, which forms the basis of the motivation behind the present study.

1.6. Present Problems Previously no work has been reported on denim apparel washing considering sustainability. The present study is an investigation with the best value for the purpose of sustainable designs production. In the present investigation, two different types of washes are considered. One is cellulase washing with various concentrations, temperatures and times in a fixed amount of washing liquor. Second one is cellulase with pumice stone in denim garment washing with various concentrations of pumice stones, temperatures and times. The proposed studies are expected to reveal that the denim performance in such washings are very much important from those studied in the above literature and it will therefore prove useful from the manufacturer’s and designer’s point of view in choosing the best that suit them.

1.7. Objectives The aim of this work was to define the optimum conditions for washing of denim readymade apparels in order to achieve the desired finishing effects with minimum negative impacts in environment and properties. However, the specific aims of the study were: ● ●

To investigate the chemical effects and the mechanisms of these effects on denim apparel washing. To study the effects of different cellulases on denim apparel properties.

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Md. Ibrahim H. Mondal and Mashiur Rahman Khan ● ● ●

To describe how to produce a sustainable denim apparel. To develop a dynamic washing method for denim apparels. To carry out the validation of the present wash methods for denim washing includes enzyme wash, and stone-enzyme wash.

To find out the best washing conditions with specifications for washing denim apparel with enzyme and /or stone-enzyme that will develop existing method and new dynamic method will be introduced.

2. EXPERIMENTAL DETAILS 2.1. Materials The denim apparel and chemicals used in these experiments are listed as:

2.1.1. Denim Apparel Fabric: All fabric used in this investigation was of 100% cotton twill weave (3/1 LHT. 381 g/m2) denim, manufactured in a Textile mill in Bangladesh. Apparel: Denim apparels (trouser) were manufactured using the stated denim fabric. The denim apparel used in these experiments is shown in Figure 2.1 and a summary of the denim fabric properties is listed in Table 2.1.

Figure 2.1. A portion of denim apparel used.


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Table 2.1. Properties of the denim fabric used Property Material Warp count, weft count EPI, PPI Weight (g/m2) Weave Type of dyestuff Tensile strength-warp (kg-f) Tensile strength-weft (kg-f) Elongation-warp (%) Elongation-weft (%) Dimensional stability (%)

Denim fabric 100% Cotton 10 Ne, 9 Ne 70, 42 381 3/1 LHT Indigo 246 137 24 16 2.25

Table 2.2. Properties of the pumice stone used Property Material /composition Size (cm) Surface Color Nature Weight (g/pc) Source Origin

Specifications SiO2 73.14%, Al2O3 12.36%, Fe2O3 1.38%, Na2O 3.79%, K2O 2.7%, MgO 0.13%, CaO 0.88%, FeO 0.66%, TiO2 0.1%, others-rest 4-5 Rough White-slightly Perforated, water floated Light (10-12) Volcanic explosion Turkey

2.1.2. Cellulase Enzyme Two different natures of cellulase enzymes, acid cellulase (Genzyme SL, Multichemi Ltd, Sri Lanka) and neutral cellulase (Bactosol JCP, Clariant Ltd, Swizerland) were used. In addition, mixtures of acid and neutral cellulases 50/50 were also used. The cellulases are biochemical substance that behaves as a catalyst toward specific reactions. According to manufacturer, the activity of enzymes; acid enzyme- pH 4.5-5.5, temp 45-650C; neutral enzyme- pH 6.0-7.0, temp 40-550C. In washing, the enzymes break some of the fibers on the surface and hence give the fabric a soft, faded and old look effect. The cellulose loosens the indigo dye and fading effect is produced rapidly during washing. 2.1.3. Pumice Stone Fresh pumice stones were used for the treatments of stone-enzyme washing. The stones are available in three sizes i.e., small (2-3 cm), medium (4-5 cm) and large (5-7 cm). Medium size stone was used for the experiments. These stones are perforated, rough surface, light weight and floats on water. The pumice stone used in these experiments is shown in Figure 2.2. A summary of the pumice stone properties is listed in Table 2.2.

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Figure 2.2. Pumice stone used in the experiments.

2.2. Methods Following processes have been used to perform washing. These are as follows –

2.2.1. Desizing The desizing was conducted in liquor containing Hostapur WCTH 0.6 g/L (a detergent, BASF, Germany), Luzyme FR-HP 1.2 g/L (a desizing agent, BASF, Germany), AntistainLP30 0.4 g/L (an anti-back staining agent, GDS, India) and material to liquor ratio of 1:10 in an industrial horizontal sample washing machine (model-NS 2205, Ngai Shing, Hong Kong) at temperature 60°C for 20 min in order to remove the size materials of warp yarns which was applied in fabric manufacturing to reduce yarn breakage. After that washed with hot water at 70°C, followed by cold water wash at 25°C. 2.2.2. Washing Desized denim trousers were treated with chemicals (depends on wash type) in a sample washing machine at different concentrations of chemicals, temperatures and times using the enzyme and stone-enzyme washing methods followed by the standard washing procedure. All treatments were involved in a rotary cylindrical washing machine at 30 rpm. 2.2.3. Hydro-Extracting Process Chemically processed denim trousers were squeezed in a laboratory scale hydro-extractor machine (Roaches, England) to remove excess water from the apparels at 200 rpm for 4 min. The hydro-extracting machine is shown in Figure 2.4.


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Figure 2.3. Industrial sample washing machine.

Figure 2.4. The hydro-extracting machine.

2.2.4. Drying Process The hydro-extracted denim trousers were dried in a steam tumble drier (Opti-Dry, England) at 75°C for 40 min. Treated denim apparels were then evaluated by characterizing of their physical and mechanical properties. The drying machine is shown in Figure 2.5.

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Figure 2.5. The tumble drying machine.

2.3. Analysis Various instruments and machines are used to determine physical and mechanical properties of denim apparels. The fabric analyses carried out during this study are listed in Table 2.3.

2.3.1. Measurement of Tensile Strength and Elongation at Break Tensile strength and elongation at break of denim samples were carried out using a horizontal (Goodbrand, UK) tensile strength tester according to ASTM D 5034 Grab test method [56]. Tensile strength and elongation were measured in the warp and weft directions in treated samples. The Grab test uses two jaws. The specimens are cut to a size of 5 in wide and 10 in long and then frayed down in the width 4 in (10 cm). The sample is then placed between the jaws and set the distance 6 in (15 cm) between the jaws, then pulled away from other. The sample is broken in 20 ± 3sec. At the point of break, tensile force was taken from the dial and at the same time the value of elongation was taken from the attached scale in the machine. The force and elongation at this point are noted. Any breaks that occur within 1 cm of the jaws should be rejected. The mean breaking force and mean extension as a percentage of initial length are reported. 2.3.2. Measurement of Weight Loss Fabric weight loss of treated denim samples was measured after conditioning for 24 h at 200C and 65% RH (ASTM D 1776) [57] with a standard cutter and digital balance according to ASTM D 3776 [58].


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The weight loss (%) was calculated from the difference in fabric weight (grams/square meter) before and after the chemical treatments. The apparatus used for weight loss measurement consists of a circular cutter with a rubber board and a digital balance. First apparel was placed on a flat table and using scissor fabric is cut 12 x 12 in. Then placed on rubber board and fabric was cut by circular cutter (dia. 10.1 cm) and then kept the cut sample on digital balance and taken weight. The weight loss was calculated as percentage using the weight of untreated and treated samples.

2.3.3. Measurement of Color Change The effects of the chemical treatments on denim apparel color were evaluated by estimating the color change value with an AATCC Gray scale to color change according to AATCC Evaluation Procedure 1 [59]. According to this standard, the changes in the color of the fabric being tested, that is color fading. A numerical assessment of each effect is made by comparing the changes with standard Gray scale to color change. The visual difference between the original and treated denim fabric is compared with the differences represented by the Gray scale. The difference in the color change is given a numerical value ranging from 5 to 1. Class 5 indicates no change in the original color/shade. Class 1 indicates a noticeable change in color/shade. Gray scale for color change consists of nine pairs of standard gray chips, each corresponds a difference in color/shade corresponding to a numerical color change rating. In order to evaluate color change rating, the specimen was cut from the untreated denim trouser. Then another specimen was cut from the chemically treated denim trouser and these two specimens were placed side by side in the same plane and compare with the Gray scale. 2.3.4. Measurement of Fabric Stiffness In order to determine the fabric stiffness for this study, a stiffness test were conducted and measured the bending length of denim samples by Shirley stiffness tester according to BS 3356 [60] at 200C and 65% RH. The higher the bending length, the stiffer is the fabric. To measure the bending length a horizontal strip of fabric as specimen was cut to a size of 1 in wide and 6 in long. The fabric sample was then placed under a template. When the tip of the specimen reaches a plane inclined at 41.50 below the horizontal, the overhanging length was then observed in centimeters directly from the Shirley apparatus. The bending length is dependent on the weight of the fabric and its flexibility. 2.3.5. Measurement of Water Absorption The effects of the chemical treatments on water absorption (rate of uptake) of denim fabric were measured according to BS 3449 [61]. The water absorption (%) was calculated from the difference in water absorbed before and after the chemical treatments. The static immersion test was used for measuring the total amount of water that a fabric will absorb. In the test weighted samples of the fabric were immersed in water for a given length of time (20 min), taken out and the excess water removed by shaking. They were then weighted again and the weight of water absorbed was calculated as a percentage of the dry weight of the fabric. The specimens were cut to a size of 80 x 80 mm at 450 to the warp direction. Then the samples was conditioned and was taken weight each sample. The samples were then immersed in distilled water at a temperature of 20 ± 10C to a depth of 10 cm.

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A sinker was used to hold the specimen at the required depth. In this position the samples were left for 20 min. After that the samples were taken from the water and the surface water was removed immediately by shaking them ten times. Then the samples were reweighted and mean percentage absorption is calculated from the formula: Absorption = mass of water absorbed / original mass of fabric x 100%

2.3.6. SEM Analysis Scanning Electronic Microscopy photographs (SEM) were obtained of the chemically treated denim samples and monitored surface appearance and morphological value. The scanning electronic microscope (model-S 3400N, Hitachi, Japan) used in this experiment is shown in Figure 2.6. 2.3.7. FM Analysis Fluorescence Microscopy photographs (FM) were obtained from the chemically treated denim samples and analyzed physical changes of yarns in fabrics. The fluorescence microscope (model- IX71, Olympus, Japan) used in this experiment is shown in Figure 2.7.

3. RESULTS AND DISCUSSION 3.1. Effects of Cellulase Enzyme Concentration In this experiment, enzymatic treatment of denim apparels with acid, neutral and mixture of acid and neutral cellulases was performed in the washing machine under the concentrations of 0.5, 1.0, 2.0, 3.0 and 3.5% (owg).

Figure 2.6. The view of scanning electronic microscope.


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Figure 2.7. The view of fluorescence microscope.

Table 2.3. Analyses used for denim sample Analysis Tensile strength Stiffness Color change Weight Water absorption Microscopy Microscopy

Method used Grab test Bending length Gray scale Dry weight, conditioning Static immersion test SEM FM

Ref. ASTM D 5034 BS 3356 AATCC Evaluation 1 ASTM D 3776 BS 3449

The cellulase enzyme hydrolyse cellulose and allowing changes on color and fiber polymer chain which affects on the fabric properties. The effect of cellulase enzymes with various concentrations of 0.5-3.5% on the properties of denim apparels in terms of tensile strength, stiffness, color fading, weight and water absorption was determined and is shown in Tables 3.1-3.4. From these Tables 3.1-3.4, it can clearly be understood the washing effects from the each others. Tensile strength is the measure of the breaking force of the fabric which affects fabric mechanical property. The tensile strength evolution after enzyme washing with various concentrations can be seen in Table 3.1. On washing at various concentrations of cellulase enzymes the tensile strength decreased due to the cellulose hydrolysis by enzymes. As a result, the warp and weft both yarns in the fabric are affected by enzyme and the weft yarns are more affected in its strength than warp due to the undyed weft yarns are more hydrolysed by enzyme.

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It can be seen from Table 3.1 that, at low concentration (0.5%) of enzyme, 6.5%, 5.6% and 5.0% strength losses were observed in warp direction when the apparels were treated with acid, neutral and mixed enzymes; and 22.7%, 19.5% and 18.5% strength losses, respectively were observed with higher enzyme concentrations (upto 3.5%). Whereas, 11.0%, 8.8% and 8.0% strength loss and 33.0%, 30.8, and 28.6% strength losses were observed in weft respectively. The decrease in tensile strength at 0.5 to 3.5% was higher with acid cellulase than neutral cellulose due to the different amino acid compositions of acid and neutral celluloses. Campos et al. [62] reported that differences in amino acid residues of acid and neutral cellulases seem to be the main reason for their hydrolysis behavior to cellulose. Hydrolysis of cellulose would certainly affect fabric tensile strength. Cavaco-Paulo et al. [42] investigated that during dyeing the insoluble indigo is known to form agglomerates in aqueous solutions and these indigo molecules bind on warp yarn surface. As a result, in denim washing, firstly indigo agglomerates are fractioned into smaller particle with cellulases, and then hydrolyse the cotton yarn/cellulose. On the other hand, cellulases directly hydrolyse the undyed weft yarns. This seems to be the main reason for high strength loss in undyed weft than colored warp. Buchert and Heikinheimo [37] and Kleman-Leyer et al. [63] have previously been obtained similar results for tensile strength with undyed cotton cellulose. Table 3.1. Effect of enzyme washing with different concentrations of cellulase on the tensile strength of denim apparel in warp and weft directions

Cellulase conc. (%) 0.0 0.5 1.0 2.0 3.0 3.5

Loss in tensile strength in warp direction, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 6.5 5.6 5.0 10.5 8.9 8.5 16.6 13.4 12.6 22.7 17.0 16.6 22.7 19.5 18.5

Loss in tensile strength in weft direction, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 11.0 8.8 8.0 13.9 11.7 11.0 22.0 21.3 19.1 28.6 27.2 26.4 33.0 30.8 28.6

Table 3.2. Effect of enzyme washing with different concentrations of cellulase on the fabric weight and color shade of denim apparel in warp and weft directions Cellulase conc. (%) 0.0 0.5 1.0 2.0 3.0 3.5

Fabric weight loss, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 1.6 1.4 1.1 2.9 2.4 2.5 3.4 3.3 3.2 4.2 3.7 3.4 4.5 4.2 3.7

Color shade loss, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 10 10 10 20 10 20 30 20 30 40 30 30 40 30 40


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Table 3.3. Effect of enzyme washing with different concentrations of cellulase on the stiffness of denim apparel in warp and weft directions Cellulase conc. (%) 0.0 0.5 1.0 2.0 3.0 3.5

Stiffness loss in warp direction,(%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 28.9 22.2 22.2 31.1 28.9 28.9 44.0 43.1 43.1 44.7 43.3 43.1 44.9 44.0 43.1

Stiffness loss in weft direction, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 6.2 6.2 6.2 9.3 9.3 6.2 15.6 12.5 12.5 18.7 15.6 12.5 18.7 15.6 12.5

Table 3.4. Effect of enzyme washing with different concentrations of cellulase on the water absorption of denim apparel Cellulase conc. (%) 0.0 0.5 1.0 2.0 3.0 3.5

Acid enzyme 0 15.1 19.1 23.0 23.8 23.8

Water absorption, (%) Neutral enzyme 0 17.5 20.6 21.4 23.0 23.0

Mixed enzyme 0 16.7 20.6 23.8 25.4 25.4

It is seen from Table 3.2 that, treatment of denim garments under investigation with acid, neutral and mixed cellulase decreased the weight loss and this decrease is little bit higher at higher enzyme concentrations up to 3.5%. The main reason of weight losses is the hydrolysis behavior to cellulose by enzymes. With higher enzyme concentration the rate of hydrolysis increased and weight loss is increased. During washing, acid and neutral both cellulases are hydrolysed cotton. First, it attacked on projecting fibers (micro-fibrils) on surface, then attacked on yarn portion, hydrolyzed them slowly and penetrated inside the fabric. As a result, fibers are hydrolysed and broken down quicker with the friction of rotating cylinder of the washing machine. Hydrolysis of cellulose would certainly affect fabric weight losses in washing process. Table 3.2 shows that acid cellulase caused up to 4.5% weight loss, neutral cellulase up to 4.2% loss and mixed cellulase up to 3.7% loss at the concentrations of 3.5%.. It is observed that the weight loss decreased more in acid enzyme than neutral enzyme, and weight loss is less when denim apparel washed with mixed enzymes. Again, denim hydrolysis was measured by monitoring the color shade change. It can be seen from the Table 3.2 that the color shade decreased with higher concentrations from 0.5% to 3.0%. The color shade is not decreased more, with the increasing of concentration from 3.0 to 3.5%. In enzyme washing, the part of the primary wall of indigo-dyed denim apparel is always in contact with cellulase. At the contact point, the surface dyes are partly detached from the main fiber chain and indigo dye bonds are broken from the yarn surface. As a result, the treated denim apparel becomes duller and color is faded. In addition, mechanical friction inside washing machine accelerate cellulose hydrolyses and destroy color.

36


Grieve et al. (2006) has previously been obtained similar result for color fading of denim apparels. The results disclose that increasing the cellulase concentration from 0.5 to 3.0% has effect on color fading and from 3.0 to 3.5% has no effect on color shade change, because most indigo agglomerates are fractioned into smaller particle at 3.0% cellulase concentration, and with increased concentration up to 3.5% cellulases, remaining indigo agglomerates are not fractioned into smaller particle, as a result color will not fade further. It can be seen from the Table that acid cellulase caused 10 - 40% color loss, neutral cellulase 10 - 30% loss and mixed cellulase caused 10 - 40% loss. It is observed that the decrease in color shade at 3.5% was higher with acid cellulase than neutral cellulose. This means that indigo color fading also depends on the nature of cellulase enzymes with increasing cellulose concentrations. It can be seen from the Table 3.3 that the stiffness of denim apparels decreased after they were exposed to acid, neutral, and mixed enzymes at concentrations of 0.5 - 3.5%. After treatments, the starch of warp yarns are removed first, then it hydrolyzed cellulose similar to color fading mechanism by cellulases discussed earlier. As a result, bending length was less and stiffness decreased in comparison to untreated denim for all the three cases. The decrease in stiffness at concentrations of 0.5 to 3.5% was higher with acid cellulase than neutral cellulase. Cavaco-Paulo et al. [42] investigated that acid cellulases have a higher affinity for indigo than neutral cellulases. Thus, more hydrolyses occurred by acid cellulase and stiffness decreased. It can be seen from the Table that acid cellulase caused 28.9-44.9%, neutral cellulase 22.2-44.0% and mixed cellulase caused 22.2-43.1% stiffness loss in warp direction and 6.2-18.7%, 6.2-15.6%, 6.2-12.5% respectively in weft direction. Water absorption is the measure of the level of water in the denim apparel which affects fabric properties. Table 3.4 shows the changes in water absorption with the increasing of concentration of cellulases from 0.5-3.5% in denim washing, due to the loosening of surface fibers by enzymatic treatment. The loosening of surface fibers would certainly affect fabric water absorption. From the Table it can be seen that, the water absorption increased 15.1-23.8% at 0.5-3.0% concentration with acid cellulase, 17.5-23.0% with neutral enzyme, and 16.7-25.4% with mixed cellulase, and does not cause any further increase of water absorption when the concentration increased from 3.0 to 3.5%. With increased water absorption, the denim apparel shows increased water vapor permeability that means comfortness or softness increased. Therefore, there is a strong relationship between water absorption and fabric comfortness and softness; which affects the properties of denim apparels.

3.2. Effect of Temperature in Cellulase Enzyme Treatment of denim apparels with acid, neutral and mixed cellulase was performed under the influence of 40, 50, 55, 60 and 65 °C. The onset of temperature on loss in tensile strength, stiffness, color fading and fabric weight, and gain in water absorption is shown in Tables. The changed /modified value of different physico-mechanical properties of acid, neutral, and mixrd cellulases treated denim apparels against the effect of various temperatures are listed in Tables 3.5 - 3.8. Enzyme washing with the effect of temperatures on the strength properties of denim apparels was measured and is shown in Table 3.5. The effect of temperature at 400C had practically little effect on the strength properties of denim apparels (6.5-9.3% loss in warp and 11.0-13.2% loss in weft direction); those at the highest temperature of 650C big effects on tensile strength (21.5-22.7% in warp and 27.2-30.1% in weft direction) were observed.


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Table 3.5. Effect of enzyme washing with different temperatures of cellulase on the tensile strength of denim apparel in warp and weft directions

Temp. (oC) 0.0 40 50 55 60 65



Table 3.6. Effect of enzyme washing with different temperatures of cellulase on the fabric weight and color shade of denim apparel in warp and weft directions

Temp. (oC) 0.0 40 50 55 60 65

Fabric weight loss, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 2.3 1.8 1.8 2.8 2.3 2.3 3.4 3.3 3.2 4.9 4.4 4.4 5.5 4.5 4.4

Color shade loss, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 10 10 10 20 10 20 30 20 30 40 30 30 40 40 40

However, by increasing the temperature upto 650C, 22.7% loss in strength in warp and 30.1% loss in weft direction by acid enzyme was obtained, whereas 21.5% loss in warp and 27.9% loss in weft by neutral enzyme, and 22.35 loss in warp and 27.2% loss in weft by mixed enzymes was obtained. From the Table 3.5, it is observed that decrease in tensile strength at 40 to 650C was higher with acid cellulase than neutral cellulase. This is occurred, due to more fiber degradation with raising temperature in cellulose washing with acid enzyme than neutral and mixed enzymes. Table 3.6 shows the decreases in weight of fabric with the increasing of temperature from 40 to 650C. This is due to the removal of projecting fuzz fibers from the fabric surface with the effect of temperature. With higher temperature, at 650C, the weight loss was higher for the acid enzyme (5.5%) than for the neutral (4.5%) and mixed enzyme treated (4.4%) denim apparels. It can be seen from the Table that acid cellulase caused 2.3-5.5% weight loss, neutral cellulase caused 1.84.5% loss and mixed cellulase caused 1.8-4.4% loss. The effect of temperature on color fading was monitored and also shown in the same Table. It can be seen from the Table 3.6 that the denim apparel washing with acid, neutral, and mixed enzymes decreased the color shade with the increase of temperature from 40 to 650C. From the Table, it is observed that the decreases in color shade from 40 to 600C was higher for the acid enzyme (40%) than for the neutral enzyme (30%). In cellulase washing, raising

38


the temperature enhanced the color fading quicker, due to more hydrolysis of cellulose by the effect of temperature. The effect of temperature on stiffness was monitored. It can be seen from the Table 3.7 that the decreases in stiffness of denim apparel with the increasing of temperature from 40 to 650C. From the Table 3.7, it is observed that the decreases in stiffness from 40 to 650C were higher for the mixed enzyme (45.3%) in warp direction than for the acid (44.8%) and the neutral enzymes (44.4%), whereas, the decreases in stiffness from 40 to 650C were almost similar in weft direction for the acid enzyme (15.6%), neutral enzyme (15.6%) and the mixed enzymes (15.6%). In cellulase washing, raising the temperature decreases the stiffness, due to more hydrolysis of cellulose. Table 3.8 shows enzyme washing at 400C caused increase in water absorption to 13.4%, 15.1% and 15.8% for acid, neutral and mixed enzymes respectively and the increase was higher at higher temperature up to 650C. After enzyme treatment, the water absorption increased to 26.1% at 600C by the mixed enzyme, 24.6% with neutral enzyme and 23.8% with acid. Therefore, the mixture of acid and neutral enzymes is the most effective enzyme to increase water absorption when washing was performed at 600C. The water absorption does not cause further increase when temperature increased from 60 to 65°C in all the three cases. Table 3.7. Effect of enzyme washing with different temperatures of cellulase on the stiffness of denim apparel in warp and weft directions

o

Temp. ( C) 0.0 40 50 55 60 65

Stiffness loss in warp direction,(%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 33.3 31.1 28.8 38.2 37.7 36.8 44.0 43.1 43.1 44.7 44.4 44.8 44.8 44.4 45.3


Table 3.8. Effect of enzyme washing with different temperatures of cellulase on the water absorption of denim apparel Temp. (oC) 0.0 40 50 55 60 65

Acid enzyme 0 13.4 15.8 23.0 23.8 23.8


Mixed enzyme 0 15.8 19.8 23.8 26.1 26.1


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3.3. Effects of Time in Cellulase Enzyme Treatment of denim apparels with acid, neutral and mixed cellulase was performed under the influence of treatment time 20, 30, 40, 50 and 60 min. The onset of time on loss in tensile strength, stiffness, color fading, fabric weight and gain in water absorption is shown in Tables 3.9 - 3.12. It can be seen from the Table 3.9 that the decreases in tensile strength of denim apparel decreases with the increase of washing time from 20 to 60 min. From the Table 3.9, it is observed that the decrease in tensile strength from 20 to 60 min are higher for the acid enzyme (22.7% in warp direction) than for the neutral enzyme (21.9%) and for the mixed enzyme (44.4%), whereas, the decrease in tensile strength in weft direction are 30.1%, 27.2% and 25.2% respectively. Table 3.9. Effect of enzyme washing with different times of cellulase on the tensile strength of denim apparel in warp and weft directions

Time (min) 0.0 20 30 40 50 60



Table 3.10. Effect of enzyme washing with different times of cellulase on the fabric weight and color shade of denim apparel in warp and weft directions

Time (min) 0.0 20 30 40 50 60

Acid enzyme 0 1.8 2.3 3.4 4.4 5.2

Fabric weight loss, (%) Neutral Mixed enzyme enzyme 0 0 1.0 1.5 1.5 2.0 3.3 3.2 3.6 3.9 4.9 4.0

Acid enzyme 0 10 20 30 30 40

Color shade loss, (%) Neutral Mixed enzyme enzyme 0 0 10 10 10 20 20 30 30 30 40 40

In enzyme washing, raising the washing time decreases the tensile strength, due to more hydrolysis of cellulose with longer time. The decrease in strength mostly occurred with the time between 40 and 60 min. Increasing the time from 20 to 60 min affects on fabric strength as well as the durability of apparels. With increasing time, the loss in tensile strength in weft is higher than warp direction; due to the direct hydrolysis on the undyed weft yarns by

40


enzymes than colored warp yarns. This seems to be the main reason for high strength loss in weft yarns than warp yarns. Table 3.11. Effect of enzyme washing with different times of cellulase on the stiffness of denim apparel in warp and weft directions

Time (min) 0.0 20 30 40 50 60

Stiffness loss in warp direction, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 33.3 24.4 33.7 35.7 31.1 36.4 44.0 43.1 43.1 44.5 44.0 44.4 44.8 44.0 44.8


Table 3.12. Effect of enzyme washing with different times on the water absorption Time (min) 0.0 20 30 40 50 60

Acid enzyme 0 15.0 19.0 23.0 23.8 25.3


Mixed enzyme 0 17.4 22.2 23.8 26.9 28.5

Table 3.10 shows the decrease in weight of fabric after enzyme washing with the increasing of time from 20 to 60 min. With higher time for 60 min, the weight loss was higher for the acid enzyme (5.2%) than for the neutral enzyme (4.9%) and mixed enzyme (4.0%). It can be seen from the Table 3.10 that the color shade of denim apparel decreases with the increasing washing time from 20 to 60 min. The decrease in color shade from 20 to 40 min were higher for the acid enzyme (30%) than for the neutral enzyme (20%), whereas, with increasing time more than 40 min similar results obtained for all the three cases. The changes in color shade with the increasing of time which affects worn look of denim garments. Table 3.11 shows the decreases in stiffness with the increase of time from 20 to 60 min which affects softness of the denim apparels. Table 3.12 shows the changes in water absorption of denim apparels after washing with acid enzyme, neutral enzyme, and mixed enzyme from 20 to 60 min. Enzyme washing for 20 min caused increases in water absorption of 15.0%, 11.1% and 17.4% for acid, neutral and mixed enzymes respectively and this increase was higher at higher time up to 60 min. The water absorption of denim fabrics treated with mixed enzymes, acid enzyme and neutral enzyme for 60 min are 28.5%, 25.3% and 24.6%, respectively.


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3.4. Effects of Pumice Stone Concentration In this study, mechanical abrasion was achieved by pumice stone in the washing machine. The addition of pumice stone in cellulase treatments accelerates more mechanical abrasion and allowing enzymatic hydrolysis quicker which affects on the fabric properties. Cavaco-Paulo et al. [30] have pointed out the importance of mechanical agitation on cellulose hydrolysis in enzymatic treatments. Liu et al. [64] reported that mechanical agitation depends on rotation speed, liquor ratio, load size and processing time. In this study, stone washing effects in presence of enzyme on fabric properties were determined. A combination of high level of abrasion by pumice stone and enzyme action may generate fibrillar material on the fabric surface reported by CavacoPaulo et al. [30] Pumice stone gives a used look appearance on denim distinctly. In this part of study, mechanical abrasion was achieved by pumice stone in the rotating cylinder of the washing machine at 30 rpm. The effect of pumice stone with various concentrations (10-70%) (owg) on the properties of denim apparels was determined and is shown in Tables 3.13-3.16. Table 3.13. Effect of pumice stone-enzyme washing on the tensile strength of denim apparel in warp and weft directions

Pumice stone, (%) 0.0 10 20 30 40 50 60 70

Loss in tensile strength in warp direction, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 14.6 9.7 7.3 18.3 14.6 13.0 22.3 17.8 15.8 27.2 24.3 20.7 29.3 25.2 23.5 33.3 26.4 25.2 34.9 30.0 28.4

Loss in tensile strength in weft direction, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 11.0 11.0 9.5 16.1 14.7 12.5 24.2 22.0 19.8 30.1 29.4 28.6 33.8 31.6 30.8 34.5 33.0 32.3 34.5 33.8 33.8

Table 3.14. Effect of pumice stone-enzyme washing on the fabric weight and color shade of denim apparel Pumice stone, (%) 0.0 10 20 30

Fabric weight loss, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 2.3 1.8 1.8 3.4 2.6 2.9 4.2 3.4 3.9

Color shade loss, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0 30 20 10 30 20 20 40 30 40

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Md. Ibrahim H. Mondal and Mashiur Rahman Khan Table 3.14. (Continued)

Pumice stone, (%) 40 50 60 70

Fabric weight loss, (%) Acid Neutral Mixed enzyme enzyme enzyme 4.5 3.9 4.5 4.9 4.5 4.5 5.2 4.9 4.9 5.5 4.9 5.2

Color shade loss, (%) Acid Neutral Mixed enzyme enzyme enzyme 50 40 50 60 50 60 60 60 60 60 60 60

Table 3.15. Effect of pumice stone-enzyme washing on the stiffness of denim apparel in warp and weft directions

0.0

Loss in stiffness in warp direction, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0

Loss in stiffness in weft direction, (%) Acid Neutral Mixed enzyme enzyme enzyme 0 0 0

10

31.1

28.9

33.3

9.3

6.2

6.2

20

37.7

35.5

40.0

12.5

9.3

12.5

30

44.4

40.0

46.6

15.6

12.5

15.6

40

46.6

44.4

46.6

15.6

12.5

15.6

50

46.6

44.4

46.6

18.7

18.7

18.7

60

48.8

46.6

51.1

18.7

18.7

18.7

70

48.8

48.8

51.1

18.7

18.7

18.7

Pumice stone, (%)

Table 3.16. Effect of pumice stone-enzyme washing on the water absorption of denim apparel Pumice stone, (%) 0.0 10 20 30 40 50 60 70

Acid enzyme 0 15.8 19.8 25.4 26.1 26.9 27.7 27.7

Water absorption, (%) Neutral enzyme 0 17.5 20.6 22.2 23.8 25.4 25.4 25.4

Mixed enzyme 0 16.7 20.6 26.1 26.9 27.7 28.5 28.5

The tensile strength evolution after stone-enzyme washing can be seen in Table 3.13. On washing at various concentrations of pumice stones the tensile strength decreased due to the rubbing action provided by the pumice stones. The weave of the fabric used in this study is a 3/1 twill, so the effect of abrasion is more concentrated on warp yarns than weft yarns. When


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garments are washed with stone, the surface yarns are aggressively affected by the stone rub action thereby underside yarn surfaces can be retained away from the rub directly. As a result, warp yarns are more affected by stone in acid enzyme than neutral and mixed enzymes. When the pumice stone and the mixture enzyme are combined in the washing solution, the fiber’s degradation become more important and causes an intensive increase of hydrolysis, which effects on fabric tensile strength. Klahorst et al. [31] reported that cellulase hydrolyses the cellulose, yielding long chain cellulose polymer to a short chain polymer. The hydrolysis of cellulose link breaks the molecule in several pieces, which decompose fiber, consequently the tensile strength are greatly reduced. It is observed that, at low concentration of pumice stone (10%), the decreases in tensile strength were 14.6%, 9.7% and 7.3% in warp for acid, neutral and mixed enzymes. However, at high concentration of pumice stone (70%), high reduction in strength of denim was obtained for the case of acid enzyme than the neutral and mixed enzyme. The cellulase attacks and mechanical agitation may have caused more damage on the fabric surface by cutting the cellulose chains. Acid enzyme with pumice stone (70%) caused the highest strength loss (34.9%), whereas the neutral enzyme (30%) and mixed enzyme (28.4%) had less effect on the strength properties. In practice such high strength loss values are not acceptable. Table 3.14 shows the impact of pumice stone on the weight loss of denim apparels. High weight loss of 5.5% was obtained with 70% pumice stone for acid enzyme, compared to the weight losses of 4.9% for neutral enzyme and 5.2% for mixed enzyme. Treatments showed that the mechanical action by pumice stone caused higher weight loss of fabric. It can be seen from the Table 3.14 that the color shade decreased after they were treated to acid, neutral, and mixed enzymes at higher pumice stone concentrations particularly from 30 -70%. From the Table 3.14, it can be observed that the decrease in color shade at 10-70% was higher for acid enzyme than for neutral enzyme and pumice stone with acid, neutral, and mixed enzyme caused 10 - 60% color loss. Table 3.15 shows the losses in stiffness of denim garment. It can be seen from the Table 3.15 that pumice stone with acid cellulase caused 31-49% stiffness loss, neutral cellulase caused 29-49% loss and mixed cellulases caused 33-51% loss. The stiffness loss is highest in mixed cellulase than acid and neutral cellulases. From the Table 3.15, it can clearly be differentiated each value from the others due to the differences in amino acid residues in cellulases and abrasion by pumice stone. Table 3.16 shows the effect of pumice stone concentration on water absorption. The water absorption is increased when washing was performed by pumice stone with acid, neutral and mixed cellulases due to the loosening of surface fibers by the abrasion of pumice stones. The water absorption increased approximately 15-26% at 10-30% concentration of pumice stones. Water absorption does not cause any further increase when the pumice stone concentration increased from 50 to 70% for all the three cases.

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3.5. SEM Analysis The changes in surface appearance of the denim apparels after enzyme washing and stone-enzyme washing were examined by scanning electron microscope (Model 3400N, Hitachi, Japan). The surface appearances of the untreated denim samples were also examined by SEM. The surface appearances as well as denim apparel properties are affected by enzyme washing and stone-enzyme washing. Figure 3.1 shows the SEM image of untreated cotton denim apparel. The Figure shows parallel ridges and no fibrils (projecting fibers) and ruptures visible in the image, because the yarns are coated with size materials and projecting fibers are not visible on surface. The Figure 3.2 shows the Scanning Electron Microscopy photograph of enzyme treated cotton denim apparel. The enzyme treatment was carried out according to the method described in this chapter with an enzyme concentration of 2.0% (owg) acid cellulase at 550C for 40 min. After enzyme treatment, a clear increase of cracks, disorients and wrinkle surface was observed compare to unwashed sample. Figure 3.3 shows stone-enzyme treated sample and damaged surface in the image are due to fiber degradation by hydrolysis and abrasion by pumice stone in the washing machine during processing. As observed in Figure 3.3 there are more cracks on the surface of fibers. This is caused by cellulase washing of cotton denim garments and pumice stone enhances more cracks on surface.

Figure 3.1. Scanning electron microscopy image of untreated denim sample.


Figure 3.2. Scanning electron microscopy image of enzyme treated denim sample.

Figure 3.3. Scanning electron microscopy image of stone-enzyme treated denim sample (hydrolysed and damaged form).

45

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3.6. FM Analysis Figures 3.5-3.6 shows the changes in physical appearance on the yarn surface of denim apparel after washing with cellulase enzyme and stone-enzyme treatment which were observed by fluorescence microscope (FM) (model IX71, Olympus, Japan). Figure 3.4 shows the FM image of untreated warp yarn.

Figure 3.4. Fluorescence microscopy image of untreated warp yarn.

Figure 3.5. Fluorescence microscopy image of enzyme treated warp yarn.


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Figure 3.6. Fluorescence microscopy image of stone-enzyme treated warp yarn.

As the yarns are dyed and coated with size materials, the surface is smooth and fibrils or projecting fibers are not visible on surface. Figure 3.5 shows the fluorescence microscopy photograph of warp yarn treated with the 2.0% concentration of acid cellulase at 550C for 40 min. It is observed that the yarn surface is somewhat damaged by the action of cellulase enzyme and the extent of damage is increased with the increasing of enzyme concentration. The Figure 3.6 shows the FM photograph of warp yarn of denim fabric treated with 30% pumice stone combined with 2.0% (owg) acid cellulase at 550C for 40 min. It is observed that the yarn surface is highly damaged by the rubbing action of pumice stone and the extent of damage is increased with the increasing of stone concentration in washing.

CONCLUSION An experimental study on the effect of chemicals in denim apparel washing has been studied by enzyme and stone-enzyme treatments. The works reported in this research are basically dependent on parameters namely: (i) chemical concentrations (ii) treatment temperatures (iii) times and (iv) pumice stone concentrations. Cellulase enzymes and pumice stone-enzyme washing are important chemicals in the apparel washing industry for processing denim ready-made apparels. Cellulase enzymes provide an ecological way to treat cotton denim apparels. Although cellulases have been used for biofinishing cotton in textile industry since the 1980s, many varieties of cellulases are still used in textile processes today and recently used in denim washing industries. Pumice stones mixed with cellulases have been used for biostoning denim to get distressed worn look.

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A problem associated with treatments with cellulases and mixtures with pumice stone is that the treated garments exhibit high strength and weight losses. Pumice stones mixed with cellulase enzyme have been used for denim washing to get more worn look appearance. The study has been confined to the modification of denim apparels with chemicals in washing processes. In case of enzymatic treatment the effect of cellulase enzyme on the fabric properties as well as the characteristics of denim apparels in washing process with the introduction of parameters has been determined. In case of enzymatic treatment with pumice stone the effect of pumice stone on the fabric properties as well as the characteristics of denim apparels has also been determined in this research. On the basis of the analysis the following conclusions have been drawn: i)

The results obtained provide new information on the effects of acid, neutral and mixture of acid and neutral cellulases on denim apparels. The use of 2.0g/L mixed cellulase was found to be the most effective in preventing strength and weight loss, determined the most positive results with specific washing effects. In addition, the results obtained with defined cellulase mixtures provided useful knowledge for designing new production. It was also shown that neutral cellulase improves water absorption. Acid cellulase is the most effective at removing color from denim fabrics. Treatment temperature, time and concentrations of cellulase had a major impact on enzymatic treatments. ii) Pumice stone has influence on the properties of denim apparels. The results obtained in enzymatic washing with pumice stone provide new information on the effects of pumice stone in acid, neutral and mixture of acid and neutral cellulases on denim apparels. The use of 30% pumice stone in cellulase washing for all cases was found to be the most effective in preventing strength and weight loss, determined the most positive results with washing effects.

For optimal performance in denim apparel washing, the process parameters should be selected on the basis of fabric type and quality in order to achieve the desired finishing effect with minimum negative impact. Pumice stone in cellulase treatments gives a used look appearance on denim apparel distinctly and the properties of denim fabrics are varied depending on the amount of pumice stone used. It is possible to suggest that any or all of the parameters in both enzyme washing and stone-enzyme washing methods are responsible to damage denim apparel through excessive hydrolysis/unwanted abrasion by pumice stone and changes the values of denim properties. The washing condition should be predetermined for optimum result.

ACKNOWLEDGMENTS One of the authors research work was supported by the NSICT Fellowship under the Ministry of Science, Information and Communication Technology of The People’s Republic of Bangladesh.


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[41] Fornelli, S. (1992). Magic enzymes, product information leaflet. Sandoz Chemicals Ltd, Muttenz-Basel, Switzerland. [42] Cavaco-Paulo, A., Morgado, J., Almeida, L., Kilburn, D. (1998b). Indigo back-staining during cellulase washing. Text. Res. J. 68(6), 398-401. [43] Cavaco-Paulo, A. (1998b). Mechanism of cellulase action in textile processes. Carbohydr. Polym. 37, 273–277. [44] Nevell, T. (1995). Cellulose, structure, properties and behaviour in the dyeing process. In: Cellulose dyeing. Shore, J. (Ed.). Society of Dyers and Colorists 1-26. [45] Hartzell, M. M., Hsieh, Y. L. (1998). Enzymatic scouring to improve cotton fabric wettability. Text. Res. J. 68(4), 233-241. [46] Mori, R., Haga, T., Takagisi, T. (1999). Bending and shear properties of cotton fabrics subjected to cellulase treatment. Text. Res. J. 69(10), 742-746. [47] Walker, L. P., Wilson, D. B. (1991). Enzymatic hydrolysis of cellulose: An overview. Bioresource Technology 36, 3-14. [48] Pederson, G. L., Screws, G. A., Cedroni, D. M. (1992). Biopolishing of cellulosic textile fabrics. Can. Text. J. 109, 301-305. [49] Buschle-Diller, G., Zeronian, S. H., Pan, N., Yoon, M. Y. (1994). Enzymatic hydrolysis of cotton, linen, ramie, and viscose rayon fabrics. Text. Res. J. 61(5), 270-279. [50] Radhakrishnaiah, P., Meng, X., Huang, G., Buschle-Diller, G., Walsh, W. K. (1999). Mechanical agitation of cotton fabrics during enzyme treatment and its effect on tactile properties. Text. Res. J. 69(10), 708-713. [51] Heine, E., Hocker, H. (1995). Enzyme treatments for wool and cotton. Rev. Prog. Coloration. 25, 57-63. [52] Tarhan, M., Sariisik, M. (2009). A comparison among performance characteristics of various denim fading processes. Text. Res. J. 79(4), 301-309. [53] Zeyer, C., Rucker, J. W., Joyce, T. W., Heitmann, J. A. (1994). Enzymatic deinking of cellulose fabric. Textile Chemist and Colorist 26(3), 26-31. [54] Kochavi, D., Videbaek, T., Cadroni, D. (1990). Optimizing processing conditions in enzymatic stone washing. American Dyestuff Reporter 9, 24-28. [55] Feki, I., Ghith, A., Sakli, F. (2004). Effect of stone wash treatment on the denim’s mechanical properties, world textile conference, 4th AUTEX Conference, Roubaix, France. [56] ASTM D 5034 (2001). Standard test method for breaking force and elongation of textile fabrics (Grab test), American Society for Testing and Materials, Annual Book of ASTM Standards, Vol. 07.01., ASTM International, West Conshohocken, PA, US. [57] ASTM D 1776 (2008). Standard practice for conditioning textiles for testing, American Society for Testing and Materials, Annual Book of ASTM Standards, Vol. 07.01., ASTM International, West Conshohocken, PA, US. [58] ASTM D 3776 (1996). Standard test methods for mass per unit area (weight) of woven fabric, American Society for Testing and Materials, Annual book of ASTM Standards, Vol. 07.02., ASTM International, West Conshohocken, PA, US. [59] AATCC evaluation procedure 1 (2007). Gray scale for color change, American Association of Textile Chemists and Colorists, Technical Manual of the AATCC, Research Triangle Park, N.C., US. [60] BS 3356 (1990). Method for determination of bending length and flexural rigidity of fabrics.

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[61] BS 3449 (1990). Testing the resistance of fabrics of water absorption (static immersion test). [62] Campos, R., Cavaco-Paulo, A., Andreaus, J., Gubitz, G. (2000). Indigo-cellulase interactions. Text. Res. J. 70(6), 532-536. [63] Kleman-Leyer, K., Gilkes, N., Miller, R., Kirk, K. (1994). Changes in the molecularsize distribution of insoluble celluloses by the action of recombinant Cellulomonas fimi cellulases. Biochem. J. 302, 463-469. [64] Liu, J., Otto, E., Lange, N., Husain, P., Condon, B., Lund, H. (2000). Selecting cellulases for bio-polishing based on enzyme selectivity and process conditions. Textile Chemist and Colorist and American Dyestuff Reporter 32(5), 30-36.



Chapter 3

DIGITAL TEXTILE PRINTING USING COLOR MANAGEMENT Dejana Javoršek*, Primož Weingerl and Marica Starešinič University of Ljubljana, Faculty of Natural Sciences and Engineering, Ljubljana, Slovenia

ABSTRACT The chapter presents the possibilities and a correct procedure for a color management application in the field of digital printing onto textile substrates. The introduction of color management into the field of digital textile printing enables better quality control, faster prepress, reduction in the use of material and better repeatable color prints on textile substrates. Due to the high price of printing colors used in digital textile printing, and the costs connected with the pre- and aftertreatment of printed fabrics, an appropriate preparation of color patterns and simulated prints is of even greater importance. The aim of this chapter is hence to present how long-term and expensive pre- and aftertreatments of textile substrates can be avoided with the help of an appropriate use of printer color profiles for all print devices included in the workflow, e.g., print simulation on paper printed with a laser or inkjet printer. On the basis of simulated prints on paper, a customer can decide on the color that gives the best results on a selected pattern. Digital printing on a textile substrate – a banner made for indoor and outdoor applications, using the color profiles is presented as well. This includes experimental data and the methods for testing the lightfastness and weatherability of the substrate with a Xenotest, and for defining the uniformity of prints – mottling. The method for defining the uniformity of prints is included in the draft of the standard ISO 15311 and is also proposed by the German Printing Association FOGRA. In addition, the importance of the optical brightener used for the improvement of substrate whiteness in digital textile printing is discussed. Furthermore, the calculation of the color inconstancy index CMCCON02 when defining the influence of different illuminants on the color change of substrates is presented. *

Corresponding author: Dejana Javoršek, University of Ljubljana, Faculty of Natural Sciences and Engineering, Snežniška 5, 1000 Ljubljana, Slovenia, E-mail: [email protected].

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Dejana Javoršek, Primož Weingerl and Marica Starešinič

Keywords: Color management, ICC profiles, digital textile printing, print simulation, color inconstancy index CMCCON02

INTRODUCTION The technology of digital printing is more and more established [1] in the field of textile printing [2–5] as it allows unlimited color sampling and good durability of prints, as well as in the field of pharmaceutical research [6,7], electronics and micro-engineering industries for printing electronic materials, such as printed circuit boards (PCB) [8, 9] and a humidity sensor directly printed on a textile using the inkjet printing technology [10], and even food decorating uses the digital printing technique as a major working tool. Recently, the inkjet technology has also been successfully applied in the biomedical field [11], where the DNA molecules have been directly printed onto glass slides using commercially available inkjet printers for the high-density DNA microarray fabrication [12], and inkjet printers were used to print cells and biomaterials for 3D cellular scaffolds [13]. In the case of inkjet technology, printing on various substrates is performed by means of non-impact printing or jetting drops of ink on a substrate. The most important component of inkjet technologies is the printing ink alone, which greatly affects the quality and reliability of the output [14]. Thus, in the digital textile printing, various inks that are designed for different needs and requirements are used, including reactive, acid, disperse and pigment dyes [15]. Despite the advantages and widespread use of pigment dyes [16–18], reactive dyes still occupy an important position in the printing of textiles, especially with thermal (bubble) inkjet printers. Reactive dyes are used for the printing on cotton fabrics and their blends, and on linen and silk fabrics. Reactive dyes for the printing with inkjet printers are now widely accessible to everyone yet relatively expensive. Therefore, a number of studies aimed at the improvement of digital printing on cotton with reactive dyes. Yang and Naarani researched the printing of cotton with reactive dyes using the inkjet printer. They studied the impact of matting conditions on the cotton print and how to improve the lightfastness of printed cotton with reactive dyes [19,20]. Digital textile printing with reactive dyes is different from conventional printing, especially: 



in the substrate pretreatment with appropriate chemicals, as ink due to viscosity and stability does not contain chemicals that are necessary for the binding of the dye to fibers, and in the aftertreatment when a chemical bond between the fibers and the reactive dye is formed, resulting in excellent wet fastness of color prints.

A lot of research has been conducted in this area [21–23]. It is known that these two, preand post-processing treatments, are essential as they further influence the change in color tone [24]. Moreover, the dimensional stability of the fabric patterned with the inkjet printer was controlled as well [25]. Weiguo et al. also analyzed the color print on the cationic agent printed cotton with reactive dyes and established that a color print is better on the cotton which was treated with a cationic agent than on the cotton treated with alkali, urea and

Digital Textile Printing Using Color Management

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thickener [26], while some other researchers preferred modified chitosan pretreatment of polyester fabric for the printing with inkjet ink where the pretreated fabrics produced a much better color quality than the untreated fabrics [27], and preferred the pretreatments of the silk fabric with amino compounds for the inkjet printing where the amino compound pretreatments held and fixed the additional ink on the fabric surfaces resulting in a wider color gamut of the inks [28]. Kaimouz et al. provided a quantitative insight into the effect of pretreatment chemicals on the color strength, dye fixation and ink penetration on the inkjet printed Lyocell and cotton fibers, using a statistical analysis approach [29]. The trend in small print collections and unique products requires greater flexibility of printing companies and a fast production of color patterns and products. By using graphic programs, the expectations of textile and clothing designers and of small businesses are growing. In most cases, they require that a specific color pattern or color sample presented on paper be exactly reproduced on the textile substrate. However, the path from the model presented on paper to the final product printed on a textile substrate is relatively complex. Problems arise when discrepancies between the color patterns on paper, computer screen and the textile substrate occur. In graphic technology, color management and the use of ICC (International Color Consortium) color profiles ensure a consistent color reproduction throughout the technological process and on all kinds of devices, regardless of the color space, including the original, scanner, digital camera, display screen and color printer. Color management has been used in graphics for a number of years, which is evident from the literature [30–35]. By introducing color management into the field of digital textile printing, the time required for prepress could be shortened and the use of materials could be reduced, which would lower the printing process costs [36]. Due to the high price of printing colors used in the digital textile printing and the costs connected with the pre- and aftertreatment of printed fabrics, an appropriate preparation of color patterns and simulated prints is very important. A print simulation in textile printing can be observed on a screen (i.e., soft proof) or conducted on another printer (i.e., hard proof), which enables – with appropriately built profiles for any device and their correct use – a simulation of particular color patterns on a different output device. In one typical research [36], the linearization and characterization of three printers for paper and textiles, two inkjet and one electrophotographic (“laser”) printer, were implemented. It was demonstrated that an accurate creation of color profiles ensured the top quality of prints and successful hard proof on both laser and inkjet printers. While digital printing has become a link between the traditional and electronic media, the need for an accurate color reproduction is increasing. The users’ expectations have risen, representing new challenges for both, the color reproduction and manufacturers of a variety of substrates. In the textile industry, more and more optical brightening agents (OBA) are used in order to increase the whiteness of a fabric. With the same purpose, they are integrated in detergents, wherein they optically increase the whiteness of washed goods. Nevertheless, the performance of optical brighteners can be the source of incorrect and inaccurate measurements caused by errors in the measurements. In one study, they assessed the impact of the optical brightener in the fabric, before and after the treatment with washing agents [37]. This means that in addition to the initial treatment of the fabric with an optical brightener, the perception of the fabric color and the printed colors is clearly affected by the amount of optical brighteners in detergents that bond with the fabric during the washing process.

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When color profiles for all devices involved in the process of printing (i.e., display screen, printer and printer for hard proof) are generated, it is recommended to test the colors under different illumination, since patterns are usually observed under various light conditions. This can be predicted by calculating the color inconstancy index, which is described below [38, 39]. The quality of prints can be controlled in different ways. One possibility is the calculation of the heterogeneity footprint with the M-Score method [40].

EXPERIMENTAL In our research, three substrates were used:  

textile cotton fabric which was printed with the inkjet printer Mimaki Textile Jet Tx2-1600 (Mimaki, Japan) using 8 reactive dyes [36], and two textile synthetic fabrics, i.e., banner and textile banner made for indoor and outdoor applications, which were printed with Canon Image Prograf W8400.

In the first case [36], we focused on hard proofing, where the matching between the original colors and hard copy simulation of the colors was investigated using the color difference equations ∆E00. The purpose of the researches was to establish whether a print on a textile made with a digital printer produced by Mimaki can be simulated with a print on a paper with an inkjet (Canon Image Prograf W8400, Canon, Japan) and laser (Canon Image Press C1+, Canon, Japan) printer. In the second case, we focused on defining the print quality of presentational posters substrate – banner, using the color difference equations ∆E00. This included experimental data and methods for testing the lightfastness and weatherability of the substrate with a Xenotest Alpha (Atlas, USA), and for defining the uniformity of prints – mottling. The method for defining the uniformity of prints is included in the draft of the standard ISO 15311 and is also proposed by the German Printing Association FOGRA.

Materials The cotton fabric used in the research was provided by Tekstina Plc, Ajdovščina, Slovenia. The basic fabric properties are as follows: raw material: 100% cotton, plain weave, warp thread density: 54 threads/cm, weft thread density: 29 threads/cm, mass per square meter: 130 g/m2, breaking force in warp direction: 38.0 daN, breaking force in weft direction: 26.0 daN, breaking elongation in warp direction: 17.6%, breaking elongation in weft direction: 12.0% and fineness of warp and weft threads: 14 tex. Two textile synthetic substrates, namely the high-impact, highly durable textile substrates were used, i.e., a vinyl banner (in the text called banner) and a textile (in the text called textile) produced in China. The basic fabric properties are as follows: material: PES (polyester), plain weave, Sample 1: mass: 1.1213 g/dm2, thickness: base – 0.180 mm, print – 0.182 mm; Sample 2: material: PES (polyester), mass: 1.9526 g/dm2, thickness: base – 0.321 mm, print – 0.322 mm. Since the substrates were treated with a coating, only warp thread


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density: 23 threads/cm, weft thread density: 30 threads/cm for Sample 1 (cf. Figures 1 and 3) was defined. The analysis performed under a stereomicroscope (Leica EZ 40) and SEM microscope JEOL 6060LV is presented in Figures 1–4.

Figure 1. Sample 1, Print/Base, Leica EZ 40.

Figure 2. Sample 1, SEM microscope JEOL 6060LV.

Figure 3. Sample 2, Print/Base, Leica EZ 40.

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Figure 4. Sample 2, SEM microscope JEOL 6060LV.

Color Measurements After a few days of color stabilization, the measurements with the instrument EyeOne (XRite, USA) were performed. Instead of diffuse geometry, the measurement geometry 45/0 was used, as it is supported by the color management program (Texprint) for digital textile printing. The differences in the color between the original colors (print on inkjet printer Mimaki) and simulated prints (prints on inkjet printer Canon and laser printer Canon), and the differences between the prints made on a banner and textile were calculated with the ∆E00 color differences equation [41]. The color differences between the original colors on a banner and textile, and the colors after the treatment on a Xenotest were calculated using the ∆E00 color differences equation. The results are presented as the calculated average color differences of all samples. All calculations were performed using the program Octave 3.0.0 [42].

LINEARIZATION AND CHARACTERIZATION OF INKJET PRINTER Defining Parameters The first step was to define the substrate type (cotton, linen, blend of cotton and polyester), the number and type of colors, and print quality. Each time, the type of substrate, finishing and colors were changed to create a new color profile. In one research [43], the quality of prints made with the inkjet printer Canon Image Prograf W8400 using two different papers, matt coated and glossy photo paper, was determined. In addition, the impact of Wasatch softRIP settings – draft and high – on the print quality was researched. The software package ProfileMaker 5.0.8 was employed for the creation of the ICC color profiles for both printing quality settings and both papers. The results show that the changes in the RIP printing quality settings (draft vs. high) produced only small differences in prints and when calculating color differences; it can hence be


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concluded that the printing quality parameters, colorimetrically speaking, do not have any special effect on the prints.

Achieving Repeatability and Optimal Color Gamut In the second step, the printer was set to achieve the repeatability and optimal color gamut:

A. Defining Ink Limit of Individual Color The linearization chart (i.e., chart that contains color patches from 0 to 100% area coverage of an individual CMYK color) was made in the ProfileMaker Pro 5.0 Measure Tool (X-Rite, USA) and printed without color management. After the printing, spectral data were measured using the spectrophotometer EyeOne, and the CIELAB and CIELCh values were calculated. The CIELAB values were used to define the ink limit from the a*, b* diagram for CMY (C – cyan, M – magenta and Y – yellow) and from lightness L* in dependence of the area coverage of K (K – key, black ink) expressed in percent, L* (area coverage). An example of the a*, b* diagram is represented in Figure 5. On the a*, b* diagram, the point (percent of the area coverage) where the chromaticity C*ab stops increasing and the color hue hab starts changing was determined, this point defining the ink limit. In the end, the ink limit was set on Wasatch SoftRIP software (RIP – Raster Image Processor). Figure 1 also represents the difference in defining the ink limit on banner and textile substrates. It is evident that a banner could accept more ink than the textile substrate. B. Linearization Afterwards, another linearization chart chosen from the Wasatch SoftRIP software was printed and measured (Wasatch SoftRIP – Setup – Color Properties – Halftone Properties – Calibration – Calibration Curves). After the measuring and final linearization process, the linearization chart was printed and measured once again to ensure that the linearization was performed appropriately. C. Defining Total Ink Limit (TIL) This step included the printing of a chart with black patches printed with all four inks (area coverage 0–400%) and defining the color patch where the ink was not bleeding. In general, this parameter was important when the test chart and the final ICC profile were elaborated.

Creation of Test Chart In the third step, the test chart was made in the program ProfileMaker Pro 5.0 Measure Tool and printed. The views of the professional public about how many patches are required for a quality color description of devices vary; however, mostly there are generic test charts on which the number of patches is related to the chosen type of print quality (draft, medium or high).

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Figure 5. Defining maximum ink limit of cyan, magenta and yellow (above) and black (below).

The number of color patches also depends on the instrument used, since manually measuring of test charts with a large number of color patches is very time consuming. There are frequent speculations about the adequacy of too many color patches on generic color test


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charts, which are used sometimes. The reflection in this direction is also triggered by the fact that the process of the color profile creation is time consuming and expensive, as the creation of the profile for a digital printer generally requires first pre- and then aftertreatments of the textile substrate. At the same time, the digital printing technique, where it is necessary to follow the customer requirements, results in frequent changes of textile substrates, which should be followed by the color profiles. In practice, therefore, for the reasons described above, color management is not yet fully implemented and most printers, instead of proper color profiles for each substrate, use a color profile designed only for one type of textile substrates. Accordingly, optimal results cannot be achieved and printers are only wasting their time by editing colors in one of the programs. This method can be used in the case of very small differences between the base substrate (for which the basic color profile was made) and the new one. In digital inkjet printing, a color test chart can be made, using programs which are payable, e.g., ProfileMaker Pro 5.0 Measure Tool or free open source software, e.g., Argyll CMS by Graeme Gill [44]. Although the creation of a color test chart and later the creation of the ICC color profile using programs bring good results, the possibility to determine the parameters and settings of the program is rather limited. With Argyll CMS, it is possible to change a larger number of these parameters and, in this case, we know for certain, that the algorithm used is OFPS (Optimized Farthest Point Sampling) for the production of the color test chart with the help of which a point in the 4-dimensional space of the device (C, M, Y, K) is allocated so that the distance between two individual points is minimized. The color test charts differ in form, depending on the type of the instrument used for measuring. An example of a color test chart for making the printer profile, made in the program ProfileMaker, is shown in Figure 6.

Figure 6. Example of test chart for printer characterization.

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For a color test chart made in one of the programs that make this possible (Measure Tool, Argyll), we took into consideration the following: 

      

number of colors with CMYK; we can also use other non-processing (spot) colors, e.g., orange, green, blue (in case of additional colors, it is usually necessary to know the CIELAB value), maximum area coverage, GCR (Gray Component Replacement), black max – maximum black (typically 100), black start – start adding black component (usually 10), black width – adding black component in saturated tones, determine the number of fields of color on the color plate and determination of the instrument used to measure the color test chart, as the layout and size of the color patch depend on that.

After the color test chart is created, printing takes place the following day and the measurement with the instrument which was set in its creation.

Figure 7. Comparison of color gamut for banner and textile in CIE a*, b* color diagram.


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Creation of Color Profile In the fourth step, the printed test chart was measured using the spectrophotometer EyeOne and the ICC profile was made using ProfileMaker Pro 5.0. The generated color profile has the extension.icc and contains information about the connection between the color values of the device (in this case the printer), i.e., CMYK, and the color values independent of the device, i.e., CIELAB or CIEXYZ. The appropriately generated color profiles were used afterwards, for the print of a newly designed plate with 725 color fields on the two media – banner and textile. Figure 7 shows a comparison of the color gamut for two different materials on which we wanted to achieve the best possible reproduction by retaining all the details with the lowest optimal area coverage of all colors (in both cases 100%). The details were controlled during the creation of a color profile by adding extra color patches or boxes made of thin lines. Despite the same maximum area coverage (TIL), i.e., 100%, the textile has a slightly larger color gamut, especially in the area of blue and magenta (cf. Figure 7).

USE OF OPTICAL BRIGHTENERS

Figure 8. Reflection spectra of cotton fabrics, O1 – treated with optical brightener, B – bleached, O2 – treated with optical brightener, instrument EyeOne, measured without UV-cut filter (O1 and B) and with UV-cut filter (O2).

In the textile industry, optical brighteners (Optical Brightening Agents, OBAs or fluorescent Brightening Agents, FBAs) – colorless organic compound that fluoresces, are used to enhance the whiteness on chemically bleached fabrics [47]. For the same reason, they are used in detergents to optically increase the whiteness of laundered goods, in the manufacture of plastics (added in the phase of polymer dissolution), in the fashion industry

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and certain warning signs (emergency vehicles, buses, traffic signs etc) [46]. In one research, a preparation of inkjet inks with fluorescent brighteners as antifraud markers for inkjet printing on polyester and polyamide substrates was performed [47]. High whiteness of the textile substrate enhances the contrast on the printed surface, allowing a more specific appearance of the printed pattern and increases the color gamut of the print. Optical brighteners absorb invisible ultraviolet light and convert it into visible light [48]. UV radiation is near the blue area of the spectrum and therefore increases the reflection of light in the blue area of the spectrum. Therefore, the substrate observed under natural daylight, which also contains UV radiation, appears whiter. The most commonly used optical brighteners absorb light at the wavelengths between 300 nm and 400 nm, and reflect it in the range of the visible part between 400 nm and 480 nm [45], which results in increased reflection of blue. The reflection spectra of the used materials are shown in Figure 9. The ISO whiteness (R at 457 nm) for the banner is 87.69 and for the textile 95.84, measurements being made with EyeOne without a UV-cut filter.

Figure 9. Reflection spectra of used materials.

Usually, spectrophotometers have a tungsten lamp with the color temperature of 2800 K. A spectrophotometer measures the light reflected from the sample at selected wavelengths and the result is given as a spectral reflection value between 0 and 100% (cf. Figure 8 – Sample B). To produce an ICC color profile, the standard illuminant D50 is used. It is therefore clear that the instrument measures the reflected light on a single type of light (standard light A or white LED) and the result is given as the value of CIEXYZ under different light (e.g., D50) with the use of a simple calculation.


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The problem occurs when the measurement is performed on the substrate, which was treated with optical brighteners. The latter disrupts the simple calculation, as the light is reflected at a different wavelength than absorbed. This can lead to a shift in hue [49]. The experiment results showed that the proportion of UV radiation of the light source affects the color printed on the substrate which contains optical brighteners. Due to the impact of the proportion of UV radiation, the color shade moves to the blue shade. The experiment results also show that the proportion of UV radiation in the light source affects the colors close to white and blue more than the colors close to yellow and black. One solution is to use spectrophotometers containing a UV-cut filter, which can retain UV radiation, whereas the second solution is to avoid the substrates with optical brighteners for test prints – the latter nowadays being almost impossible. A better solution is to use the software which takes into account the effect of optical brighteners. To create a color profile in ProfileMaker 5.0 (X-Rite), an optical brightener compensation (OBC) module is used to compensate for optical brighteners in combination with the instrument i1iSis for an automatic spectral measurement of color patches on the test chart with an included UV-cut filter, using only UV radiation [50]. The Argyll program uses the algorithm FWA (Fluorescent Whitening Agent) [51], which can successfully compensate for optical brighteners; however, it requires the measurement of quantity and types of optical brighteners used on the substrate, and sufficient information on the observation environment to predict the behavior/impact of optical brighteners. To determine the amount of optical brighteners in the substrate, the instrument must enable illumination of the sample with a certain level of UV radiation. In the field of color management, for the creation of printer color profiles for a variety of substrates that contain different amounts of optical brighteners, it is recommended to use instruments which do not contain a UV-cut filter (cf. Figure 8) [51]. If the instrument contains a UV-cut filter, it is not suitable to compensate for optical brighteners since they cannot be activated. For this purpose, Greame Gill developed the algorithm to compensate for them. The X-Rite’s compensation module (OBC) is the industry’s first integrated module that takes into account the amount of the optical brightener on various substrates [50]. The most common example of using the FWA compensation is the creation of test prints (hard proof) when the two media contain a different level and type of optical brighteners, i.e., the paper on which the hard proof is performed and the print. The use of the FWA compensation in the generation of color profiles for output devices and for the devices on which we are going to perform a test print, and also the use of the absolute colorimetric rendering intent can lead to very good colorimetric matching.

TEST PRINTS A test print presents in the process of printing a very important step, since it accurately displays the appearance of the final print. The test print can be seen on the display screen (soft proof) or it can be printed on a different printer or on a dedicated printing machine (hard proof). Using print simulations on a screen or test print allows us to simulate certain color patterns on any other output device with a proper creation of color profiles for any device – both input and output. A simulation of the print on a screen is cheaper than the test print on a

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printer. In this case, we encounter two media, i.e., observation on the screen and observation of prints on paper [52, 53]. This could lead to variations in the color perception: 1 2 3

due to possible differences in the color gamut of devices – a screen usually has a larger color gamut than a printer or printing machine, when performing the simulation of a print on the screen, only substrate whiteness can be simulated and not the feel of the substrate, simulation of the print on a screen depends on the screen light source, which means that in this case, we are dealing with a self-luminous medium and in the case of the print, with a reflective medium.

The introduction of color management in the field of textiles has increased the possibility of faster and easier preparation of the color pattern for printing. Moreover, it can lead to controlled, high quality and repeatable color print on a textile substrate. Due to the high price of inks for digital textile printing and costs associated with the preparation and then aftertreatment of printed textiles, especially when using reactive dyes, a simulation of the print on a display screen and the execution of the test print on paper are even more important.

Figure 10. Comparison of color gamut of printers in CIE a*, b* diagram.

The simulation of prints was conducted with a laser printer (Canon Image Press C1+) and an inkjet printer (Canon Image Prograf W8400), using CMYK [37]. For the color transformations from the source printer (Mimaki) to proof printers (both Canon), an absolute


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colorimetric rendering intent was used for the simulation of prints. This intent colorimetrically transforms in-gamut colors from the source to the destination color space taking into account the change of the media white point (using chromatic adaptation transform to the standard illuminant D50), while the out-of-gamut colors are clipped to the gamut boundary of the destination color space. On the basis of the average values of color differences of all samples between the original colors (print on inkjet printer Mimaki) and simulated prints (print on inkjet printer Canon and laser printer Canon), it was established that a print simulation on an inkjet printer is better than the simulation on a laser printer. The color gamut of the inkjet printer, i.e., Canon 1, is in the whole color range larger than the color gamut of the laser printer, i.e., Canon 2, while it is the smallest at the inkjet printer for textiles, i.e., Mimaki (cf. Figure 10). The CIELAB diagram shows that the inkjet printer colors are more saturated than the colors from the laser printer (cf. Figure 10). Prior to the analysis, each sample was categorized according to the magnitude of its ∆E00 value into one of the four groups: 0–1 (color difference undetectable with a human eye), 1–3 (small color difference between two patches) [54], 3–6 (perceivable difference) or > 6 (large difference). At the average color differences for 0 < ∆E00 < 1, it was established that both printers simulate very well to approximately the same extent. Nevertheless, differences occurred with regard to the number of colors, since the inkjet printer simulated well (1 < ∆E00 < 3) a larger number of samples (733) than the laser printer (457) (cf. Table 1). Both printers simulated equally well a larger number of colors for 3 < ∆E00 < 6. Table 1. Number of color patches in dependence of ∆E00, simulated with laser and inkjet printer ∆E00 0–1 1–3 3–6 >6

laser Canon 32 457 983 400

inkjet Canon 40 733 914 185

COLOR INCONSTANCY INDEX CMCCON02 An important component that creates a visual impression of the color and color change, apart from the observer, is light. To ensure the matching of two colors, samples should be observed under a number of different light sources. While most offices have illuminations that include fluorescent lights (illuminants from F1 to F12) and at home, the incandescent light (illuminant A) is used most frequently, daylight is most important outdoors [55]. The CIE recommended several standard daylight illuminants with the color temperatures at 5000 K (known as D50), 5500 K (D55), 6500 K (D65) and 7500 K (D75) [56]. A problem arises when the colors of two materials with a different surface structure (textile substrate and paper) should match under a particular illuminant. To determine the illuminant influence on the change in the color appearance of samples, i.e., textile fabric and their proofs on paper under different illumination, the color constancy of samples was defined as well. The color constancy was computed using the color inconstancy index CMCCON02, which uses the

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CAT02 chromatic adaptation transform and is the current recommendation by CIE [40, 57]. Furthermore, the recommendation has been incorporated into the ISO Standard 105 [40].

Calculation of CMCCON02 The color constancy of samples was investigated with the calculation of the color inconstancy index CMCCON02. To calculate the color inconstancy index, R, G and B, which describe cone responses, were calculated with Equation 1 [40, 41, 58]:

R  X  G   M   CAT 02 Y     B   Z 

(1)

where

M CAT 02

 0.7328 0.4296  0.1624   0.7036 1.6975 0.0061   0.0030 0.0136 0.9834 

(2)

Rw, Gw and Bw were calculated from tristimulus values under the test illuminant (Equation 3):

 Rw  X w  G   M   CAT 02 Yw   w  Bw   Z w 

(3)

Rc, Gc and Bc are cone responses for the reference illuminant (D65) (Equations 4–6):

 R Rc  R  D wr   Rw

    1  D   

(4)

 G Gc  G  D wr   Gw

    1  D   

(5)

 B Bc  B  D wr   Bw

    1  D   

(6)


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where Rwr, Gwr and Bwr represent the cone responses to the reference white under D65 reference illumination. D is the degree of adaptation. The calculation of the CMCCON02 index for the samples of such textiles recommends that D be set to 1. The calculation of tristimulus values of a corresponding color in the illuminant D65 is represented in Equation 7:

 Rc  Xc  Y   M 1 G  CAT 02  c   c   Bc   Z c 

(7)

where

M

1 CAT 02

 1.096124  0.278869 0.182745   0.454369 0.473533 0.072098  0.009628  0.005698 1.015326 

(8)

On the basis of the color difference (where the CMC (1 : 1) equation was used) between the reference (XYZ values under reference illuminant D65) and chromatic adaptationtransformed values, the CMCCON02 index was computed. Usually, it is important to calculate the CMCCON02 index, since the standard illuminants A (incandescent light), F2 (CWF – cold white fluorescent light) and standard daylight illuminants, e.g., D50, D55 and D75, are the most commonly used.

Figure 11. Average color inconstancy index for illuminants A, D50, F2, D55 and D75, reference illuminant D65 for prints made on cotton fabric (Mimaki) and paper (laser and inkjet Canon).

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Figure 12. Average color inconstancy index for illuminants A, D50, F2, D55 and D75, reference illuminant D65 for prints made on banner and textile (inkjet Canon).

Figure 13. Spectral power distributions of A, D50, D55, D65, D75 and F2.

The results of the average CMCCON02 index lead to the conclusion that lower average index values were obtained when using daylight D75 followed by D55, D50, while A and F2 had the highest CMCCON02 index (cf. Figures 11 and 12) [37]. The latter was also expected, since the illuminants D50, D55 and D75 are according to the spectral power distribution fairly similar to the illuminant D65 (cf. Figure 13), while the illuminants A and F2 have a fundamentally different spectral power distribution. The highest average CMCCON02 index was acquired when the transition from the fluorescent light F2 to D65 was performed. In the case of prints made on the cotton fabric and Mimaki printer, the CMCCON02 index was lower than in the transition from A to D65, whereas in the case of prints made on


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the textile and Canon inkjet printer, the CMCCON02 index was higher than in the transition from A to D65. From the research results, it could be concluded that the illuminants A and F2 are not appropriate for the comparison of all colors, especially in the case of a simulation with an inkjet printer Canon, since the average CMCCON02 index > 5 in the first case (cf. Figure 11) and > 3 in the second case (cf. Figure 12).

MOTTLING Print mottle can be defined as perceived inhomogeneity in the solid print area due to the variations in the reflectance of the printed surface. The emphasis is on perceived inhomogeneity, since perception is often not in linear correlation with the physical characteristics of the print. Print mottle can be stochastic, with randomly distributed noise, or systematic, with periodic and/or regular pattern (bands, streaks or even more complex textures). Both forms are common on the prints made with inkjet printing systems. From the aspect of inkjet printing, mottle is primarily caused by incompetent properties of the printing substrate or a malfunction of the printing process (print head or substrate movement) [59]. In recent years, several methods have been proposed for the evaluation of print mottling [60–64]. In spite of the similarity in some segments, they differ from each other in basic principles, their complexity and limitations. In this paper, the method proposed by the German Printing Association FOGRA was used to determine the level of print mottle on both materials. The M-Score (i.e., Melcer-Score) method is based on analyzing the color difference (CIE DE2000 is recommended) in the vertical and horizontal direction. Despite M-Score not taking the human visual system directly into account, the results correlate well with the perception of mottling when mottling takes a systematic form [42]. For the sake of simplicity, M-Score computes a single value between 0 (“poor reproduction – clearly visible mottling) and 100 (no mottling present). For more precise interpretations of the obtained values confer Table 2. Table 2. Interpretation of M-Score values M-Score > 95

Meaning Perfect

> 80

Very Good

> 70

Good

> 60

Satisfactory

> 50

Adequate

< 50

Poor

Comments No visible inhomogeneity Print with slightly visible inhomogeneity. Randomly distributed noise, no periodic or systematic structures. Print with visible randomly distributed inhomogeneity, but almost no visible periodic or systematic structures. Visible randomly distributed and systematic inhomogeneity. Still accepted by most observers. Clearly visible randomly distributed and systematic inhomogeneity. Acceptance is dependent on printed image. Clearly visible randomly distributed and systematic inhomogeneity. Not accepted as high quality print.

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The test form used in this study was generated on the basis of ISO 12647-8 [65] and consists of three large solid areas of sizes 29.2 × 18.4 cm. The following tone value combinations were used (cf. Figure 14): a).= C: 65%, M: 50%, Y: 50%, K: 50%; b).= C: 40%, M: 30%, Y: 30%, K: 30%; c).= C: 20%, M: 15%, Y: 15%, K: 15%.

Figure 14. Test form based on ISO 12647-8.

According to the size of solid area, 984 measurements (41 patches in the horizontal and 24 patches in the vertical direction) were performed by the spectrophotometer EyeOne Pro and automated scanning table iO (X-Rite, USA). Algorithm: 1 2 3

Print test forms with large solid (uniform tint) areas, using tone value combinations defined in ISO 12647-8. Measure all patches in each test form with a spectrophotometer and average CIELAB measurements across the lines and columns to get vertical and horizontal “profiles”. Compute CIELAB color differences (ΔE00) between neighbor profiles and sum them up separately for the vertical and horizontal projection, according to Equation 9:

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Digital Textile Printing Using Color Management n1

Evertical  10  Ei (LABi , LABi1 ) i1

m1

Ehorizontal  10 Ei (LABi , LABi1 )

(9)

i1

where m is the number of patches in the vertical direction and n is the number of patches in the horizontal direction. 4

Normalize and sum up color differences to get general ΔEgen (Equation 10):

Egen  5

Ehorizontal Evertical  m 1 n 1

(10)

Compute M-Score based on exponential transformation of general ΔE00, as shown in Equation 11:

1

M  Score  100 2

 2 Egen   15 

(11)

Table 3. Computed M-Score values Tone Value Combinations (%) 20/15/15/15 40/30/30/30 65/50/50/50 Average

Figure 15. Results of mottling analysis.

M-Score values textile 70.42 75.59 84.16 76.72

banner 81.77 70.72 65.31 72.60

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It is evident from the results that inhomogeneity occurred on both materials, commonly as randomly distributed noise and rarely as periodic or systematic structures. As it can be seen from Figure 15 and Table 3, inhomogeneity is slightly more visible on the banner, especially on the prints with larger tone value combinations (darker area). However, on the prints with small tone value combinations (light area), inhomogeneity is more distinguishable on the prints made on the textile substrate. It should be noted that the testing performance of the M-Score method (correlation between results and visual perception) is not within the scope of this paper and could be included in future work.

TESTS FOR COLOR FASTNESS For the material printed on a textile substrate, for an indoor and outdoor presentation, to be exposed to light for a longer period of time in various weather conditions – sun and rain, it makes sense to analyze the stability of color patterns to these conditions. The tests for color fastness on both substrates – banner and textile, were made on a Xenotest Alpha (Atlas, USA) according to the standard SIST ISO 105-B02 [66], SIST ISO 105-B04 [67] under the following conditions:    

measurement and control of irradiance (42 W/m²), temperature in test chamber (35°C), relative humidity (dry conditions: 70%, wet conditions: 35% for 29 min and 100% water spray for 1 min), filter: WINDOW GLASS (320 nm) in the case of SIST ISO 105-B02 and XENOCHROME 300 (300 nm) in the case of SIST ISO 105-B04.

The results of color fastness are represented in Tables 4–7. Color measurements were performed with the instrument EyeOne after 16 and 32 h in the case of exposure to water spray, and after 30 and 72 h in the case of exposure to artificial light. Table 4. Tests for color fastness after exposure to rain made on banner Ink/area coverage (100%) C/100 M/100 Y/100 K/100 C/50 M/50 Y/50 K/50

ΔE00 after 16 h 2.78 1.95 1.24 1.56 2.71 2.62 1.00 3.01

after 32 h 2.74 2.28 1.66 1.78 2.76 2.95 1.47 3.15


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The color differences in the case of the banner after the exposure to rain are within the acceptable ranges (less than 6, maximum value is 3). The differences between 16 and 32 h are very small, regardless of the coverage area (50 or 100%). Table 5. Tests for color fastness after exposure to artificial light made on banner Ink/area coverage (100%) C/100 M/100 Y/100 K/100 C/50 M/50 Y/50 K/50

ΔE00 after 30 h 1.90 1.01 1.03 1.26 2.60 2.33 1.04 2.59

after 72 h 2.27 1.45 1.05 0.79 2.67 2.63 0.81 2.98

The color differences in the case of the banner after the exposure to artificial light are acceptable, in the case of cyan, magenta and black with the area coverage of 50% being slightly higher. From the color differences calculated for the banner, it can be concluded that the printed substrate, i.e., banner, is appropriate for both indoor and outdoor posters for promotional purposes, since the color differences are still acceptable after 32 h of exposure to rain and 72 h of exposure to artificial light. Table 6. Tests for color fastness after exposure to rain made on textile Ink/area coverage (100%) C/100 M/100 Y/100 K/100 C/50 M/50 Y/50 K/50

ΔE00 after 16 h 2.87 2.84 2.93 4.03 1.67 2.37 2.37 0.59

after 32 h 2.65 3.69 3.39 3.56 1.62 2.83 2.82 0.99

The color differences in the case of textiles after the exposure to rain are acceptable in all cases. The maximum ΔE00 is in the case of black (100%) after 16 h. The color differences on textiles after the exposure to illumination after 30 h and 72 h are acceptable (less than 6). The maximum value of ΔE00 is 3.46 in the case of yellow (50%) after 72 h. From these results, it can be concluded that the printed textile substrate is also suitable for indoor and outdoor applications, the same as the banner. The results on the banner are slightly better, as ΔE00 is smaller.

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Dejana Javoršek, Primož Weingerl and Marica Starešinič Table 7. Tests for color fastness after exposure to artificial light made on textile

Ink/area coverage (100%) C/100 M/100 Y/100 K/100 C/50 M/50 Y/50 K/50

ΔE00 after 30 h 1.81 1.76 1.83 2.16 1.50 2.05 2.15 0.31

after 72 h 3.03 1.90 1.96 2.75 2.41 2.80 3.46 0.51

CONCLUSION In this work, we presented digital inkjet printing on textile substrates and the importance of using color profiles made for a particular substrate, ink and pretreatment chemicals. The reactive dyes are the most commonly used dyes that create the covalent chemical bond between the dye and fibers, while the unreacted dye is washed off from the fabric with an aftertreatment in various washing baths. On the paper itself and on the promotional substrates printed with the inkjet printer Canon, the whole print remains on the surface; therefore, the simulation procedure is a complex process, which requires apart from the knowledge on the textile substrate and printing ink, and their physical-chemical characteristics also the knowledge in the fields of color measuring, physical principles of the printing and the knowledge of hardware and software. By calculating the color inconstancy index CMCCON02, the illuminant influence on the color change of the substrates under different illumination could be determined. From the results of the CMCCON02 index, it could be concluded that simulated colors should be compared with original colors under daylight illuminants (D50, D55 and D75), while the indoor illuminants A and F2 are not appropriate for a comparison of all colors. The research results of the print simulation on paper demonstrated that most colors from the printer Mimaki (color difference up to 6) could be fairly successfully simulated on a Canon laser and inkjet printer, whereby slightly better results were acquired with an inkjet printer. The experimental prints on paper are cost- and time-saving, since the pre- and aftertreatment of the textile substrate are in comparison with paper obligatory. In order to determine the level of inhomogeneity on both materials, we examined test charts with three different tone value combinations using the M-Score method, described in the methodology section. It is evident from the results that inhomogeneity occurred on both materials, commonly as randomly distributed noise and rarely as periodic or systematic structures. The results of testing the lightfastness and weatherability of the substrate with a Xenotest shows that the printed substrate, banner and textile, are both appropriated for both indoor and outdoor posters for the promotional purposes, the results of ΔE00 being slightly better in the case of the banner.


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[18] Leelajariyakula, S., Noguchib, H., Kiatkamjornwonga, S. (2008). Surface-modified and micro-encapsulated pigmented inks for ink jet printing on textile fabrics. Progress in Organic Coatings 62 (2), 145–161. [19] Yang, Y., Naarani, V. (2004). Effect of steaming Conditions on Color and Consistency of Inkjet Printed Cotton Using Reactive Dyes. Coloration Technology 120 (3), 127– 131. [20] Yang, Y., Naarani, V. (2007). Improvement of the lightfastness of reactive inkjet printed cotton. Dyes and Pigments 74 (1), 154–160. [21] Yuen, C. W. M., Ku, S. K. A., Choi, P. S. R., Kan, C. W. (2004). The Effect of the Pretreatment Print Paste Contents on Color Yield of an Ink-jet Printed Cotton Fabric. Fibers Polymer 5 (2), 117–121. [22] Yuen, C. W. M., Ku, S. K. A., Choi, P. S. R., Kan, C. W. (2005). Factors Affecting the Color Yield of an Ink-Jet Printed Cotton Fabric. Textile Research Journal 75(4), 319– 325. [23] Aston, S.O., Provost, J. R., Masselink, H., (1993). Jet Printing with Reactive Dyes. Journal of the Society of Dyers and Colourists 109(4), 147–152. [24] Fan, Q., Kim, Y.-K., Lewis, A.-F., Peruzzi, M.-K. (2002). Effects of Pretreatments on Print Qualities of Digital Textile Printing. IS&T NIP18: International Conference on Digital Printing Technologies, 236–241. [25] May-Plumlee, T., Bae, J. (2005). Behavior of Prepared-For-Print Fabric in Digital Printing. Journal of Textile and Apparel: Technology and Management 4(3), 1–13. [26] 26Weiguo, C., Shichao, Z., Xungai, W. (2004). Improving the Color Yield of Ink-Jet Printing on Cationized Cotton. Textile Research Journal 74(1), 68–71. [27] Noppakundilograt, S., Buranagul, P., Graisuwan, W., Koopipat, C., Kiatkamjornwong, S. (2010). Modified chitosan pretreatment of polyester fabric for printing by ink jet ink. Carbohydrate Polymers 82 (4), 1124–1135. [28] Phattanarudee, S., Chakvattanatham, K., Kiatkamjornwong, S. (2009). Pretreatment of silk fabric surface with amino compounds for ink jet printing. Progress in Organic Coatings 64 (4), 405–418. [29] Kaimouz, A. W., Wardman, R. H., Christie, R. M. (2010). The inkjet printing process for Lyocell and cotton fibres: The significance of pre-treatment chemicals and their relationship with color strength, absorbed dye fixation and ink penetration. Dyes and Pigments 84(1), 79–87. [30] International Color Consortium [E-text type]. (2006). http://www.color.org. [31] Giorgianni, E. J., Madden, T. E. (1998). Digital Color Management: Encoding Solutions. Reading: Addison-Wesley, 203–317. [32] Drew, J. T., Meyer, S. A. (2005). Color management: A comprehensive guide for graphic designers. Hove: Rotovision, 162–194. [33] Plaisted, P., Chung, R. (1997). Construction Features of Color Output Device Profiles. IS&T/SID Fifth Color Imaging Conference, Scottsdale, Ariz., 141–146. [34] Fairchild, M. D. (1998). Color appearance models. Reading: Addison-Wesley, 337–362. [35] ISO 12646:2004. Graphic technology – Displays for color proofing – Characteristics and viewing conditions, 12. [36] Javoršek, D., Javoršek, A. (2011). Color management in digital textile printing. Coloration Technology 127(4), 235–239.


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[37] Esteves, M. F., Noronha, A. C., Marinho, R. M. (2004). Optical Brighteners Effect on White And Colored Textiles. World textile Conference – 4th AUTEX Conference, 1–6. [38] Luo, M. R., Li, C. J., Hunt, R. W. G., Rigg, B., Smith, K. J. (2003). CMC 2002 color inconstancy index: CMCCON02. Coloration Technology 119, 280–285. [39] ISO 105-J05:2007(E). Textiles – Test for color fastness – Part J05: Method for the instrumental assessment of the color inconstancy of a specimen with change in illuminant (CMCCON02), 1–2. [40] Evaluation of ‘within sheet uniformity’ by means of the M-Score, FOGRA [E-text type]. (2012).http://www.fogra.org/dokumente/upload/dbd47_2010_en_mscorev1_ ak.pdf [41] Guarav, S., Wu, W., Dalal, E. N. (2004). The CIEDE2000 Color-Difference Formula: Implementation Notes, Supplementary Test Data, and Mathematical Observation. Submitted to Color Research and Applications, 21–30. [42] Octave [E-text type]. (2012). http://www.gnu.org/software/octave/ [43] Javoršek, D., Veselič, D., Weingerl, P., Hladnik, A. (2012). Study of inkjet print quality using colorimetry and principal components analysis. Tekstilec 55(3), 169–175. [44] Argyll color management system home page [E-text type]. (2012). http://www. argyllcms.com [45] Simončič, B. (2009). Teoretične osnove barvanja (1. Izdaja). Ljubljana: Naravoslovnotehniška fakulteta, Oddelek za tekstilstvo, 29–32. [46] Adams, R. (2009). Whiter Than White – With Optical Brightener & Without UV Quenchers. Focus on Pigments 2012 (8), 1–4. [47] Karanikas, E. K., Nikolaidis, N. F., Tsatsaroni, E. G. (2012). Novel digital printing inkjet inks with “antifraud markers” used as additives. Progress in Organic Coatings 75(1–2), 1–7. [48] Aspland, J. R. (2000). Whither textile color application research?. Dyes and Pigments 47(1–2), 201–206. [49] Liu, W. (2008). The Influence of UV Light in Color Measurement. CSSE '08 Proceedings of the 2008 International Conference on Computer Science and Software Engineering, Washington: IEEE Computer Society Washington, 268–271. [50] i1 iSis Optical Brightener Compensation (OBC) Module User Guide, X-Rite [E-text type]. (2012). http://www.xrite.com/documents/literature/en/OBC_User_Guide_en.pdf [51] Argyll Color Management system Home Page, Fluorescent Whitener Additive Compensation (FWA Compensation) [E-text type]. (2012). http://www.argyllcms. com/doc/FWA.html [52] Fairchild, M. D. (1993). Chromatic Adaptation in Hardcopy/Soft-copy comparisons. Proc. SPIE 1912, Color Hard Copy and Graphic Arts II, 14–61. [53] Fairchild, M. D. (2005). Color Appearance Models (Second Edition), Massachusetts: Addison-Wesley, 158–159. [54] Schläpfer, K. (2002). Farbmetrik in der grafishen Industrie, Dritte Auflage. UGRA, 61. [55] Thiry, M. C., (2004). Turn on the light: The importance of lighting for textiles in a retail environment. AATCC Review 4, 34. [56] Xu, H., Luo, M. R., Rigg, B. (2003). Evaluation of daylight simulators: Part 1: Colorimetric and spectral variations. Coloration Technology 119, 59–69.

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[57] Maroney, N., Fairchild, M. D., Hunt, R. W. G., Li, C., Luo, M. R., Newman, T. (2002). The CIECAM02 color appearance model, Proc. IS & T/SID 10th Color Imaging Conference, 24–25. [58] Bračko, S., Šolar, A., Forte Tavčer, P., Simončič, B. (2009). Color constancy of vart prints on cotton fabric. Coloration Technology 125, 222–227. [59] Fahlcrantz, C. (2005). On the Evaluation of Print Mottle [doctoral thesis]. Stockholm, 40–45. [60] Sadovnikov, A., Lensu, L., Kamarainen, J., Kalviainen, H. (2005). Quantified and Perceived Unevenness of Solid Printed Areas. Progress in Pattern Recognition, Image Analysis and Applications: Lecture Notes in Computer Science 3773, 710–719. [61] Fahlcrantz, C., Johansson, P. A. (2004). Comperison of diffrent print mottle evaluation models. Proceedings of the Technical Association of the Graphic Arts, 511–525. [62] ISO/IEC 13660:2001. Information technology – Office equipment – Measurement of image quality attributes for hardcopy output – Binary monochrome text and graphic images, 1–27. [63] Dubé, M., Mairesse, F., Boisvert, J., Voisin, Y. (2005). Wavelet Analysis of Print Mottle. IEEE Transactions On Image Processing, 1-8. [64] Hladnik, A., Debeljak, M., Gregor-Svetec, D. (2010). Assessment of paper surface topography and print mottling by texture analysis. ImageJ User and Developer Conference, 150–155. [65] ISO 12647-8:2012. Graphic technology – Process control for the production of halftone color separations, proof and production prints – Part 8: Validation print processes working directly from digital data, 1–16. [66] BS EN ISO 105-B02:1999. Textiles - Tests for color fastness. Color fastness to artificial light: Xenon arc fading lamp test, 1–26. [67] ISO 105-B04:1994. Textiles - Tests for color fastness - Part B04: Color fastness to artificial weathering: Xenon arc fading lamp test, 1–8.



Chapter 4

INKJET PRINTED PHOTO-RESPONSIVE TEXTILES FOR CONVENTIONAL AND HIGH-TECH APPLICATIONS Shah M. Reduwan Billah* Department of Chemistry, Durham University, Durham, UK and The School of Textiles and Design, Heriot-Watt University, Galashiels, UK

ABSTRACT Inkjet printing technology, a modern non-impact printing technique, is in the process of revolutionizing the whole printing industry, including textile printing, for producing almost any print design on textiles within a very short time. It provides inkjet printing a cutting edge over other conventional printing techniques. Photo-responsive inkjet printed textiles have many applications, some of which include, fashion and design, selfindicating alert systems, anti-counterfeit, security and brand protection. Both photochromic dispersed and photochromic acid dyes can be used to formulate inkjet inks to produce photo-responsive inks for inkjet printing on different types of textiles (for example, cotton, wool, silk, nylon) for potential conventional and high-technology applications. Formulation of inkjet inks using functional dyes, such as, photochromic dyes needs proper care for producing jettable inks which can retain functional behaviour for a considerable period along with other desired properties (for instance, high print quality and robust technical performances of printed textiles). In addition, the porosity of the substrate plays a significant role on the absorption or penetration behaviour of an inkjet ink or more simply regulates its spreading on a substrate thus controlling inkjet printed image quality and the technical performances of an ink to some extent. As a result, it is necessary to control a number of influencing factors to produce desired high quality printed responsive substrates with good technical performances for various applications. This chapter briefly point out some of these issues along with the applications of inkjet printed textiles for a variety of conventional and high-tech applications.

*

Dr. Shah M. Reduwan Billah, 7 Laurel Grove, Galashiels TD1 2LA, Scotland, UK, E-mail: reduwan. [email protected] or [email protected].

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Shah M. Reduwan Billah

Keywords: Inkjet printing, photo-responsive, printed-textile, conventional and high-tech applications.

INTRODUCTION Inkjet printing, a non-contact printing technology, allows deposition of ink droplets on various substrates, such as, textiles, paper, leather, ceramic, glass and also on many other substrates for different purposes [1-7]. It is capable to meet the market demand for producing samples and product within a very short time compared to screen printing technology and also suitable for mass customisation along with the scope of adaptation to unlimited design possibilities with respect to repeat size and colour range. Inkjet printing techniques can also be used for the digital dyeing of textiles using a very innovative technique where the colorants and related additives can be applied on the substrates in the form of a jettable ink disposing through the inkjet print head which is commonly used for inkjet printing technology. Inkjet printing techniques are increasingly gaining the momentum to produce very high quality printed substrates using a wide variety of materials, including, conventional dyes, functional dyes, pigments to meet the demand for a wide variety of coloured substrates for their different applications. Photochromic dyes are classed as functional dyes which usually change the colour from a colourless state to a coloured state when exposed to UV light or sunlight and the inks produced using these dyes also retain the same functional character to impart this unique colour change behaviour to inkjet printed substrates making them suitable for a huge range of applications. For a better understanding on the nature of photo-responsive inkjet printed textiles which is the main concern of this chapter it is important to briefly discuss different aspects of inkjet printing technology and also to analyse its features which made it so important as a technique to draw very high attention both in academia and in industry to replace conventional printing techniques with this technique.

A Brief Historical Overview on Inkjet Printing The idea of inkjet printing goes back to the eighteenth century when Abbé Nollet published his experiments where he analysed the effect of static electricity on a stream of droplets in 1749 [8]. After almost a century later, in 1833, Felix Savart found that an acoustic energy could be used to break up a laminar flow-jet into a train of droplets and Joseph Plateau investigated the formation of liquid jets from nozzles in 1856 which in turns forms the basis of modern day inkjet printing technology [9]. However, it was only between 1858 and 1867 when Lord Kelvin at first developed inkjet like recording device for recording signal of the Atlantic Cable [10]. The Belgian physicist Joseph Plateau (in 1856) and the English physicist Lord Rayleigh (in 1878) studied the break-up of liquid streams and are, therefore, considered as the founders of modern inkjet printing technology [11]. After these different pieces of theoretical work at different times, the first actual form of a continuous inkjet printing device was patented by Elmqivist of Siemens-Elma in 1951 [12]. Then after a relative short period of time there was significant development in the field of inkjet printing technology. In 1965, M. Naiman at first patented thermal inkjet where he

Inkjet Printed Photo-Responsive Textiles for Conventional and High-Tech …

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developed a sudden stream printer [13] and Richard G. Sweet patented device for direct writing signal using fluid droplet recorder [14]. In 1972, Steven I. Zoltan of Clevite Corporation, USA patented a squeeze mode piezoelectric inkjet print head for pulsed droplet ejecting system [15]. After that in 1973 Nils Gustaf Erick Stemme of Sweden patented bend mode piezoelectric inkjet print head which he used it for writing on paper with coloured liquid using the device and also stated the detail mechanism of writing system [16]. In 1976, Sears et al., patented certain method and apparatus for recording with writing fluids and drop projection systems [17]. In 1984, Stuart D. Howkins of Exxon Research and Engineering, USA patented push mode piezoelectric inkjet print head and explained the detail operating principles of a push mode piezoelectric print head [18]. Since then there is a huge upsurge in the development in the field of inkjet as a micro-disposal technique also as a technique for inkjet printing on textiles. Figure 1 shows a brief history of different stages of development in inkjet technology in the form of a chart presentation.

Co n t r i b u t o r J e a n An t o i nNo l l e t e J o s e p hPl a t e a u

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1 8 5 8 / 1 8 6 7

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1 9 5 6

At f i r s t p a t e n t e dt h e r ma l i n k j e t ‘ Su d d e n St r e a mPr i n t e r ’ ( USPa t e n t No . 3 1 7 9 0 4 2 )

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1 9 7 2

Pa t e n t e ds q u e e z emo d ep i e z o e l e c t r i ci n k j e t ‘ Pu l s e d Dr o p l e t Ej e c t i n gSy s t e m’ ( USPa t e n t No , 3 6 8 3 2 1 2 )

Ni l sGus t a fEr i c kSt e mme ,Swe d e n

1 9 7 3

Pa t e n t e db e n dmo d ep i e z o e l e c t r i ci n k j e t ‘ Ar r a n g e me n t o f wr i t i n gme c h a n i s msf o r wr i t i n go n p a p e r wi t hc o l o r e dl i q u i d ’ ( USPa t e n t No . 3 7 4 7 1 2 0 )

St ua r tD,Ho wki nso fExx o n Re s e a r c ha n dEn gi n e e r i n g ,USA

1 9 8 4

Pa t e n t e dp u s hmo d ep i e z o e l e c t r i ci n k j e c t ‘ I n k j e t me t h o da n da p p a r a t u s ’ ( USPa t e n t No . 4 4 5 9 6 0 1 )

SI NCETHENTHEREARESI GNI FI CANTDEVELOPMENTSI NTHEFI ELDOFI NKJ ETPRI NTI NGTECHNOLOGY

Figure 1. Brief presentation of different stages of development in inkjet technology.

History of Inkjet Printers for Textile Printing Introducing colour in our surrounding environments and also into our life styles involves a huge variety of arts, sciences, technologies, businesses and industries- where textile printing for producing lucrative colourful design enjoys a significant importance. The findings during different archaeological excavations to explore the nature of civilization in ancient Egypt bear

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the hallmarks of textile printing which used to be carried out using curved wooden printing blocks [19]. In Europe textile printing industry flourished in a much later date which is evidenced by the discovery of first crafted textile printing samples in 15th century. During 18th century there was a remarkable growth in textile printing particularly in the UK reaching at its zenith just before the First World War which trend faced a gradual decline after the war and this decline continued at a higher speed even after the Second World War [20]. The introduction of new fibres and also new colorants (such as, reactive and disperse dyes) contributed for a significant development in textile printing during the second half of the 20th century [21]. However, it is very interesting to observe that textile printing saw a significant competition between different techniques at the last few decades of 20th century. For example, screen printing, especially with rotary screens, has continued to replace roller printing and during this period new machinery with level of sophisticated control was introduced into the printing industry [22]. A precise alignment of screens using digitally controlled electromechanical systems is a notable achievement of this time which at present controls around 80% of all printed textiles which are produced by using flat o rotary screens [23, 24].

Inkjet Printing of Textiles Textile dyeing and printing industry is in the verge of new digital era where digital solutions are increasingly playing an important role as the intensity in competition between the level of versatility and flexibility available in different printing processes are intensified. Digital printing and analogue printing use different type of techniques for representing data and methods during print reproduction. In the analogue systems if the computer is used it is used to make a variation in continuous phenomena such as voltage or pressure during the transmission of print data, however, in the digital printing systems digital signals are transmitted using computers which completely rely on discontinuous pattern transmission using discrete amount of electricity or light for data communication [25]. In usual terms digital printing covers a range of technologies including, inkjet printing, thermography, electrophotography, electrostatic printing, ionography and magnetography. In all these cases digital data may be used to produce images. Inkjet printing technique has the highest potential compared to these other techniques for textile applications [26]. Table 1 demonstrates a brief historical review on the significant development on the direct inkjet printing of textiles from 1975 till 2004 and after that period the inkjet printing of textiles has reached to maturity stage in a number of areas which is beyond the scope of this current chapter. It is important to note that relative contemporary developments from different companies also contributed to the direct inkjet printing of textiles, some of which are, development of Fast Jet single pass print head of Inca Digital, M class piezo MEMS and water tolerant piezoelectric print head from Spectra, Xaar 1001 series print heads, Picojet 256 all stainless piezoelectric print heads from Picojet and also the improvement of pigmented binder-less inkjet inks by BASF have profound impacts on the total development process. Additionally, developments in the areas of sublimation ink and sublimation transfer printing techniques have significant contributions on the indirect digital printing of textiles. Some of the most important developments are – (a) Roy DeVries sublimation transfer printing method in 1974, (b) Donal Hare T-shirt decoration method in 1978, (c) inkjet sublimation method by


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Crompton and Knowles in 1982, (d) RPL-QLT inkjet sublimation method in 1988, (e) Saw grass patent on sublimation ink in 1991, (f) development of Fotoware-Canon inkjet transfer paper in 1994 and (g) soft link method by Hanes in 1999 [27]. Table 1. A brief historical overview on the significant developments on the direct inkjet printing of textiles Year 1975 1976 1990 1993 1996 1997 1998 2001 2002 2003

2004

Significant developments Milliken-Millitron carpet printer Zimmer-Carpet printer Seiren-Parallel processing Embleme-Water UV direct T-shirt Perfecta/Zund-Flatbed Rhome Revolution-Direct T-shirt Encad and Mimaki-Textile proofing L&P-UV-curable textiles and Dupont Artisti 3210 Mimaki-GP 0604 Mimaki TX 3, DupontArtisti 2020, L&P UV-cure dye, Robustelli Mona Lisa, Reggiani DReAM, Zimmer Chromotex USSPI Fast T-Jet & USSPI Fast T-Jet Jombo, Kornit 930 and Kornit 931

Inkjet Printers for Textiles Inkjet printing systems are used different areas of textile printing, some of the most widely used areas are – fashion accessories, sports and swimwear, home textiles (e.g., curtains, sheets, towels, table settings, furniture upholstery), flags and banners, t-shirts and specialties, automation and transportation upholstery, architectural textiles, medical textiles (e.g., trans-dermal dosing) and also in some types of technical textiles. Some of the most notable inkjet printers used for digital textile printings are – Colorspan Display Maker XII, Mimaki TX2 and TX3, Dupont Artisti 2020, Legget & Platt UV-dye, Robustelli Mona Lisa, Reggiani DReAM, Zimmer Chromotex and Imaje-Osiris. For direct T-shirt printing different types of inkjet printers are used, some of which are – Mimaki (e.g., Mimaki GP-1810, Mimaki GP – 604) and Kornit (e.g., Kornit 930, Kornit 931) printers. Digital inkjet printing of textiles can be divided into different categories, such as wide format direct, wide format indirect, single pass printing and inkjet T-shirt printers [27, 28].

Inkjet Print Head Technologies All inkjet technologies are basically precise micro-disposal techniques where digitally controlled the fluid droplets (e.g., the inks) are ejected from the print head onto a substrate. Various techniques can be used for a digital control on the fluid droplet ejection from the print head to the substrates which are sometimes used as a basis for the classification of inkjet

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print heads. For example, continuous inkjet printing technique or drop-on-demand inkjet printing technique are two mostly used terms for a broader classification of industrial inkjet printing technology (although there are variants within each class). The print head that uses continuous inkjet technology ejects drops continuously (Figure 3) where the drops are either directed to the substrate or to a collector for recirculation and reuse. On the other hand, the print head which uses drop on demand type inkjet printing technology ejects drops only when required (Figure 4). A brief classification of inkjet print heads are shown in Figure 2. Continous inkjet print heads are of two type in terms of the use of inks – continuous inkjet print heads which uses aqueous inkjet inks (such as, Kodak, Versamark) and continuous inkjet print heads which uses solvent or UV curable inks (such as, Danaher, Dover, Domino, ITW, Mathews). In this same sense, drop-on-demand print heads can be divided into different classes- (a) thermal inkjet print heads which only use aqueous inks (e.g., Hewlett-Packard, Cannon, Lexmark, Kodak), (b) piezoelectric print heads which use all types of inks (e.g., Epson, Dimatix, Xaar, Richoh, Konica-Minolta, Toshiba Tec, Panasonic) and (c) valvejet print heads which mainly uses solvent based inks, however, they can be used for all types of inks (e.g., VideoJet, Imaje, Crayon, Loveshaw, Kortho, Foxjet, Miliken, Zimmer, Danaher, Dover, Domino, ITW, Mathews). However, based on deflection mode continuous inkjet print heads can be divided into two categories – (a) binary (such as, Stork, Scitex, Iris, Siemens, Domino, Kodak, Versamark) and (b) multi-deflection (such as, VideoJet, Danaher, Imaje, Dover, Linx, Willet). Based on printed head technologies, piezoelectric print heads are of five types, they are – push mode (e.g., Ricoh, Trident, Brother, Epson), bend mode (e.g., Sharp, Epson, Xerox, PicoJet, Dimatix Samba & M-class, Kyocera), squeeze mode (e.g., Siemens, Gould), shear wall shear mode (e.g., Xaar, Konica, Minolta, Toshiba Tec, Seiko II, Brother, Kodak, Microfab) and shear mode (e.g., Dimatix) [27, 28].

Figure 2. A schematic representation of the classification of the inkjet print heads.


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Continuous Inkjet (CIJ) Printing Technique Continuous Inkjet printing is an amateur micro-disposal technique popularly used for marking and coding of products and packages. In a CIJ disposal technique, a pump directs fluid from a reservoir to small nozzles that eject a continuous stream of drops at high frequency (in the range of roughly 50 kHz to 175 kHz) using a vibrating piezo crystal. In addition, the drops are charged using an electrostatic field which are then allowed to pass through a deflection field to determine landing position of the charged the drops while at the same time the unprinted drops are collected and returned to the reservoir for reuse. The high drop frequency of continuous inkjet micro-disposal system makes this technique suitable for a direct translation into a very high speed printing system as evidenced by such applications as the date coding of beverage cans using continuous inkjet printing technique. It also shows very high drop velocity which allows micro-disposal at relatively (compared to other inkjet technologies) large distances from the print head to the substrate for useful in industrial environments. CIJ shows advantage over other inkjet technologies in its ability to use inks based on volatile solvents that allow rapid drying and aiding in adhesion on different substrates. However, CIJ shows relatively low print resolution but requires very high maintenance and environmentally not friendly due to the use of volatile solvent-based fluids which need to be charged for printing.

Figure 3. A schematic representation of a continuous inkjet printing system.

In principle, the continuous inkjet printers apply a pressure wave pattern to an orifice in order to break a continuous liquid jet into droplets of equal size and spacing. During the formation of droplets they are selectively charged and the stream of drops is passed through an electric field to deflect the charged droplets. According to the nature of the printer either the charged or uncharged drops are used for image generation while the unused drops are collected for recirculation. Based on the mechanism of image generation, the continuous inkjet printers may be of different types, such as, (a) the binary or multiple deflection, (b)

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hertz, and (c) microdot types. The continuous printers are mostly used in industrial marking processes and also in the field of graphic arts. These printers usually generate a smaller drop size, a high drop velocity, and a higher drop generation rate (up to 1 MHz) compared to other inkjet printers. However, they are expensive and difficult to control the satellite drop formation. Figure 3 illustrates a schematic diagram of a continuous inkjet printing system [29, 30].

Drop-on-Demand Inkjet (DOD) Printing Technique In broad terms it refers to an inkjet technology which allows the micro-disposal of inkjet inks (in the form of droplets) when required using pressure pulse. In addition, DOD print heads are classified in different sub-categories based on the technique which is used to generate this pressure pulse and these are – thermal, piezo and electrostatic. Besides these print heads, MEMS print heads are also often merged into this drop-on-demand type of print heads which are invariably still based on either piezo or thermal inkjet technology. In a drop on demand type inkjet print head, it uses a vacuum method to control drops and eject only when the drops are in demand. It applies a negative pressure in the print head to keep the ink inside until a local pressure wave at the nozzle is generated which can eject a droplet. DOD inkjet print heads are more advanced compared to continuous inkjet print heads as they are free from some requirements which are highly required in the continuous print heads, such as, starting up and shutting down, complicated charging, deflection hardware and also the need for an ink recirculation unit. Different pieces of work for producing inkjet printed high performance photo-responsive surfaces reported in this chapter has widely used piezoelectric inkjet print head (DOD Xaar Omnidot 760) so this chapter will briefly cover different aspects of piezoelectric printing technology along with other print head technologies [31, 32].

Thermal Inkjet Technology In a thermal inkjet system, drops are generated from a rapid heating of a resistive element (of the print head) in a small chamber containing the ink. During the heating of the resistive element temperature rises very fast (such as, from 350°C to 400°C) that causes a vaporisation of a thin film of ink above the heater for a rapid creation of a bubble that in turns creates a pressure pulse to force the ink (in the form of a droplet) through the nozzle. When the drop is ejected it leaves a void in the ink chamber which is subsequently replaced and filled by the ink in preparation for the creation of the next drop for a continuation of this droplet formation (in Figure 4A, illustrates a thermal inkjet print head). Thermal inkjet print heads are comparatively cheaper and have the potential in producing very small drop sizes along with higher nozzle density suitable for compact devices. However, the print head must have to withstand the effects of ultra-high local temperature which is usually used to vaporise the ink for the creation of ink droplet in the form of the bubble. Thermal inkjet inks are usually based on aqueous systems and the ink formulation needs significant level of accuracy; otherwise, there are chances to form a hard coating on the resistive element which in turns limits the efficiency of the print head causing a total failure in


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long term. This type of print head is not suitable to dispose most of functional inks because the high temperature often has very high detrimental effect on the functionality [33, 34].

Principle of Operation for a Piezoelectric Print Head A piezoelectric print head uses a piezoelectric element (such as, lead zirconate titanate or PZT) to modulate a pressure based deformation on the ink flow for the physical displacement of the ink droplet by the way of sending the electrical impulse. For printing an electrical impulse is sent to a piezoelectric element of the print head to cause physical displacement by way of changing the elongation or bends of the piezoelectric element. This physical displacement creates a volumetric change in the nozzle chamber to produce a pressure wave to push the droplet through the nozzle orifice. Figure 4 shows a schematic representation of different print heads – (A) thermal, (B) piezoelectric and (C) electrostatic. Piezoelectric print heads have comparably higher manufacturing costs although they have a long operation life. This high manufacturing cost is one of the main limitations of the piezoelectric print heads which categorically hinders the miniaturisation of the nozzles. In addition, piezoelectric print heads are also sensitive to the air bubbles trapped in the nozzles which also limits their printing qualities. It is an important requirement for the inks to be used the piezoelectric print heads that the ink must remain incompressible in order to maintain a controllable propagation of mechanically generated pressure waves in the nozzle chamber. Air bubbles in the nozzle disturb this condition and de-gassing operation should be carried out to remove the air or dissolved gases before actual printing. It is commonly used technique to purge a considerable amount of ink through the print head before printing in order for ensuring the total removal the air or bubbles to produce high quality printing images or high quality disposal of inks to a desired substrate [35, 36]. Piezoelectric drop-on-demand inkjet printers are usually used in graphic designs, textile printing, commercial printing, industrial and digital fabrications and also in biomedical applications. Thermal piezoelectric print heads are normally used as desktop printers and also used in graphics, commercial and biomedical printings. Electrostatic drop-on-demand print heads mostly used in the printing on beverage cans while valve jet printers most got their applications for carpet printing, coating, marking and coding. In addition, continuous inkjet print heads are widely used in proofing, marking, coding and sometimes also in textile printing.

Figure 4. A schematic representation of different print heads – (A) thermal, (B) piezoelectric and (C) electrostatic.

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Inkjet printing techniques can also be used for graphic designs which have been used in a wide variety of fields some of which include – textile printing, coding and marking, carpeting, office inkjet printing, addressing direct mails, proofing, CAD, wide format graphics (for billboards and signage), flags, T-shirts, wall covering, floor covering, ceramics, photo finishing, food decorations, packaging, and also other types of commercial printings [27, 28].

Choice of Technology and the Selection of Inkjet Print Heads Inkjet printing technology as a micro-disposal technique has a wide range of applications in different fields, including in electronics, photovoltaic, electronic displays, 3D additive manufacturing, chemical formulations, tissue engineering, high-throughput screening, biomedical applications. However, during the selection of an inkjet print head for a particular application needs rigorous study on the different aspects of the inkjet print head, available facilities, properly defined objectives of the project where the print head to be used, nature of the substrates, nature of the inks to be used, technical performance, the market, costs and related many other fundamentals issues. For example, during the selection of print heads proper care and advices from different manufactures and others involved in the supply chain is instrumental because one particular type does not necessarily meet or even suitable for all desired applications. Briefly, some important characters of a print head needs careful consideration (during matching it to different applications) include, (a) single-pass throughput, (b) firing frequency, (c) fluid firing viscosity range, (d) types of fluids the print head can tolerate (e.g., effective pH range for aqueous inks where print head can be operated), (e) drop velocity, (f) native dpi (depth per inch) of printed image, (g) nature of crosstalk, (h) print line length, (i) nozzle diameter, (j) nozzle pitch, (k) drop size, (l) drop firing straightness, (m) greyscale capability, (n) drop through distance, (o) nature of the heater (in the case of thermal inkjet print head and (p) maximum operating temperature [28,37-39]. There are different elements in inkjet technology which virtually control the whole system, some of the main elements include – (a) the nature of a print head, (b) firmware, driver, RIP (raster image processing) and image generation software, (c) print controller electronics, (d) print head monitoring and maintenance, (e) print head and/or substrate movement, (f) substrate transport and handling, (g) the nature of an ink or a fluid, (h) the ink delivery system, (i) colour control, (j) nature of pre-treatment or post treatment on the substrate, (k) curing, fixing and drying processes, (l) the system integration and (m) tailoring and tuning components to meet specific requirements. [40, 41]. Some recently introduced printers for textile application includes, Durst Kappa (Ricoh Gen4), MS LaRio (Kyocera Kj4B), Konica Minolta Nassenger Pro 1000 (KM 1024 – 4 lines for 256 nozzoles), SPG Prints (Stork), La Meccanica (Kyocera KJ4B), Kornit Allegro (Dimatrix Nova AAA), D-gen Teleios Grande (Ricoh Gen4L), Shima Seiki new SIP flat bed (Ricoh Gen 4L), AnaJetmPower (Ricoh Gen4). [27, 28].


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Table 2. Types of inkjet inks Different types of inks Division based on solvent or and the method Different types of inks Aqueous solution, dispersion or micro-emulsion Non-aqueous inks Oil based or solvent based Phase change inks Liquid to solid, liquid to gel Reactive inks UV curable inks Division based on the colorants used in the ink formulation Dye based inks Acid, Reactive, Direct, Disperse, Vat, Sulphur, Solvent Pigment based inks Inorganic pigments (e.g., Carbon Black), and organic pigment based Polymer based inks Aqueous, Non-aqueous, Polymer blend based

Different Types of Inkjet Inks There are different types of inkjet inks and a brief division is shown in Table 2 and the inkjet print heads which suitable to certain types of inkjet inks are shown in Table 3. Table 3. A brief presentation of different inkjet print heads suitable for specific ink classes Print head model Oil Xaar 1001 √ Trident 256Jet √ Epson TFP √ HP X2 √ Richo Gen 4 √ Fujifilm Dimatix PQ-512/15 √ Fujifilm Dimatix Scan PAQ QS-10 √ Fujifilm Dimatix QS-256/10 √ Fujifilm Dimatix Samba √ Panasonic 600X600 √ Kyocera KJ4A √ Kyocera KJ4B √

x √ √ x √ x √ √ √ √ √ √

Different types of inks Water Solvent √ √ √/ x x √ √ √ √ x x x x

UV-cure √ √ x √ √ √ √ √ √ √ x √

DESIGN AND DEVELOPMENT OF INKS AND TYPICAL INK COMPONENTS The ink and the print head are the two vital components of the inkjet printing system (in exception to the nature of the substrates which have significant importance), because even they are improved individually to an outstanding level, it is finally the cooperation of both, which defines the printing performance. This section focuses on the challenges for designing

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and developing inkjet inks. The composition of the inks is not trivial and the inks must fulfil several essential requirements to be jettable also to produce high quality prints.

Design Requirements of Inkjet Inks Sometimes specific requirements for certain print heads exert challenges in the design and development of particular classes of inkjet ink formulations. These requirements define the nature of inkjet inks, some of the important features are – intrinsic characteristics of the inks, ink performance in the printers and interaction of the ink with print media. Since all of these requirements are intricately related to each other so during designing the ink a compromise between these categories is important. The intrinsic ink characteristics are basically the physicochemical properties of an ink particularly relating to the ink composition. Other important properties which need rigorous considerations include, viscosity, surface tension, pH, conductivity, purity of the components, drop velocity, dye solubility, visible spectrum, density (specific gravity), solid content, and stability of the inks as well as health, safety, and environmental considerations. As some these properties are more specifically related to the print head technology (such as, the type or model of the print head) so these properties must be optimised to meet the specific operation range of the print head used for the printing purpose. Jettability and drop placement accuracy of the inkjet print head depend on the interaction of inks with the print head and its components. It also important to note that nature of ink plays a vital role in terms of technical performance which is defined by the level of interactions between the inks and the substrates. A primary consideration is the ink must be compatible with the printer print head and should not cause any corrosion to the metallic parts, softening or swelling of the organic parts along and any type of contaminations. Inks should be free from chemical reactions, biological or fungal growth, particle agglomeration or precipitation or foaming must during the operation and storage. The ejected inkjet drops should be of identical volume and velocity. The drop break off length should be uniform without any satellite or secondary droplet formations. The ink should be resistant to any pH changes, decomposition and evaporation. The ink should neither clog the orifice nor wet the face plate. The ink droplets should show desired criteria when the printed on the substrates to achieve desired print quality. It is expected that the ink drops should reveal proper wetting and spreading on the substrate and dry reasonably quickly. When printing is carried out nonporous media (such as glass) the surface energy of the substrate and the surface tension of the ink are most likely to define the spreading and the dot size. However, during the printing on porous substrates (such as, a textile substrate), the ink vehicle usually wets the surface and penetrates into it to set the correct dot size to provide a printed image. It is also expected that during penetration and evaporation, errors like bleeding, feathering, mottling, or line banding should not occur. Additionally, the printed patterns should have high print quality and high technical performances. A quality inkjet ink is usually designed considering all the above mentioned points [42, 43].


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REQUIREMENTS FOR DIFFERENT INKJET PRINTING TECHNOLOGIES Different inkjet print heads uses different techniques to jet the inkjet inks onto different substrates. Inkjet inks are required to meet certain criteria (such as, physical and chemical requirements) to be jetted from a particular type of inkjet print head. So, in order for such inks or fluid compositions to be deposed from a certain type of print head the compositions may be formulated to meet the characteristics as specified in Table 4.

Rheological and Other Requirements for a Good Jettable Fluid The nature of inkjet fluid is of immense importance which controlled the quality and performances of both printed images as well as the productivity and printing performances of the inkjet print heads. Different selected properties of the inkjet fluid is briefly summarised here. Table 4. Jet fluid property requirements for specific print head technologies Property

Drop on demand (DOD) Thermal (TIJ) Piezo Valvejet

Viscosity (cP) (at operating 1-4+/- 0.25*b temp*a) Surface tension(dynes/cm) 30-50 Conductivity (uS/cm) 0

2-15+/-0.25-0.5*b 2-20 25-45 0

25-50 0

Salt content Chlorides (ppm) Particle size limit (um) pH % solids(residual) Stable to shear rate of (s-1) Dot diameter (um) Droplet volume (pico-litre)

<10 0.5 4-10 <4 105 20-250 2-200

<100 1 4-10*d <20*e 105 20-250 2-200

Droplet velocity (m/s) Firing frequency (kHz)

15 30

5-10 30

<100 5 4-10 <20 105 100-5000 150100,000 10 <2

Continuous (CIJ) Binary Multideflection deflection 1-2.5+/-0.25*b 2-4+/-0.5*b 20-50 20-50 >500+/- 20%*a >500+/20%*c <100 <100 0.5 2 4-10 4-10 <4 <15 106 106 50-300 100-2000 50-250 50-750 20 64-1000

20 60

N. B. In this case, a*illustrates that DOD print heads may have temperature control where CIJ print heads generally operate at ambient temperature, b* shows typical ink manufacturing batch to batch tolerance, c* indicates the tolerance during operation (re-circulation of ink), d* shows the pH profile unless a ceramic print head is used which can operate at any pH and lastly e* indicates the exception for UV curing inks which may be up to 100% solids.

Viscosity Inkjet requires low viscosity fluids compared to most dispensing techniques. In a thermal print head, it is often heated to reduce the viscosity of a fluid to allow the print head to print. However, this also reduces the effect of changes in ambient temperature on printing reliability. It is an important feature of most modern DOD print heads which can regulate the temperature of the print head to change the viscosity. It is important to note that the temperature control of CIJ printers is not usually controlled by a thermal management system

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and the printer is usually operated at ambient temperature. The viscosity of a fluid controls the jettability (ability to be jetted from the print head), for example Newtonian fluids are preferred for inkjet deposition; however shear thinning fluids may be used with care whereas shear thickening fluids should be avoided. However, the assurance of a proper control on the viscosity for a fluid does not necessarily guarantee inkjet printing success as other aspects of the fluid’s flow properties are also important to the inkjet printing process. For example, a highly viscoelastic fluid may not exhibit proper jet breakup even though it may appear to have the correct viscosity for jetting.

Surface Tension Surface tension plays an important role to control the wetting of the fluid inside the print head. When the surface tension is too high, the fluid does not wet the internals of the print head properly which may leave some air pockets to cause unreliable printing. However, a too low surface tension of the fluid does not allow a proper meniscus formation in the print head nozzle and in the case of DOD which causes the fluid to flow spontaneously onto the print head face plate (also known as faceplate wetting) producing an unreliable jetting. In the case of CIJ also, a droplet break-up becomes unreliable. In addition, surface tension has a tendency to affect the drop size and satellite formation. Conductivity Conductivity is an important issue as the continuous inkjet printing technique requires deflected charged droplets for printing using an electric field. However, for all other inkjet techniques conductivity is undesirable as it may cause corrosion of metal components in contact with the ink. Salt Content In different printing techniques (especially in continuous inkjet printing techniques) sometimes salts are used mostly to control conductivity, however, some specific salts such as chlorides are particularly undesirable as they are more corrosive compared to other salts. So, a proper care is essential to select a salt during the formulation of inkjet inks for a continuous inkjet printing system to minimize its corrosion effects. In addition, multi-valent metal salts (such as, magnesium and calcium based salts) should be avoided during the formulation of inks for thermal inkjet printing as these types of salts often cause kogation (crusting of the print head heater element) eventually leading to a premature failure of the print head. Particle Size Particle size of the different ingredients of an inkjet ink formulation has a limiting effect on printability since the inkjet nozzles are very narrow (typically of the range of 20-75 microns in diameter). So, to avoid higher particle sizes (usually over 2 microns in diameter) repeated filtration is necessary to get rid of the maximum particle size or the aggregates present in the fluid to prevent blocking of the print head nozzles. pH Usually a specific pH is used to control solubility or dispersion stability of active components in the ink fluid. Additionally, the pH range where a print head can operate is limited because of the chances of corrosion of the print head (since most of the print head are


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usually made from steel). However, there are some piezoelectric drop-on demand ceramic print heads which allow a reliable jetting of fluids from across the full range of pH.

Solids Percentage Different factors such as viscosity, elasticity and the particle size directly control the amount of solids which can be present in an ink fluid. Because, when the solids content of the fluid is too high it may dampen the pressure pulse which is necessary to eject or break up the inkjet drop and also may prevent reliable printing. Shear Inkjet printing is a high shear technique so proper cares are needed during the selection of materials for inkjet ink formulations, in this case materials which can tolerate some level of shear resistance is desired. Because, there are chances that materials that are not stable to high shear may decompose in the print head nozzle to block it (or the return gutter for a continuous inkjet printing system) and also may cease to provide the desired application or end user properties on the printed substrate. Particularly for continuous inkjet printing technology, the nozzle experiences a higher shear compared to the other inkjet techniques. Dot Diameter It is the diameter of a drop that the printed droplet provides when disposed from an inkjet print head to the substrate. It is also a function of a number of things including, the nature of interactions of the droplet with the substrate. Sometimes the substrates are pre-treated using different techniques to modify their wetting behaviours such as hydrophobicity, absorbency which have a direct impact on the levels of interactions of the ink droplet towards the printed substrates which subsequently controls the dot diameter. In addition, shapes of the substrate also have pronounced control on the nature of ink and substrates interactions. Drop Volume

Drop volume (picoliter)

45 36 27 18 9 0

Kyocera KJ4A

Kyocera Panasonic Xaar 1001 KJ4B 600X600

Trident Ricoh Gen Epson TFP HP X2 256Jet 4

Xaar 1001

Print heads Figure 5. Average drop volume (in picoliter) of different inkjet print heads.

Trident 256Jet

Fujifilm Fujifilm Fujifilm Dimatix Dimatix Dimatix PQ Scan PAQ QS 512/15 QS - 10 256/10

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Figure 6. Average DPI (dot per inch) per drop volume (in picoliter) of different inkjet print heads.

The drop volume is usually determined by a number of influencing factors, including the physical size of the nozzle that makes up the print head. Some other prominent factors are the firing frequency and the force by which the drop is ejected also control drop volume. It is important to note that the firing frequency is usually determined by the nature of waveform or voltage used during firing (may also called disposing) from the print head. Figure 5 indicates the average drop volume (in picoliter) of different inkjet print heads while Figure 6 shows the average DPI (dot per inch) per drop volume (in picoliter) of different inkjet print heads [27, 28].

Drop Velocity The nature of drive electronics in combination with the physical parameters of the disposing fluid usually determine the droplet velocity as it emerges from the print head. Firing Frequency It is an indication of the rate of the ability of a print head how much it can deliver in each second when it disposes ink fluid onto a substrate which is usually counted by the number of droplets ejected from a print head in one second. Settling and Sedimentation Settling and sedimentation are unexpected from an inkjet ink; however, in a functional ink fluid sometimes it may contain particulate material. So, it is important to ensure that settling or sedimentation is either eliminated or minimized using a proper control on the maintenance regime to avoid both the blockage in the print head nozzles and unreliable printing performance.


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BASIC REQUIREMENTS IN THE COMPOSITION OF AN INKJET INK FLUID Table 5. Jet fluid disposing compositions Different components Solvent Co-solvent Humectant Viscosity control agent Conductivity agent Surfactant Biocide pH modifier Corrosion inhibitor Wetting Agent Active agent(s)

Binary CIJ Multi-deflection CIJ Thermal Inkjet (TIJ) 70-95 50-90 70-95 0 0-20 0-3 0-3 0-5 10-30 0-2 0-25 0-0.5 0-0.5 0-0.5 0-0.5 0-0.5 0-0.5 0-0.5 0-1 0-1 0-1 0-0.2 0-0.2 0-0.2 0 0.01-0.3 5-20 5-30 1-5

Piezo DOD 60-90 0-5 10-35 0-25 0-0.5 0-1 0-0.2 0.01-0.3 5-30

N.B. In all the cases, compositions defined by the percentage (% ) of weight.

Some typical compositions of inkjet disposing fluids are given in Table 5 for each of the print head technologies. The list shows the composition in the form of an example of the number of components that may make up a formulation. However, it is important to note that not all formulations may require each and every component to be present for successful operation.

Effect of Components in the Formulation The main aim of the inkjet ink composition described in Table 5 is to provide some examples for a jettable composition by adjusting the parameters that have influence on the ejection of the fluid from different types of print heads. There are complex inter-relationships between these components in stabilizing the ink fluid and for a better understanding of the role of each component is briefly described here.

Solvent In most cases to apply functionality on printed textiles the solvent or vehicle used in the inkjet ink formulation should preferably be de-ionized, de-mineralized water which provides the ink a highly significant chemical basis for the interaction of the active agents or the colorants with the textile after printing. Sometimes post treatment is required on inkjet printed textiles for a number of reasons including the enhancement of technical performances. In this type of cases sometimes alternative inkjet ink compositions using non-water based solvents such as ethanol or lactates may also be used which fulfill the desired characteristics. There is a wide range of solvents which can be used in different types of inkjet ink formulations which can meet particular requirements which are expected from the inks.

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Co-Solvent A co-solvent can be used along with a main solvent in an ink formulation to address certain desires aspect from the formulated ink. For instance, in a drying ink formulation a cosolvent is often required to provide solubility for the conductivity agent in which case a small amount of ethanol is used to dissolve a conductivity agent that is not soluble in MEK alone. Additionally, a co-solvent may also be used to improve the solubility of the active component(s) and their compatibility with the conductivity agent (where the incompatibility between these materials is a common formulation issue). More particularly, in continuous inkjet printing systems the non-printing fluid is often mixed with air during the recirculation process which has a tendency to lead to air entrapment related to foaming issues. In these cases, co-solvents are usually used to control foaming in these systems. Humectant Usually a humectant is a low volatility, high boiling point liquid which is used in the inkjet ink formulation to prevent crusting of the nozzle when the jet(s) are not active. During different types of inkjet inks formulations humectants are generally selected from the group consisting of polyhydric alcohols, glycols, especially polyethylene glycol (PEG), glycerol, nmethyl pyrrolidone (NMP). There is no hard and fast rule for this selection, for example, during certain formulations it may appear that more than 5% humectant is being used, however, it is in fact the case that the same material may also be present as a viscosity modifier. Viscosity Control Agent Viscosity control agent is the most important component of ink. Because it has a significant control on the inkjet printing reliability and the quality of droplet formation and break up process. Additionally, sometimes it acts as an active component and provides some of the end user properties particularly in the cases of functional inkjet inks. During the selection of viscosity controlling agent high molecular weight polymers should be avoided, because of their higher elastic nature sometimes they cause difficulty in jets breaking up of inkjet inks. Some of the widely used viscosity control agents are, polyvinyl pyrrolidone, polyethylene oxide, polyethylene glycol, polypropylene glycol, acrylics, styrene acrylics, polyethyleneimine, polyacrylic acid. Conductivity Agent Particularly in the cases of inkjet ink formulations for continuous inkjet systems conductivity imparting agents (such as, electrolytes) are used to produce charged ink droplets which can be deflected during actual printing. An electrolyte is usually used when there is insufficient conductivity in the ink. It is important to note that conductivity agents should be compatible with the other components of the ink formulation and they should not promote corrosion. Some commonly used conductivity agents are lithium nitrate, potassium thiocyanate, dimethylamine hydrochloride, thiophene-based materials. These materials show different level of conductivity, for example, it was observed that the use of a small amount of potassium thiocyanate was sufficient to provide required level of conductivity to produce uniformly jettable continuous inkjet inks.


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Surfactant In typical inkjet ink formulations, surfactants are usually used either to reduce foaming of the formulation and release dissolved gases or to lower the surface tension of the droplet and to improve wetting. Some usually used surfactants are – Surfynol DF75, Surfynol 104E, Dynol 604 (Air Products, USA) and Zonyl FSA (Du Pont, USA). Additionally, BYK 022 (BYK-Chemie) and Respumit S (Bayer, Germany) are both silicone based antifoam agents that have proved very effective for smooth and uniform jetting purposes. Biocide Sometimes a small amount of biocide is usually used in an aqueous based inkjet ink formulation to prevent bacterial growth in the inks when stored for a long time. However, in the solvent based inkjet ink formulation biocides are not usually required, for example, when solvent like isopropyl alcohol is present in the composition in sufficient amount it can prevent bacterial growth. pH Modifier Different types of buffer solutions or pH modifiers are sometimes used in the inkjet ink formulation to maintain a pH at which the components of the ink formulation are soluble or make a stable dispersion. In typical formulation the pH is usually neutral (pH 7.0) or slightly alkaline. Additionally, the pH modifier may also be used to modify the chemical interaction between the different suitable components of the ink and the printed substrates (such as, textile). Some usually used pH modifers are, ammonia, morpholine, diethanolamine, triethanolamine and acetic acid. However, it is desirable from an inkjet perspective to use relatively neutral solutions to reduce corrosion in the print heads. Corrosion Inhibitor A corrosion inhibitor is mostly used in an inkjet ink formulation to prevent unwanted ions present in the ink fluid (as impurities coming from the active components) that may cause corrosion to the printer. Wetting Agent Wetting agents are usually in ink formulations to improve the surface wetting of the fluid on the internal capillaries of the digital nozzles. Some of the usually used wetting agents are based on acetylinicdiols. In addition, sometimes, surfactants and co-solvents may also act as wetting agents. Active Ingredients The active ingredients (such as in this case photochromic dyes) are the materials which are usually used in the inkjet ink formulation to impart desired properties on the printed substrates. For example, when the photochromic dye based inkjet inks were disposed onto the textile substrates, all the printed substrates showed photochromic colour change under UV or sunlight exposure, so in this particular case photochromic dyes played as active ingredients.

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RECENT TRENDS IN HIGH PERFORMANCE INKJET PRINTING TECHNOLOGIES Recent studies indicates that there is very significantly increasing growing demand for environmentally friendly high performance and technically robust inkjet ink system which can be used for wide format inkjet printing on different substrates including textile printing. So, a very precise discussion within the very limit of this chapter will focus on selective important aspects of UV inks, inkjet technologies that use UV inks for wide format inkjet printing systems is included here in the following subsequent sections.

UV Inks and Inkjet Printing Ink Jet printing technologies that use UV inks need a UV curing set up to cure the printed substrates. Industrial inkjet printing with UV inkjet inks requires the integration of inkjet print heads, printing mechanisms along with the proper curing systems which have already been effectively addressed by different inkjet print head manufacturers. UV-curable inks are widely used for the decoration of the sheathing of wire and fibre optic cable, automotive hoses and packaging for marking for high level of technical performances. There is a significantly increasing demand of UV-curable inkjet inks and associated inkjet technologies for high performance graphic arts printing systems on different substrates, including as PVC, acrylics and textiles. It is also interesting to note that some analog printing equipment manufacturers are also trying to incorporate UV-curable ink jet printing systems into analog printing set up for an effective use of the ability of the digital printing system which can print variable information with the high speed and quality. UV inkjet inks and related systems are used for rapid prototyping, signage and other industrial applications. The recent advances in UV-curable ink chemistry successfully mitigating different requirements and limitations of UV-inkjet inks and ink jet technology for a wide range of industrial exploitations, including wide format high performance inkjet printed textiles. As some of them are already stated somewhere in an above section, there are many advantages of using UV curable inks, some of which include - no VOCs (volatile organic compounds), little or no air pollutants, high print quality, low odour after curing, reduced ink wastage, constant ink composition, no print-head clogging, low energy requirements and the ability to print on a wide range of substrates. UV inks are highly viscous and have limited flow on the substrate. This particular nature when combined with the instant or spot fixation offered by UV curing lamps provides an opportunity to have very high print quality and fast overall operating speeds. It is an advantage of UV inkjet system that there is no evaporation of volatile solvents in the print head which minimises waste and time spent on maintenance. UV inks can provide good colour value and when optimised accurately. UV inks can be used to produce a very clean colour gamut. An additional feature is that as the UV ink does not cure before it is exposed to UV light there is minimum or no risk for a premature drying of the ink which in turns extend the life of the print head to ensure less down time when the UV inks are stored and managed properly. Usually UV inks are typically 100% solids which imply that when they are printed on the substrate after curing they almost remain there. As


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there are no volatile carbons they are more environment friendly making it a good green technology option. However, there are situation which limits the uses of UV inks. UV inks are typically highly viscous which limit their ability to print smooth consistent thin films to meet certain application demands. The generation of heat from UV lamps used during curing has the ability to damage thin or delicate substrates, however, with the introduction of UV LED technology this issue mitigated to some extents. Additionally, sometimes there is risk of over-curing which may reduce the adhesion of the ink to the substrates and a drastic over-curing may turn the ink film to flake. Use of UV ink needs some training for the effective uses of UV light where an inefficient use risks huge health problem to the workers and also the handling uncured materials carries potential health hazards which needs significant level of considerations. UV inkjet system needs UV system setup (such as, UV lamps, devices to run the systems, ancillary devices to dissipate heat) for curing which also involve an operational cost which is often expensive. There are still issues relating to poor adhesion which sometimes require modification when printed on difficult substrates (e.g., polypropylene) though UV inks have a wide variety of printing applications on nonporous substrates. In addition, UV light requires to reach all the way through the ink layer in order for it to polymerise otherwise there are chances of improper curing causing a serious issue of overall adhesion properties and printed image quality. It requires a careful optimisation of ink chemistry, studying the absorption nature of the substrate along with the modification UV intensity to ensure full curing [44-46]. Besides some of these limitations of UV inks, with the improvements in technology UV inks are now in the road to capture new markets. For example, UV digital inkjet printing systems are dominant in the printing of rigid substrates for the POP market and continue to increase its market share in areas such as outdoor signage, film packaging and other areas.

Integration of UV Curable Inks and Inkjet Print Heads with Analog System Some technical difficulties delay the progress to some extents in the current trend to integrate screen printing with inkjet printing systems that use UV inks. The combined systems have many advantages, some of which include – (a) eliminating the cost and time for making films, plates and screens and set up, (b) printing short-run images more economically, (b) permitting variable information printing and customization, (c) printing for long term outdoor durable images and (d) minimising the cost and waste associated with lamination from many applications. For example, some of these types of printers are available from Barco, Inca, Durst, Sias, Zund, Tampoprint or Leggett and Platt. UV inkjet inks are suitable to use for printing a wide range of flexible substrates including paper, textile fabrics, banner materials, vinyl, polyester, polycarbonate and other plastics. It is important to note that the flatbed models have the capability to print on different rigid substrates, for examples, rigid plastics, wood, glass, tile, metal, and foam and corrugated board. There are scopes for the use of UV-curable inks and ink jet multi-colour printing which will help to grow to supply an increasing part of the demand for advertising, display graphics, posters, signs, banners, rigid boards, outdoor graphics, exhibition and stage graphics, architectural graphics and murals, backlit displays, flags, fleet and vehicle graphics, bus shelters graphics and bus wraps. Additionally, UV-curable inkjet inks are much less substrate dependent compared to water, oil and solvent-based ink jet inks. For example,

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Leggett and Platt showed the additional possibilities of fixing and curing textile dyes and other colorants using UV curing system.

The Nature of UV Inkjet Inks UV are prepared from a composition of different materials, where the main components are – (a) reactive monomers, (b) photo initiators, (c) oligomers, (d) colorants (such as, dyes or pigments) and (e) other additives. In this case, the usual mechanism is, during the curing process the ink reacts to UV light and the monomers polymerise to form a tough film. UV curable inks are also used in different traditional printing methods as well, for example, flexographic, lithographic, rotogravure and screen printing systems. UV curable inks used in inkjet large-format printing mainly are of two types – (a) free radical and (b) cationic; however, the vast majority of UV-curable inks are used in the industry today are based on free radical chemistry. One of the basic differences between free radical and cationic systems is based on the solidification process when exposed to UV light. Both free radical and cationic UV-curable inks are available in two forms – (a) solvent diluted and (b) 100% solids form. For example, HP Scitex UV-curable inks are based on free radical chemistry and are formulated with 100% solids which mean they do not contain solvents. It is important to note that the term ‘100% Solids’ should not be confused with a hot-melt ink, also called a ‘solid ink’ where the solid inks are a waxy solid at normal temperatures. During printing, they are heated and melted for jetting, and then solidify by freezing on the substrate.

UV Curable inks Free radical Solventdiluted Water

100% solids

Organic

Figure 7. Classification of UV inkjet inks.

Cationic Solventdiluted Water

100% solids

Organic


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Wide Format Inkjet Printing Recently there is an upsurge in wide format inkjet printing technology and it is making more and more in-roads into print shops. This is mainly because there are significant improvements in wide format inkjet technology in last few years which make the market more stable and affordable. Thermal, piezoelectric and MEMS based wide format inkjet printers are now available in the market.

Functional Inkjet Inks and Certain Selective Issues The main objective of a functional inkjet ink is to retain its functional behaviour in the pot life or ink life of the formulated inkjet and also the printed substrates should show this functional behaviour for a long time. The technical performances of both the inks and inkjet printed images are very important. Now this chapter will concentrate on different aspects of photochromic dye based inkjet inks and analyse different functional behaviour of the inks and also the inkjet printed textiles when exposed to UV light at different environmental conditions after a brief discussion on coloured inkjet printed textiles.

COLOURED INKJET PRINTED TEXTILES Colorants (such as, a dye or a pigment or a mixture different dyes or a mixture of different pigments) are one of the main components for an ink formulation for the inkjet printing of textiles. They can be divided into two groups - conventional colorants (such as, acid dyes, basic dyes, direct dyes, vat dyes, reactive dyes, disperse dyes, pigments, etc.) and functional colorants (such as, photochromic, thermochromic, ionochromic dyes, etc.). Functional dyes are used for a variety of conventional and high-technology applications, including, optical data storage, light harvesting, analytical detections, security printing and anti-counterfeit applications [47]. Currently, these functional dyes are also used for the coloration of textile and leather substrates using a variety of ways, including, inkjet printing, conventional and digital dyeing (using inkjet print head) techniques to impart different functionalities on the printed or dyed substrates for different specific applications [48-54]. Many functional dyes are stimuli responsive. The development of technology and devices using of stimuli responsive surfaces to detect changes in the ambient environment by applying sensoric materials is an active field of research with immense commercial potentials [55]. There are some functional dyes which change their colour from a colourless or faintly coloured state to another colour under the influence of different external stimuli. Photochromic, thermochromic, ionochromic and electrochromic dyes are responsive to UV irradiation or sunlight, thermal condition, pH and electrical field, respectively, and change their colour from one state to another under appropriate influence of a certain stimulus or a combination of different stimuli. [56] For example, some particular spirooxazine and spiropyran based photochromic dyes give a colour change both under UV irradiation and also by the application of appropriate thermal condition. Selective textile and leather substrates

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which are dyed, printed or coated with specific functional dyes can be used as stimuli responsive flexible matrices to produce controlled and measurable colour change with a variety of potential applications, including, fashionable functional protective materials for clothing or footwear. There are potentials for the integration of these functional materials with digital warning systems by appropriate incorporation of the colour change mechanism on their surfaces when exposed to different stimuli, such as, UV irradiation, temperature, humidity and chemical exposure [57-60]. This current chapter will focus on the various aspects of selected functional dyes, such as, photochromic dyes when they were applied for the coloration of different type of textiles using inkjet printing technology. There are huge challenges to produce technically standard textile based printed stimuli responsive surfaces using inkjet printing technology, this chapter will also selectively highlight on some of these issues along with other selected aspects of conventional and high-tech applications of these inkjet printed textiles.

Photo-Responsive Inkjet Printed Textiles Photo-responsive inkjet printed substrates is usually produced by the formulation of inkjet inks using a suitable photo-responsive material (such as a photochromic dye) as a colorant where it can retains its colour change behaviour in the ink for a desired time. However, the development of high performance photo-responsive stable inkjet ink through the incorporation of appropriate photochromic dye in inkjet inks, and their subsequent applications on to suitable textile or related substrates to produce photochromic colour change under UV light or sunlight exposure is very challenging for a number of reasons. These include – (a) acceptable criteria for the inkjet ink to meet the requirements of the print head, (b) good jettability, (c) storage stability of the ink, (d) appropriate reversible colour changing capability of the printed image under UV light or sun light exposure and (e) good technical performances (such as, wash fastness and light fastness properties). So, in order to understand the photochromic nature of different types of photochromic dyes which have the potential for inkjet ink formulation for textile applications the following sections briefly discuss the nature of different types of photochromic systems.

Photochromic Dyes and Principles of Photo-Responsive Colour Changes Photochromism is a reversible colour change phenomenon usually observed in photochromic systems (such as, photochromic dyes and photochromic dye doped polymers). For example, when a photochromic molecule A is exposed to UV light or sun light transformed into B showing a different absorption spectra (Scheme 1). In some particular photochromic system, this colour change is an obvious effect detectable without any scientific tools and causes to generate difference in optical, physical and chemical properties [61-64].

Scheme 1. A reversible photo-induced transformation between two forms of a photochromic dye.


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When a photochromic molecule undergoes a photochromic reaction when exposed to UV light or sun light it also causes a significant change in the geometrical structure, oxidation/reduction potential, refractive index and dielectric constant of two states of a photochromic molecule. All these changes are the direct results of chemical transformations observed in majority of the reversible photochromic systems with unimolecular reactions. There are two main types of photochromic systems classified according to the nature of thermal stability of the photochemically generated isomer(s). For example, T-type photochromic compounds which comprise most photochromic dyes, show thermal reversion whereas P-type photochromic compounds only show a reversion when irradiated with visible light. Spirooxazines, one of the most commonly studied classes of T-type photochromic dyes, show very high level of photochromic colour build up and technical performances so this current chapter will concentrate on the different aspects of this dye class and its applications in the formulation of inkjet inks along with other selective photochromic dye classes (for example, naphthopyrans) for inkjet printing on textiles for different purposes. Besides spirooxazines, azobenzenes (Scheme 2) and spiropyrans (Scheme 3) are the two mostly studied compounds. Azobenzenes undergo a reversible photochemical cis-trans photoisomerization during UV irradiation, however, the cis form of an azobenzene is more unstable which goes back to the trans form by a thermal isomerization (or reversion). On the other hand, when exposed to UV light on a spiropyran, it opens up the electrocyclic ring of the pyran that generates a charge at the indoline nitrogen followed by a subsequent rearomatization of the phenyl ring with an extensive change in the polarity of the zwitterionic form [61-64].

Scheme 2. The reaction mechanism of a photochromic azobenzene (substituted).

Scheme 3. The reaction mechanism of a photochromic spiropyran (substituted).

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Scheme 4. The reaction mechanism of a photochromic naphthopyran (substituted).

Photochromic napthopyrans are well-known for their commercial applications in lightsensitive ophthalmic lenses due to their ability to undergo a reversible colour change when irradiated with ultraviolet (UV) light [61-64]. Naphthopyrans (also known as chromenes) show thermal decolourization when UV irradiation is ceased and are usually used to develop a broad range of intense colours depending on their electronic substitution and also demonstrate a significant fatigue resistance when exposed to light. In a napthopyran the photochromic reaction proceeds through a heterolytic cleavage when the C-O bond in the pyran moiety is ruptured due to UV irradiation and produces isomeric open forms (merocyanines) which are coloured due to their extended conjugation and quasi-planar structures. During the conversion from a closed form to an open form the molecule undergoes a large intramolecular rotation to form coplanar structure in its coloured (open or merocyanine) form or orthogonal structure in its colourless (closed) form (Scheme 4). Naphthopyrans have the potentials for textile applications. [60] Selectively several naphthopyran dyes have been used for inkjet ink formulations.

Scheme 5. The reaction mechanism of a photochromic fulgide.


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Scheme 6. The reaction mechanism of a photochromic diarylethene.

Photochromic furylfulgides (Scheme 5) and diarylethenes (Scheme 6) are P-type photochromic molecular switches. In the cases of fulgides and diarylethenes the geometric shape of molecule A as shown in Scheme 1 is open and B is closed. The thermally stable Ptype switches have potential for practical textile applications including, responsive surface, brand protection, security, authentication, camouflage and in fashion and design. During UV irradiations both of these classes of compounds show a electrocyclic photochromic reaction. In this case, ring-closed isomer shows some types of stability where the reversible ringopening process proceeds with an irradiation using a visible light. Diarylethenes are the most promising candidates for future applications due to the possibility of incorporating a huge variety of substituents during the synthesis of these compounds [61-65]. Photoisomerization reactions of photochromic fulgides, fulgimides, diarylethenes based on the molecular structures of these compounds may be divided into two major categories, such as electrocyclic ring closed (coloured) and opened (colourless) structures. Fulgides, fulgimides and diarylethenes show photochromic reaction due to photo-induced reversible electrocyclization. The closed forms of fulgides, fulgimides and diarylethenes show an absorption band in the visible spectral range so they are coloured in their closed forms (which in contrast to spirooxazines and spiropyrans where closed forms are colourless), however, in the open forms exhibit their first absorption band at significantly shorter wavelengths resulting colourless forms. When these compounds are excited in the respective first absorption bands, the molecules undergo reversible photoisomerization between their two forms. However, spiropyrans and spirooxazines show a photo-induced heterolytic bond cleavage on excitation with UV light leading to the amphoteric ionic structures of merocyanines with an onset of absorbance in the visible region. The usual reaction time in certain types of fulgides, fulgimides and diarylethenes is very fast which has a real impact on the overall performance of these molecules when used as molecular switches. These molecules are often judged in terms of their efficiency and photostability when exposed to light (such as, UV light for forward reaction and visible light for reverse reaction) either embedded in a solid matrix or dissolved in a solution. However, different studies also revealed that photo-excited organic molecules very easily undergo unwanted side reactions and also susceptive to quenching processes with other molecules along with radiative or nonradiative transitions. From a usual analysis, it is also observed that the photoisomerization reactions of these photochromic compounds (such as fulgides and diarylethenes) take place within a femtosecond time scale. In addition, on this fundamental femtosecond time scale, the

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movement of atoms in a molecule takes place and side reactions are minimized, since a few molecular degrees of freedom are involved in the photoreaction [66].

EVALUATION OF PHOTO-RESPONSIVE BEHAVIOURS OF INKJET PRINTED TEXTILES Photochromic colour build up and fading as well as the technical performances of a inkjet printed photo-responsive textile substrate can be evaluated using a variety of ways, where colour measurement is one of the most important techniques. Colour can be measured from a solution by measuring the transmission properties of the liquid or in opaque material using reflectance measurements. However, the colour of photochromic dyed, printed or coated substrates may be assessed using reflectance measurements. These colorimetric attributes of material can be used to calculate the difference in colour between samples before and after UV irradiation [47-53]. In different studies, the Kubelka-Munk function shown in equation (A) is has been used to determine the colour strength of dyed photochromic substrates [4753]. K/S = (1-R)2/2R

(A)

where, K is the co-efficient of absorption, S denotes the co-efficient of scattering, and R is reflectance of an opaque object at a specific wavelength. In the case of inkjet printed photoresponsive textiles it is assumed that scattering is solely due to that from the substrate and variations in the amount of dye in the substrate, up to an upper limit, have a linear relationship with the K/S. However, in some cases it may be necessary to sum up the individual K/S values over the visible spectrum to determine the effect of variation in conditions on colour strength of the dyed substrate. During this study, the K/S function and colour difference (∆E) have also been used to analyse the technical performance of inkjet printed photo-responsive (also termed as photochromic) substrates (for detail procedure, please see the references from 6-8).

BEHAVIOURS OF INKJET PRINTED PHOTO-RESPONSIVE TEXTILES Photo-responsive printed textiles were produced by using inkjet printing technique (with a piezoelectric drop on demand print head, e.g., Xaar Omnidot 760 print head) where photochromic dyes were used as colorants during inkjet ink formulations. These photochromic dyes were then printed on different textile substrates using the inkjet print head and the printed substrates were dried in the open air. The printed textiles showed photochromic colour change when exposed to UV light or sunlight which is described as the photo-responsive behaviour of the inkjet printed textiles in this chapter. This photoresponsive behaviour of the inkjet printed textiles is only due to the presence of photochromic dyes (which may also be called as photoswitches) in the inks. Photochromic dyes show photoswitching which is the isomerisation of a photochromic compound resulting from irradiation with UV light. While many photochromic molecules undergo electronic transitions


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under UV/visible irradiation, only a few reversibly isomerise as a result of a transition. It is highly desired that to fulfil the ideal molecular switching or photoswitching requirements, the photoisomerisation process should have high quantum yield and proceed to completion quickly without side reactions. In addition, the isomer formed should be stable to ambient light conditions and to the initial isomerisation wavelength, but be readily isomerised back to the initial state by isomerisation at a different wavelength. During the formulation of suitable inkjet inks using photochromic dyes, several relatively effective photoswitches that fulfil most of these criteria have been carefully studied and selectively some of them were used for the ink formulations which are briefly discussed here.

Colour Build Up and Fading Behaviour of Spirooxazine Based Inks on Cotton Photochromic colour change in the solution state, such as, in the inkjet ink is very quick which even active in visible light although in solid state (in the form of inkjet printed substrate) it requires UV light to initiate this photochromic colour change reaction. It was observed that during inkjet ink formulation just after the addition of photochromic colorants into the ink compositions (such as, a humectant, a solvent and other additives) the ink were colourless for about 1 to 15 seconds and then they started to become coloured absorbing the photons of visible light [3]. This nature of the rate of colour change depends on the nature of photochromic molecules and the surrounding environments. For examples, naphthopyran (Scheme 4) based inkjet inks retain the yellow colour build up state in visible light within 5 to 7 seconds from a colourless state while spirooxazine (Scheme 7) based inkjet inks almost instantly (within 1 to 3 seconds) convert into blue photochromic inkjet inks just after the addition of the dye molecules into the ink formulations [3].

K/S

0.46

Before UV irradiation After UV irradiation for 1' After UV irradiation for 2' After UV irradiation for 3' After UV irradiation for 4'

0.23

0 400

450

500

550 600 Wavelength (nm)

650

700

Figure 8. Photochromic (photo-responsive) colour build up on photochromic spirooxazine based inkjet ink printed cotton after UV irradiation for specific times (in min).

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0.48

Before UV After UV irradiation for 3' Fading after 1'

0.32

K/S

Fading after 2'

0.16

0 400 430 460 490 520 550 580 610 640 670 700 Wavelength (nm) Figure 9. Gradual fading behaviour of inkjet ink printed cotton from the colour build up state (reached after continuous UV irradiation for 3 min) after removal from the source of UV irradiation.

where, R = H (Spirooxazine 1) or -SO3 Na (Spirooxazine 2)

Scheme 7. Reaction mechanism of spirooxazines 1 and 2 when exposed to UV light and visible light.

0.7

Before UV irradiation After UV irradiation for 1 min After UV irradiation for 2 min After UV irradiation for 3 min After UV irradiation for 4 min

0.56 K/S

0.42 0.28 0.14 0 400

430

460

490

520 550 580 610 Wavelength (nm)

640

670

700

Figure 10. Photochromic (photo-responsive) colour build up on photochromic diarylethenes1 based inkjet ink printed cotton after UV irradiation for specific times (in min).


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0.68

K/S

0.51 0.34 0.17 0 400

450

500 550 Wavelength (nm)

600

650

700

Before UV irradiation Colour builp up after continuous UV irradiation for 4 min Fading (from colour build up state reached after continuos UV irradiation for 4 min) after 70 min of removal from the source of UV irradiation

Figure 11. Fading behaviour of inkjet ink printed cotton from the colour build up state (reached after continuous UV irradiation for 4 min) and then after 70 min of removal from the source of UV irradiation.

Figure 8 shows the photochromic colour build behaviour of inkjet printed cotton where a spirooxazine 2 (see the structure and reaction mechanism in Scheme 7) based inkjet ink was used during inkjet printing. It reaches to its highest level of colour up under continuous UV irradiation for 3 min and further continuous irradiation causes a decrease in the colour build up due to generation of heat which initiates the thermal back reaction thus resulting in lower colour build up. Figure 9 demonstrates the fading behaviour from the colour build up state of inkjet printed cotton after removal from UV light and it nearly regains its original colour just within 5 min. So, it is clear from this study that spirooxazine based inkjet printed substrates, such as, inkjet printedcotton shows photochromic colour build up when exposed to UV light show a very intense photo-response in terms of a highly intense blue colour build up from an almost colourless inkjet printed background and quickly regain (within couple of min depending on the structure of photochromic spirooxazine used) the original colourless state when the printed substrates are removed from the source of UV light. However, this photochromic colour build up and fading (from the colour build up state when the substrate removed from the source of UV light) behaviours are different when diarylethenes based photochromic dyes are used for the formulation of inkjet inks for inkjet printing on textiles. For example, Figure 10 indicates the photochromic (photo-responsive) colour build up (after continuous UV irradiation for different times, such as, 1 minute to 4 min) on inkjet printed cotton substrate using a photochromic diarylethene 1 based inkjet ink. It clearly establishes that photochromic colour build up is a function of time of UV irradiation where the printed cotton reaches to its maximum level of photochromic colour build up in terms of colour intensity. However, in this case fading from the colour build up state takes a long time to reach to the original colourless state (the colourless or weakly coloured state of the printed substrate before UV irradiation) because of very slow relaxation process. Figure 11 indicates the fading behaviour of inkjet ink printed cotton from the colour build up state (reached after continuous UV irradiation for 4 min) and then after 70 min of removal from the source of UV irradiation where the printed cotton substrate still retains nearly half of its colour build up

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(reddish colour) while it usually takes couple of h to completely regain the original background colourless state (which was before UV irradiation). Again, the rate of colour build up and fading depends on the nature of diarylethene molecules used in the inkjet ink formulations and also on the natures of printed substrates (such as, cotton, wool, silk, nylon, polyester, lycra, polyester-viscose blend, polylactic acid based fabrics) along with many other controlling factors, such as, nature of UV light, humidity, temperature of the surrounding environment, etc. For instance, Figure 12 indicates, the matrix effect on photochromic colour build up on different textile substrates inkjet printed with diarylethene 1 based inkjet ink before and after exposure to UV irradiation. It is important to note that the thermal decolouration is a unimolecular process, which in solution follows a simple mono-exponential decay which can be stated using first-order kinetics as shown in Equation (1): A=A0 e-kt and ln[A] = -kt + ln[A]0 ……..

Equation 1

(where, A = concentration of the coloured species decaying with rate constant k with time t). However, when two different isomeric populations of open forms of a photochromic dye (such as, a spirooxazine) are considered as decaying with two concurrent first-order processes, the decay data normally needs to be fitted to the biexponential Equation (2). …

Equation 2

The interpretation of photochromic kinetics in polymer media (where a very close relation can be established with the inkjet printed photochromic textiles), is not straight forward. This is because the collective influences of the surrounding matrix environment introduce many complexities which need careful consideration. Some of these important aspects are - chain segmental mobility, the available free volume of the matrix, polarity, crystallinity, volume changes that accompany the structural changes involved in photochromic process, how the photochromic molecules are distributed in the matrix, as well as the behaviour of the different isomers. In addition, during the analysis of the photochromic decolouration kinetics in non-uniform inkjet printed polymer matrices (such as, inkjet printed cotton, wool, silk, nylon, polyester and their blend fabrics) a distinct departure from simple exponential kinetics is to be expected. It is worth to mention here that Levitus et al. applied two kinetic models to explain decolouration of photochromic films in the dark [67]. In this case, when a Gaussian distribution model was used, the polymer matrix was found to affect the width of the activation energy distribution while broader distributions were found for media that were more rigid. This model provided a rather static picture of each polymer on the basis of the assumption which does not change during the decay process. Besides this, a relaxation model was also put forward to provide a mean value for the relaxation time of the matrix, taking into account the possibility of change of the environment during the decay. However, this model did not consider the micro-heterogeneity of solid samples, and was deemed less appropriate for describing the kinetic behaviour of highly rigid media, as compared to the intermediate range between a highly rigid polymer and a very labile, liquidlike environment. But these models have been applied to describe the thermal decolouration


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behaviour of the photochromic dyes with reference to the complexities of the solid matrices for a long time. On the contrary, a less absolute, yet a meaningful approach has been used by different group to fit thermal decolouration data in solid media to the bi-exponential equation (3) [68]. This allows quantitative comparisons to be made between decolouration kinetics in different polymers as a means to optimize photochromic performance and by passes the mathematical expertise that is required from the other described methods above. Equation 3 In Equation 3, A(t) is the optical density at the maximum of coloured form at time t, A1 and A2 are the contributions to the initial absorption A0, Ath is the residual colouration, accounting for residual coloured forms and it is assumed that molecules are decolourized with different rate constants. If we consider a uniform distribution of free volume, the separated constants k1 and k2 are understood as empirical mean values between the fast and the slow constants, as opposed to absolute values of decolouration for the different isomers. In addition, in some cases, the above equation permits some deductions regarding the homogeneity of the environment around the photochromic substrates to be made by analyzing the A1/A2 ratio. It is also observed that the photochromic kinetics of photochromic doped hybrid organic–inorganic matrices, have been quantified using both Gaussian and biexponential models, the latter allowing a comparison of photodynamics with those of organic polymers [68]. It was noted that different studies were carried out to analyse the thermal decoloration kinetics of spirooxazine, spiropyran and naphthopyran-doped hybrid organic-inorganic matrices using both mono and biexponential kinetics [69, 70]. Figure 12 illustrates that inkjet printed cotton shows the highest level of photo-responsive colour change from a nearly colourless state to deep red colour build up when exposed to UV light exposure for one minute which is closed followed by the photochromic colour build up in polylactic acid (PLA) fabric. However, the photochromic colour build up in nylon, wool and lycra is comparatively higher than the photochromic colour build up on silk, polyester and polyester-viscose blend fabrics. The photochromic performance of the inkjet printed substrates (such as, inkjet printed cotton, wool, silk, polyester, nylon fabrics) is strongly connected to the nature of the photochromic molecule in many levels. Some of these most important behaviours are - (a) the characteristics of the polymer and the mode of incorporation (such as nature of pre-treatment or post-treatment on the printed substrates), (b) the nature of physical or chemical attachments or dissolution into a fabric. These have very significant influence on photochromic colour build up, fading and also on life-time of the retention of the photochromic functionality of the printed substrates. Micro and nanoenvironmental properties of matrices, such as local rigidity, polarity and free volume, as well as their intermolecular interactions may also affect the efficiency and properties of the photochromicinter-conversions in the inkjet printed substrates. It is a general observation that the photochromic transitions are usually slower in a polymer matrix, as compared to solution which may be attributed to the reduced segmental motion of the macromolecular chains and the limited free volume of a polymeric matrix, as compared to solution. In addition, the matrix environment imposes steric restraints by limiting the mobility of the molecules and therefore their ability to isomerize and also the aggregation of molecules within solid media may influence kinetic and spectral properties to some extent. However, to understand the

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nature of the thermal decolouration or fading kinetics of photochromic spirooxazine based inkjet printed substrates a detail look into the impact of polymer dynamics on photochromic switching is essential.

0.48

K/S

0.36

0.24

0.12

0 400

435

470

505 540 575 610 Wavelength (nm)

645

680

0 min (cotton)

1 min (cotton)

0 min (lycra)

1 min (lycra)

0 min (nylon)

1 min (nylon)

0 min (PLA)

1 min (PLA)

0 min (polyester)

1 min (polyester)

0 min (polyester-viscose blend)

1 min (polyester- viscose blend)

0 min (silk)

1 min (silk)

0 min (wool)

1 min (wool)

Figure 12. Matrix effect on photochromic colour build up on different textile substrates inkjet printed with diarylethene 1 based inkjet ink, where ‘0 min’ indicates colour of the inkjet printed substrate (in terms of K/S value plotted against wavelength from 400 – 700 nm) before exposure to UV irradiation and ‘1 min’ indicates colour of the substrates after exposure to UV irradiation for one minute.


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Effect of the Nature of Dye Molecules on Photochromic Colour Build Up Figure 13 illustrates the result of a comparative study on the photochromic colour build up performances of different photochromic dyes when inkjet printed on different substrates and also on the matrix effect on photochromic colour build up in terms of the colour difference from colour build up state after UV irradiation to nearly background colourless state of inkjet printed substrates before UV irradiation on different textile substrates (cotton, wool, silk, polyester, nylon, PLA, polyester-viscose blend and lycra) inkjet printed with three diarylethenes 1, 2 and 3 (Scheme 8); two spirooxazines 1 and 2 (Scheme 7) and a naphthopyran (Scheme 9) based inkjet inks. It indicates that diarylethenes 3 and spirooxazine 2 based inkjet printed cotton shows the highest level of photochromic colour build up which closely followed bythe photochromic colour build up on polylactic acid (PLA) based inkjet printed substrates which were printed with these two dyes based inks. UV light transmission through cotton is more pronounced compared to other textiles which may have a positive impact to stimulate more photochromic dye molecules within the inkjet printed area of cotton allowing it to produce higher colour build up after UV irradiation. As a dye class spirooxazine and naphthopyran based photochromic inkjet printed textiles show very quick response to photochromic colour change under UV irradiation while this response is quite quick in the cases of printed textiles printed with diarylethene 3 based inks while it is a bit slower in the cases of other two diarylethenes (1 and 2) based inkjet printed substrates. So, this study clearly establishes that the nature of individual dye molecule plays a very vital role on determining the photochromic performances of inkjet printed substrates. Another important point is the porosity; texture and other component of the fabric matrix also play a very significant role because these properties are directly related to the adsorption and the penetration behaviour of the inkjet inks onto the fabric surface and also inside the fabric structure. A general observation is after UV irradiation on the printed substrates, diarylethene 1 based inkjet printed substrates showed red colour build up from a nearly colourless (with a very pale reddish tone) state, diarylethene 3 based inkjet printed substrates showed very highly intense reddish purple colour build up from an almost colourless state while diarylethene 2 based inkjet printed substrates showed yellow colour build up from a colourless state (with a pale yellow colour). However, after UV irradiation on both spirooxazines 1 and 2 based inkjet printed substrates showed intense blue colour build up from nearly colourless state (with a very pale bluish tone) while naphthopyran based inkjet printed substrates showed yellow colour build up from a natural colourless background states of different fabrics obtained after inkjet printing. Different studies on the technical performances in terms of retention of photochromic colour changing functionality of the inkjet printed substrates after exposure to simulated environmental conditions (such as, exposure to light fastness and wash fastness test) revealed that spirooxazine based inkjet printed substrates retained significant amount of original photochromic colour change capability even after several of controlled washing cycles and continuous exposure to continuous exposure to Xenotest (simulation of artificial day light using Megasol based light fastness test) for 50 h. However, the technical performances of the textile substrates inkjet printed with diarylethes or other classes of photochromic dyes (such as, napthopyrans) based inkjet inks are not so pronounced as seen in the cases of spirooxazine based inkjet printed substrates [3].

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So it is understood from different studies that photochromic materials show transformation from a colourless ground state to a coloured excited state during excitation with light of different wavelengths as an external stimulus [3]. The two forms generally differ in their physicochemical properties, for examples, the molecular geometry, electronic delocalization, colour and reactivity. A better understanding on the nature of photochromic molecules, the matrix where they would be used and also other very important influencing factors, including methods of application, pre-treatment of the matrix before applying photochromic dye and after treatment of techniques, nature of additives, surrounding environment require a high level of consideration for any product developments, especially, in inkjet printed photo-responsive textile based products. From a series of studies on different types of photochromic dyes (such as, photochromic spirooxazine based disperse dyes and water-soluble photochromic acid dyes) the author noticed that thermal degradation and acidic decomposition restricted the practical utilisation of photochromic dyes for a variety of potential applications. However, it was also observed that these barriers can be effectively removed using a careful selection of suitable additives during inkjet ink formulations using photochromic dyes, optimising the treatment techniques (such as, pre-treatment and posttreatment techniques to modify the nature of the substrate to be printed), selecting high performing photochromic dyes with particular functionalities to retain the photochromic funcationality on the inkjet printed substrates for a long period.

Scheme 8. Reaction mechanism of diarylethenes1, 2 and 3 when exposed to UV light and visible light.


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∆E

Scheme 9. Reaction mechanism of naphthopyran when exposed to UV light and visible light.

54 45 36 27 18 9 0

Diarylethene 1 Diarylethene 2 Diarylethene 3

Inkjet printed textile substrates Figure 13. Comparative study on the photochromic colour change of different photochromic dyes when inkjet printed on different substrates and also on the matrix effect on photochromic colour build upin terms of the colour difference from colour build up state after UV irradiation to nearly background colourless state of inkjet printed substrates before UV irradiation on different textile substrates (cotton, wool, silk, polyester, nylon, PLA, polyester-viscose blend and lycra) inkjet printed with three diarylethenes1, 2 and 3 (Scheme 8); two spirooxazines1 and 2 (Scheme 7) and a naphthopyran (Scheme 9) based inkjet inks.

APPLICATIONS OF PHOTO-RESPONSIVE INKJET PRINTED TEXTILES FOR CONVENTIONAL AND HIGH-TECH APPLICATIONS A good quality inkjet printed photo-responsive textile show photochromic colour change for a long time and show a substantial retention of its reversible photo-coloration behaviour even after exposed to different environmental conditions. This behaviour make it suitable for many potential applications, including in security, responsive surface, brand protection, authentication, actinometry, self-indicating UV warning system, active and adaptive camouflage, environmental warning system, electrophoretic textile based display, interior design, exterior design and also in fashion and design applications. In addition, inkjet printed photo-responsive textiles has the potential for healthcare applications as well. The possibility to bind a photochromic molecule onto a naturally occurring receptors and enzymes which in turn bind with an inkjet printed photo-responsive textile using certain techniques provides the opportunity to photo-regulate their binding and catalytic activities. In future, this type of

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photo-responsive textiles may be used for different therapy, bio-sensing and also in wound care along with their (already stated) applications [3, 47-53].

CONCLUSION AND PERSPECTIVE Inkjet printing technology has been increasingly successful for producing almost any print design on textiles within a very short time providing this technique a cutting edge over other conventional printing techniques, for example, screen printing. For high performance textiles which can ensure different functionalities (such as, sensing ambient environment and also working as printed design based fashion items) at a relatively low cost have a strong appeal to the users for a variety of reasons. Photo-responsive inkjet printed textiles have many applications, some of which include, fashion and design, self-indicating alert systems, anticounterfeit, security and brand protection. Both photochromic dispersed and photochromic acid dyes can be used to formulate inkjet inks to produce photo-responsive inks for inkjet printing on different types of textiles (for example, cotton, wool, silk, nylon) for potential conventional and high-technology applications. Formulation of functional inks using functional dyes, such as, photochromic dyes needs proper care for producing jettable inks, retaining functional behaviour for a considerable period along with other desired properties, for instance, high print quality and robust technical performances of printed textiles. In addition, the porosity of the substrate plays a significant role on the absorption or penetration behaviour of an inkjet ink or more simply regulates its spreading on a substrate thus controlling inkjet printed image quality and the technical performances of an ink to some extent. As a result, it is necessary to control a number of influencing factors to produce desired high quality printed responsive substrates with good technical performances for various applications. A technically robust photochromic inkjet printed textile substrate would be suitable for a huge variety of conventional and advanced applications. The current inkjet print head technology are focused to ensure next generation of developments in different aspects including, higher drop frequency, MEMS construction, single-pass, higher aqueous tolerance, integrated system with multiple head types, LED-UV curing system, efficient monitoring for drop-outs and fluid recirculation. Some of the main objective of this advanced technologies are trying to ensure sustainability and eco-friendly character, hybrid system with integration of analog and digital technologies, automatic maintenance system along with higher temperature and humidity controls to ensure top quality fluid disposal system. There are considerable trends in lowering the price of the print heads in terms of lower cost per nozzle, larger arrays of print heads and lower cost per print. Inkjet technology is evolving by the day, for example, it is going from binary to grayscale, from macro to MEMS micro machining, from scanning heads to single pass, from fitting application to match inkjet technology to designing inkjet technology to match application requirements, from sub-boiling temperature operation to high temperature performance and 2D graphic designs to 3D fabrications including high quality additive manufacturing for a huge range of applications. So, the effective inclusion of required functionalities (such as, in this case photochromic performances) on printed textiles using appropriate inkjet printing techniques can provide a significant breakthrough in value addition, fashion and design along with high-tech applications.


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Chapter 5

SYNTHESIS AND GRAFTING OF CELLULOSE DERIVATIVES FROM CELLULOSIC WASTES OF THE TEXTILE INDUSTRY Md. Ibrahim H. Mondal* and A. B. M. Fakrul Alam Polymer and Textiles Research Lab, Department of Applied Chemistry and Chemical Engineering, University of Rajshahi, Bangladesh

ABSTRACT Wastes from cotton based garment and textile industries contain good quality of αcellulose. These cellulosic wastes can easily be used to produce commercially valuable cellulosic derivatives, viz. carboxymethyl cellulose (CMC), cellulose acetate (CA) and cellulose nitrate (CN); and consequently reduce the pollution problem. Carboxymethyl cellulose was synthesized by reaction with sodium hydroxide in aqueous ethanol followed by reaction with mono-chloroacetic acid. The synthesized crude CMC was washed with 80% ethanol and dried over P2O5 in a desiccator. CA was synthesized by pretreatment with glacial acetic acid and then by reaction of acetic anhydride in presence of concentrate H2SO4 followed by hydrolysis. The synthesized crude CA was washed with distilled water, stabilized by Na2CO3 solution and then dried over P2O5 in a desiccator. On the other hand, CN was synthesized by reaction in the P2O5 and HNO3 medium in an ice bath. The synthesized crude CN was washed with cold water, stabilized with boiling water, rinsed with methanol and then dried in an oven at 50 oC for 1 h. Low substituted to high substituted products were obtained from single to seven reaction steps in all cases. These processes permit to produce low cost different grades of CMC, CA and CN. The products were identified and their physical characteristics were determined. Solubility, degree of substitution and molecular weight of the products were found to be increased gradually with the increase of reaction steps, and the optimum levels were obtained at the fourth step of synthesis in all cases. The structures of CMC, CA, CN and grafted CMC, CA, CN were investigated by FTIR, 13C NMR and SEM test. Grafting of prepared CMC, CA and CN films with methyl methacrylate (MMA) monomer was found to increase their strengths to 86.11%, 73.61% and 71.43%, respectively. However, decreased rigidity and moisture content due to the incorporation of hydrophobic MMA *

E-mail: [email protected].

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Md. Ibrahim H. Mondal and A. B. M. Fakrul Alam monomer were observed. The prepared CMC was also applied as a sizing agent to fabric and yarn to develop the physico-chemical characteristics.

Keywords: Cellulose derivatives, carboxymethyl cellulose, cellulose acetate, cellulose nitrate, knitted rag, textile wastes, degree of substitution, molecular weight, grafting

CARBOXYMETHYL CELLULOSE Introduction Carboxymethyl cellulose (CMC) is one of the most versatile cellulosic derivatives of the present day world, and is tremendously used in textiles and many other industrial fields including in food products, paper, cosmetics, pharmaceuticals, and adhesives [1]. Hence it is most important in the textile manufacturing and in everyday life. It is true for present day that Bangladesh is a textile industry-based country, and large amount of CMC is being imported to meet its demand for textile sector in every year; and the demand of CMC is increasing day by day. It has been reported that CMC was prepared from different cellulosic sources by different researchers following different methods [2,3,4a,5-7]. The different cellulosic sources considered by the researchers include paper sludge [2], hyacinth [3], wood residue [6], cotton linters [7,8], bagasse [9] etc. No worth mentioning work has been performed on the synthesis of CMC from knitted rag. Knitted rag contains high amount of good quality α-cellulose which is 95–98 % [10]; and huge amount of knitted rags are deposited as textile wastes in different garment industries that have virtually no use. The wastes contain both colored and noncolored rags. These are normally dumped in nearby area, and degraded naturally. Hence, these create environmental pollution. As the rag contains high amount of good quality αcellulose and as this can be easily collected with almost free of cost, it can act as a great raw material source for the manufacture of CMC and other derivatives of cellulose. The purpose of the present work is to explore the use of the knitted rags to synthesize different grades of CMC by applying carboxymethylation techniques in multiple steps in order to obtain lucrative CMC with good solubility and fair degree of substitution (DS). The unique features of this report include the recycling of ethanol, attainment of high DS, grafting ability and its application to textiles.

Experimental Materials The knitted rag as raw material was collected from Mozart Knit Ltd, Ashulia, Saver, Dhaka. The analytical grade ethyl alcohol (Merck, Germany), hydrogen peroxide (BDH, England) sodium hydroxide (Merck, India), mono-chloroacetic acid (BDH, England), sodium carbonate (BDH, England), standard CMC (BDH, England), potassium bromide (Merck, Germany), methyl methacrylate (MMA) (BDH, England) etc. were used without further purifications.

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Preparation of Sample The collected knitted rag contained both non-colored and colored rags which were hand sorted. The non-colored knitted rag was washed with 1% Na2CO3 solution at 60 oC [8]. The colored knitted rag was immersed in bleaching liquor consisting of 1.5% (w/w) hydrogen peroxide, 2.5% sodium silicate and 1% sodium hydroxide on the basis of fiber in the ragliquor ratio of 1: 50 at 40 oC for 1 h. The temperature was gradually raised to 85 oC and held for 3 h with occasional stirring [11]. Resulting non-colored knitted rag were washed with sufficient fresh water and then dried in air. The non-colored knitted rag obtained by either washing or bleaching was used as a source of cellulose in preparation of CMC, CA and CN. Carboxymethylation The CMC was synthesized by the conversion of cellulosic rag to alkali cellulose on swelling by aqueous NaOH solution followed by reaction with mono-chloroacetic acid (ClCH2COOH) in rectified spirit. The reaction conditions were as follows: (a) Basification In this step of reaction, alkali cellulose was formed. An aliquot of 1g knitted rag was immersed in 18% NaOH solution in rectified spirit at 30 oC for 3 h in the rag-liquor ratio of 1:14 with occasionally stirring In the basification (also known as steeping ) step, the following reaction was taken place: [C6H7O2(OH)3]n + nNaOH = [C6H7O2(OH)2ONa]n + nH2O (b) Etherification In the second step, an aqueous 80% (w/v) mono-chloroacetic acid solution was added drop by drop to the above mixture at 50 oC for 6 h; so that the final pulp volume in the basification step to reagent solution volume ratio became 1:4. In etherification (also known as carboxymethylation) step, the reaction of basified cellulose with sodium mono-chloroacetate was taken place as indicated below: nClCH2COOH + nNaOH = nClCH2COONa + nH2O [C6H7O2(OH)2ONa]n + nClCH2COONa = [C6H7O2(OH)2OCH2COONa]n + nNaCl Single step carboxymethylation only gave low substituted product. The highly substituted CMC could however be prepared by the technique of multi-step carboxymethylation. For this purpose, CMC obtained in the previous step was purified with aqueous 80% ethanol solution and subjected to carboxymethylation by fresh addition of NaOH and ClCH2COOH solutions. Finally the synthesized crude Na-CMC (the sodium form of carboxymethyl cellulose is commonly known as CMC) was purified by water dissolution and precipitation by rectified spirit method followed by washing with 80% ethanol solution, then filtered and dried over P2O5 in a desiccator under vacuum.

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Md. Ibrahim H. Mondal and A. B. M. Fakrul Alam

Scheme 1. Flow chart for the preparation of Na- CMC from knitted rag.

Determination of Degree of Substitution One gram of dried CMC was added to 100 ml of distilled water and 12.5 ml of 1 N NaOH. After dissolving the mixture was titrated by 1 N HCl. The degree of substitution (DS) in CMC was determined [3,12] as: DS = 0.162A / (1 – 0.058A) where, A is the milliequivalent of sodium hydroxide required per gram of sample.

Determination of Molecular Weight On dissolving Na-CMC in aqueous 0.8 M NaOH solution, the intrinsic viscosity was measured by an Ostwald viscometer at 35 oC. From the value of the intrinsic viscosity, the molecular weight was calculated with the help of ‘‘Mark-Houwink-Sakurada equation [13] as given below: [η] = KMa,


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where, [η] is the intrinsic viscosity, M is the molecular weight of Na-CMC, K is a constant, and ‘‘a’’ is the polymer shape factor.

Determination of CMC Content in Prepared Sample An aliquot of exactly 1.5 g CMC was stirred with 100 mL of aqueous 80% methanol solution for 10 min and filtered. The cake was washed by 100 mL of aqueous 80% methanol solution, dried to constant weight [5]. The CMC content was calculated using the relation below: CMC content, % = 100M2 / M1 where, M1 and M2 are the weights (g) of samples before and after washings, respectively.

Determination of NaCl in Na-CMC Two grams of Na-CMC was kept immersed in 250 mL of aqueous 65% methanol solution for 5 h. On filtration, 100 mL of liquid phase was neutralized by 0.1 N HNO3 and titrated with 0.1 N AgNO3 solution [5]. The NaCl content was calculated using the following formula: NaCl, % = 1.461V / M where, V (mL) is the amount of AgNO3 solution required in titration and M (g) is the weight of dried sample used.

Grafting Procedure Graft polymerization of CMC was carried out with 80% methyl methacrylate (MMA), 5% K2S2O8, 5% FeSO4 at 60 oC for 90 min in the CMC-liquor ratio of 1:30. Graft yield and grafting efficiency were calculated according to the following formulas [14,15]: Grafting yield, % = [(W1 – W0) / W0] × 100 Grafting efficiency, % = [(W1 - W0) / W2] × 100 where, W0, W1 and W2 are the weights of non-grafted CMC film, MMA-grafted CMC film and total monomer used, respectively.

Moisture Content The grafted and non-grafted 2% CMC films were weighed accurately and dried at 105 oC for 2 h in a forced convection oven (FC-610, Toyo Seisakusho Co. Ltd., Tokyo, Japan). These were then cooled in a desiccator over silica for about 30 min and weighed again. Moisture content was determined using the equation given below [14]: Moisture content, % = [(W0 – W1) / W0] × 100 where, W0 and W1 are weights of air and oven dried films, respectively.

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Water Absorption The grafted and non-grafted 2% CMC films (6 cm × 4 cm) were weighed out accurately and immersed in distilled water for 15 h at 30 oC. The films were then taken out and wiped using tissue paper and weighed again. Water absorption was determined using the relation [16]: Water absorption, % = [(W1 – W0) / W0] × 100 where, W0 and W1 are weights before and after immersion, respectively.

Gel Content Gel content of the grafted and non-grafted 2% CMC films was determined by dissolution of gel in hot toluene. The weighted film (6 cm × 4 cm) was subjected to extraction using a Soxhlet apparatus with 250 mL toluene for 6 h. After that, the sample was taken out for vacuum drying and weighed to a constant weight. Gel content of grafted and non-grafted CMC films was calculated accordingly [16] as: Gel content, % = (W1 / W0) × 100 where, W0 and W1 are weights before and after extraction, respectively.

Tensile Strength To determine the tensile strength of CMC and modified CMC films (2 cm × 1 cm) was used and measured by a Tensile Strength Tester (Harada Co. Ltd. Nagano-ken, Japan). The distance between jaws of the film was 1 cm. FTIR Spectroscopy The washed knitted rag and prepared CMC were dried at 50 oC and powdered by a motarpastle. The powder was mixed with KBr in the ratio of 1:125, and a pellet was prepared. IRspectra of the KBr pellet were recorded with a FTIR Spectrophotometer (Model: FTIR-8900, Shimadju, Japan) within 4000–400 cm-1. Application of CMC to Cotton Fabric as Sizing Agent The cotton fabric was washed with 1% Na2CO3 solution at 60 oC for 2 h. After drying, this was immersed in 3% CMC solution as sizing agent at 60 oC for 2 h. Then the CMC sized fabric was dried and calendered. 13

C NMR Spectroscopy The non-grafted CMC film was dissolved in D2O and MMA-grafted CMC film was dissolved in dimethyl sulfoxide (DMSO). Then the non-grafted and grafted CMC films were examined by 13C NMR spectra with proton decoupling at 25 oC by a Bruker AV400 NMR Spectrometer (Switzerland) at a frequency of 400 MHz and with 14536 scans. The spectrum range carried out was from 0 to 200 ppm.


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Scanning Electron Microscopy The surface morphology of washed and CMC-sized cotton fabrics was examined by a Scanning Electron Microscope (SEM, Hitachi, Model-S 3400N, VP SEM, Japan). The micrographs were taken at magnifications of 500 and 1000 times using accelerating voltage (kV).

Results and Discussion The synthesis of Na-CMC from knitted rag (1 g) was carried out according to the Scheme 1. The potentiality of the process was the re-use of ethanol after washing of the crude NaCMC. Effects of solvent system, alkali concentration in basification, concentration of monochloroacetic acid for etherification, time and temperature of each reaction step on the degree of substitution (DS) were optimized. Table 1. Preparation of Na-CMC by multi-step carboxymethylation method No. of Reaction step 1 2 3 4 5 6 7

Amount of NaOH, g 2.52 2.52 2.52 2.52 2.52 2.52 2.52

Amount of ClCH2COOH, g 3.2 3.2 3.2 3.2 3.2 3.2 3.2

Yield of Na-CMC, % 360 751 1052 1231 1304 1404 1494

Remark Partially soluble in water Soluble in water Highly soluble in water Highly soluble in water Highly soluble in water Highly soluble in water Highly soluble in water

The yields of Na-CMC obtained in carboxymethylation process from first to seventh step are shown in Table 1. The optimized condition for the synthesis of Na-CMC was established as ethanol to cellulose ratio of 12:1 (v/w), water to cellulose ratio of 2:1 (v/w), overall NaOH concentration of 18% (w/v), steeping time of 3 h, steeping temperature of 30 oC, monochloroacetic acid concentration of 80% (w/v), carboxymethylation time of 6 h and carboxymethylation temperature of 50 oC. It can be seen from Table 1 that yield of CMC is increased with increasing number of reaction step used in carboxymethylation. The 360% yield of Na-CMC in the 1st step is increased to 751%, 1052%, 1231%, 1304%, 1404% and 1494% in the 2nd, 3rd, 4th, 5th, 6th and 7th steps, respectively. Solubilities of produced Na-CMC samples has been tested in water. The Na-CMC obtained by the multi-step carboxymethylation showed a high water solubility. The role of solvent in carboxymethylation is to provide accessibility of the etherifying reagent to the reaction site of cellulose chain [17]. The DS of the prepared Na-CMC has been determined by the acid-base titration method [3,12]. The step wise DS data are given in Table 2. It can be seen from Table 2 that DS is increased rapidly at the initial steps and then almost levelled off at the 6th step. The DS achieved in the 1st step is 0.91 which is increased to 2.72 at the 4th step and 2.84 at the 8th step. The reason of this phenomenon is due to the fast substitution reaction for initial steps under alkaline conditions. The hydroxyl group of cellulose in rag fiber is very active, and to

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be replaced by carboxymethyl group in the initial stages; but decreased the number of OH group in later stages decreases substitution rate. Table 2. Determination of DS in CMC prepared from knitted rag at different etherification steps No. of reaction step 1 2 3 4 5 6 7

Milliequivalent of NaOH required per gram of sample, A 4.21 6.07 7.93 8.49 8.63 8.68 8.70

Degree of substitution 0.91 1.52 2.38 2.72 2.82 2.83 2.84

Figure 1 shows that the yield of CMC is increased gradually with the increase of DS. Complete carboxymethylation of cellulose (DS=3) is not possible. That is why above the 4th reaction step, the increase in DS is slowed down. It might have occurred that successive treatment with NaOH generated “activated” hydroxyl groups for substitution. The carboxymethylation depends upon the accessibility of reagent and the availability of the activated hydroxyl groups. Increase of DS by successive treatment with alkali clearly shows activation of the free secondary hydroxyl groups.

Yield of Na-CMC, gm

16

12

8

4

0 0.5

1

1.5

2

2.5

3

Degree of substitution (DS) Figure 1. Plot of yield of Na-CMC vs DS.

Table 3 represents the intrinsic viscosity and molecular weight of CMC obtained at different etherification steps. Table 3 shows that the molecular weight of the prepared NaCMC is increased gradually with the increase of reaction step. The reason is obvious that as the DS increased with successive steps, number of OH groups attached to cellulose molecule


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is replaced by carboxymethyl groups. As the molecular weight of carboxymethyl group is higher than that of the OH group, the molecular weight of final product Na-CMC is also increased with the reaction steps. Table 3 shows that increase of DS and molecular weight is string down with the number of successive steps indicating the DS of Na-CMC went on to the completeness of the substitution reaction. Table 3. The intrinsic viscosity and molecular weight of Na-CMC obtained at different etherification steps (K = 37× 10-5 dl/g and a = 0.61 at 35 oC) [13] No. of reaction step Degree of substitution

Intrinsic viscosity

Molecular weight

1 2 3 4 5 6 7

0.54 0.61 0.66 0.68 0.71 0.72 0.73

153886 187888 213796 224543 241046 246603 252231

0.91 1.64 2.46 2.72 2.80 2.82 2.84

The amount of CMC, NaCl and others contents in Na-CMC are listed in Table 4. From Table 4 it can be seen that percentages of CMC and NaCl are increased gradually with the increase of DS (or, number of reaction steps) and at the same time percentage of other materials is decreased. This result confirms the increased yield of CMC with increase of reaction step. Table 4. The contents of CMC, NaCl and others in synthesized Na-CMC samples No. of reaction step 1 2 3 4 5 6 7


Na-CMC, %

NaCl, %

Others, %

72.60 76.80 79.00 81.40 82.80 83.80 85.00

3.07 3.29 3.44 3.51 3.58 3.65 3.65

24.33 19.91 17.56 15.09 13.62 12.55 11.35

Table 5. Effect of MMA concentration on modification of CMC film (DS=2.72) No. of experiment 1 2 3 4 5

MMA concentration, % 40 60 80 90 100

Grafting yield, % 10.29 12.76 20.58 13.51 12.35

Grafting efficiency, % 25.74 19.60 19.40 15.15 12.35

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Table 5 shows that maximum graft yield is obtained at 80% MMA concentration and then decreases with further increase of MMA concentration due to homopolymer formation at the higher concentration of MMA. The moisture content, water absorption, gel content, tensile strength and elongation at break of CMC and grafted CMC are listed in Table 6. It can be seen from Table 6 that moisture content and water absorption value of CMC are 2.86% and 7.69%, respectively. These values are much higher than the value of MMA-grafted CMC. This indicates that MMA has been grafted successfully with the prepared CMC film, and due to the incorporation of MMA, the grafted film losses its moisture absorption capacity. The gel content of grafted film is 97.03% which is lower than that in the CMC film. The high gel content means the high reactivity [14-16]. It is proved that MMA has been successfully grafted to the prepared CMC film. Table 6 indicates also that the breaking load and elongation of CMC film are 0.72 MPa and 2.6 %, respectively; and those of grafted-CMC film are 1.34 MPa and 1.7%, respectively. It is seen that the tensile strength is increased but the elongation percentage at break is decreased on grafting. The tensile strength of grafted CMC film is higher due to the incorporation of MMA monomer to CMC film and this reasonably increased the rigidity of the grafted film and hence lowered elongation at break. Table 6. Comparison of physical properties of CMC (DS=2.72) and MMA-grafted CMC film (3% CMC film) Name of sample CMC film Grafted CMC film

Moisture content, % 2.86 1.08

Water absorption, % 7.69 1.78

Gel content, % 99.47 97.03

Tensile strength, MPa 0.72 1.34

Elongation at break,% 2.6 1.7

FTIR Analysis of CMC and Grafted CMC Films The FTIR spectra of standard CMC film (DS = 0.8), prepared CMC film (DS = 2.72), and MMA-grafted CMC film powder pelleted with excessive KBr are shown in Figure 2. It can be seen from Figure 2 that the peaks assigned at 1630 cm-1 and 1420 cm-1 indicate the presence of carboxymethyl substituent in both standard CMC and prepared CMC films [Figures 2b and 2c]. The carboxylate ion [18] gives rises to two bands: a strong asymmetrical stretching band near 1650–1550 cm-1 and a weaker symmetrical stretching band near 1400 cm-1. Two weak peaks near 1630 cm-1 and 1420 cm-1 in cellulose are observed which are due to absorbed water and CH2, respectively. Hence the occurrence of strong peaks in CMC films confirms the formation of CMC by the process of etherification between knitted rag and mono-chloroacetic acid in strong alkaline alcoholic medium. An extra absorption band at 1741 cm-1 is observed in grafted CMC film indicating the stretching of C = O group, which is due to the introduction of ester carbonyl group of the grafted MMA [19,20]. So the appearance of new peak in the spectrum of MMA-grafted CMC film suggests that MMA has been successfully grafted to prepared CMC film.


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Figure 2. FTIR Spectra of (a) knitted rag (cellulose), (b) standard CMC film (DS = 0.8), (c) prepared CMC film (DS = 2.72) and (d) MMA-grafted CMC film.

Application of CMC to Textiles CMC is extensively used as protective coating solution for textiles and in many other fields. The prepared CMC was applied as sizing agent to develop the physico-chemical characteristics of both fabric and yarn which was investigated by FTIR and SEM tests.

Figure 3. FTIR spectra of (a) washed cotton fabric, (b) 3% CMC modified (DS = 2.46) cotton fabric.

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FTIR Analysis of Cotton and CMC Modified Cotton Fabrics FTIR spectra of washed and CMC-modified cotton fabrics are shown in Figure 3. From Figure 3b it can be observed that an absorption band at 1638 cm-1 is assigned to the stretching vibration of C = O in CMC modified cotton fabric. The spectra suggest that CMC has been successfully deposited on the modified cotton fabric. 13

C NMR Analysis of CMC and Grafted CMC Films

Figure 4. 13C NMR spectra of (a) prepared CMC film (DS = 2.72) recorded in D2O at 25 oC (number of scans 13223) and (b) MMA-grafted CMC film (DS = 2.72) recorded in DMSO at 25 oC (number of scans 13223). 13

C NMR spectra of prepared CMC film and MMA-grafted CMC film are shown in Figure 4. The molecular structure of CMC was analysed by means of 13C NMR spectroscopy of the intact polymer. Figure 4a shows a 13C NMR spectra of CMC film with a DS value of 2.72, and the typical signals with their chemical shifts of the modified anhydroglucose unit are in the range of 60-105 ppm as well as peaks assigned for carboxymethyl groups at C8=178.9 (C=O) and C7=70.2 ppm respectively [21,22]. Here new peaks are due to the esterification of hydroxyl groups of C2, C3 and C6. From Figure 4b, it can be observed that the chemical shift of ester C=O and CH3-groups (which come from carbonyl bearing monomer MMA) are at 179.7 ppm and 21.8 ppm respectively. The appearances of these two strong sharp signals in the NMR spectra of MMA-grafted CMC film give the supporting evidence on the success of grafting.


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SEM Analysis of Cotton and CMC Modified Cotton Fabrics

Figure 6. Scanning electron micrograph of (a) washed cotton fabric (magnified 500 times), (b) washed cotton fabric (magnified 1000 times), (c) washed cotton fabric after 3% CMC treatment (magnified 500 times), (d) washed cotton fabric after 3% CMC treatment (magnified 1000 times).

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Washing with soda ash was done to remove impurities and adventitious dirt. The surface morphologies of washed and CMC modified cotton fabrics was examined by SEM and are shown in Figure 6. Figures 6a and 6b show SEM image of washed cotton fabric at two magnifications. From the Figures 6a and 6b it can be seen that the image of cotton fiber surface is loosened, ruptured, and cracked for washing with soda ash. Figures 6c and 6d show SEM images of 3% CMC-modified cotton fabric at two magnifications and it is noticed that the surface of the fiber is very smooth and no rupture is visible as the surface of yarns were sized with CMC and projecting fibers are not noticed on the surface. This indicates deposition of CMC on the fabric fiber. The deposited CMC might form probably chemical bond by abstracting a hydrogen atom from the fabric fiber backbone.

CELLULOSE ACETATE Introduction Cellulose acetate (CA) is one of the most common cellulosic derivative of the present day world. It is widely used in textiles and many other industrial fields including fibers, films, sheets, coatings and plastic moldings. It is also extensively used in wearing apparel, such as woven fabrics, knits, braids, woven fashion etc. and is often blended with other fibers to make combination yarns [23]. Hence it is a very useful ingredient in textile manufacturing and in everyday life. The importance of CA is increasing day by day. CA is prepared from different cellulosic sources by different methods [24-26]. As Bangladesh is textile industry based country, a large amount of CA is required to meet its demand for textile sectors. Textile industries of Bangladesh produce huge amount of cellulosic rags that have virtually no use. The purpose of the present part is to explore the possibility of synthesis of a high grade CA from the rags by applying multiple steps acetylation method. As the rags, especially knitted rag contains high amount of good quality -cellulose, it will be a great source for the manufacture of CA and acetyl derivatives of other polysaccharides. In the present research work, a lucrative method for producing novel CA with good solubility and fair degree of substitution at a low cost from knitted rag has been explored to satisfy its need in Bangladesh.

Experimental Materials The knitted rag was collected from Mozart Knit Limited, Ashulia, Saver, Dhaka. Glacial acetic acid (GAA; BDH, England), acetic anhydride (AA; BDH, England), hydrogen peroxide (Merck, India), sulfuric acid (Merck, India), standard cellulose acetate (Fluka, Switzerland) etc. were purchased as analytical grade and used without further purification. Preparation of Sample Preparation of sample from both non-colored and colored knitted rag for acetylation has been discussed in the CMC Part.


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Preparation of Cellulose Acetate The CA was synthesized by the conversion of dry knitted rag swollen in glacial acetic acid with acetic anhydride in presence of conc. H2SO4. The production of CA was carried out by the following three steps [4b]: (a) Pretreatment In the first step,1g knitted rag was immersed successively in distilled water and glacial acetic acid (GAA) at 30 oC for 30 min with occasional stirring. Then, it was filtered and dewatered by washing with the GAA. (b) Acetylation In the second step, a mixture of GAA and conc. H2SO4 was added to the above wet sample and was shaken vigorously for 5 min. Then acetic anhydride (Ac2O) was added to the mixture and shaken vigorously for another 5 min and then the system was continuously shaken for further 1 h at 30 oC.

(c) Hydrolysis In the third step, a mixture of distilled water and GAA at the ratio of 1:2 was added to the system obtained on acetylation with high speed stirring for 5 min at 30 oC. Then the temperature was raised to 55 oC and continued the reaction for 30 min with occasional stirring. The product was precipitated in distilled water and held overnight. Then the CA was carefully filtered with a Buckner funnel.

Single step acetylation gave only low substituted product. Highly substituted CA can be prepared by performing multi-step acetylation. In each step, acetylation was done with fresh addition of GAA and Ac2O. The synthesized crude CA was washed with distilled water, stabilized with Na2CO3 and then dried over P2O5 in a desiccator.

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Scheme 2. Flow chart for the preparation of CA from knitted rag.

Determination of Acetyl Content, Acetic Acid Content and Degree of Substitution Acetyl content, acetic acid content and degree of substitution (DS) of the products were determined by the alkali saponification method. In aliquot of 1 g dried sample was put into a flask containing 40 mL of 75% ethanol, heated at 50 oC for 30 min followed by addition of 40 mL of 0.5 N NaOH solution and saponified at 30 oC for 24 h. The excess alkali was back titrated with 0.5 N HCl. The acetyl content, acetic acid content and DS of CA were calculated by the following equations [4b]: Acetyl content, % = [(A - B) Nb – (C - D) Na] × 4.3 / W Acetic acid content, % = % Acetyl × 1.395 and DS = 3.86 × % acetyl / (102.4 - % acetyl)


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where, A, B, C, D Na and Nb are mL of NaOH added to sample, mL of NaOH added to blank, mL of HCl added to sample, mL of HCl added to blank, normality of HCl solution and normality of NaOH solution, respectively; and W is weight of sample (g). Factor 4.3 is % acetyl, equivalent to CH3CO group.

Determination of Molecular Weight Cellulose acetate was dissolved in dimethyl sulfoxide (DMSO) and the molecular weight was determined by the viscosity measurement method. The procedure was as in CMC part. Grafting Procedure The procedure for graft polymerization of CA was as in CMC part. Moisture Content, Water Absorption and Gel Content The procedure for determination of moisture content, water absorption and gel content were as in CMC Part. Tensile Strength The procedure for tensile strength is similar to CMC part. FTIR Spectroscopy The procedure is similar to CMC Part. 13

C NMR Spectroscopy The non-grafted CA film was dissolved in acetone and MMA-grafted CA film was dissolved in dimethyl sulfoxide (DMSO). Then 13C NMR spectra of non-grafted and grafted films were determined as in CMC part. Scanning Electron Microscopy The procedure is similar to CMC Part.

Results and Discussion The synthesis of CA from knitted rag (1 g) was carried out according to the Scheme 2. The potentiality of the process is the recovery of GAA by distillation method and its reuse. The parameters investigated were the effect of solvent system, GAA concentration for pretreatment, concentration of Ac2O in presence of conc. H2SO4 for acetylation, and GAA concentration for hydrolysis, time and temperature of the reaction for the acetyl content and degree of substitution. The acetylation reaction was optimized with respect to the DS by varying each parameter.

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Md. Ibrahim H. Mondal and A. B. M. Fakrul Alam Table 7. Preparation of CA by multi-step acetylation

No. of reaction steps 1 2 3 4

Volume of GAA, ml 20 20 20 20

Volume of Ac2O, ml 6 6 6 6

Yield of CA, % 158.6 172.1 176.0 180.3

5

20

6

182.0

6

20

6

182.8

7

20

6

183.2

Solubility Insoluble in CHCl3 but soluble in acetone Soluble in both CHCl3 and acetone Soluble in CHCl3 but insoluble in acetone Highly soluble in CHCl3 but insoluble in acetone Highly soluble in CHCl3 but insoluble in acetone Highly soluble in CHCl3 but insoluble in acetone Highly soluble in CHCl3 but insoluble in acetone

The yield of CA obtained from acetylation process for one to seven steps is shown in Table 7. The optimized condition for the synthesis of CA was established as GAA to cellulose ratio of 20:1 (v/w), acetic anhydride to cellulose ratio of 6:1 (v/w), pretreatment time of 30 min, pretreatment temperature of 30 oC, acetylation time of 1 h, acetylation temperature of 30 oC, hydrolysis time of 30 min, hydrolysis temperature of 55 oC and H2SO4 to cellulose ratio of 0.1:1 (v/w). It can be seen from Table 7 that yield of CA is increased with the increase of the number of reaction step in the optimized condition of acetylation. The yield of product of CA in first step of acetylation after hydrolysis is 158.6%, but for the second to seventh successive steps, yields are between 172.1% and 183.2% respectively. Solubilities of the produced CA samples was tested in CHCl3 and acetone. The CA obtained from multiple steps acetylation shows a high solubility in CHCl3 than the product of single step. The role of the solvent in the acetylation reaction is to provide accessibility of esterifying reagent to the reaction centre of the cellulose chain [16]. Table 8. Determination of DS in CA prepared from knitted rag at different acetylation steps No. of reaction step 1 2 3 4 5 6 7

Yield of CA, % 158.6 172.1 176.0 180.3 182.0 182.8 183.2

Acetyl content, % 39.95 41.87 43.14 43.96 44.14 44.24 44.25

Acetic acid content, % 55.73 58.41 60.18 61.32 61.57 61.71 61.73


The DS of the prepared CA was determined by the acetyl method [4b]. The acetyl content, acetic acid content and DS data of all steps are listed in Table 8. It can be seen from Table 8 that DS is increased considerably at the initial steps, but after the 4th step the


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increasing rate is slowed down. Hence fourth step is considered as optimum. The reason of this phenomenon is due to the fast substitution reaction for initial steps under acetic conditions. The hydroxyl groups of cellulose in knitted rag are very active and can be replaced by acetyl group, which decreases the number of OH groups rapidly. Table 8 also shows that the yields of CA and acetyl content in CA is increased gradually from the initial steps to the successive steps with the increase of DS. Acetyl content and acetic acid content are directly related to DS, and hence this increasing rate is very harmonic to each other. Complete acetylation of cellulose is practically not possible. That is why above the 4th reaction step, the increase in DS as well as yield of CA is slowed down. The acetylation depends upon the accessibility of reagent into cellulose and the availability of the activated hydroxyl groups on the cellulose surface. DS increased more than one by successive treatment with GAA clearly shows activation of the free secondary hydroxyl groups. Table 9 shows that the molecular weight of the prepared CA is increased gradually with the increase of reaction steps. The reason is that as the DS increased with successive steps, number of OH groups attached to cellulose molecule was replaced by acetyl groups. As the molecular weight of acetyl group is higher than that of the OH group, the molecular weight of final CA product is also increased with the reaction steps. Table 9 shows that increase of DS and molecular weight is string down with the number of successive steps indicating the DS of CA went on to the completeness of the substitution reaction. Table 9. Determination of molecular weight of CA products at different acetylation steps using DMSO as (K= 171× 10-5 dl/g and a = 0.61 at 25 oC) [13] No. of reaction step 1 2 3 4 5 6 7


Intrinsic viscosity 1.6 1.8 1.95 2.05 2.1 2.15 2.16

Molecular weight 74,249 90,063 102,691 111,465 115,956 120,517 121,437

From Table 10 it can be seen that high graft yield is obtained at 80% MMA concentration, whereas high grafting efficiency is found at 40% MMA concentration. The graft yield is decreased at the high MMA concentration due to the formation of homopolymer. With the increase of monomer concentration, grafting efficiency is decreased. Table 10. Effect of MMA concentration on modification of cellulose acetate film (DS=2.90) No. of experiment 1 2 3 4 5


Grafting yield, % 10.29 12.76 18.50 13.51 12.35


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The moisture content, water absorption, gel content, tensile strength and elongation at break of CA and grafted CA are listed in Table 11. It can be seen from the Table 11 that the moisture content and water absorption value of CA film are lower than those of grafted CA film. These values for CA film are 1.71% and 1.22%, and those for grafted CA film are 0.98% and 0.87%, respectively. It proves that MMA has been successfully grafted with prepared CA film, and due to the incorporation of MMA in grafted CA film a somewhat hydrophobic nature is developed. The percentage of gel content of grafted film is less than CA film. The high gel content means high reactivity. It is also proved that MMA has been fruitfully grafted to the prepared CA film. Breaking load and elongation at break of CA film are 1.00 MPa and 3% (Table 11), and those of grafted CA film are 1.73 MPa and 2%, respectively. This result shows that the tensile strength of grafted CA film is higher than CA film and the elongation of grafted CA film is lower than CA film. The higher tensile strength of grafted CA film is due to the incorporation of MMA to CA film. This reasonably increased the rigidity of the grafted film, and hence lowered elongation at break. Table 11. Comparison of physical properties of CA film (DS=2.90) and grafted CA film (2% CA film) Name sample CA film Grafted CA film


Water absorption, % 1.22 0.87

Gel content, % 99.18 96.77

Tensile strength, MPa 1.00 1.73

Elongation at break,% 3 2

Figure 6. FTIR spectra of (a) cellulose, (b) standard CA film (DS=2.47), (c) prepared CA film (DS= 2.90) and (d) MMA-grafted CA film.


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FTIR Analysis of CA and Grafted CA Films The FTIR spectra of knitted rag (cellulose), standard CA film (DS=2.47), prepared CA film (DS=2.90) and prepared MMA-grafted CA film are shown in Figure 6. From Figure 6, it can be observed that the characteristic broad absorption bands of –OH and C-O groups are at around 3430-3470 cm-1 and 1051-1057 cm-1 respectively [19,27,28]. However, the graft copolymer prepared with carbonyl-bearing monomer MMA shows an ester C=O group stretching band near 1751 cm-1, in addition to the original bands associated with cellulose [29] such as OH and bound water [14]. Here the appearances of strong sharp peak in the spectrum of prepared MMA-grafted CA film supports the evidence for the grafting, and suggests that MMA has been successfully grafted to prepared CA film. 13

C NMR Analysis of CA and Grafted CA Films

Figure 7. 13C NMR spectrum of (a) prepared CA film (DS=2.90) recorded in CHCl3 at 25 oC (number of scans 13417) and (b) MMA-grafted CA film (DS=2.90) recorded in DMSO at 25 oC (number of scans 13417). 13

C NMR spectrum of prepared CA film and MMA-grafted CA film are shown in Figure 7. From Figure 7(a) it can be seen that the two new peaks at C7 and C8 are appeared in addition to the typical peaks of anhydroglucose unit. This spectrum proves the molecular structure of CA. The chemical shift of C8 (acetyl methyl) and C7 (carbonyl) are in the range of 20.1 – 20.8 ppm and 169.3 - 170.4 ppm respectively [30-32]. It can be observed from Figure 7(b) that the chemical shift of ester C=O group (which come from carbonyl bearing monomer MMA) is at 170.5 ppm. Here the appearance of strong sharp signal in the NMR spectra of prepared MMA-grafted CA film give the supporting evidence for the successful grafting.

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SEM Analysis of Cotton and CA Modified Cotton Fabrics

Figure 8. Scanning electron micrograph of (a) washed cotton fabric (magnified 500 times), (b) washed cotton fabric (magnified 1000 times), (c) washed cotton fabric after 3% CA treatment (magnified 500 times and scale 100 µm), (d) washed cotton fabric after 3% CMC treatment (Magnified 1000 times and scale 50 µm).

Figures 8a and 8b show SEM images of washed cotton fabric and its magnified image, respectively. It can be seen from the Figures 8a and 8b that the image of cotton fiber surface is loosened, ruptured and cracked, which are due to washing with Na2CO3 solution. Figure 8c


145

and 8d show SEM images of 3% CA treated cotton fabric. It can be seen from the Figures 8c and 8d that the surface of the single fiber is very smooth, and no rupture is visible in the images, because surface of the yarns are sized with CA and projecting fibers are not the visible on surface. This indicates the CA deposition to the fabric fiber surface occurred, and this is a good agreement with the FTIR results.

CELLULOSE NITRATE Introduction Cellulose nitrate (CN) is also one of the important cellulosic derivative used in textiles and many other industrial fields including films, sheets, safety glass, thermoplastic materials, composite materials, and coating agents in metal industry. It is also extensively used in cellulose nitrate membrane, art conservation, pottery reconstructions, diagnostic test, immobilization of proteins, adhesive for stone and ceramics [33-37]. Hence it is vastly important in everyday life, and the demand is increasing day by day. Like CMC and CA, the purpose of the present part is to explore the possibility of synthesis of high grade CN from the knitted rags by applying multi-steps nitration method.

Experimental Materials The knitted rag was collected from Mozart Knit Limited, Ashulia, Saver, Dhaka. Phosphorus pentaoxide (BDH, England), nitric acid (BDH, England), methanol (Merck, India), ethanol (Merck, India), sulfuric acid (Merck, India), sodium thiosulfate pentahydrate (BDH, England), salicylic acid (Merck, India) etc. were used without further purification. Preparation of Sample Preparation of sample from both non-colored and colored knitted rag for nitration has been discussed in CMC Part. Preparation of Cellulose Nitrate 1. Preparation of the reagent 200 g of P2O5 was slowly added to 100 g of cold 70% nitric acid in an ice bath. After the reaction, the composition of the mixture was 64% of nitric acid, 26% of phosphoric acid and 10% of phosphorus pentaoxide.

146


2. Nitration In this step, 1 g dry knitted rag was added to 50 ml of the above prepared reagent at 0 oC for 2 h with occasional stirring. After nitration the CN was carefully filtered on a fritted glass crucible. The reaction for the synthesis of CN was taken place mentioned below:

Single step nitration only gave low substituted product. Highly substituted CN could be prepared by multi-step nitration. In each step, nitration was done with fresh addition of the reagent. 3. Washing and stabilization The synthesized crude CN was washed with cold distilled water, stabilized with boiling water, rinsed with methanol and then dried in an oven at 50 oC.

Scheme 3. Flow chart for the preparation of CN from knitted rag.


147

Determination of Yield, Nitrogen Content and Degree of Substitution Yield of CN at the different steps was calculated by the following equation: Yield, % = (wt. of product / wt. of cellulose) × 54.6 Nitrogen content and degree of substitution of the products were determined by the Kjeldahl method. 25 mg dried CN was weighed out and put into a Kjeldahl flask containing 2 mL of conc. H2SO4 and 0.1 g of salicylic acid. After overnight immersion 0.3 g of sodium thiosulfate pentahydrate, 0.6g of K2SO4 were added. The mixture was warmed gently for 10 min and finally refluxed for about 6 h. The solution was diluted with 15 mL of water and made alkaline by the addition of 20 ml of 35% NaOH, then distilled with 25 mL of 0.8% boric acid solution containing indicator. After 10 min, the boric acid solution was titrated with 0.03 N HCl. The nitrogen content and DS of CN are determined by the following equation [4c]: Nitrogen, % = (meq. of acid × 1400) / mg of sample and DS = (1.62 × % N) / (14 - 0.45 × % N)

Determination of Molecular Weight Cellulose nitrate was dissolved in dimethyl sulfoxide (DMSO) and the molecular weight was determined as in CMC part. Grafting Procedure The procedure for graft polymerization of CN was as in CMC part. Moisture Content, Water Absorption and Gel Content The procedure for determination of moisture content, water absorption and gel content was as in CMC Part. Tensile Strength The procedure for tensile strength was as in CMC part. FTIR Spectroscopy The procedure of identification of CN and graft were similar to those of CMC Part. 13

C NMR Spectroscopy The procedure is similar to CA Part.

Scanning Electron Microscopy The procedure is similar to CMC Part.

148


Results and Discussion The synthesis of CN from knitted rag (1 g) was carried out according to the Scheme 3. The potentiality of the process is the re-use of reagent after washing of crude CN. Effects of solvent system, preparation of the reagent, preparation of the sample, concentration of reagent for nitration, time and temperature of reaction for nitration step on the degree of substitution were optimized. Table 12. Preparation of CN by multi-steps nitration method No. of reaction step 1

Volume of reagent, mL 50

Yield of CN, % 169.26

2

50

182.36

3 4

50 50

197.00 208.14

5

50

212.06

6

50

214.04

7

50

215.56

Solubility Insoluble in pyridine but soluble in acetone Insoluble in pyridine but soluble in acetone Soluble in both pyridine and acetone Highly soluble in both pyridine and acetone Highly soluble in both pyridine and acetone Highly soluble in both pyridine and acetone Highly soluble in both pyridine and acetone

The yield of CN obtained by nitration process from 1st to 7th steps is shown in Table 12. The optimized condition for the synthesis of CN was established as preparation of the reagent, cellulose to reagent ratio of 1:50 (w/v), nitration time of 2 h and nitration temperature of 0 oC. It can be seen from Table 12 that yield of CN is increased with increasing number of reaction step in nitration. The yield of product of CN in the first step of nitration is 169.26 %, but for the 2nd to 7th successive steps these values are between 182.36 % and 215.56 % respectively. Solubilities of the produced CN has been tested in pyridine and acetone, and is listed in Table 12. The CN obtained by multi-steps nitration showed a higher solubility in pyridine than the product of initial step. The role of solvent in nitration reaction is to provide accessibility of esterifying reagent to the reaction site of the cellulose chain [16,38]. The DS of the prepared CN was determined by the Kjeldahl method [4c]. The % nitrogen content and the corresponding stepwise DS data are given in Table 13. It can be seen from Table 13 that DS is increased rapidly at the initial step but after the 4th step, the increasing rate of DS is slowed down. Hence, the DS value obtained at the fourth step is considered as optimum. The reason of this phenomenon is due to the fast substitution reaction for initial steps under acetic conditions. The hydroxyl group of cellulose in knitted rag fiber are very active; and can be replaced by NO2 group in the initial stages, as a result decreased the number of OH groups very fast in the latter stages. Table 13 also shows that the yield of CN and nitrogen content in CN are increased gradually from the initial to the successive steps with the increase of DS. Nitrogen content is directly related to DS, and hence this increasing


149

rate is very harmonic to each other. The nitration is dependent upon the accessibility of reagent and the availability of the activated hydroxyl groups in cellulose. Increase of DS by successive treatment with reagent mixture clearly shows activation of the free secondary hydroxyl groups. Table 13. Determination of DS in prepared CN from knitted rag at different nitration steps by the Kjeldahl methods No. of reaction step 1 2 3 4 No. of reaction step 5 6 7

Yield of CN, % 169.26 182.36 197.00 208.14 Yield of CN, % 212.06 214.04 215.56

Nitrogen content, % 12.49 13.20 13.70 13.96 Nitrogen content, % 14.02 14.03 14.04

Degree of substitution 2.41 2.65 2.83 2.93 Degree of substitution 2.95 2.96 2.96

The molecular weight of the prepared CN is increased gradually with the increase of reaction steps and the results are listed in Table 14. The reason is that as the DS increased with successive steps, number of OH groups attached to cellulose molecule is replaced by NO2 groups. As the molecular weight of NO2 group is higher than the OH group, the molecular weight of final CN product is also increased with the nitration reaction. Table 14 shows that increase of DS and molecular weight is string down with the number of successive steps indicating the DS of CN went on to the completeness of the substitution reaction. Table 14. Determination of molecular weight of CN obtained at different steps using acetone as solvent (K = 6.93 × 10-5 dl/g and a = 0.91 at 25 oC) [13] No. of reaction step 1 2 3 4 5 6 7


Intrinsic viscosity Molecular weight 2.50 2.70 2.88 3.03 3.10 3.15 3.18

101,841 110,829 118,974 125,801 128,998 131,287 132,661

From Table 15 it can be seen that high graft yield is obtained at 80% MMA concentration, whereas high grafting efficiency is found at 40% MMA concentration. The graft yield is decreased at the higher MMA concentration as homopolymer is formed at the higher concentration of MMA. The grafting efficiency is decreased with the increase of monomer concentration.

150

Md. Ibrahim H. Mondal and A. B. M. Fakrul Alam Table 15. Effect of MMA concentration on modification of CN film (DS=2.93) No. of experiment 1 2 3 4 5


Grafting yield, % 10.29 11.76 15.50 13.51 12.35


The physical properties, viz. moisture content, water absorption, gel content and tensile strength of CN and grafted CN are listed in Table 16. It can be seen from the Table 16 that the moisture content and water absorption value of CN film are lower than those of grafted CN film. These values for CN film are 2.11% and 1.29%, and those for grafted CN film are 1.06% and 0.88%, respectively. It is proved that MMA has been successfully grafted to the prepared CN film and due to the incorporation of MMA in grafted CN film hydrophobic nature is developed. The percentage of gel content of grafted film is less than CN film. The high gel content shows high reactivity. It is also proved that MMA has been fruitfully grafted to prepared CN film. Breaking load and elongation of CN film are 0.72 MPa and 2.6%, and those for grafted CN film are 1.25 MPa and 1.8% respectively (Table 16). This result shows that the tensile strength of grafted CN film is higher than CN film, and elongation at break of grafted CN film is lower than CN film. The higher tensile strength of grafted CN film is due to the incorporation of MMA to CN film, and thus reasonably increased the rigidity of the grafted film; and hence lowered elongation at break. Table 16. Comparison of physical properties of CN (DS=2.93) and MMA-grafted CN films (2% CN film) Name of sample CN film Grafted CN film


Water absorption, %

Gel content, %

Tensile strength, MPa

Elongation at break, %

1.29 0.88

99.21 96.90

0.72 1.25

2.5 1.8

FTIR Analysis of CN and Grafted CN Films The FTIR spectra of knitted rag cellulose, prepared CN film (DS=2.93) and MMAgrafted CN film are shown in Figure 9. It can be observed from Figure 9 that the characteristic broad absorption bands of CH2, ONO2 and C-C-O groups stretching are at around 2968 cm-1, 1651 cm-1 and 1069 cm-1 respectively [39]. However, the graft copolymer prepared with carbonyl-bearing monomer MMA showed an ester carbonyl group stretching band near 1756 cm-1 in addition to the original bands associated with cellulose [14,29]. Here the appearances of strong sharp peak in the spectra of MMA-grafted CN film give supporting evidence for the grafting and suggests that MMA has been successfully grafted to prepared CN film.


151

Figure 9. FTIR spectra of (a) cellulose, (b) prepared CN film (DS= 2.93) and (c) MMA-grafted CN film. 13

C NMR Analysis of CN and Grafted CN Films

Figure 10. 13C NMR spectra of (a) prepared CN film (DS = 2.93) recorded in acetone at 25oC (number of scans 14536) and (b) MMA-grafted CN film (DS = 2.93) recorded in DMSO at 25 oC (number of scans 14536).

152


Figure 11. Scanning electron micrograph of (a) washed cotton fabric (magnified 500 times), (b) washed cotton fabric (magnified 1000 times), (c) washed cotton fabric after 3% CN treatment (magnified 500 times and scale 100 µm), (d) washed cotton fabric after 3% CN treatment (Magnified 1000 times and scale 50 µm). 13

C NMR spectra of prepared CN film and MMA-grafted CN film are shown in Figure 10. As the number of carbon atom in anhydroglucose unit and cellulose nitrate are same, i.e., 6, the chemical shift of the anomeric carbon is sensitive to the presence or absence of a nitro group after nitration of cellulose hydroxyl groups at C2, C3 and C6 positions, because the electron attracting induced effect of nitro group is stronger than that of hydroxyl group. It can be seen from Figure 10a that the chemical shift of C1 appeared at 101.5 ppm, and that of C6 appeared at 69.3 ppm. The upfield signal of C1 and the downfield signal of C5 and C6 as well as weaker signals (peaks) of C2, C3 and C6 of typical anhydroglucose unit prove the


153

molecular structure of CN [38,39). From Figure 10b it can be observed that the chemical shifts of ester C=O and CH3 groups (which come from carbonyl bearing monomer MMA) are at 178.2 ppm and 21.3 ppm respectively. Here the appearances of strong sharp signal in the NMR spectrum of MMA-grafted CN film suggest that MMA has been successfully grafted onto prepared CN film.

SEM Analysis of Cotton and CN Modified Cotton Fabrics Figures 11a and 11b show SEM images of washed cotton fabric and its magnified images, respectively. From the Figures 11a and 11b, it can be seen that the image of cotton fiber surface is loosened, ruptured, and cracked which are produced due to washing with Na2CO3 solution. Figure 11c and 11d show SEM images of 3% CN treated cotton fabric and its magnified images, respectively. It can be seen from Figures 11c and 11d that the surface of the single fiber is very smooth, and no rupture is visible in the images; because yarn surfaces are sized with CN as sizing materials and projecting fibers are not visible on surface. This indicates that the CN deposition to the fabric fiber surface is occurred, and the formation of bond between CN and fiber backbone is observed by FTIR spectra.

CONCLUSION Huge amount of knitted rag are dumped as textile wastes by different garment and textile industries, those have virtually no use. High performance carboxymethyl cellulose, cellulose acetate and cellulose nitrate (high degree of substitution, purity and molecular weight) were successfully synthesized from knitted rag, a cellulosic waste, which contains high amount of good quality α-cellulose. Hence, production of different grades CMC, CA and CN using cellulosic wastes of garment and textile industries can be considered as a feasible alternative way for generating value-added products, and those will be ultimately helped to reduce the pollution problems.

ACKNOWLEDGMENTS The authors would like to acknowledge the Ministry of Education in Bangladesh for funding the project as Higher Education Research Grant in 2011 (Project no. MoE/Branch 17/ 10 M-15/ 2007 (Part-2)/40(36). We also would like to thank to Professor C. M. Mustafa of Department of Applied Chemistry and Chemical Engineering, Rajshahi University, Bangladesh and Dr. Jacqualyn Eales of Bangor University, UK for checking the language and technical points.

REFERENCES [1]

Bokias, G., Mylonas, Y., Slaikos, G., Bumbu, G.G., Vasile, C. (2001). Synthesis and aqueous solution properties of novel thermoresponse graft copolymers based on carboxymethyl cellulose backbone. Macromolecules 34, 4958-4964.

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[20] Adinugraha, M.P., Marseno, D.W., Haryadi, (2005). Synthesis and characterization of sodium carboxymethyl cellulose from cavendish banana pseudo stem (Musa cavendishi LAMBERK), Carbohydr. Polym. 62, 164-169. [20] Aguir, C., M’Henni, M.F. (2006). Experimental Study on Carboxymethylation of Cellulose Extracted from Posidonia Oceanica. J. Appl. Polym. Sci. 99, 1808-1816. [21] Ramos, L.A., Frollini, E., Heinze, Th. (2005). Carboxymethylation of cellulose in the new solvent dimethyl sulfoxide/tetrabutylammonium fluoride, Carbohydr. Polym. 60, 259-267. [22] Law, R.C. (2004). Application of cellulose acetate. Macromol. Symp. 208, 255-265. [23] Sato, H., Uraki, Y., Kishimoto, T., Sano, Y. (2003). New process for producing cellulose acetate from wood in concentrated acetic acid. Cellulose 10, 397-404. [24] Saka, S. (2004). Wood as natural raw materials for cellulose acetate production, Macromol. Symp. 208, 7-28. [25] Saka, S. (2004). Cotton fibers as natural raw materials for cellulose acetate production, Macromol. Symp. 208, 29-35. [26] Mondal, Md.I.H., Farouque, F.I., Salam, M.A. (2006). Graft copolymerization of acrylate monomers onto sulfonated jute-cotton blended fabric. J. Applied Polym. Sci. 100, 4393-4398. [27] Sugiyama, J., Persson, J., Chanzy, H. (1991). Combined infrared and electron diffraction study of the polymorphism of native celluloses. Macromolecules 24, 2461– 2466. [28] Marchessault, R.H., Liang, C.Y. (1960). Infrared spectra of crystalline polysaccharides, III, Mercerized cellulose. J. Polym. Sci. 43, 71-84. [29] Wu, J., Jun, Z., Hao, Z., Jiasong, H., Qiang, R., Meili, G. (2004). Homogeneous acetylation of cellulose in new ionic liquid. Biomacromolecules 5, 266-268. [30] Yasuyuki, T., Yoshikazu, T. (1995). Determination of substituent distribution in cellulose acetate by means of a 13C NMR study on its propanoated derivative. Carbohydr. Res. 273, 83-91. [31] Buchanan, C.M., Edger, K.J., Hyatt, J.A., Wilson, A.K. (1991). Preparation of cellulose acetate and determination of monomer composition by NMR spectroscopy. Macromolecules 24, 3050-3059. [32] Shari, Li. X., Glen, E. F., Chongin, W., James, Y. (2007). Templating mesoporous hierarchies in silica thin films using the thermal degradation of cellulose nitrate. Microporous and Mesoporous Materials 99, 308-318. [33] Haixiang, S., Shengnan, L., Baosheng, Ge., Xing, Li., Huanlin, C. (2007). Cellulose nitrate membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. J. Memb. Sci. 295, 2-10. [34] Kreplak, L., Wang, H., Aebi, H., Pong, P. (2007). Atomic Force Microscopy of Mammalian Urothelial Surface. J. Mol. Biol. 374, 365-373. [35] Selwitz, C. (1988). The Getty Conservation Institute. Research in Conservation 2, 1-8 and 41-49. [36] van Schil, G.J., (1980). The Use of Polyester Film Base in the Motion Picture Industry. SMPTE Journal 89, 106-110. [37] Jiugao, Y., Ying, W., Shaomin, W., Xiaofei, M. (2007). The preparation of cellulose nitrate derivatives and their adsorption properties for creatinine. Carbohydr. Polym. 70, 8-14.

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[38] Saunders, W.C., Taylor, L.T. (1991). Solution infrared and nuclear magnetic resonance studies of cellulose nitrates. Applied Spectroscopy 45(4), 604-610.



Chapter 6

HISTORY, SYNTHESIS AND PROPERTIES OF AZO PYRIDONE DYES Dušan Ž. Mijin, Gordana S. Ušćumlić and Nataša V. Valentić Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia

ABSTRACT Azo dyes are synthetic organic colorants bearing chromophoric azo group. Over 50% of the colorants used belong to the azo compounds. Such a wide range of usage of azo dyes is due to the number of variations in chemical structure and methods of application which are generally not complex. Cotton, paper, silk, leather, and wool can be dyed by azo dyes. Also, there are azo dyes for dying polyamides, polyesters, acrylics, polyolefins, viscose rayon, and cellulose acetate. They can be used for the coloring of paints, varnishes, plastics, printing inks, rubber, foods, drugs, and cosmetics. Azo colorants are also used in diazo printing and color photography. Among azo colorants arylazo pyridone dyes have become important in the last several decades. The high molar extinction coefficient, the medium to high light and wet fastness properties are very favourable. They find application generally as disperse dyes. Disperse dyes are characterized by low aqueous solubility and are applied to hydrophobic fibers from an aqueous system, in which the dye is present in a highly dispersed state. The importance of disperse dyes increased in the 1970s and 1980s due to the use of polyester and nylon as the main synthetic fibers. Also, disperse dyes were used rapidly since 1970. in inks for the heat-transfer printing of polyester as well as for other applications including hot-melt inks, ink-jet inks and color filters for liquid-crystal display panels. Pyrydone azo dyes generally produce yellow shades on fabrics but other shades were also reported. Dye structure affects the intensity of color and fastness properties. Azo pyridone dyes which have OH or NH group in ortho position to azo group show an azohydrazone tautomerism which was investigated in a number of papers. Azo-hydrazone tautomerism was studied in solvents as well as by crystallography. Generally, azo



E-mail: [email protected]

158

Dušan Ž. Mijin, Gordana S. Ušćumlić and Nataša V. Valentić pyridone dyes exist in hydrazone form in the solid state while in solvents azo-hydrazone equilibrium can be found.

1. INTRODUCTION A hundred years ago, the usual way to apply dyes to cotton, wool, silk etc. (natural fibers) is to make an aqueous dye solution. When after the First World War a man-made fiber, cellulose acetate, was introduced, only a few available dyes had affinity for the new fiber due to its hydrophobic nature. This led to development of disperse dyes [1]. The first dyes developed for the application to acetate fibers were the Ionamine dyes [13]. They are characterized by the presence of hydroxyl and amino groups and a relatively low molar mass. These dyes which are water soluble were hydrolyzed to produce the sparingly soluble free base in the form of a very fine suspension which was then absorbed by the fiber. The use of disperse dyes was increased when new man-made fibers as nylon and acrylic were introduced in the late thirties and early forties. The real boom in disperse dyestuff development was not until late forties when polyester fibers were commercially introduced [1]. Disperse dyes are non-ionic compounds which have very limited solubility in water at room temperature and have substantivity for hydrophobic fibers such polyester, nylon and acetate. To achieve efficient diffusion into fibers these dyes are usually applied as a fine aqueous dispersion. The molar mass of dyes should be in the range 400-600. Also, disperse dyes should be able to withstand various dyeing conditions, pH and temperature [1,4,5]. In thermofixation and heat transfer printing the dyes must first sublime into single molecules before diffusion into the fiber. Usually, disperse dyes contain no water solubilising groups and they are marketed in the form of either an easily dispersible powder or a concentrated aqueous dispersion. A surfaceactive agent is needed in order to keep dye particles in dispersion [1]. There are several methods for the classification of disperse dyes. In the 1970s, ICI (Imperial Chemical Industries) divided disperse dyes according to their sublimation fastness and dyeing properties. The dyes were placed into categories from A to D, where dyes in class A had low relative molar masses and hence poor sublimation fastness. Dyes in class D had high relative molar masses and good sublimation fastness. Therefore dyes in class A had desirable dyeing properties while dyes in class D had poorer dyeing properties. Dyes in classes B and C were between these two border classes. Other dye manufacturing companies also introduced their own similar systems of disperse dye classification [1]. The Disperse Dye Committee of the Society of Dyers and Colourists has classified the dyeing characteristics of disperse dyes according to the results of several tests (the build up, leveling properties, rate of dyeing and temperature range properties). The dyes are divided in two classes: low energy and high energy disperse dyes. The low energy disperse dyes comprise small dye molecules with low polarity. They are levelling, rapid dyeing dyes with poor heat resistance. The high energy disperse dyes are more polar, higher molar mass dyes. They have low dyeing rates, poor migration during dyeing but good heat and sublimation fastness [6]. Acording to Koh [1] the Colour Index in 1992 listed around 1,150 disperse dyes. Among them monoazo dyes of relatively low molar mass were the majority. They are generally

History, Synthesis and Properties of Azo Pyridone Dyes

159

nonionic, although they may be quite polar. Anthraquinone derivatives made a significant portion of the disperse dyes, but they are being gradually replaced (because of cost and environmental problems). In the last several decades newer disperse dyes were developed based on the heterocyclic components [5]. Disperse dyes can be divided by chemical structure as: monoazo, anthraquinone, benzodifurane, methine, nitrodiphenylamine, naphthalimide and quinoline derivatives. Azo dyes are synthetic organic colorants bearing the chromophoric azo group. On one side the azo group is attached to an aromatic or heterocyclic nucleus and on the other, to an unsaturated molecule of the carbocyclic, heterocyclic, or aliphatic type [7]. IUPAC defines azo compounds as: "Derivatives of diazene (diimide), HN=NH, wherein both hydrogens are substituted by hydrocarbyl groups, e.g., PhN=NPh azobenzene or diphenyldiazene" [8]. Commercially, azo colorants are the largest and most versatile class of organic dyestuffs. As published in Kirk-Othmer Encyclopedia of Chemical Technology [7] in 2003, there were more than 10,000 Colour Index (C.I.) generic names assigned to commercial colorants. Approximately 4,500 of them are in use, and over 50% of these belong to the azo compounds. Azo dyes can be divided according to the number of azo groups to monoazo, disazo, trisazo and polyazo, and also further subdivision can be achieved according to the solubility or according to the types of component used. The wide range of usage of azo dyes is due to the number of variations in chemical structure and methods of application which are generally not complex. Cotton, paper, silk, leather, and wool can be dyed by azo dyes. Also, there are azo dyes for dying polyamides, polyesters, acrylics, polyolefins, viscose rayon, and cellulose acetate. They can be used for the coloring of paints, varnishes, plastics, printing inks, rubber, foods, drugs, and cosmetics. Azo colorants are also used in diazo printing and color photography. The shades of azo dyes cover the whole spectrum [7]. Monoazo disperse dyes are largely based on the parent compound aminoazobenzene, C.I. Solvent Yellow 1 (Figure 1). Aminoazobenzene dye polyester of yellow with such poor fastness so it is not used as a disperse dye. By introduction of different groups in aminobenzene molecule a number of monoazo disperse dyes with different properties can be obtained. Some of them are listed in Figure 2. In comparison to anthraquinone dyes the azo group is usually 2 or 3 times stronger in tinctorial strength. Due to their simplicity and the ease of manufacturing, the cost of manufacturing of azo dyes is comparatively lower than the expensive anthraquinone dyes. On the other hand, they have duller shades, lower fastness to light and breakdown into carcinogenic amines. Nevertheless, the cost effectiveness compensates the drawbacks [1,5].

H2N

N N

Figure 1. C.I. Solvent Yellow 1.

The color ranges of disperse dyes based on aminoazobenzene are very broad, but the color of aminoazobenzene derivatives do not extend into the area of greenish yellows. These dyes are with high extinction coefficients, but are not noted for their brightness [5].

160

Dušan Ž. Mijin, Gordana S. Ušćumlić and Nataša V. Valentić O

HO

CH3CN

N

O2N

N

H

N

1

CH2CH2CN

2

CH3

CN

Cl O2N

CH2CH3

N

O2N

N N

N

CH3CN

N(CH2CH2COCH3)2

N

N(CH2CH2COCH3)2

O

H3C

3

4

Br

H

OMe O2N

N N O NO2 CH3CN H

N(CH2CH2COCH3)2 5

Figure 2. Monoazo disperse dyes: C.I. Disperse Yellow 3 (1), C.I. Disperse Orange 25 (2), C.I. Disperse Red 167 (3), C.I. Disperse Violet 33 (4), C.I. Disperse Blue 79 (5).

O

NH2

O

NH2 O

O

6

O

OH

O

NHCH3

O

7

OH NH2 O O

O

8

NH2

O

9

NH2

Figure 3. Anthraquinone disperse dyes: C.I. Disperse Red 15 (6), C.I. Disperse Red 60 (7), C.I. Disperse Violet 4 (8), C.I. Disperse Violet 26 (9).

Anthraquinone disperse dyes (Figure 3) are among dyes which were used for cellulose acetate as well as for polyester fibers. They produce bright dyeings with color shades from yellow to even turquoise blue depending on substituents and their position. Also these dyes show high light fastness and no dye stability problems during dyeing [1]. Benzodifurane disperse dyes gives hues that range from yellow to blue [5]. The example is C.I. Disperse Red 356 a bright red disperse dye (Figure 4).


161

O O

O O

O(CH2)3CH3

Figure 4. C.I. Disperse Red 356.

Coumarin disperse dyes are principally bright fluorescent yellows such as C.I. Disperse Yellow 82 (Figure 5). Among these dyes some derivatives are used as fluorescent brighteners [5]. H N

CH2CH3 CH3CH2

N N O

O

Figure 5. C.I. Disperse Yellow 82.

Although methine based disperse dyes give brilliant yellows [5], the brightest blue disperse dye available, C.I. Disperse Blue 354 belongs to these disperse dyes (Figure 6). H 3C CN H N(C6H13)2

NC SO2

Figure 6. C.I. Disperse Blue 354.

Disperse dyes which are naphthalimide derivatives include some brilliant, fluorescent compounds [5]. C.I. Disperse Yellow 11 is an example of such dyes (Figure 7). O H2N

CH3

N O

Figure 7. C.I. Disperse Yellow 11.

CH3

162

Dušan Ž. Mijin, Gordana S. Ušćumlić and Nataša V. Valentić

Nitrodiphenylamine disperse dyes are yellow dyes. They have high light fastness on polyester but poor on nylon. Also they have low extinction coefficients [5]. Examples are C.I. Disperse Yellow 42 and C.I. Disperse Yellow 59 (Figure 8). H N

H N O

O N

NO2

S O

H

CH3(CH2)3-N-S

10

NO2 11

O

H

Figure 8. C.I. Disperse Yellow 42 (10) and C.I. Disperse Yellow 59 (11).

Quinoline disperse dyes are also yellow dyes (Figure 9). C.I. Disperse Yellow 54 is the unsubstituted parent compound and is suitable for many general applications. This is a low energy dye while C.I. Disperse Yellow 64 has higher energy and better resistance to sublimation [5]. Br OH

OH

O

N

O

N

12

13

O

O

Figure 9. C.I. Disperse Yellow 54 (12) and C.I. Disperse Yellow 64 (13)

In order to improve further brightness, color range, and economics chemists have prepared new azo disperse (mono, dis, tris) using different heterocyclic components. Many heterocycles have been used; some of them are azothiophenes, azobenzothiazoles, azopyrazolone and azopyridones, or aryl azo pyridone dyes.

-O

-O

+ N O Et

H O

Cl

O

N

Me 14

O

Et

H O

N

N

+ N O N

N

O Me

15

O

Me

H O

N

N

N

CN

S

O

N

Me

CN

CN

16

Figure 10. Structure of C.I. Disperse Yellow 119 (14), C.I. Disperse Yellow 211 (15) and C.I. Disperse Yellow 114 (16). (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

163


Among azo colorants arylazo pyridone dyes (Figure 10) have become important in last several decades. The high molar extinction coefficient and the medium to high light and wet fastness properties are very favourable. They find application generally as disperse dyes. The importance of disperse dyes increased in the 1970s and 1980s due to the use of polyester and nylon as the main synthetic fibers. Also, disperse dyes were used rapidly since 1970 in inks for the heat-transfer printing of polyester [7]. They can be used in the production of color filters using them with excellent light and heat resistance [9]. Also, there are basic and reactive azo pyridone dyes as well as dyes and pigments for usage in printing inks [10]. In the following text synthesis of azo pyridone dyes is illustrated on certain examples including mono, dis and tris azo dyes. After the overview of synthesis discussion of fastness and tautomerism is given.

2. SYNTHESIS 2.1. Synthesis of Monoazo Dyes The main synthetic route for the preparation of azo dyes is the coupling reaction between an aromatic diazo compound and a coupling component. Of all dyes manufactured, about 60% are produced by this reaction [7]. The success of azo colorants is due to the simplicity of their synthesis by diazotization and azo coupling, and to the almost innumerable possibilities presented by variation on the diazo compounds and coupling components [11]. All coupling components used to prepare azo dyes have the common feature of an active hydrogen atom bound to a carbon atom. Generally, arylazo pyridone dyes can be prepared with pyridone moiety as a coupling component along with various diazonium salts using a well known reaction [11]. Pyridones can be also prepared using known procedures [12-15]. Figure 11 show the general synthesis of monoazo pyridone dyes. 3-Cyano-6-hydroxy-4-methyl-2-pyridone (19), prepared from ethyl cyanoacetate (acetoacetic ester, AAE (17)) and cyanoacetamide (18), is coupled with diazonim salts derived from 4-nitroaniline (21).

O O

+

CN

1. KOH, 

O

2. HCl

NH2

CH3CH2O 17

CH3

NC

H3C

HO

N

O

H 19 +

18

NH2

N2

NaNO2, HCl H2O, 0-5 oC NO2

NO2

O2N

20

CH3 N

N

HO 21

CN N

O

H

Figure 11. Synthesis of arylazo pyridone dye from pyridone. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

164


As a result 3-cyano-6-hydroxy-4-methyl-5-(4-nitrophenylazo)-2-pyridone (21) is formed [16]. For the preparation of diazonium salts different substituted anilines or other heterocyclic derivatives can be used. Different monoazo pyridone dyes were prepared from 3-cyano-6-hydroxy-4-methyl-2pyridone or 1-substituted 3-cyano-6-hydroxy-4-methyl-2-pyridones [17-32]. Disperse azo dyes useful for dyeing polyester fibers fast brilliant yellow shades were described in 1972 by Burkhard et al. These dyes were prepared by coupling diazotized anilines with 3-cyano-6hydroxy-4-methyl-2-pyridones in AcOH at 0-5 oC and pH 4.5 [17]. Starting from different anilines disperse dyes were prepared and used in dyeing or printing polyester fibers with fast, yellow [18,19] to greenish yellow shades [20]. In addition, disperse azo dyes were manufactured and used to dye synthetic fibers fast greenish yellow to red shades, by further modification of amino component (e.g., 5-amino-4,6-dicyanoindan) [20]. Lightfast yellow shades were obtained by dyeing poly(ethylene terephthalate) (PTT) fibers with azo dyes where molecules like decyl 4-aminobenzoate was diazotized and coupled with 3-cyano-6hydroxy-4-methyl-2-pyridone [33]. Besides yellow shades, polyester fibers were dyed fast orange shades [21]. It was shown that dye prepared from p-toluidine and 3-cyano-6-hydroxy4-methyl-2-pyridone is useful for dyeing and printing hydrophobic synthetic fibers, e.g., polyester, in a mixture with Disperse Yellow 54 and/or Disperse Yellow 64 [34]. By coupling diazotized 2,4,3,5-(NC)2Me2C6HNH2 with 3-cyano-6-hydroxy-1,4-dimethyl2-pyridone in aqueous NaOH, the yellow azo dye was prepared and used for dyeing polyester fibers light- and sublimation fast yellow shades [22]. Another azo dye was prepared by coupling diazotized 3-H2NC6H4SO3Ph with 3-cyano-6-hydroxy-1,4-dimethyl-2-pyridone and used for dyeing polyester fibers a fast greenish yellow shade [23]. In addition, azo dyes prepared by coupling diazotized 2,4-O2N(RO)C6H3NH2 (R = Me(CH2)3CHEtCH2, Me(OCH2CH2)2, Me(CH2)9) with the same pyridone, were used to dye polyester fibers fast orange shades from aqueous dispersions and from tetrachloroethylene [24]. Dyes were also prepared from 3-cyano-1-ethyl-2-hydroxy-4-methyl-6-pyridone [25-27], 3-cyano-2-hydroxy-4-methyl-1-propyl-6-pyridone [26,27] and 1-butyl-3-cyano-2-hydroxy-4methyl-6-pyridone [26-28]. These dyes dye polyester fabric fast yellow to greenish yellow shades. Other 1-substituted 3-cyano-6-hydroxy-4-methyl-2-pyridones were used as coupling components. When 1-substituents were: (un)substituted Ph, C3-4 alkenyloxy, C3-4 alkynyloxy, PhO and (un)substituted C1-8 alkoxy, azo dyes were obtained with different substituents in arylazo part of dye. Thus, 4-H2NC6H4CO2CH2CO2CH2Ph was diazotized and coupled with 1butyl-3-cyano-6-hydroxy-4-methyl-2-pyridone to give dye that gave brilliant greenish yellow on polyester fibers, both in polyester fabrics and in polyester-cotton blends [29]. By coupling diazotized 2-nitroaniline with 3-cyano-1-(2-ethylhexyl)-6-hydroxy-4-methyl-2-pyridone an azo dye insoluble in water was obtained which produce heat- and wetfast greenish yellow on polyester fibers [30]. The water-soluble disperse azo dyes series including light yellow, yellow, orange, red, violet and blue colors were obtained by introduction of methyl, methoxy and HOOCCH2SO2 group [31] or methyl, HOCH2CH2, Me2NCH2CH2, dodecyl [32] in position 1 of pyridone ring. Reactive azo dyes for cotton as well as a cationic azo dye for polyacrylonitrile fiber, a disperse azo dye for hydrophobic fibers, and an acid azo dye for nylon were prepared from 1(2-aminoethyl)-3-cyano-2-hydroxy-4-methyl-6-pyridone [35]. The yellow dyes were prepared from 1-(alkoxyalkyl)-3-cyano-6-hydroxy-4-methyl-2-pyridones, and used to produce ink


165

which was used for thermal-transfer recording [36]. Also, azo disperse dyes based on pyridone moiety which contain -sulfatoethylsulfonyl group were used to dye poly(trimethylene terephtalate). The dyes showed alkali-clearing property and exhibited good to excellent fastness on the PTT fabric [37]. Pyridone component was further modified by introduction of phenyl group in position 4 or 2. So, azo dyes were prepared from 3-cyano-4hydroxy-2-phenyl-2-pyridone as well as from 3-cyano-6-hydroxy-4-phenyl-2-pyridone, and coupling with diazotized aniline and 4-substituted anilines (Me, OMe, Cl) [38]. Cyano group in position 3 of pyridone ring can be substituted by pyridinium group. Basic dyes can be prepared from 1-substituted 6-hydroxy-4-methyl-3-pyridinium-2-pyridones using above mentioned procedure and used to dye acrylic fibers fast yellow shades [39] or used in ink-jet inks [40]. In addition, pyridone azo dyes were prepared from 2-pyridones with a trifluoromethyl [41,42] or a carboxy group in position 4 of pyridone ring [42]. A series of new aryl azo pyridone disperse dyes were derived by the reaction of 5-cyano6-hydroxy-4-methyl-2-pyridone with POCl3. The obtained 3-cyano-2,6-dichloro-4methylpyridine were further transformed by the reaction with ethanolamine and then another primary amine. The dyeing ability of such dyes toward polyester fiber was generally poor, while wash and rubbing fastness were excellent and light and sublimation fastness were good [43]. Synthesis of 5-arylazo-2,6-dichloro-3-cyano-4-methylpyridines and their application on polyamide fiber as disperse reactive dyes were also reported [44]. Reactive pyridone monoazo dyes were prepared from (disulfoanilino)dihalotriazine and the appropriate azo pyridine, which are useful in dyeing or printing of cotton or polyamide fibers. Synthesis of one such dye is given in Figure 12 [45]. Diazonium salt was prepared from 4-acetylamino-2-aminobenzensulphonic acid (22) and coupled with 3-amido-1-ethyl-6hydroxy-4-methyl-2-pyridone (23) to give compound (24). The compound (24) then reacts with (disulfoanilino) dihalotriazine (27) prepared from 1-amino-3,4-benzendisulphonic acid (25) and 2,4,6-trichlorotriazine (26). The obtained monoazo pyridone dye (28) dyes cotton to a greenish yellow shades. The printings exhibit excellent light and wet fastness properties. More yellow reactive dyes were prepared when instead of 2,4,6-trichlorotriazine, 2,4,6trifluorotriazine was used [46]. When the amino component is concerned, it should be pointed out that disperse azo dyes prepared from 5-amino-isoindole-1,3-dione and pyridone had improved wash fastness in dyeing of hydrophobic fibers [47]. Also, disperse dyes were prepared from 2-aminothiophene derivatives, such as 2-amino-3-cyano-4,5,6,7-tetrahydrobenzo[b]tiofene and ethyl 2-amino4,5,6,7-tetrahydrobenzo[b]tiofene-3-carboxylate, and 5-cyano-1-ethyl-6-hydroxy-4-methyl-2pyridone [48,49]. Basic dyes were obtained from [-(4-aminobenzenesulfonamido)ethyl]pyridinium chloride which was diazotized and coupled with 3-cyano-1-ethyl-2-hydroxy-4-methyl-6pyridone. The dyes were used to dye polyacrylonitrile fast yellow shades [50]. Disperse azo dyes were also prepared from cumarin derivatives and used in dyeing and in jet and hot-melt printing. These dyes are suited for application to hydrophobic and synthetic textiles with good fastness [51]. In addition, acid dyes containing silver can be used to prepare anti-bacterially functional fiber [52]. Another group of pyridone azo dyes which contains the quaternary ammonium salt was used to stain acrylic fibers and can kill or inhibit both Gram positive and Gram negative bacteria [53].

166

Dušan Ž. Mijin, Gordana S. Ušćumlić and Nataša V. Valentić O NH2

CH3CN

NaNO2, HCl

H

N2

HO3S

H2O, 0-5 oC

SO3H

+

SO3H

22

CH3 CONH2

1. NaOH,

SO3H

+

Cl

N

Cl

HO3S

N

NH2

HO

N

O

C2H5 23

N 2. HCl, 75-80 oC

Cl

25

26

H2N CH3

NaNO2, HCl, H2O, 0-5 oC

N HO3S

HO3S

H N N

HO3S 27

CONH2

HO

N

O

C2H5

24

Cl

N

N

N Cl

NaOH, pH=7, 5-10 oC

HO3S HO3S

H N

Cl

N N

N

HN CH3 HO3S 28

N N HO

CONH2 N

O

C2H5

Figure 12. Synthesis of reactive dye from (disulfoanilino) dihalotriazines. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

Azo pyridone dye derived from substituted 2-amino benzothiazole was used for dyeing and/or printing leather, cellulose materials (e.g., paper, wood, cardboard), and for producing inks and formulations for contactless printing (e.g., inkjet printing) [54]. Azo pyridone dyes were used in order to provide an optical recording medium. This medium had a recording layer improved in light stability capable of recording and regeneration of high-density optical information by short-wavelength laser beams. The recording layer contained a metal complex of pyridone azo compounds which was obtained from a 6-hydroxy-2-pyridone structure as a coupler component and an isoxazole, 1,2,4-

167


triazole or pyrazole structure as a diazo component and an ion of bivalent metal, such as Ni, Co, Fe, Zn, Cu or Mn [55]. Also, Cr-complex azo dyes were obtained from o,o'dihydroxyphenylazopyridone intermediates and ammonium chromium sulfate [56]. Azo pyridine thermally stable yellow pigments were obtained by coupling diazotized 2,51 R CO(R2CO)C6H3NH2 (R1, R2 = MeO, NH2) with 5-cyano-2-hydroxy-4-methyl-6-pyridone. The pigments were stable up to 350 C and resistant to organic solvents and suitable for plastics and baking varnishes [57]. Also, by treatment of azo pyridone dye, obtained from 2pyridones (e.g., 3-cyano-6-hydroxy-4-methyl-2-pyridone), with BaCl2 yellow azo pigments were obtained and used in printing inks [58]. Arylazo dyes containing pyridone ring can also be prepared from arylazo diketones or arylazo ketoesters (obtained by coupling -diketones or -ketoesters with diazonim salts) by condensation with cyanoacetamide. The synthesis of 3-cyano-4,6-dimethyl-5-(4nitrophenylazo)-2-pyridone (31) is presented in Figure 13. Diketo arylazo compound (30), produced by the reaction of acetylacetone (29) and diazonium salt, reacts with cyanoacetamide in the presence of sodium ethoxide to give arylazo pyridone dye (31) [59,60]. Instead of diketone keto esters can be used, e.g., ethyl acetoacetate [61]. In the same manner arylazo pyridone dyes were prepared with Me or Ph group in position 4 and with OH or C6H5NH in position 6 of pyridine ring [62]. In addition, azo dyes were prepared from thiopyridones which were obtained by the reaction of thiocyanoacetamide with MeCOC(COMe)=NNHPh and sodium ethoxide [59]. + N2

H 3C O

+

5-10 oC, CH3COONa, CH3CH2OH

H3 C

O 2N

N N

O H 3C

O

NO2

O

30

H 3C

29

NC , CH3CH2ONa, 

O

NH2

O 2N

CH3 N

N

H3 C 31

CN N

O

H

Figure 13. Synthesis of arylazo pyridone dye from arylazo intermediate. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

Recently, a new procedure for the synthesis of arylazo pyridones, according to Figure 13, using microwave irradiation was reported. The advantages of this procedure are short reaction times, high yields and aplication in the synthesis of azo dyes from different 2-pyridones [63].

168


The synthesized derivatives of 3-cyano-4,6-dimethyl-2-pyridone (Table 1, entry 1-6) were obtained with nearly quantitative yield, while the derivatives of 3-cyano-4,6-diphenyl-2pyridones (Table 1, entry 7-9) were obtained in a lower yields. Synthesis of 3-cyano-4,6dimethyl-5-phenylazo-2-pyridone in a conventional manner [60] also takes place in the presence of a base in ethanol, except that this synthesis occurred during 3 h with somewhat lower yields (70 – 80 %). Table 1. Synthesized arylazo 3-cyano-4,6-dimethyl-2-pyridone, 3-cyano-4,6-diphenyl-2pyridone, 3-cyano-6-hydroxy-4-methyl-2-pyridone and 3-cyano-6-hydroxy-4-phenyl-2pyridone dyes with their yields (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia) R1

R2 N R3

R4 CN

N 5

R

N

O

H

Entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1

2

3

R

R

R

R4

R5

Yield (%)

H H Br Br H H H Br H H Br Br H H

H H H Me Me H H Me Me H H Me Me H

H NO2 H Me Me I H Me Me H H Me Me H

Me Me Me Me Me Me Ph Ph Ph Me Me Me Me Ph

Me Me Me Me Me Me Ph Ph Ph OH OH OH OH OH

99 100 92 100 100 100 72 72 83 47 93 80 50 78

Another microwave procedure for the synthesis of arylazo pyridone dyes was reported. Arylazo pyridone dyes (Figure 14) were synthesized from cyanoacetamide and azodisperse dye obtained from the reaction of corresponding dianalides with diazotized aromatic amines. The microwave synthesis gave dyes with yields of around 60 % for 3-5 min, while conventional heating gave dyes with yield of around 80 % but after 4 h. The fastness properties of silk screen printed polyester using these synthesized dyes have been investigated and it was concluded that the prints posses very good washing, rubbing, perspiration and light fastness [64].


169

Cl H

X N H

N CN

N N

N

O

H

Cl

Figure 14. A recent new class of arylazo pyridone dyes. OH

NH2

HO3S 33

SO3H 1. 0-5 oC, pH=7, KOH

SO2CH2CH2OSO3H

SO2CH2CH2OSO3H 2.

NaNO2, HCl 0-5 oC +

H 2N

N2

32

HO3SOCH2CH2O2S

OH

N N HO3S 34

HO3S

NH2

1. NaNO2, HCl, 0-5 oC

CH3 CONH2

2.

HO

HO3SOCH2CH2O2S

N

O

C 2H 5

35

OH

N N HO3S

CH3 HO3S

N N HO

36

CONH2 N

O

C2H5

Figure 15. Synthesis of a reactive disazo pyridone dye from 2-[(4-aminophenyl)sulfonyl] ethyl hydrogen sulfate and 6-amino-1-hydroxy-3,5-disulfonaphthalene. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

170


2.2. Synthesis of Disazo Dyes Disazo pyridone dyes can be prepared in different ways using diazo coupling reaction. One example is shown in Figure 15. Synthesis of disazo dye (36) starts with the diazotization reaction of 2-[(4-aminophenyl)sulfonyl]ethyl hydrogen sulfate (32), and the resulting diazonium salt is coupling with 6-amino-1-hydroxy-3,5-disulfonaphtalene (33). The resulting azo compound (34) is then diazotized and coupled with 3-amido-1-ethyl-6-hydroxy-4-methyl2-pyridone (35) to form a disazo dye (36). The reactive azo dyes prepared can be used for dyeing cellulosic and polyamide fibers [65]. In a similar manner 5-[(4-arylazophenyl)azo]-3cyano-6-hydroxy-4-methyl-2-pyridones were obtained [66]. New disazo dyes were prepared by successive reactions of diazo coupling. The starting amino compounds were 5-amino-4-hetarylazo-3-methyl-1H-pyrazole and 5-amino-4hetarylazo-3-methyl-1-phenylpyrazole, and their diazonium salts were coupled with 3-cyano6-hydroxy-4-methyl-2-pyridone [67]. This synthesis is shown in Figure 16. N S

NH2

37 NaNO2, H2SO4, 0-5 oC

N

NC

+

N2

S

NH2

+ H

CN

N

CH3COONa, pH=5-6, 0-5 oC

S

CH3 38

NH

N N H 39

CH3

1. PhNHNH2 2. 

CH3 CN N HO

N

S

O

N N

NH2

H 19 H3C

1. KOH, 0-5 oC, CH3COONa, pH=5-6

N

40 NaNO2, H2SO4, H2O, 0-5 oC

N S

N

N N

N2

+

2.

H3C

N

N

CN H3C

N S

N N

N N

O N

H

OH H3C

N 41

N

Figure 16. Synthesis of disazo pyridone dye from 5-amino-4-benzothiazole-2-ylazo-3-methyl-1phenylpyrazole and 3-cyano-6-hidroxy-4-methyl-2-pyridone. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

171


The starting 2-aminobenzothiazole (37) is diazotized and the resulting diazonium salt is coupled with 3-aminocrotonitrile (38) giving 2-benzothiazolylhydrazon-3ketiminobutyronitrile (39). In the next step nitrile (39) reacts with phenylhydrazine to give 5amino-4-benzothiazole-2-ylazo-3-methyl-1-phenylpyrazole (40). Finaly, the compound (24) is diazotized and coupled with 3-cyano-6-hydroxy-4-methyl-2-pyridone (19). The disazo compound can be also synthesized by the diazotization reaction of diamino compound (42) and coupling of diazonium salt with 1-substituted pyridone (43), as given in Figure 17 [68]. The produced disazo pyridone compound (44) was used in the production of colored plastics or polymeric color particles. Dyes had good heat resistance, migration resistance, tinctorial strength, and fastness when used for bulk coloration. In the same manner different disazo pyridone colorants can be prepared for use in phase change inks [69-72]. CH3 O3S

SO3

CH3

CH3 NH2

CN

H2N

42

HO

CH3COOH, HCl, H2O, NaNO2, 0-5 oC

N

O

(CH2)3O(CH2)2O 43 1. NaOH, H2O, pH=4-5, 0-5oC

CH3 O3S +

N2

2.

SO3 CH3

+

N2

CH3 O3S

SO3 CH3

N

N

CH3

NC

CN

HO

N OH

N O(CH2)2O(CH2)3

N

H3C

N O

O

(CH2)3O(CH2)2O

44

Figure 17. Synthesis of disazo pyridone dye by coupling of diazotized diamino compound with 1substituted pyridone. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

Another reaction pathway for the preparation of disazo pyridone compounds is the synthesis of compound (51) shown in Figure 18. The disazo pyridone compound was prepared here from bispyridone derivative. Specifically, in this synthesis dodecamethylen dipyridone (50) is synthesized first, starting from 1,12-diaminododecane (48), ethyl cyanoacetate (49) and acetoacetic ester. The diazonium salt prepared from octadecyl-2-

172


aminobenzoate (47) is then coupled with synthesized dodecamethylen dipyridone (50) to yield disazo compound (51). Octadecyl-2-aminobenzoate was obtained by the reaction of 1octadecanole (45) and isatoic anhydride (46). The resulting green-yellow disazo pyridone colorants were used in phase change inks [72-74]. In a similar manner disazo colorants were prepared for dyeing or printing cotton and polyamide materials [75]. The dipyridone structure can be obtained by the reaction of two moles of 1-ethyl-6-hydroxy-2-pyridone with one mole of glutaraldehyde sodium hydrogen sulphite. Obtained dipyridone is then coupled with two mole of diazotized 4-(2-sulfatoethylsulfonyl)aniline to form reactive disazo yellow dye [76]. CH3(CH2)17OH 45

+

O

+

NH2

100-150 oC

COO(CH2)17CH3

O

N2

1. CH3COOH 2. NSA, 0-5 oC

COO(CH2)17CH3

47 N

O

46 H

H2N(CH2)12NH2 48

+

CNCH2COOCH2CH3 49

NC 1. 150 oC

H3C

N

2. AAE, piperazine, DMF, 120 oC 3. 25 oC, HNO3

OH

CN

O

O (CH2)12

CH3

N HO

50

1. H2O, NaOH, CH3COONa, iPrOH 2.

NC H3C

N N

CH3(CH2)17OOC

CN

O

O (CH2)12

CH3

N HO

OH

N

N

N

COO(CH2)17CH3

51

Figure 18. Synthesis of disazo pyridone dye from bispyridone derivative. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

Disazo reactive dyes, which dye cotton in yellow shades, containing hydroxyl pyridone and fluorotriazine groups were also prepared. Thus, pyridone dye (53) was obtained from 5[(3-amino-6-sulfophenyl)azo]-1-ethyl-6-hydroxy-4-methyl-3-(sulfomethyl)-2-pyridone (52), 2,4,6-trifluorotriazine and 1,4-diphenylamine [77].


173

HO3S CH3 HO3SH2C O

NH2

N N N

OH

CH2CH3

52

1. NaOH, H2O 2. 0 oC, 2,4,6-trifluorotriazine, NaOH 3. 0 oC, 1,4-diphenylamine

HO3S CH3 HO3SH2C O

O

NH

N N N

N

OH

N

CH2CH3

F

N

NH

CH2CH3

F

N

NH

N

HO3SH2C

OH

N

N N

N NH

CH3 HO3S 53 Figure 19. Synthesis of a reactive disazo dye from 2,4,6-trifluorotriazine and 1,4-diphenylamine. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

2.3. Synthesis of Trisazo Dyes Synthesis of trisazo pyridone colorants is given in Figures 20 and 21. Synthesis of trisazo pyridone dye (56) is similar to the synthesis of disazo pyridone dye (51) given in Figure 18. Here, diazonium salt obtained from substitute aniline (47) is coupled with tripyridone (55). Tripyridone was prepared from tris(aminoethyl)amine (54), ethyl cyanoacetate (49) and ecetoacetic ester [78]. The obtained trisazo azo pyridone dye is used in yellow hot-melt inks.

174


CH3(CH2)17OH 45

+

O

2. NSA, 0-5 oC

47

CN

46 H HO

+ CNCH2COOCH2CH3 49

COO(CH2)17CH3

CH3

O

N(CH3CH2NH2)3 54

N2

1. CH3COOH

COO(CH2)17CH3

O N

+

NH2

100-150 oC

N

O

CH2CH2

1. 150 oC

CH2CH2

2. AAE, piperazine, DMF, 120 oC 3. H2O, HNO3, CH3OH

HO

N

N CH2CH2

O O

N

OH

CN CH3

NC CH3

55

1. H2O, NaOH, CH3COONa, iPrOH 2.

CH3 CN

N N CH3(CH2)17OOC

HO

N

O

CH2CH2 CH2CH2 HO

N

N CH2CH2

O O

N

N

OH

CN

N CH3

NC

N

COO(CH2)17CH3

N

CH3 COO(CH2)17CH3 56

Figure 20. Synthesis of trisazo pyridone dye from tripyridone. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

The trisazo pyridone dye can be prepared using the procedure presented in Figure 21. First, triazine derivate (58) is prepared from 2,4-diaminobenzensulfonic acid (57) i 2,4,6trichlorotriazine (26). The obtained intermediate (58) is then diazotized and coupled with pyridone (59). Trisazo pyridone dye (60) is used for dyeing poliamide fibers such as nylon 6 [79].

175

History, Synthesis and Properties of Azo Pyridone Dyes SO3H NH2 Cl

SO3H NH2 3

N

+ Cl

NH2

NH

N N

N

Cl

26

H2 N

N H

N H N

N

57

58

HO3S

SO3H NH2 1. NaNO2, HCl, H2O, 0-5 oC CH3 CN

2. NaOH, pH=6, HO

N

O

CH2CH3

59

CN H 3C

O

SO3H

N

N N

CH2CH3

OH CN

CH3CH2

NH

CH3

O N

N

N OH

N

N H

N N

H N

HO3S

SO3H N HO CH3CH2

N CH3

N

CN O

60

Figure 21. Synthesis of trisazo pyridone dye from 2,4,6-trichlorotriazine. (Reproduced from Hemijska Industrija Journal with permission by Association of Chemical Engineers of Serbia).

3. PROPERTIES 3.1. Fastness A number of authors have studied the fastness properties of azo pyridone dyes on different materials [43,47-49,51,65,66,68,80]. For example, Helal have published the synthesis of monoazo pyridone dyes given in Figure 13 [81]. This azo dyes were mono and disubstituted on arylazo component, and pyridones were 3-cyano-6-hydroxy-4,6-dimethyl-2-

176


pyridone or 3-cyano-6-hydroxy-4-methyl-6-phenyl-2-pyridone. The synthesised dyes were used to dye polyamide and polyester fabrics, and the color characteristics of the dyed fabrics varied due to the difference in the nature of substituents present on the dye molecules. The study revealed that the synthesised compounds, on polyester and polyamide fabrics, have high color strength, good wash fastness, good rub fastness, good perspiration fastness as well as good light fastness. Dyes from 3-cyano-6-hydroxy-4-methyl-6-phenyl-2-pyridone showed better fastness than dyes from 3-cyano-6-hydroxy-4,6-dimethyl-2-pyridone. Wang and Wang have studied the photofading kinetics of 5-(4- and 2-substituted arylazo)-5-cyano-2-hydroxy-4-methyl-6-pyridone dyes in amide solvents (DMF, HCONH2, and AcNMe2) and n-hexane [82]. It was established that a fair linear correlation existed between the observed rate constant and the free energies of transfer, suggesting the possibility that the photofading rate increased with increasing solvation of dyes. The rate was increased by the presence of two electron-withdrawing substituents (NO2 and Cl) on the benzene ring. The same authors have also studied photostability of 3-(mono- and disubstituted arylazo)-5cyano-2-hydroxy-4-methyl-6-pyridones in N,N-dimethylformamide [83]. Photodegradation was observed when dyes were irradiated by 254 nm light. It was established that the primary photochemical reaction with pyridone azo dyes involved hydrogen abstraction from the amide solvent. Also, it was found that the simultaneous presence of two electron-withdrawing substituents in diazo component of dyes caused a bathochromic effect and an increase of fading rate, while introduction of a alkylol group to coupling component resulted in hypsochromic shifts and in decrease of fading rate. In addition, Wang and Wang [84] applied synthesized monoazo pyridone dyes to polyester fabrics and studied dyeing properties, fastness of dyed fabrics, fading rate of the dyes, and their color parameters. They found out that electron-withdrawing substituents on aniline increased the photostability and improved the sublimation fastness of the azo dyes on polyester, while the β-hydroxyethyl group increased the fading rate. When the dye had a 1st-order fading rate curve, its light fastness was very low. In another work, a yellow disperse azo dye was synthesized from 2,6-dichloro-4nitroaniline and 3-cyano-6-hydroxy-1,4-dimethyl-2-pyridone and its dyeing, fastness, and photodegradation behavior on polyester fabric was investigated. It was found that the buildup and light fastness of the dye derived from pyridone was not good [85]. Introduction of various substituents can have different impact on dye properties. So when in dyes presented in Figure 22 a long perfluoroalkyl group was introduced a lowered film-forming ability and sensitivity but good photostability was achieved [86]. When 5-(2-benzothiazolylazo)-3cyano-1-ethyl-6-hydroxy-4-methyl-2-pyridone was compared to other asymmetrical and symmetrical bis(hetaryl)azo dyes it was found that only the pyridone derivative showed remarkable difference of decomposition temperature [87]. R3

R2

CN

O

N N

N HO

R1

61

Figure 22. Azo pyridone dyes with good photostability (R1 = H, Me, C3H7, C4H9, C6H13, C8H17, Ph; R2 = Me, CF3; R3 = CF3, C4F9, C6F13, C8F17).


177

Besides direct photodegradation, photocatalytic degradation of 3-cyano-6-hydroxy-4methyl-5-(4-sulphophenylazo)-2-pyridone in the presence of commercial TiO2 (Degussa P25), in aqueous solutions by simulated sunlight was studied [88]. It was found that the optimal catalyst concentration was 1.0 g dm–3. Concerning the initial dye concentration, it was observed that the increase in the initial dye concentration lead to decrease in photodegradation. The photodegradation is favored in acidic and basic media. Measurement of the total organic compound loss during the reaction showed that under investigated conditions (dye concentration 20 mg dm–3, catalyst concentration 1 g dm–3) almost complete dye mineralization occurred within 240 min. Results indicate that 54% of total organic compound remained when 100% of the dye was decolorized. Further optimization showed that after 240 min, the TOC loss was larger than 90%, revealing that the dye could be efficiently demineralized using TiO2 photocatalytic degradation [89].

3.2. Tautomerism A number of studies can be found in literature in which substituent and/or solvents effects were discussed in a series of arylazo 177yridines. So, dyes derived from 3-cyano-6-hydroxy4-methyl-2-pyridone [90,91], 3-amino-5-cyano-1-ethyl-6-hydroxy-4-methyl-2-pyridone [92], 4-amino-6-hydroxy-2-pyridones, 4,6-diamino-3-cyano-2-pyridone and 2,4-diamino-3-cyano6-pyridone [93], 5-(2-pyrido-5-yl)azo-thiophene derivatives [94], 4-(p-substituted) phenyl-2(2-pyrido-5-yl)azo-thiazole derivatives [95], 5-(arylazo)-3-cyano-4-methyl-6-methyl/phenyl2-pyridinones [81] and 1-butyl-3-cyano-6-hydroxy-4-methyl-2-pyridone [96] were studied among others. In these studies, often azo-hydrazone tautomerism was investigated. Thus, three series of dyes were prepared by coupling diazonium salts to 2-(ethylthio) and 2(butylthio)-4,6-diaminopyrimidine as well as to 3-cyano-6-hydroxy-1,4-dimethyl-2-pyridone. IR spectra and visible absorption spectroscopy indicated that the arylazopyrimidines existed in the azo tautomeric form, while the 177yridine dyes existed as hydrazones [97]. Also, absorption spectra of ten 5-(4-substituted arylazo)-3-cyano-6-hydroxy-4-methyl-2-pyridones have been recorded in fifteen solvents in the range 200-600 nm. Besides the effects of the substituents on the absorption spectra and the effects of solvent polarity and solvent/solute hydrogen bonding interactions, azo-hydrazone tautomerism (Figure 23, X = OH, OCH3, CH3, C2H5, H, Cl, Br, I, COOH, NO2) was studied and it was concluded that equilibrium depends on the substituents as well as the solvents [16]. The significant role of substituent effects on azo-hydrazone tautomerism was observed since the azo group is stabilized by the more electron-donating substituents, while an electron-accepting group stabilizes the hydrazone form. This is in accordance with canonical structures of hydrazone and azo form of these dyes (Figure 23, structures 5 and 6). It was also shown that 5-(substituted arylazo)-3-cyano-6hydroxy-4-methyl-2-pyridones exist in solid and in DMSO-d6 in hydrazone form, while in solvents there is an azo-hydrazon equilibrium [16,98]. Song et al. [99] prepared azo dyes from 5-amino-3-cyano-1-ethyl-6-hydroxy-4-methyl-2-piridone as diazo component and find that dyes exist in solid in hydrazone form, while in solvents there is azo-hydrazon equilibrium. Ertan I Gurkan [90] have concluded that azo 177yridine dyes obtained from 3-cyano-6hydroxy-4-methyl-2-pyridone and substituted anilines exist in solid in hydrazone form as well as in CF3COOD/CDCl3 mixture. When NMR spectra of 177yridine azo dyes obtained from 1-

178


alkyl-3-cyano-6-hydroxy-4-methyl-2-pyridone were recorded in CDCl3 and DMSO-d6 it was also confirmed that dyes exist in hydrazone form [100]. Cheng et al. [101] have shown earlier that arylazo 178yridine dyes prepared from 3-cyano-6-hydroxy-1,4-dimethyl-2-pyridone exist in hydrazone form. Generally, arylazo 178yridine dyes have different color in solutions of different pH. Color change is caused by the presence of acidic hydrogen. In acidic and neutral solutions arylazo 178yridine dyes are dominantly in hydrazon form and in basic solution as an azo anion [102-104]. It was shown that hydrazon-azo anion equilibrium exists in solutions according to UV-vis spectra [105]. Thiadiazolazopyridones easily dissociate in polar solvents and proton-accepting solvents (ethanol, dimethylformamide, dymethyl sulfoxide, pyridine) and in these solvents dyes are in azo anion form (Figure 23, structure 3).

- .. X

.. : +H O N .. N

H

+

N O

X

.. H O .. _ .. N .. N ..

CN

H3C

H N O CN

H 3C (6)

(5)

.. H :O

X

H

.. N .. N

N O

X

.. H O .. .. N .. N

CN

H 3C

X

.. N .. .. N

-

H

+

OH

H N O

(2)

CN

(4)

.. :O

H 3C

O

H 3C

(1)

OH

H N

CN

X

H

+

.. :O .. .. N .. N H 3C (3)

H N O CN

Figure 23. The equilibrium between hydrazone form (1) and azo form (2) of 5-(4-substituted arylazo)3-cyano-6-hydroxy-4-methyl-2-pyridones, azo (3) and hydrazone anion form (4) and canonical structures (5) and (6).


179

In proton-donating solvents (chloroform and glacial acetic acid) dyes are dominantly in hydrazon form, while in acetone, cyclohexanone benzene there is equilibrium between these two forms. Hydrazon form is dominant in all solvents in substituted phenylazo 179yridines. In organic solvent-water mixture, by the addition of a base, there is an equilibrium between hydroxyl anion and hydroxyazo form (Figure 23, structures 3 and 4) [106]. Azo-hydrazone tautomerism was also studied by crystallography. So 2-(2methoxyethoxy)ethyl 4-[(5-cyano-1-ethyl-4-methyl-2,6-dioxo-1,2,3,6-tetrahydropyridin-3ylidene)hydrazino]benzoate crystallizes in the hydrazone form [107]. The same conclusion was obtained for C.I. Disperse Yellow 114 (5-cyano-2-hydroxy-1,4-dimethyl-6-pyridone component) [108]. C.I. Disperse Yellow 119 and C.I. Disperse Yellow 211 (pyridine-3cyano-1-ethyl-4-methyl-2,6-dione backbone) (Figure 10) also crystallize in the hydrazone form [109]. Besides azo-hydrazon tautomerism, pyridone azo dyes exibit another type of tautomerism, naimely 2-pyridone/2-hydroxypyridine. Examples of such tautomerism were found in 5-(3- and 4-substituted arylazo)-3-cyano-4,6-dimethyl-2-pyridones and 3-cyano-4,6diphenyl-5-(3- and 4-substituted phenylazo)-2-pyridones [60,110,111]. It was found that 2pyridone/2-hydroxypiridine tautomeric equilibration depends on the substituents as well as on the solvents. On the basis of the above results, it may be concluded that the azo colorants containing hydroxyl and amino substituents ortho or para to the azo groups can in principle exist as mixtures of azo and hydazone tautomers. While azo–hydrazone tautomerism is quite interesting from a theoretical viewpoint, it is also important from a practical standpoint because the two tautomers have different technical properties and dyeing performances [103,112].

CONCLUSION Arylazo pyridone dyes were intensively synthesized from the early 1970s and first used as disperse dyes for polyesters. The synthesis of these dyes is based on coupling reaction of various diazonium salts with pyridones or on cyclization of azo compound with cyanoacetamide or substituted cyanoacetamide to obtaine pyridone moity. Due to variety in the synthesis of amino as well as pyridone parts of dye, a large number of arylazo pyridone dyes were prepared. These dyes give, usually, yellow shades with generally good fastness. Besides disperse dyes, basic and reactive dyes were prepared. Arylazo pyridone dyes were also used in printing inks, hot-melt inks and in phase change inks as well as in the production of color filters. Arylazo pyridone dyes can show azo–hydrazone tautomerism which is important from a practical point of view because the two tautomers have different technical properties and dyeing performances. The azo–hydrazone equilibrium depends on the substituents as well as the solvents used. The significant role of substituent effects on azo-hydrazone tautomerism was observed since the azo group is stabilized by the more electron-donating substituents, while an electron-accepting group stabilizes the hydrazone form. In acidic and neutral solutions arylazo pyridone dyes are dominantly in hydrazon form and in basic solutions as an azo anion.

180


ACKNOWLEDGMENTS The authors are grateful to the Ministry of Education, Science and Technological Development for financial assistance (project 172013).

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[95] Yen, M.S., Wang, I.J. (2004). A facile syntheses and absorption characteristics of some monoazo dyes in bis-heterocyclic aromatic systems part II: syntheses of 4-(psubstituted) phenyl-2-(2-pyrido-5-yl and 5-pyrazolo-4-yl)azo-thiazole derivatives. Dyes Pigm. 63, 1-9. [96] Ertan, N., Eyduran, F. (1995). The synthesis of some hetarylazopyridone dyes and solvent effects on their absorption spectra. Dyes Pigm. 27, 313-320. [97] Cheng, L., Chen, X., Gao, K., Hu, J., Griffiths, J. (1986). Color and constitution of azo dyes derived from 2-thioalkyl-4,6-diaminopyrimidines and 3-cyano-1,4-dimethyl-6hydroxy-2-pyridone as coupling components. Dyes Pigm. 7, 373-388. [98] Alimmari, A., Mijin, D., Vukićević, R., Božić, B., Valentić, N., Vitnik, V., Vitnik, Ž., Ušćumlić, G. (2012). Synthesis, structure and solvatochromic properties of some novel 5- arylazo-6-hydroxy-4-phenyl-3-cyano-2-pyridone dyes. Chem. Centr. J. 6, 1-8. [99] Song, H., Chen, K., Tian, H. (2002). Synthesis of novel dyes derived from 1-ethyl-3cyano-6-hydroxy-4-methyl-5-amino-2-pyridone. Dyes Pigm. 53, 257-262. [100] Peng, Q., Li, M., Gao, K., Cheng, L. (1990). Hydrazone-azo tautomerism of pyridone azo dyes: Part 1- NMR spectra of tautomers. Dyes Pigm. 14, 89-99. [101] Cheng, L., Chen, X., Gao, K., Hu, J., Griffiths, J. (1986). Colour and constitution of azo dyes derived from 2-thioalkyl-4,6-diaminopyrimidines and 3-cyano-6-hydroxy-2pyridone as coupling components. Dyes Pigm. 7, 373-388. [102] Peng, Q., Li, M., Gao, K., Cheng, L. (1991). Hydrazone-azo tautomerism of pyridone azo dyes. Part II: Relationship between structure and pH values. Dyes Pigm. 15, 263274. [103] Trotter, P.J., (1977). Azo dye tautomeric structures determined by Laser-Raman spectroscopy. Appl. Spectroscopy 31, 30-35. [104] Saito, Y., Kim, B.K., Machida, K., Uno, T. (1974). Resonance Raman spectra of acidbase indicators. II. Hydroxyarylazobenzene derivatives. Bull. Chem. Soc. Jpn. 47, 21112114. [105] Peng, Q., Li, M., Gao, K., Cheng, L. (1992). Hydrazone-azo tautomerism of pyridone azo dyes. Part III- Effect of dye structure and solvents on the dissociation of pyridone azo dyes. Dyes Pigm. 18, 271-286. [106] Lyčka, A., Hensen, P.E. (1984). Deuterium isotope effects on 13C and 15N nuclear shielding in o-hydroxyazo dyes. Org. Magn. Reson. 22, 569-572. [107] Qian, H.F., Wei, H. (2006). An azo dye molecule having a pyridine-2,6-dione backbone. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. C62, o62-o64, C.A. 145/2001 177596. [108] Huang, W., Qian, H. (2008). Structural characterization of C.I. Disperse Yellow 114. Dyes Pigm. 77, 446-450. [109] Huang, W. (2008). Structural and computational studies of azo dyes in the hydrazone form having the same pyridine-2,6-dione component (II): C.I. Disperse Yellow 119 and C.I. Disperse Yellow 211. Dyes Pigm. 79, 69-75. [110] Mijin, D.Ž., Ušćumlić, G.S., Perišić-Janjić, N.U., Valentić, N.V. (2006). Substituent and solvent effects on the UV/vis absorption spectra of 5-(3- and 4-substituted arylazo)4,6-dimethyl-3-cyano-2-pyridones. Chem. Phys. Lett. 418, 223-229. [111] Alimmari, A.S., Marinković, A.D., Mijin, D.Ž., Valentić, N.V., Todorović, N., Ušćumlić, G.S. (2010). Synthesis, structure and solvatochromic properties of 3-cyano-

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Chapter 7

SMART TEXTILES AND THE EFFECTIVE USES OF PHOTOCHROMIC, THERMOCHROMIC, IONOCHROMIC AND ELECTROCHROMIC MOLECULAR SWITCHES Shah M. Reduwan Billah* Department of Chemistry, Durham University, Durham, UK and The School of Textiles and Design, Heriot-Watt University, Galashiels, UK

ABSTRACT Smart textiles have been successful to draw very high levels of active current research interests within different areas of research on textiles and related fields. The wide range of application potentials of smart textiles made them a hub for a variety of interdisciplinary research fields. There are various ways for producing smart textiles; one of the methods is to incorporate environmentally stimuli responsive switches which can sense the surrounding environment. These types of stimuli-responsive smart textiles have numerous application potentials, including, safety, security, comfort, fashion, health care, remote sensing, along with a variety of other biomedical and intelligent applications. This current chapter briefly focuses on different aspects of smart textiles and the method of production of these textiles using different types of stimuli-responsive molecular switches, such as, photochromic, thermochromic, ionochromic and electrochromic molecular switches. As the successful incorporation of these stimuli-responsive switches into smart textiles needs certain level of basic understandings on the nature of these molecular switches, a brief discussion is also included to highlight different features on different types of stimuli-responsive systems and their mode of application for producing high performance stimuli-responsive smart textiles for a variety of applications.

Keywords: Smart textiles, molecular switches, photochromic switches, thermochromic switches, ionochromic switches, electrochromic switches *

Address for correspondence: Dr. Shah M. Reduwan Billah, 7 Laurel Grove, Galashiels TD1 2LA, Scotland, UK, Email: [email protected] or [email protected].

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INTRODUCTION In last two decades, there have been many multi-disciplinary approaches in textile research to incorporate multi-level of functionalities along with other distinct features generally expected from usual as well as special types of clothing based on smart and intelligent textiles along with other useful features sometimes expected from ordinary textiles. With the advancements in different related technologies (such as, nanotechnology, information technology, biotechnology, flexible display techniques, etc.) now there are scopes for new possibilities to enhance textiles with a variety of new functionalities. Some of these possibilities including the production of multifunctional new fibre structures, composite materials and coatings at the nano and micro levels to the visible integration of wearable electronic assemblies into clothing system. Currently, there is a high level of convergence of different sophisticated technologies, for example, biochemistry, polymer chemistry and computer processor based techniques which are miniaturised to produce ‘lab-on-achip’ diagnostics, and new forms of textile sensors, actuators and other components that are now available. As a result, many high quality previous efforts to produce high performance functional and intuitively wearable computing systems based on textiles are slowly becoming a practical reality. [1-10] Smart textiles incorporated with different functionalities have many uses in a variety of fields; some of them are widely used in the fields of biomedical or healthcare applications. For more specific information, some of the important fields of applications are briefly summarized here:(a) medical textiles (in general), (b) smart wound-care materials, (c) textilebased drug release systems, (d) phase change and shape memory based smart textiles for different applications, (e) textile based sensors for healthcare, (f) smart medical textiles for particular types of patient (e.g., intelligent garments for pre-hospital emergency care), (g) smart medical textiles in rehabilitation, (h) smart medical textiles for monitoring pregnancy, (i) smart textiles for monitoring children in hospital, (j) wearable textiles for rehabilitation of disabled patients using pneumatic systems, (k) wearable assistants for mobile health monitoring, (l) smart medical textiles for monitoring patients with heart conditions, and (m) textiles in surgical implants, tissue engineering and wound care. [11-22]

Advanced Materials Used in Different Technologies for Smart or Intelligent Textiles Current trends in the manufacture of smart or intelligent textiles involve a variety of established and also emerging technologies with different level of adaptations in different areas. As a result, now-a-days it is extremely important to have meaningful interdisciplinary collaboration for high quality product development. For example, the electronics industry is concentrating on required level of knowledge on different types of textiles (where electronics are increasingly incorporated into clothing systems to produce specific products) to solve problems in wearable electronics. So, it is important to have fundamental knowledge on standard commercial textile production methods along with the knowledge of wearable electronics for an effective adaptation of new developments in both electronics and in textile

Smart Textiles and the Effective Uses of Photochromic, Thermochromic …

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to produce high quality textile based electronics for specific applications in different target areas within affordable costs. [23] In recent years, different materialshave been incorporated into the structure of textile or related materials used in the clothing systems to serve different purposes, some other advanced materials and techniques have also been used to improve the performance of smart (to some cases also for biomedical) textiles, some of the most important materials and method are – (a) phase change materials, (b) photochromic materials, (c) thermochromic materials, (d) shape memory alloys and polymers, (e) conductive fibres and yarns – metals, wires and conductive polymers, (f) quantum tunnelling composites for switching devices, (g) piezoelectric resistance, (h) organic or plastic electronics, (i) biomaterials, (j) light-emitting polymers, (k) light-emitting diodes, (l) fibre optics, (m) photovoltaic and solar cells, (n) photoluminescence, (o) holography, (p) plasma technologies, (q) nano technologies for fibre and fabric coating, (r) micro encapsulation for therapy delivery, (s) global positioning and wireless communications, (t) radio frequency identification (RFID) tags, and (u) microelectronic mechanical systems (MEMS). [24-27] Some of the selected basic features of smart textiles produced by using certain types of molecular switches are briefly covered in this chapter.

SMART TEXTILES It is a new field in textile research with no universally accepted definition, however, different terms, such as ‘intelligent’, ‘smart’ or ‘active’ materials and textiles are mostly used in the expression of different aspects of this types of textile which are sometimes inter changeable and also obviously not confined within the very frame of these different words. With the progress of active research in this area there have been different approaches to define these words into moreacceptable forms. Here is an attempt to show the differences in different definitions which have been used by some famous scholars of smart textiles, some of the selected definitions are: a) ‘Smart materials and structures can be defined as the materials and structures that sense and react to environmental conditions or stimuli, such as those from mechanical, thermal, chemical, electrical, magnetic or other sources’ – a definition by Tao. Then she extended her approach by adding divisions ofsmart materials into different groups, such as- (i) passive smart (sensitive to environmental conditions or stimuli), (ii) active smart (sense and react to the conditions or stimuli) and (iii) very smart materials (sense, react and adapt themselves accordingly); [27] b) ‘smart is a term used to define a material that reacts in a particular way when exposed to stimuli such as environmental changes, for example, temperature or electronic currents’ – Baurley adopted this to define smart textiles; [11] c) ‘smart textiles’ utilise integrated or applied electronics such as sensors, actuators, etc., whereas ‘intelligent textiles’ produce predictable effects and phenomena by interacting with the environment and the wearer; [28] d) ‘textiles with integrated electronics and microsystems which could be in clothes and in technical textiles’ are smart textiles as defined by Strese, et al. They further define

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Shah M. Reduwan Billah three levels of integration but without specific names, such as, (i) solutions adapted to clothes, e.g., mobile phone in a pocket, (ii) electronics and micro systems integrated into clothes or textiles withconnectable modules (e.g., with textile conductors) and (iii) functions integrated into the textile via direct insertion into textile fibres (e.g., woven displays); [29] e) ‘fabrics and textiles that cognitively respond or interact to environmental or electrical stimuli’ – a definition endorsed by the Venture Development Corporation, a USAbased technology market research company (on the definition of ‘smart fabrics and intelligent textiles’ in their report of January 2005). They also concentrate on applications that utilise electrical stimuli further outline these responses as – (i) conducting, transferring or distributing various properties through the material or across the material’s membrane; such properties include electrical current, light energy, molecular or particulate matter, and thermal energy and (ii) changing physical characteristics or phase, such as colour, permeability, porosity, rigidity, shape, size (VDC 2005); [30] f) ‘smart materials’ are ‘materials that form part of a smart structural system that has capability to sense its environment and the effects thereof, and if truly smart, to respond to that external stimulus via an active control mechanism’ this is a definition given by the Foresight Smart Materials taskforce, a UK government initiative, which recently reviewed the potential for wealth creation and strategies for UK industry and academia, which concludes that competitive advantage will depend on products with increasing levels of functionality. In this report ‘degrees of smartness’ is defined for different materials which can be transposed to a textile system. The Foresight report also includes that the terms ‘smart’, ‘functional’, ‘multifunctional’, and ‘intelligent’ are often used interchangeably. In this context this is reasonable, if confusing, for the first three terms but the last certainly suggests a degree of consciousness that does not exist in any non-biological system. Additionally, there is arguably no such thing as a ‘smart material’– only materials that exhibit interesting intrinsic characteristics which can be exploited within systems or structures that, in turn, can exhibit ‘smart’ behaviour; [31] g) ‘smart textiles’ are an interesting class of electronic and photonic textiles which are capable of monitoring their own ‘health’ conditions and structural behaviour, as well as sensing external environmental conditions and sending the information to other locations,a definition given by El-Sherif. [16, 27]

As we see it is not easy to categories the stimuli-responsive materials based textiles whether they are smart or intelligent or smart and intelligent textiles. Because, it is possible to use some members of photochromic, thermochromic, ionochromic and almost all members of electrochromic switches to produce different types of colour change (both passive and active types) when used in different suitable systems or device constructions based on textile media. In depth discussion on the device constructions using these switches is beyond the scope of current chapter, as a result it only focuses on the general aspects of the nature of these switches and also on their uses in textiles for smart or intelligent applications to serve different purposes. This chapter also concentrates on different aspects of certain types of selective environmental stimuli-responsive materials or more simply selective stimuliresponsive molecular switches (such as, photochromic, thermochromic, ionochromic and


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electrochromic material based stimuli responsive switches) and their potential uses in the production of smart textiles. Before going to in-depth discussion on molecular switches a few related aspects of smart textiles in smart clothing system and smart clothing design are briefly discussed here.

Smart Textiles in Smart Clothing System Smart textiles are mainly focused for their important inclusion during smart clothing design to serve certain specific purposes along with usually expected particular aspects from some distinctive clothing which is usually designed to fulfil required desired features. Smart clothing, a new type of apparel, usually uses a fusion technology to combine electronic engineering and apparel design. It requires a combination of several generically distinctive features, for examples - electronic efficiency, electrical safety, physical comfort and aesthetics of a garment. As a result, the multi-faceted factors are of significant importance during smart clothing design. Sometimes there are practical difficulties for the apparel designers to avoid confronting fatal limitations in reflecting their vision into the design process when they apply the traditional apparel design process to the creation of an apparel line of smart clothing. In some cases one of the main reasons for this situation is simply because many of the steps for a very novel design may have never been used before even when the multivariate consideration is not uncommon to be included in the traditional design process. For successful smart clothing design it is a prerequisite to modify the traditional apparel design process to combine some appropriate steps for interdisciplinary creation. [712, 27]

Variables during the Inclusion of Smart Textiles in Smart Clothing Design In industrial design, a design refers to a process that usually starts from an analysis of design requirements and ends with the synthesis into some visualized forms. In this process design requirements are devised by the expectations held by consumers and manufacturers toward the object to be designed in the contexts of aesthetics, functionality, ergonomics, safety, and price. These fundamental design requirements usually modify different features to producea harmonious reflection in most of the high quality designed products. In many times, there are critical changes in the design process when it requires accommodating new design features to fulfil certain specific needs. The territory of design needs for apparel in the case of smart clothing sometimes needs widening to include new categories, for example, embedding digital functions or the interaction between parts of digital function and human body. In the field of smart clothing, some researchers have analysed design needs (or requirements) according to their varying definitions. There are a number of analyses on design requirements in the field of smart clothing when we see the varying nature of these design aspects. There are many considerations during the design of smart clothing, however, some of the important aspects for the design include – (a) functionality, (b) connectability, (c) durability, (d) maintainability, (e) usability in combat (especially, for defence uses), (f) manufacturability, (g) wearability, and also (h) affordability. [27] In another point of view, thermal and moisture management, along with other aspects, for examples – (a) mobility, (b) flexibility, (c) sizing

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and fit, (d) durability, and (e) garment care are of significant importance. [32] Additionally, smart clothing is also defined as digital clothing and categorized the requirements into different features, some of which include – (i) durability, (ii) easy care, (iii) comfort, (iv) safety and also (v) aesthetic satisfaction. [33] As a result when we think about safety, fashion, warning system along with other different features of smart clothing, it is sometime possible to attain these features by the judicious utilisation of molecular switches in terms of their applications on textiles using dyeing, printing (both screen printing and inkjet printing), coating, dipping techniques to produce smart textiles. In this case, one of their main goals is to incorporate into smart clothing systems to serve specific desired purposes. In a series of publications we have shown that molecular switches have many important application potentials for smart textile applications. So, in successive sections different features of molecular switches within the clear boundary of the main objectives of the chapter are briefly discussed here.

MOLECULAR SWITCHES A molecular switch is a switch which can exist in more than one (usually two or more) stable states (more specifically metastable states) where it shows significant difference in physical, chemical or biological properties. These properties can be reversibly shifted between these metastable states in response to external stimuli, such as, change in pH, light, temperature, electrical current or potential. As for instance, pH indicators are well-known examples of synthetic molecular switches which show distinct colours as a function of a change in pH (for detail classification of molecular switches, see Table 2). As a result, a simple molecular switch has a potential (when incorporated in a complex molecular system) to act as a trigger to turn off and on important physical, chemical or biological properties of the system, such as surface wettability, polymer elasticity, host-guest recognition, catalysis, enzyme activity, fluorescence, neural activity and membrane activity for intracellular drug delivery. [33] However, for this current chapter a particular emphasis is given on the nature of colour changes of a molecular switch when exposed to different environmental stimuli (such as, light, pH, temperature, electrical potential, etc.) with a specific aim to integrate the system in terms of textile applications for environmental sensing (more specifically producing a notable colour change) for a variety of purposes. In this context, a very brief discussion will highlight selected fundamental mechanisms of colour production using different systems.

FUNDAMENTAL MECHANISM OF COLOUR PRODUCTION AND THE NATURE OF MOLECULAR SWITCHES Our eyes are stimulated with rays of light with wavelengths ranging from the ultra-violet to infra-red regions of electromagnetic wave spectrum, which is popularly termed as the visible region. However, within this visible region, different wavelength ranges give rise to different colours. In collective term they produce a white effect which is usually composed of seven basic colours – violet, indigo, blue, green, yellow, orange and red. The production of


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colour can be divided into five broad fundamental mechanisms which are summarized in Table 1. [34] Table 1. Major fundamental mechanisms of colour production Effects Vibrations and excitations Ligand field effects Transitions between molecular orbitals

Transitions between energy bands Geometrical and physical optics

Causes and examples External heat or energy transfer within molecules (such as, in vapour lamps, incandescence and a few lasers) Usually caused by single electrons in ions and complexes of transition metals (for examples, in phosphorescence and lasers) This is usually observed from dyes and pigments of both organic and inorganic origin, and also from some fluorescent molecules (e.g., dyes, pigments, etc.) Usually seen in metals and semi-conductors (such as, in WO3, TiO2, etc.) Observed due to the interference phenomenon, iridescence diffraction and liquid crystals (such as, photonic crystals, liquid crystals)

Different types of molecular switches show colour change due to a number of reasons(detail discussion on the mechanism is beyond the scope of the chapter), some of the important reasons are, change in conjugation in molecular structures (for example, spirooxazine, spiropyan, naphthopyran based photochromic molecular switches, when exposed to certain stimuli, such as, light and heat they show change in conjugation when exposed to these stimuli and show the colour change), vibrations and excitations, transitions between molecular orbitals, transitions between energy bands, change in geometrical and physical properties. Molecular switches show their presence in different metastable state when exposed to different environmental stimuli, so they can also be term as chromic switches which is briefly covered in next sections.

Chromism from the Colour Change Behaviours of Molecular Switches Chromism refers to colour change phenomena of different substances and the materials show this behaviour are usually called chromic materials. In general terms, chromic phenomena are related to different processes that cause reversible colour change, absorption and reflection of light, absorption of energy and emission of light, absorption of light and energy transfer or a conversion and manipulation of light. [34] It is a general observation that a reversible colour change is usually observed when there is a change of the electronic state, especially involving pi-electrons (π-electrons), physical change of the material or rearrangement of molecules in a matrix. In all these cases, these type of colour changes are stimuli-responsive which means these materials show a distinctive colour change when they are exposed to a suitable stimulus or even sometimes responsive to a combination of different stimuli (such as, light, heat, pH, gas, time, sound, mechanical force, electrical force, magnetic force, etc.). A brief classification of selective chromic materials is shown in Table 2.

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Shah M. Reduwan Billah Table 2. Different major types of molecular switches (or materials)

Materials or switches Photochromic

Thermochromic

Usual responsive stimulus Light (and heat in some cases) Temperature

Ionochromic/Halochromic pH, ions Electrochromic

Electrical field

Usual nature of changes Colour, geometric shape, dipole moment, refractive index, etc. Colour, geometric shape, refractive index, etc. Colour, producing different ionic form Colour, producing different ionic form

Example Spiropyrans, spirooxazines, diarylethenes, chromenes, fulgides Spirolactones, bianthrones, etc. Phenol Red, Cresol Red, Bromocresol Green, etc. Viologens

As already stated previously, there are many uses of different molecular switches in the production of smart textiles for a variety of applications. Among different molecular switches photochromic, thermochromic, ionochromic and electrochromic switches are most frequently used in variety of smart textiles. So, most discussion on this chapter will concentrate on these four types of molecular switches along with their possible effective utilisation on smart textile productions.

PHOTOCHROMIC MOLECULAR SWITCHES AND THEIR APPLICATIONS IN SMART TEXTILES A photochromic molecular switch is a photochromic dye or pigment or material which changes colour reversibly under the effect of ultra-violet irradiation. Photochromic materials (especially, spirooxazines, spiropyrans, naphthopyrans, fulgides, diarylethenes) have attracted intensive current research interest due to their variety of applications including sun-screening, security printing and optical data storage. Photochromic dyes are commonly applied in a polymer matrix. There are numerous potential applications of photochromic dyes on textiles and leather to produce novelty or fashionable colour change design effects, intelligent textiles for sensing exposure to sunlight and other sources of UV light, in camouflage, for military purposes, and for security purposes such as in brand protection. Photochromism is a chemical phenomenon, in which a chemical species transforms reversibly from one form to another form under electromagnetic radiation. [35-45] The word photochromic originates from the Greek word phos (light) and chroma (colour). In 1950, Hirshbergh proposed to use the word ‘photochromism’ for light- induced colour changes in non-biological systems. [37] Photochromism may also be termed as a reversible change of a single compound between two molecular states that show different absorption or emission spectra under electromagnetic radiation. Photochromic materials show reversible transformation under photoexcitation between two forms A and B, absorbing photons at different wavelengths (λAmax, λBmax). Besides the different absorption spectra of the isomers, they also show different chemical and physical properties, such as refractive indices,

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dielectric constants, oxidation-reduction potential and geometrical structures. In addition, most photochromic systems are unimolecular as shown in Scheme 1.

Chemical species (λmax1)

A

External stimulus (hν1)

Removal of stimulus (or hν2)

Chemical species (λmax2)

B

Scheme 1. Transformation of chemical species in a unimolecular photochromic system.

Photochromism and its various aspects are used for variety of purposes. These applications can be classed into several general categories: 1) Applications depending on the colour change due to the molecular and electronic structures of the two species (A and B) and their corresponding absorption or emission spectra: (a) variable-transmission optical materials (such as photochromic ophthalmic lenses or camera filters), (b) fluid flow visualization, (c) optical information storage, (d) novelty items (toys, T-shirts), (e) authentication systems (security printing inks), (f) cosmetics. 2) Applications depending on the changes in the physical or chemical properties that occur along with the easily perceivable colour change at the time of photochromic reaction. Some examples of these properties are conductivity, refractive index, electrical moment, dielectric constant, chelate formation, ion dissociation, phase transitions, solubility and viscosity. 3) Potential applications using the physical and chemical changes due to the shift in the absorption maxima, such as, optoelectronic systems (modulated by photochromic pigments), reversible holographic systems, optical switches, optical information storage, photochemically switchable enzymatic systems, nonlinear optical devices. Among all of these potential applications, some of them are more demonstrably commercially successful (such as photochromic glasses, opto-electronic applications), some of them are gaining access into commercial markets (novelty items and security printing inks) or demonstrated to be useful (fluid flow visualization). [38-44] In the cases of printing these photochromic materials are commonly used in the form of microcapsules. Photochromic dyes can be applied on textiles using different techniques, including dyeing, printing (e.g., screen printing, inkjet printing), coating, dipping techniques for producing photo-responsive textile for a huge range of potential applications. [46-57] Different types of photochromic dyes can be used for producing photochromic textile based smart textiles for their various applications so a proper selection of photochromic dyes is a very important step.

Selection of Photochromic Dyes for Producing Photochromic Smart Textiles An effective selection of a photochromic dye and understanding its behaviour in different matrices is one of the most important issues relating to the photochromic phenomena of dyed,

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printed or coated photochromic textiles. One of the most important fundamental requirements for a photochromic dye to be used for dyeing, printing or coating of photochromic textiles is that the photochromic molecule (or switch) must have a photoisomerisable chromophore to show a clearly visible and reversible colour change for a long time. The molecule should have enough resistance to degradations (degradation due to oxidation, air, heat, light) during dyeing, printing, coating operations and it should not produce a clearly observable background colour (because for a pure photochromic dye, it should produce colourless dyed/printed/coated substrates). The behaviour of a photochromic molecule is analogous to a switch, for example, similar to a switch it has two states – on and off. If this rationale is applied to a textile substrate which is dyed with a photochromic spirooxazine dye, the coloured state under UV light can be considered as ‘on’ state and normal colourless state can be considered as ‘off’ state. There are many requirements to select a high quality photochromic dye or photochromic molecular switch suitable to be used for producing photochromic smart textiles and some of these requirements are - (i) the dipole moment of the dye and also its excited state or merocyanine structure which should exhibit significant difference between the ‘on’ and ‘off’ states, (ii) the thermal back reaction is sufficiently slow that the molecule can have a lasting effect to show an observable colour change in a dyed photochromic textile, (iii) very higher fatigue resistance or technical properties (such as, higher photostability, good affinity or adhesion properties), (iv) the colourless or the ground state (‘off’ form)on the dyed photochromic textile (before UV irradiation) contains no or very insignificant amounts of the colour after dyeing, printing or coatingand also (v) the relative simplicity to synthesize the photochromic dye or photochromic molecular switch.

The Ideal Behaviour of Textiles Dyed, Printed or Coated with a High Quality Photochromic Molecular Switch It is expected from a high-quality photochromic molecular switch (or simply photochromic dye) that it shows enough resistance to degradation, a quick colour change from a photochromic dyed, printed or coated textiles; retains its photochromic colour build up for a long time along with other high level of technical performances. The evaluation of photochromic colour build up and to enhance the photochromic life of the dyed, printed or coated photochromic textiles is very important to understand the nature of the photochromic dye. Additionally, the nature of the dyed, printed or coated photochromic substrates clearly is a function of a number of things, including, the nature of the dye or photochromic molecular switch, concentration, nature of the light source, time of UV irradiation, surrounding environments, nature of the matrices, the method used to apply photochromic switch on the substrates. So, it is highly recommended that dyeing, printing or coating techniques must be carefully adjusted to promote the nature of photochromic dyed substrates to show photochromic colour build up for a long time for practical useful applications. So, some important points of many additional features expected from a dyed, printed or coated photochromic textile are - good colour build up on exposure to UV light, a controlled fading behaviour (return to colourless state from a coloured state), producing a colourless background state after dyeing, printing or coating and also a long product life along with the retention of the colour changing performance for many cycles. [46-57]


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Photochromic Molecular Switches Relevant to Smart Textiles Some of the most important photochromic molecular switches relevant to smart textile applications are – (a) spirooxazines, (b) spiropyrans, (c) naphthopyrans, (d) diarylethenes, (e) fulgides, (f) fulgimides, (g) azulenes (dihydroindolyzenes) and some particular types of photochromic supra-molecular switches. The behaviour of spirooxazines, spiropyrans, naphthopyrans and diarylethenes basedmolecular switches are discussed in the chapter on ‘Inkjet printed photo-responsive textiles for conventional and high-tech applications’ by this author so in this section some unique features of these photochromic molecular switches will be selectively discussed (in successive sections on photochromic molecular switches) here.

Brief History of Selected Molecular Switches and Their Potential Applications in Smart Textile Production In 1960, Feyman introduced the concept of artificial molecular machine and also highlighted their different application potentials (such as, their uses in molecular devices). [58] Shinkai et al., at first synthesised molecular machines with having crown, azacrown ethers and azo groups in their structures. Azo group present in this system has the capability to photoisomerize to show reversible switching behaviour for inducing a conformational change, for example, Azacrown Acontains two crown ether linked to one another by an azobenzene hinge which is illustrated in Scheme 2. This system shows reversible change when irradiated UV light and then with visible light. [58, 59]

Scheme 2. One of the first examples of a molecular switch.

There is no report of using photochromic azacrown in textile coloration. Additionally, one of the main limitations of azobenzene based photochromic switches is some of them revert back to original state (from where they switched to another state on exposure to UV light) at room temperature and also at wavelength below 390 nm. As a result, there is no observable colour change from many of the azobenzene species when used on textile application. [60] However, spirooxazines, spiropyrans, naphthopyrans are suitable molecular switches for a variety of textile applications. [46-57] Diarylethenes and fulgides are important photochromic molecular switches which have high potential for textile applications. As a result a few aspects of diarylethenes and fulgide based selected photochromic molecular switches are described here. Usually, diarylethenes show photoisomerization and cyclization when exposed to UV irradiation and return to their original form after exposure to visible light. For example, diarylethene A is colourless (ring open form) in hexane solution before

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exposure to UV light, however, it retains a blue colour when irradiated with a UV light (at 313 nm) (Scheme 3). [61]

Scheme 3. The nature of photo-induced switching behaviour of diarylethene Afrom ring open form (colourless) to ring close form (coloured) to give a photochromic colour change.

It is important to note that generally the ring close form of a diarylethene is thermally stable and does not revert to the ring open form. Irie et al., concluded that this thermal stability is due to the low aromatic stabilization energy when the aryl groups are furanes, thiophenes or thiazole rings. [62] On the other hand, when the ring- close form of a diarylethene contains a pyrrole, indole or phenyl ring, it shows high aromatic stabilization energy and is therefore thermally unstable. [63]Scheme 4 shows the photochromic switching behaviour of diarylethene B (a pyrrole containing diarylethene) and itreverts back to its original colourless ring open form in a very short time (e.g., 37 seconds) at 25°C. Additionally, this thermal behavior is closely related to the aromatic stabilization energy of the aryl groups.

Scheme 4. Photochromic switching behaviour of a thermally unstable diarylethene B.

So, from this two examples (as in Schemes 3 and 4) it is clearly understood that diarylethene A is suitable for application to textiles while diarylethene B is not suitable for textile application because it will not show a desired stable and observable photochromic colour change since it starts to return to the original colourless state even at a temperature (25°C) very close to the room temperature.


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Diarylethene Based Photochromic Molecular Switches for Smart Textiles Different varieties of diarylethene based photochromic switches are now available. As mentioned above not all of them are suitable for producing stable photochromic colour change on textiles when targeted for smart textile applications. There are huge variety of approaches to produce photochromic diarylethenes using different techniques mainly focused on their application as memories and switches, [63] and one of them is based on host-guest interactions. For example, a crown ether in a diarylethene unit may participate in host-guest guest interaction to show photochromic switching behaviours as shown in Scheme 5. In this reaction, Takeshita showed that the ring open form of diarylethene C forms a sandwich complex with large metal ions. [64-66] This system have different applications and one of which is the active transport of molecules and metal ions that may be suitable for photoinduced drug delivery when incorporated with a suitable system and applied in the preparation of photo-responsive dyed, printed or coated textiles for smart textile based health care applications. Using the same logic as shown in Scheme 5, a glucose molecule can be captured and released by modified diarylethene bearing boronic acid moieties by using photoirradiation. [67]

Scheme 5. A conceptual demonstration of photoswitchable cesium ion tweezers (diarylethene C based on a diarylethene functionalised with crown ether) which acts like a tweezers where metal ions are controlled by light.

So far we have seen diarylethenes which show different types of thermal behaviours (such as some are thermally stable and some are unstable) and we have also seen the feasibility of using diarylethene based system for their potential applications in photocontrolled drug release when incorporated in different substrates (such, smart textiles and other suitable systems). Now we would like to focus on a few selected features of some particular types of diarylethenes, fulgides and couple of other selected members of photoinduced molecular switches which may be considered for smart textile applications apart from their usual applications in a variety of fields. Some diarylethenes are electrically responsive, for example diarylethene D shows electrically responsive behaviours (Scheme 6). [68,69] In

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this case, the two positively charged pyridinium ion moieties interact only weakly in the ringopen form (colourless state), this colourless state can be considered as ‘off state’.

Scheme 6. Control of the electron flow through photoisomerization of diarylethene Din this figure.

However, on the other hand, the two pyridinium ion groups in the ring close form (coloured state) this interaction is more strong due to the delocalization of pi-electrons producing a coloured form, so this state can be considered as ‘on state’. These types of systems are suitable for their potential uses as switchable molecular wires in which electron flow is controlled by light irradiation. This type of switch is also suitable for electrochromic display on smart textiles for a wide variety of applications.

Selection of Diarylethene Based Molecular Switches Most of the diarylethene based molecular switches are photo-responsive even when applied in textiles using dyeing, printing or coating process. In these cases, light acts as an attractive physical stimulus which can be easily used in various media with short response times. Among a variety of molecular photo-responsive switches, dithienylethene derivatives are very prominent. These compounds show very high fatigue resistance and the coloration/decoloration cycle could be repeated more than 104 times without loss of their spectral features due to side reactions or decomposition. [63] Because of their absorption properties along with stability features, they are excellent materials which are suitable for showing photo-induced changes of physical properties. For a further example of a simple diarylethene based small photochromic molecule E, it shows repeated colouration/ decoloration switching behaviour in solution (i.e., the ring-open isomer is colourless or very pale coloured isomer when irradiated with UV light, it transforms into ring closed isomer that show a deeply coloured form and it again regains its colourless or very pale coloured ring open form when exposed to visible light, this continues for many times) (Scheme 7). Scheme 7 shows the two different absorption spectra (one for ring open form and another for the ring closed form) of diarylethene E, it indicates that the delocalisation of the π‐ electrons in closed form extends towards longer wavelengths up to the visible region spreading over the entire structure in the close‐ring form. However, in ring open (colourless)


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form, the delocalization of π‐electrons is restricted to each half of the molecule and electronic communication through the unsaturated bond of the middle ring is interrupted. In terms of an explanation similar to electrical switches, if we consider that a diarylethene E is functionalized with suitable anchor groups and immobilized between two electrodes in a junction, the coloured form or ring closed form would then correspond to the ‘ON’ state while the less conducting form ring open (or colourless) form would be referred to the ‘OFF’ state (Scheme 7). These types of diarylethene based molecular switches are suitable for smart textile applications. Apart from diarylethenes, spirooxazines, spiropyrans, naphthopyrans, some particular types of fulgides, azulene based photochromic molecular switches (to some extent) and some particular types of molecular chiroptical molecular motors and supramolecular switches are potentially suitable for smart textile applications. So, this following section will very briefly discuss some very selective features of these systems with a view to their potential applications in smart textiles.

Scheme 7. Principle of reversible photo-switching between the ring open form (colourless) and the ring closed form (coloured) of dithienylethene E in solution.

Fulgides Fulgides are bismethylenesuccinic anhydrides, they usually contain a phenyl ring on the methylene carbon atom. They were first synthesized and studied early in the 20th century by Stobbe. [70] Scheme 8 indicates the photochromic switching behaviour of a fulgide. In this case, ring open E-isomeric form of this fulgide undergoes cyclization when exposed to UV light turns into a deeply coloured ring closed form (of this fulgide). Additionally, there is concomitant transformation from the E-form to Z-form which are always colourless and when all these forms absorb UV light, inter conversions between them occur until a photostationary state is reached. Besides this, as the coloured ring closed form is the only form which can absorb visible light, so when it is exposed to visible light it disappears completely and returns

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to its original colourless form due to a change in conjugation of pi-electron systems of the fulgide molecular switch.

Scheme 8. Photochromic switching behaviour of a fulgide.

There are different types of fulgides used in various applications. [71] A wide variety of photochromic fulgides can be produced from the anhydride derivatives. Most of the fulgides produced in this usual system are mostly thermally reversible. However, in 1981, Heller et al.,, at first produced thermally stable fulgides by introducing furane derivatives instead of the phenyl group. [72, 73] This type of thermally stable fulgide (furylfulgide) is shown in Scheme 9.

Scheme 9. Photochromic switching behaviour of a thermally stable fulgide (a furylfulgide).

Thermally stable fulgides are more suitable for producing photochromic textiles. There are some fulgides which also show fluorescence behaviours. Scheme 10 shows the photoswitching behaviour of a fulgide. In this case, ring open form of furylfulgide rarely emits fluorescence unless it contains a fluorescent moiety. However, on the other hand, cyclized closed form of this compound usually shows fluorescence at low temperatures. Port et al., prepared a types of fulgides (more specifically fulgimides), where fluorescence is photo-controlled (i.e., a particular photo-isomer of a fulgimide shows fluorescence). [74, 75] Figure 9 shows a fulgimide which contains an anthracene, this anthracene acts as an antenna (or as an energy donor) on the thiophene ring. Additionally, in this molecule, the nitrogen atom of fulgimide is attached with an aminocoumarin with an aim to use it to work as a luminescent moiety (or as an energy acceptor). So, when the ring open form of this fulgimide


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is irradiated with a light of 320 nm wavelength, the anthracene group is excited to a higher energy level and this energy is transferred through the core of the ring open form through the coumarin and shows fluorescence. On the contrary, this fluorescence behaviour is significantly reduced when this molecule is exposed to a visible light of 520 nm due to photocyclization.

Scheme 10. Photochromic switching behaviour of a particular type of fulgide.

This type of molecular switch has the potential to apply in textiles for producing photochromic fluorescent fabrics for smart textile applications to work as multi-functional items.

MULTIFUNCTIONAL PHOTOCHROMIC MOLECULAR SWITCHES Some photochromic systems also have the capability to work as multi-functional switches. Azulenes and supra-molecular switches are some of the important types of multifunctional molecular switches which are very briefly discussed here.

Azulenes Photochromic azulenes shows photochromic colour changes when exposed to UV light. This photochromic behaviour is due to the change in the electronic structure of molecule which originates from a rearrangement molecular structure when exposed to a suitable actinic radiation (such as, UV light). Generally, this type of molecule is not thermally stable. Scheme 11 shows a precise schematic illustration of the photochromic switching behaviour of a dihydroazulene (or diamidotriazine) type photochromic azulene. The structure of this molecules also indicates that this type of azulenes have influence in the complex properties of the diamidotriazine moiety. This system is one of the good examples of a photochromically controlled supra-molecular interaction. It is important to mention here that some photochromic azulenes to multimode photochromic behaviours. For example, Scheme 12 indicates a multi-mode photochromic system of an azulene based photochromic switch where it shows a multi-addressable system with different inputs of stimuli (such as, light, heat and pH). Several multimode photochromic systems based on dihydroazulene have been reported. [76, 77] Diederich et al., have published results [43] about composing system based on dihydroazulene (DHA)/vinylheptafulvene (VHF) photochromism with a three-way molecular

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switch, which may be controlled by several different types of inputs, such as, pH, light, and heat. It is very interesting to note that all three subunits are individually addressable and have the ability to undergo individual, reversible switching cycles (Scheme 12).

Scheme 11.A precise schematic illustration of the photochromic switching behaviour of a dihydroazulene (or diamidotriazine) type photochromic azulene.

Scheme 12. Multi-mode photochromic behaviour of an azulene based photochromic switch (i.e., multiaddressable system with different input types).

Additionally, some members of photochromic azulene based molecular switches also show photo-controlled fluorescence behaviour. For example, Scheme 13 illustrates a schematic representation of photo-responsive fluorescence behaviour of a particular type of photochromic azulene based molecular switch. In this case, a light-controlled fluorescent switch has been prepared from a boron-dipyrromethene dye which acts as a fluorescent sensor and the photochromic DHA/VHF as a photochromic switch (Scheme 13). [78] So far there is no report of using photochromic azulene based molecular switches for textile applications, however, these type of molecular switches have some potential applications when considered them as photochromic disperse dye type molecular switch which may be used in polyester, nylon and other related textile in terms of dyeing, printing and coating techniques for a variety of smart textile applications. Besides this, there are some leuco-derivatives (one example is shown in Scheme 14) which show photo-induced ionisation and are useful


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candidate for hydrogels or polymers where there shapes can be controlled using actinic radiation (such as, UV light). [79] This type of materials are suitable for producing healthcare materials, photo-controlled drug release and have the potentials to be incorporated in healthcare based smart textiles for a wide variety of biomedical applications.

Scheme 13. Schematic representation of a photo-responsive fluorescence behaviour of a photochromic azulene based molecular switch.

Scheme 14. Photo-induced switching behaviour of a leuco-derivative which also shows thermal back reaction to regain its original state (which was before exposure to UV light).

The photo-induced ionisation of compounds which contain leuco-derivatives, for example, bis(4-(dimethyl amino) phenyl) (4-vinylphenyl)methyl leuco cyanide, is useful to be

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used to produce expansion and shrinkage on different polymers or gels. Scheme 14 shows the photo-induced switching behaviour of a leuco-derivative which also shows thermal back reaction to regain its original state (which was before exposure to UV irradiation). The changes in the material arise due to the change in electrostatic repulsion between the charges and the ionisation of the compound is mainly due to the effect of UV irradiation (of an UV light of wavelength 270 nm or more). In this context, cyclobutanes are other types of materials which are widely used for photo-induced shape controls in gels, hydrogels or similar types of systems which have many applications in biomedical textiles. Cyclobutanes are usually produced from cinnamic acid and also from its different derivatives. In this type of system, two cinnamic acid molecules dimerise to form a cyclobutane when irradiated with UV-light (of wavelength 300 nm or more). Scheme 15 illustrates a photo-induced dimerisation reaction of cinnamic acid when exposed to UV-light of wavelength 300 nm, or more. It also indicates that there is a reverse reaction from the changed state when it is irradiated with an UV light of shorter wavelength (such as, 254 nm) and regains its original form. [79]

Scheme 15. Photo-induced dimerisation of cinnamic acid on exposure to UV-light (of wavelength 300 nm, or more); however, when irradiate with an UV light of shorter wavelength (such as, 254nm) it shows a reversion to its original form.

These types of photo-responsive switch are particularly important for producing photoresponsive shape memory polymers which have some potential applications in healthcare based smart textiles. Finally, there are some molecular motors based on chiroptical molecular switches and some particular types of supra-molecular switches have many potential applications in smart textile applications. So, they are briefly discussed here.

MOLECULAR MOTORS Some unidirectional chiral molecular motors have the capability to mimic the rotational motion of ATP synthase and flagella motors. [81] Scheme 16 indicates the photo-switching behaviour of a unidirectional molecular motor A which work as a function of the nature of wavelength of UV light and the nature of heat. This molecular motor A (in E-form, I)


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contains a tetra-substituted photo-isomerizable alkene which has two phenanthrene derivatives. The steric hindrance of the phenanthrene substituents of the alkene introduces helical chirality in the system. In the first phase, the alkene adopts a trans-conformation which is isomerized into a highly strained cis-isomer (molecular motor A in Z-form, II) when irradiated with a UV light (>280 nm) at -55°C.

Scheme 16. Photo-switching behaviour of a unidirectional molecular motor A which work as a function of the nature of wavelength of UV light and also according to the nature of heat.

In the second phase, there is a concomitant move of the methyl substituents of the cyclohexane ring from the axial position to the equatorial position. In the third phase, when the molecular motor A (in Z-form, II) is heated at 20°C it undergoes a flipping motion of the aromatic rings around the alkene to give an oppositely twisted helicalmolecular motor A –III isomer. In the fourth phase, when the molecular motor A –III isomer is exposed to photoirradiation with a UV light of >380 nm, it undergoes a conformational change into a highly strained trans-isomer (molecular motor A –IV isomer). In addition, at 60°C, the molecule flips back to its original form to end the rotation cycle. The unidirectionality of this motor is made possible due to the chiral properties of this molecular motor A. There are a number of improved forms of these molecular motors. [80-84] There is no reports of using these type molecular motors in textiles; however, they have the potentials for multi-functional switches based high performance smart textiles for many advanced applications. Some supramolecular switches, such as, catenanes also have the potential for multi-functional switches based high performance smart textiles for a wide variety of advanced applications. The nature

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of a particular type of a catenane based supra-molecular switch is described here to conclude this section on photochromic molecular switches.

Catenanes and Rotaxanes Based Supra-Molecular Switches Interlocked molecular switches, such as, catenanes and rotaxanes are of great interest because of significant importance because of their many potential applications in different fields, for examples, sensors, memories, switches, etc. They attain some unique properties due to the cooperative or synergistic effect of each component present in the interlocked system. In last two decades different types of catenanes and rotaxanes have been prepared and their structural and dynamic properties have been investigated both in solid and solution states. [85] Stoddart et al. have prepared a variety of self-assembled catenane and rotaxane using the intermolecular charge transfer interaction between viologen and dialkoxybenzene derivatives. [86] They are based on the ability of the tetracationic cyclic viologen derivative or parabenzo-crown-ether to form inclusion complexes with pi-electron donating compounds or linear viologen units, respectively. These catenane and rotaxane showed excellent performances as the molecular machines which are driven by the chemical or electrochemical stimulus. [87] There are a few reports on the photo-induced spectroscopic properties of photochromic supra-molecular switches. [88] A recent report on the supra-molecular regulation of the photochromism by the additives shows that it is possible to interact with the photochromic molecule using inter-molecular interactions. There is an increase in the quantum yield for the photochromic reaction of diarylethenes by the complexation with the cyclodextrin. [89] It is also possible to add metal ions switched on the trans-cis isomerization of azobenzene derivatives. [90] Addition of metal ions improves the thermal stability of coloured merocyanine form of spirobenzopyran derivatives. [91] So, from this brief discussion it is clear that photochromic supra-molecular switches can be produced in various ways for a wide range of applications. There are also wide variety of catenanes which act aselectrochromic switches, for example, Scheme 17 shows electrochemically induced rearrangements of catenane (from form A to D). The detail nature of electrochromic switches are discussed later in this chapter. Usually some particular types of catenanes are interlocked with two different rings. [92, 93] In this system, one of the loops includes two coordinating units - a bidentate and a tridentate terpyridine. On the other hand, the second loop has only one bidentate complexation site. In the beginning, catenane A is immobilized on a copper (I) metal ion and adopts a 4-coordinate tetrahedral geometry which is shown in Scheme 17. Upon oxidation of the copper to the divalent state, A produces an intense green colour and transformed into structure Bspecies (which gives an absorption band at 670 nm in acetonitrile). It is important to note that this process can be triggered either by using chemical or electrochemical oxidation. In addition, due to a rotational rearrangement form B turns into a pale olive-green coloured species and takes the shape of form C. At this stage, the system includes decomplexation followed by rotation and recomplexation at the terpyridine binding site. The 5-coordinate copper (II) shows an absorption band at 636 nm which corresponds to 5coordinated copper complex. Form B has a slightly distorted tetrahedral geometry whereas form C is square pyramidal. After reduction of form C into D, rotation of the terpyridine group leads to the starting original catenane form A. This type of gliding of the ring takes


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place in a few seconds at room temperature regardless of the solvent. On the other hand, the speed of rearrangement after oxidation from B to C depends mostly on the solvent and the counter-anion. This type of device can be regarded as a molecular motor as the loop activates a complete 360° rotary motion around the copper ions. This type of systems are suitable for site specific drug delivery on human skin using particular types of high performance biomedical textiles which may be incorporated into smart textiles for multi-purpose applications.

Scheme 17. Electrochemically induced rearrangements of catenane (from form A to D).

APPLICATION OF PHOTOCHROMIC SMART TEXTILES A good quality photochromic smart textile is expected to show photochromic colour change for a long time and will retain of its reversible photo-coloration behaviour even after exposed to different environmental conditions. This behaviour makes it a suitable candidate for many potential applications. Some of the selected important application field are – (a) security, (b) responsive surface, (c) brand protection, (d) authentication, (e) actinometry, (f) self-indicating UV warning system, (g) active and adaptive camouflage, (h) environmental warning system, (i) electrophoretic textile based display, (j) interior design, (k) exterior design and also in (l) fashion and design applications. In this context, photochromic smart textiles have the potential for healthcare applications as well. It important to note that the possibility to bind a photochromic molecule onto a naturally occurring receptors and enzymes which can be bonded with a photochromic smart textile using certain techniques provides the opportunity to photo-regulate their binding and catalytic activities. Hopefully, in future, this type of photo-responsive textiles may be used for different therapy, bio-sensing and also in wound care along with their other already stated applications. [46-57]

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THERMOCHROMIC MOLECULAR SWITCHES AND THEIR APPLICATIONS IN SMART TEXTILES Thermochromic molecular switches (such as, thermochromic dyes, pigments, materials) change colour as a function of temperature either reversibly or irreversibly. The molecular switcheswhich show a reversible thermochromic colour change have their potential application in textiles, such as, leuco dyes (in appropriate composition with other additives) and cholesteric liquid crystal based thermochromic pigments. Usually a leuco dye based thermochromic switch shows a colour change from coloured to colourless or to another colour with an increase in temperature. However, a cholesteric liquid crystal based thermochromic switch exhibits a vivid range of colour change (may also be termed as a colour play) by passing through the whole spectrum with an increase in temperature. The leuco dye based active thermochromic switch usually consists of a colour former, a developer and a solvent in a specific combination where the colour former is a pH sensitive dye (e.g., a spirolactone ora fluoran) and the developer is a proton donor (e.g., an week acid like Bisphenol A). The solvent suitable for this thermochromic composition is usually a low melting hydrophobic, long aliphatic chain fatty acid, amide or alcohol and its melting point is used to associate the system with a specific temperature at which the colour former and developer can easily interact. On the other hand, the liquid crystals with a chiral centre (also known as cholesteric liquid crystals) show colour change in response to a suitable change in temperature in the surrounding environment. In the preliminary stage most liquid crystals were cholesterol derivatives, however, now-a-days synthetic chiral molecules (also known as chiral nematic liquid crystals) are also available. The cholesteric liquid crystals are usually used against a black background for the manipulation of the incident light and also for the reflection of light of selected wavelengths which vary with change in temperature. In this case, the particular reflected wavelengths are dependent on the pitch length of the helix formed by the liquid crystals and these parameters show a change with a change in surrounding temperature. Microencapsulation is a widely used technique for the integration and application of the leuco dye based and liquid crystal thermochromic pigments. For clarity and better understanding the word thermochromic material or dye or pigment used in this chapter will be used in place of a thermochromic molecular switch when necessary, which has similar type of meaning but not necessarily the same. [94-95] Commercial thermochromic pigments are available since the late 1960s for a variety of applications, including, thermographic recording materials, temperature indicators (e.g., to measure body temperature), recording thermal history (such as, to determine the temperature or history of the food storage when used in a food container). These materials also have other wide ranging applications, some of which are – (a) in medical thermography for diagnosis purposes, (b) in thermal mapping of engineering materials to diagnose faults in product design and in mechanical performance, (c)in the cosmetic industry for moisturizing and as a carrier for vitamins, (d) in memory devices for date storage,(e) in batteries for life indication, (f) in the architecture field for decoration or for its functionality, (g) authentication, (h) brand protection, and also in (i) anti-counterfeit applications. Thermochromic materials are also used as novelty materials in the manufacture of toys, ornaments, kettles, umbrellas, toilet seats, etc. However, in textiles, thermochromic materials are usually applied by printing, coating and extrusion methods. Thermochromic textiles produced from using thermochromic


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materials have many applications, including in T shirts, children clothing, jeans, electronic heat profiling circuitry, in man-made cellulose fibres and also in acrylic fibres. Although thermochromic materials have been used in textiles relatively for a longer time compared to photochromic materials but the extent of application is still not that much wide ranging. [9499]

CLASSIFICATION OF THERMOCHROMIC MOLECULAR SWITCHES In broad classification thermochromic materials are divided into two groups and they are inorganic and organic thermochromic molecular switches (or materials).

Inorganic Thermochromic Systems There are a number of inorganic molecules which show thermochromic colour change in solid or solution states. For this type of molecules which show temperature dependent thermochromic colour changes, there are a number of mechanisms, some of which are – (a) phase transitions, (b) changes in ligand geometry,(c) equilibria between different molecular structures and also (d) changes in the number of solvent molecules in the coordination sphere (for example involving dehydration). [98] Most of the inorganic thermochromic systems are originated from transition metals and organo-metallic compounds. Generally, most of the inorganic thermochromic systems show intrinsic colour changes which are direct heat dependent in nature. Some examples of inorganic thermochromic materialsare - (a) Cu2HgI4 is red at 20⁰C but black at 70⁰C,(b) ZnO is white at room temperature but yellow at higher temperatures; (c) In2O3 is yellow at a lower temperature but yellow-brown at a high temperature; (d) Cr2O3-Al2O3 is red at 20⁰C but grey at 400⁰C; (e) (Et2NH2)2CuCl4 is bright green at 20⁰C but yellow at 43⁰C; (f) CoCl2 is pink at 25⁰C but blue at 75⁰C; (g) VO2 at about 68⁰C changes from transmissive semiconductor to an infrared reflecting metallic conductor. [40, 95-101] Inorganic thermochromic materials/systems have some limitations for textile applications. Because these materials often show their thermochromic behaviour at a high temperature or in solution form and sometimes the colour change is irreversible. [102] However, it is an important requirement for the thermochromic materials to be suitable for textile applications that they show heat dependent colour changes at close to ambient temperatures, as for instance, around -10⁰C for ski wear and around body temperature at 35⁰C for apparel and smart textiles. [98] As a result, most of inorganic and organometallic materials based thermochromic systems are mostly used in temperature indicating paints and crayons for the identification of temperature change and also for providing a permanent record of thermal data.

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ORGANIC THERMOCHROMIC SYSTEMS A stark difference of organic thermochromic systems from the inorganic one is that they show reversible thermochromic colour change involving both intrinsic and indirect systems. So, now a brief discussion will concentrate on different systems involved in organic thermochromic systems.

Reversible Intrinsic Thermochromic Organic Systems Usually reversible intrinsic thermochromic organic systems show colour change when exposed to heat without depending on anything else (such as the environment) and they revert to the more stable state as they cool down after removal from the heat source. There are four different types of mechanisms generally used to explain the colour change phenomena of different thermochromic systems; they are - (a) molecular rearrangement, (b) stereoisomerism, (c) macromolecular systems and (d) supra-molecular systems.

Thermochromic Colour Change Based on Molecular Rearrangement Sometimes molecular rearrangement is observed in some of organic thermochromic systems which are mostly due to the result of tautomerism. This tautomerism may originate from acid-base, keto-enol or lactim-lactam equilibria, which lead to an increase or decrease in the electron conjugation in molecules, to form different types of chromophores. [90, 103] For example, due to hydrogen transfer Schiff bases (usually produced by the condensation of salicylaldehydes and anilines) show enol-keto tautomeric structures. [104, 105] In this case, in the tautomeric equilibrium the keto form is more favoured and the Schiff bases are planar in stucture and at this stage they show thermochromic colour changes from yellow to orange or red as shown in Scheme 18.

Scheme 18. Tautomeric forms of a Schiff base.


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Sometimes, some photochromic molecules such as, spiropyrans and spirooxazines may also show thermochromic colour change. In this case, in solid or liquid form, both spirooxazines or spiropyans may show heat induced transformation from their colourless ground state (closed form) (at lower temperature, such as, room temperature or below) to their coloured merocyanine (or ring opened) format high temperature. Additionally, these compounds also show solvatochromism in polar solvents may be due to the formation of the polar merocyanine structure. [106] Another similar example of this type of compound is bisspiropyran (as shown in Scheme 19) is colourless at lower temperature, however, it shows a red colour in n-propanol at 60⁰C and blue colour at 70⁰C. This phenomenon is mainly due to the structural formation of mono-merocyanine and bis-merocyanine respectively. [40]

Scheme 19. Sequential coloration of a bis-spiropyran with temperature.

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Thermochromic Colour Change Due to Stereoisomerism Sometimes stereoisomerism also causes thermochromic colour change which usually observed in the compounds which have at least one ethylene group, a number of aromatic rings and one hetero-atom (such as, nitrogen or oxygen) in their structure. In this case, the ethylene group present in the structure restricts a molecular orientation which in effect causes the difference in energy levels in different isomeric forms. When the type of system exposed to heating, the molecule adopts different stereoisomeric forms which eventually produces colour changes. Some particular examples of these materials are overcrowded ethylenes, such as, bianthrone, dixanthylene, and xanthylideneanthrone. [98-106] Bianthrones exhibit reversible colour change from yellow (as shown in A ) at room temperature to green (as illustrated in B) at high temperature when heated in solution (as shown in Scheme 20). [40] These types of stereoisomers based thermochromic materials are not suitable for textiles application. Because, they only show thermochromic colour changes in their molten states which commonly occur at higher temperatures.

Scheme 20. Schematic representation of thermochromic bianthrones where 1 is a folded structure and 2 represents a twisted structure of a bianthrone.

Thermochromism in Macromolecular Systems Some types of macromolecules, such as, poly(3-alkylthiophenes) and poly(3alkoxythiophenes) show thermochromic colour change in solid and solution form due to the change in conjugation. Some of them also show other types of chromism (such as, photochromism, electrochromism) when exposed to suitable environmental stimuli. Sometimes a hypsochromic reversible colour change is observed in some macromolecular systems which is usually termed as negative thermochromism. As for instance, poly[3oligo(oxyethylene)-4-methylthiophene] is violet at room temperature and yellow at 100⁰C due to a change in conjugation at high temperature from its molecular planarity at room temperature (as shown in Scheme 21).


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Scheme 21. A planar (violet coloured) form of poly[3-oligo(oxyethylene)-4-methylthiophene] at room temperature with a non-planar (yellow coloured) form at high temperature (e.g., 100⁰C) where a shift in conjugation is clearly visible.

Thermochromism in Supra-Molecular Systems Liquid crystals are some types of materials which have a special type of character that they can exist in a state between solid and isotropic liquid, in which they exhibit the properties of a liquid (e.g., the ability to flow), however, they also have a crystalline like molecular arrangement (which are usually termed as liquid crystals). Liquid crystals are anisotropic in nature usually derived from calamitic molecules and also they have a very large length to breadth ratio (which means the molecules are long and narrow in size). [107,108] Liquid crystals are usually divided into three main groups and they are – (a) smectic, (b) nematic and (c) cholesteric or chiral nematic. They can also be divided into sub groups. [107, 109, 110] However, most reversible intrinsic thermochromic systems operate at a high temperature which is not suitable for the application on textiles (with an exception to some particular types of liquid crystals). Additionally, there are significant technical problems to cover all the colours in visible spectrum which need the synthesis of many compounds.

Reversible Indirect Thermochromism in Organic Systems The chromophore responds to a change in its environment when exposed to heat in the case of reversible indirect thermochromic organic systems. The colours used using these systems are not thermochromic by themselves, however, they show change in colour due to the difference in the physical environment by the increase or decrease in surrounding temperature. Usually, the chromophores in these systems are also responsive to pH (similar to

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the features of dyes which are usually acidochromic or ionochromic in nature). Generally, indirect systems operate within an ambient temperature range which mostly matches the temperature range usually used in textile products during their life time. Some of these types of compounds are also pH sensitive and modifications are possible using suitable synthesis techniques to provide a range of colours. Thermochromic materials based from this system have a wide range of textile applications where they can be used to provide precise and predetermined colour changes at specific temperatures which is in contrast to intrinsic systems. So, in this stage a brief discussion is given to the nature of usually used organic thermochromic systems containing colour formers, their versatility and also different aspects of their compositions.

Usually Used Organic Thermochromic Systems for Specific Purposes Usually used organic thermochromic systems for specific purposes are generally prepared by judicious mixtures (in specific proportions) of three essential components which are: (a) colour formers, (b) developers and (c) co-solvents. In usual terms, these systems are coloured in their solid form but when there is a suitable rise in surrounding temperature they become colourless and also regain their original coloured state on cooling. In this case the colour former is a pH sensitive compound which accepts a proton to convert from a colourless state to a coloured state. It is a popular practice that they are applied in the form of microcapsules to avoid any change or damage to the system or variation in the proportion of components. There are versatile features of this type of organic thermochromic systems (which sometime referred to as leuco dye systems), some of which include: a) a sharp transition in colour intensity -over a few degrees temperature difference where a change from intense or deep colour to colourless is often possible; b) flexibility of temperature switching -colour changing effects can be obtained at different temperatures using a proper selection of different co-solvents with appropriate melting points; c) a wide variety of colour changing effects – it allows to produce colour change from the coloured (across whole visible spectrum available) state to colourless state, from one coloured state to another coloured state (is possible by the incorporation of pHinsensitive dyes as a base colour or by using colour formers with a secondary chromophore).

Compositions of Usually Used Thermochromic Mixtures The usual colour formers used in organic thermochromic pigments are N-acyl leucomethylene blue derivatives, fluoran dyes, diarylphthalide compounds, diphenylmethane compounds or spiropyrans compounds. In this case, crystal violet lactone analogues (diarylphthalide compounds) and fluoran dyes are mostly used compounds. [111] The ringclosed forms of these compounds are colourless and show colour after conversion to their coloured ring-opened forms which are obtained by protonation using weak acids as developers (e.g., phenolic compounds). Sometimes, this type of compounds are often referred


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to as catalysts or electron acceptors, however, they are mostly proton donors. [98] Mostly phenolic or nitrogen-containing heterocycles (such as, bisphenol B and bisphenol A) are used as developers and the latter class provides deep and high contrast colours. Bisphenol A and phenol have the same acidity level but have different effects which indicate the involvement of other factors in the efficiency of developers. [97] There are different types of materials are also used as developers during thermochromic compositions, some of the most popularly used ones are – (a) 1,2,3-triazoles (e.g., 1,2,3-benzotriazole, dibenzotriazole), (b) thioureas, (c) saccharin and its derivatives, (d) halohydrins, (e) boric acid and its derivatives, (f) guanidine derivatives (e.g., phenyl diguanide) and (g) 4-hydroxycoumarin derivatives. Some of these compounds help to improve lightfastness because phenol compounds give rise to quick fading when exposed to light. [98] There are different types of organic hydrophobic solvents which are generally used as the co-solvents in thermochromic systems and some of the important cosolvents belong to different groups, some of which are – (a) alcohols, (b) hydrocarbons, (c) esters, (d) ethers, (e) ketones, (f) fatty acids, (g) amides, (h) acid amides, (i) thiols, (j) sulphides and disulphides and (k) alcohol acrylonitrile mixtures. In most cases aliphatic solvents are widely used and are effective solvents for thermochromic systems which provide good desensitising effect at relatively low concentrations which improve the rate of colour development and also provide more complete colour change. [98] A schematic representation is shown in Scheme 22, where colour formers and developers interact in the solid form of the co-solvent and separate in the molten form.

Scheme 22. Coloured and colourless microcapsule.

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IONOCHROMIC MATERIALS AND SMART TEXTILES Recently, smart textiles have become the subject of many studies all over the world. Among the different group of smart textiles, there is a growing interest in colour change materials for the production of textiles that will produce colour change on exposure to certain stimulus, some of which are already discussed in the previous sections. In this case ionochromic materials are a distinct class of materials they change their colour on exposure to suitable ionic or pH conditions. There are many ways of incorporating ionochromic materials on textiles, some of which are – (a) dyeing, (b) printing, (c) coating, (d) extrusion, (e) microencapsulation.[40, 55, 56]

Nature of Ionochromic Materials Ionochromism is the reversible colour change caused by the addition of ions which is nearly similar to halochromism where there is a colour change due to a change in pH in the surrounding environment. The materials show this type of colour changes are usually called ionochromic materials. It is important to note that when the main ionic species is the solvated hydrogen ion, in which case the terms halochromic, or pH sensitive are often used. There are other different types of ions also produced by this class of materials and some of the most commonly observed ionsare – (a) metal ions, (b) onium cations (e.g., tertiary ammonium and phosphonium). In this case the usual reversible colour change is from colourless to coloured state or from one coloured state to another coloured state. There are different types of ionochromic materials, some of the important ones are – (a) phthalides, (b) triarylmethanes and (c) fluorans. Most of the commercially available pH sensitive dyes belong to these three classes. The pH sensitive dyes from natural sources, some of them known as anthocyanines, also show potentially effective forms of ionochromism.

Classification and Method of Application of Selective pH Sensitive Dyes Phthalides based commercially available indicator dyes which show a colour change due to a change in pH of the surrounding environment can be divided into two groups, they are – (a)the phthaleins (e.g., which are mostly available in their lactone form) and (b) the sulfophthaleins. [40] A number of commercially available indicator dyes (such as, phenol red, cresol red) can be used for the dyeing, printing, coating of different types of textiles although very rigorous studies are needed to improve different technical performances (such as, washfastness, lightfastness, abrasion resistance, perspiration resistance).

Ionochromic Dyes from Natural Sources Some natural plants based colorants show stimuli-responsive colour changes; anthocyanines (a sub class of flavinoids) are most prominent in this case. They are also available in different colours from different parts of plants, vegetables and flowers.


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Anthocyanines show a range of colour changes when exposed to suitable pH conditions in aqueous environment. A table of ionochromic materials is shown in Appendix 1, it shows the nature of pH responsive colour change of some selected synthetic indicator dyes and a few natural dyes based ionochromic molecular switches. [40, 54, 55, 150]

APPLICATIONS OF IONOCHROMIC TEXTILES Ionochromic materials have many important practical technological applications. Ionochromic textiles can be produced by using the ionochromic materials (such as, natural anthocyanines or synthetic indicator dyes). They are suitable for many practical applications; some of them are – (a) to detect noxious gases, (b) to assess humidity, (c) detect toxic metals, and (d) to monitor deterioration of functionality. They are also useful for many applications in healthcare textile products when incorporated into smart textiles along with other required suitable functionalities when used as hydrogels, ionogels or similar other types of materials. [54, 55]

ELECTROCHROMIC MOLECULAR SWITCHES AND THEIR APPLICATIONS IN SMART TEXTILES Different types of electrochromic materials (or molecular switches) are practically in use to produce electrochromic smart textiles which have many applications and one of the most obviously important one is for wearable displays. [111-115] Some of other important applications include adaptive camouflage and biomimetic systems. [116-121] There are a number of ways to incorporate electrochromic materials into textiles, such as, using conductive metal threads along with textile fabrics using knitting or weaving or coating with conductive oxides. There are some reports which showed that high conductivities of the underlying conductive fabric are not always necessary for electrochromic function to produce textile based electrochromic device architectures. In one such report it has been illustrated using spandex electrodes prepared by a method having low conductivity (such as, 0.1 S/cm) which electrochemically convert precursor polymers into conjugated forms to show electrochromic response. [122-128] It is a significant achievement because it illustrates the way how some other suitable conductors can possibly be used to prepare similar electrically responsive systems. [129-134] In this context, it is important to note that the electrochromic fabric system is not transparent and difficult to rely on reflected light to get them assembled into reflective-type devices. As a consequence, displays are an obvious extension to this situation [135-139] where informational patches can be used for the infrared (IR) attenuation capability of electrochromic materials. In this case, the preparation of user-controlled active colour changing fabric is an extension to passive colour change from photochromic textiles. As for instance, PEDOT:PSS type conductive polymers can be used for electrochromic textile production. Now different aspects of electrochromic materials are precisely covered in this chapter along with their applications for their potential uses in smart electrochromic textile production for a wide variety of potential applications. There are many applications of

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electrochromic textiles, some of which are -(a) adaptive camouflage, (b) coatings and additives, (c) on carpets, curtains, wallpapers, T-shirts, smart uniforms, etc. [139 - 141]

Methods of Applicationsof Electrochromic Molecular Switches in SmartTextiles Electrochromic materials can be doped in different fibres used in textile production (such as, extrusion, electrospinning, melt spinning, etc.) which show dynamic colour change when exposed to suitable electrical potentials. Some intrinsically conductive polymers (ICPs) and materials (such as, metal oxides, viologens, some particular type of phthalocyanines) are suitable to be doped in the textile fibres for producing electrical stimulus responsive electrochromic textiles to show dynamic colour changes. In this case, intrinsically conductive polymers (such as, polythiophene, polyannilne, polypyrrole, etc.) are easy to be processed using solution media to print them using screen printing or inkjet printing to produce electrochromic images or circuits on printed textiles; they can be even used to produce electrochromic fibres using electrospinning technique. Additionally, there are many other techniques to incorporate these materials to textile fibres, such as, coating, dipping, dyeing, weaving or knitting with conductive electrochromic threads, graft copolymerisation of conductive polymer based textile fibres with electrochromic molecules, etc.

ELECTROCHROMISM AND ELECTROCHROMIC DEVICES Electrochromism is a reversible change in optical properties of a material due to electrochemical oxidation or reduction in response to an electrical stimulus (e.g., electric current). Usually an electrochromic device is composed of three layers, such as, (a) an ion storage film, (b) the electrolyte and (c) the electrochromic layer. When a voltage difference is applied, electrons enter into the electrochromic layer while the positive ions move towards the electrochromic material to maintain charge neutrality. There are a number of materials which show electrochromic colour changes; some of these materials are – (i) transition metal oxides (e.g., WO3, V2O5), viologens (e.g., 1,1΄-disubstituted-4,4΄-bipyridinium dications) and conducting polymers (such as, polydioxythiophene-polystyrene sulphonates and their derivatives). A detail classification of different types of electrochromic materials are shown in Table 3. Table 3. Classification of electrochromic materials Electrochromic materials Examples Transition metal oxides WO3, V2O5, TiO2,and also transition metal oxides (such as, oxides of tungsten, nickel, iridium, vanadium, titanium) Conductive polymers Polypyrrole, polyaniline, polythiophene Viologens 1,1΄-disubstituted-4,4΄-bipyridinium dications, methyl viologens Prusian blue analogues Prusian blue, prussian brown Certain phthalocyanines Lutetium bis (phthalocyanine) Certain carbazoles Polyethylcarbozole


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ELECTROCHROMIC MATERIALS AND THEIR PROPERTIES A large number of electrochromic materials can be broadly grouped into different groups as shown in Table 3 some important groups which are briefly discussed here.

Transition Metal Oxides There are a number of transition metal oxides which show electrically responsive colour changes and some these types of materials are – WO3, V2O5, MoO3, TiO2. However, WO3 is by far, the mostly studied metal oxide based electrochromic material. [142] As a direct effect of electrical field when a transition metal oxide (present in a suitable set up) is reduced it shows a colour change and the small metal ions (Li+, H+, Na+, etc.) are intercalated into the lattice. For example, the electrochromic colour change of WO3 is due to the new electronic transitions raised along the intercalation process; however, the exact mechanism how it works is not fully understood. [143] WO3 (colourless) + xM+ + xe+

MxW+5xW(1-x)O3 (blue)

The rate limiting process of this reaction is usually the ion diffusion inside the metal oxide lattice, what slows down the switching time of the devices. It is important to note that in comparison to other electrochromic materials, metal oxides have excellent durability, stability and reliability but deficient in response times, narrow colour variations and relative higher cost. [141-143] Additionally, different types of transition metal oxides (TMOs) show electrochromic properties. There are many inorganic oxide based compounds which contain transition metals in their structures (some of the metals are iridium, ruthenium, tungsten, manganese, cobalt), some of them can be used as high quality inorganic oxide based electrochromic materials. [143]

Prusian Blue Analogues Prussian blue analogues show electrochromic changes. In usual practice, Prussian blue films are prepared through electrochemical reduction of a solution containing Fe+3 and hexaferrocyanate (III) ions. The resultant aqueous solution of Prussian brown, [(Fe+3Fe+3(CN)6] is reduced to give a Prussian blue [(Fe+3Fe+2(CN)6]- which is deposited in the form of a blue film. In this case the electro-neutrality is balanced due to the presence of K+ present in the electrolyte. [(Fe+3Fe+3(CN)6]0 + ePrussian brown

[(Fe+3Fe+2(CN)6]Prussian blue

Prussian blue is negative in charge and shows maximum absorbance at 690 nm. When there is a gradual increase in oxidation state the absorbance from 690 nm shows a gradual decrease whereas the absorbance at 425 nm starts to increase which correspond to

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[(Fe+3Fe+3(CN)6]0. The combination of these two types of absorbance generates the second coloured state- the Prussian green (a combination of Prussian blue and Prussian brown). Prussian green has a fixed anion composition ([Fe+33{Fe+3(CN)6}2{Fe+2(CN)6}]-). However, it is directly in contrast to the relative gradual change in the absorbance observed for Prussian blue towards Prussian green (during the increase in oxidation), the reduction of Prussian blue results in a rapid colour change to give Prussian white as an optically transparent film. [(Fe+3Fe+2(CN)6]- + ePrussian blue

[(Fe+2Fe+2(CN)6]-2 Prussian white

Potentially Electrochromic Conducting Polymers Conductive polymers used for a variety of purposes as shown in Figure 1. Some of them are useful to be used for the generation of electrochromic colour change as they are responsive to the electrical potentials. Table 4 illustrates the nature of electrochromic colour change of some selected electro-active polymers in their oxidised and reduced states. The conductivity of a conductive polymer can be adjusted which can vary over a very wide range, for example, it may start as insulating and moves towards a more conductive form (metallic form) with the variations of the concentrations of adopant. Although the conduction mechanism of conductive polymers sometimes are not well understood, it was noticed that their behaviour is similar to a semiconductor where electrons under thermal excitation jump from the valence band to the conduction band to give rise to conductivity. This is true for a narrow band-gap, but if the band-gap is very wide, then the electrons under thermal excitation at room temperature do not have enough energy to travel across the gap. So, in addition to band theory, it is essential to also study the properties of charge carriers. Most of the known conductive polymers are p-type doped and this involves formation of an abundance of mobile or carrier holes in the material, while in n-type doping the carriers are electrons. The model for the conduction mechanism of conductive polymers can be explained using band theory. [144] Table 4. Behaviour of certain electroactive polymers in different forms Electroactive polymers

Colour in Oxidised form Polyaniline Emeraldine: blue/green Perigraniline: blue/violet Poly(3,4-ethylenedioxythiophene) Almost transparent blue Poly(3-methylthiophene) Blue Polythiophene Blue Polypyrrole Dark grey

Reduced form Leucoemeraldine: white/clear Colourless Dark blue Red/purple Red Yellow


Data storage

Super capasitor

Surface protections

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Photovoltaic cells

Electrochromic devices Conductive polymers Chemical sensors and biosensors

Transistor and switch

Field emission display

Actuators

Figure 1. Different primary uses of conductive polymers.

Figure 2 shows a schematic representation of the band structure in an electronically conducting polymer. In this case, the energy difference between two frontier orbitals, such as, the energy difference of HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) orbitals, is also termed as the band-gap. This band gap is very important as the intrinsic optical property of a conductive polymer is directly related to this band gap or energy difference (which is usually expressed by the energy gap between the highest occupied π-electrons of valence band and to that of the lowest unoccupied conduction band). [145] When there is a reduction in the band gap, it makes the material more conductive so there is active research in this area to find polymers with very low band gap (close to that of metals). Examples of a few most commonly used conducting polymers include polypyrrole, polythiophene, and polyaniline (Scheme 23). [141-143]

Figure 2.A schematic representation of the band structure in an electronically conducting polymer.

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Scheme 23. Structures of some common conducting polymers.

The thin films of all conducting polymers are potentially electrochromic, they show redox switching which gives rise to new optical absorption bands associated with electron transfer. The oxidised state of a conducting polymer is doped with a counter anion (p-doping) and retains a delocalised π-electron band structure, while the HOMO-LUMO energy gap provides a first estimation of the electronic excitation energy which in turn can be measured by UV/Vis spectroscopy and provides the colours in the materials. [146, 147]

ELECTROCHROMIC MATERIALS FOR SMART TEXTILES As already stated above that electrochromism is the phenomenon displayed by some materials in which colour can reversibly change when a certain electrical potential is applied. Electrochromic colour change is observed from an electrochromic material, when it is oxidized or reduced that causes a change in the band-gap of this electrochromic material which is induced by a suitable change in the electrical potential. A large number of electrochromic materials are available from almost all branches of synthetic chemistry. Organic electrochromic materials represent a major class of materials used for electrochromic devices and they can be grouped into follow three categories: a) type I electrochromic materials -they are soluble in both reduced and oxidized states, and remains in solution at all times during electrochromic usage (such as, a methyl viologen, it changes its colour from colourless to intense blue during reduction on electrode); [148] b) type II electrochromic materials – they are soluble in one redox state, but form a solid film on the surface of an electrode during electron transfer (e.g., heptyl or benzyl viologens, three redox states of this type of viololgens is shown in Scheme 24, where the dicationic state is most stable and the solid form of 1,1'-di-n-heptyl4,4'bipyridilium (heptyl viologen) shows an intense yellow colour in its dicationic state, but in solution it appears as a pale yellow/or colourless material); [ 143, 149] c) type III electrochromic materials – usually they are conducting polymers. Intrinsically conducting and electrochemically active nature of most of these types of polymers are promising candidates for numerous applications, including in textile based electrochromic colour change and also on display applications. [143] Metal oxide based electrochromic materials, viologens and conjugated electrochromic polymers can be used in electrochromic textile production. However, conjugated electrochromic polymers are increasingly targeted because they provide more practical advantages over others in many areas.


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Scheme 24. A schematic representation of three common redox states of a viologen (where form I is colourless, form II is blue-violet and form III shows very little coloration).

CONCLUSION AND PERSPECTIVES This current chapter has briefly concentrated on different aspects of smart textiles and the method of production of these textiles using different types of stimuli-responsive molecular switches, such as, photochromic, thermochromic, ionochromic and electrochromic molecular switches. It has also briefly highlighted selected features on different types of stimuliresponsive systems and the mode of application for producing high performance stimuliresponsive smart textiles for a variety of applications. Because, certain level of basic understandings on the nature of these molecular switches are of utmost importance for a successful incorporation of these stimuli-responsive switches into the textile materials for their effective high-performance utilization in smart textiles for a wide range of applications. As already stated at different places of this chapter that stimuli-responsive smart textiles have numerous application potentials, including in safety, security, comfort, fashion, health care, remote sensing, along with a variety of other biomedical and intelligent applications. It may take some time to reach at its maturity level since there are many issues still need to be addressed properly. There is active research going on in the different fields of molecular switches as well to enhance their different properties, so in future perhaps we will see new range of molecular switches which may overcome many of the current limiting issues. However, it is possible to overcome many of the limiting factors (very selectively some of which have been stated in this chapter at different places) of the molecular switches available

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today for their effective utilization in smart textile applications for a wide range of uses in different fields.

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APPENDIX 1. THE NATURE OF PH RESPONSIVE COLOUR CHANGE OF SOME SELECTED SYNTHETIC INDICATOR DYES AND A FEW NATURAL DYES. [40, 54, 55, 150] Serial No. 1 2 3 4 5 6 7 8 9 10

Indicator dyes Methyl Violet Crystal Violet Ethyl Violet Malachite Green Methyl Green 2-(p-diethylamino phenylazo)pyridine o-Cresolsulfonephthalein (Cresol Red) Quinaldine Red p-(p-diethylamino phenylazo)-benzoic acid, Na salt (Paramethyl Red) m-(p-diethylamino phenylazo)-benzene sulfonic acid, Na salt (Metanil Yellow)

pH range (approx.) 0.0-1.6 0.0-1.8 0.0-2.4

Colour change

Preparation

yellow to blue yellow to blue yellow to blue

02-1.8 0.2-1.8 4.4-5.6

0.05% in water 0.02% in water 0.1g in 50 cm3 Methanol + 50 cm3 water yellow to blue green Water yellow to blue 0.1% in water red to yellow

0.4-1.8 7.0-8.8 1.0-2.2 1.0-3.0

yellow to red yellow to red colourless to red red to yellow

0.1g in (0.01N) NaoH water (26.2 cm3 ) 1% in Ethanol Ethanol (EtOH)

1.2-2.4

red to yellow

0.01% in water

236

Shah M. Reduwan Billah Appendix 1. (Continued)

Serial Indicator dyes No. 11 4-Phenylazodiphenylamine

pH range Colour change (approx.) 1.2-2.6 red to yellow

12

Thymolsulfonephthalein (Thymol Blue)

1.2 – 2.8 8.0-9.6

red to yellow yellow to blue

13

m-Cresolsulfonephthalein (Metacresol Purple)

1.2-2.8 7.4-9.0

red to yellow yellow to purple

14

p-(p-anilinophenylazo) 1.4-2.8 benzenesulfonic acid, Na-salt (Orange IV) 4-o-Tolylazo-o-toluidine 1.4-2.8 Erythrosine, disodiumsalt 2.2-3.6 Benzopurpurine 48 2.2-4.2 N,N-dimethyl-p-(m-tolylazo)aniline 2.6-4.8 3.0-4.0 4,4′-Bix(2-amino-1naphthylazo)2,2′-stilbenedisulfonic acid

red to yellow

Tetrabromophenolphthaleinethyl ester, K-salt 3′, 3′′, 5′, 5′′tetrabromophenolsulfoephthalein (Bromophenol Blue) 2,4-Dinitrophenol

3.0-4.2

yellow to blue

3.0-4.6

yellow to blue

15 16 17 18 19

20 21 22 23 24 25 26 27 28

N,N-Dimethyl-p-phenyl-azoaniline (p-Dimethyl aminoazobenzene) Congo Red Methyl Orange-Xylene Cyanole solution Methyl orange Ethyl orange

4-(4-Dimethylamino-1naphtholazo)-3methoxybenzenesulfonic acid Serial Indicator dyes No. 29 3′, 3′′, 5′, 5′′-tetrabromo-mcresolsulfonephthalein (Bromocresol Green) 30 Resaurin 31 4-Phenylazo-1-naphthylamine

orange to yellow orange to red violet to red red to yellow purple to red

Preparation 0.01 g in HCl 1N, 1 cm3) + EtOH (50 cm3) + Water (49 cm3) 0.1g in NaOH (0.01N, 21.5 cm3) and Water (229.5 cm3) 0.1 g in NaOH (0.101N, 26.2 cm3) and water (223.8 cm3) 0.01% in water Water 0.1% in water 0.1% in water 0.1% in water 0.1 g in NaOH (0.05N NaOH, 5.9 cm3) and water (94.1 cm3) 0.1% in EtOH

3.0-5.0 3.2-4.2

0.1 g in NaOH (0.01N, 14.9 cm3) and water (235.1 cm3) colourless to yellow saturated water solution red to yellow g in EtOH (90 cm3) and water (10 cm3) blue to red 0.1% in water purple to green ready solution

3.2-4.4 3.4-4.8

red to yellow red to yellow

3.5-4.8

violet to yellow

2.8-4.0 2.8-4.4

pH range Colour change (approx.) 3.8-5.4 yellow to blue 3.8-6.4 4.0-5.6

orange to violet red to yellow

0.01% in water 0.05-0.2% in water or aqueous EtOH 0.1% in EtOH (60%) Preparation 0.1g in NaOH (0.01N, 14.3 cm3) and water (235.7 cm3) water 0.1% in EtOH

Smart Textiles and the Effective Uses of Photochromic, Thermochromic … Serial Indicator dyes No. 32 Ethyl Red

pH range Colour change (approx.) 4.0-5.8 colourless to red

33

0.2-1.8 4.4-5.6 4.4-5.8

yellow to red red to yellow orange to yellow

0.1% in water

35

2-(p-Dimethylamino phenylazo)-pyrodine 4-p-ethoxyphenylazo)-mphenylenediaminemonohydrochlori de Lacmoid

4.4-6.2

red to blue

0.2% in EtOH

36

Alizarin Red S

4.6-6.0

yellow to red

37 38

Propyl Red 5′, 5′′-Dibromo-ocresolsulfonephthalein (Bromocresol Purple) 3′, 3′′-Dichlorophenol -sulfonephthalein (Chlorophenol red) p-Nitrophenol Alizarin

6.0-7.6

yellow to blue

34

39 40 41 42 43 44

2-(2,4-Dinitrophenylazo)-1naphthol-3,6-disulfonic acid, disodium salt 3′, 3′′-Dibromothymol sulfonephthalein (Bromothymol blue) 6,8-Dinitro-2,4(1H)quinazolinedione(mDinitrobenzoylene urea)

237

Preparation 0.1g in MeOH (50 cm3) and water (50 cm3) 0.1% in EtOH

dilute solution in water 4.8-6.6 red to yellow EtOH 5.2-6.8 yellow to purple 0.1g in NaOH (0.01N, 18.5 cm3) and water (231.5 cm3) 5.2-6.8 yellow to red 0.1g in NaOH (0.01N, 23.6 cm3) and water (226.4 cm3) 5.4-6.6 colourless to yellow 0.1% in water 5.4-6.6 colourless to yellow 0.1% in water 5.6-7.2 yellow to red 0.1% in MeOH 11.0-12.4 red to purple 6.0-7.0 yellow to blue 0.1% in water

6.4-8.0

45 46

Brilliant yellow Phelonsulfonephthalein (Phenol red)

6.6-7.8 6.6-8.0

47

Natural red

6.8-8.0

48 49

m-Nitrophenol o-Cresolsulfonaphthalein (Cresol red)

6.8-8.6 0.0-1.0 7.0 -8.8

50

Curcumin

7.4-8.6 10.2-11.8

0.1g in NaOH (0.01N, 16 cm3) and water (234 cm3) colourless to yellow 25 g in NaOH, 1M, 115 cm3) and boiling waterorin 0.292g NaCl in water (100 cm3) yellow to orange 1% in water yellow to orange 0.1g in NaOH (0.01N, 28.2 cm3) and water (221.8 cm3) red to amber 0.1g in EtOH (50 cm3) and water (50 cm3) colourless to yellow 0.3% in water red to yellow 0.1g in NaOH yellow to red (0.01N, 26.2 cm3) and water (223.8 cm3) yellow to red EtOH

238

Shah M. Reduwan Billah Appendix 1. (Continued)

Serial Indicator dyes No. 51 m-Cresolsulnaphthalein (Metacresol purple)

pH range Colour change (approx.) 1.2-2.8 red to yellow 7.4-9.0 yellow to purple

52

4′, 4′′-Bis(4-amino-1-naphthylazo)2,2′stibene disulfonic acid (Thylmol blue) o-Cresolphthalein p-Naphtholbenzene Phenolphthalein

1.2-2.8 8.0-9.6

red to yellow

8.2-9.8 8.2-10.0 8.2-10.0

colourless to red orange to blue colourless to pink

Ethyl-bis(2,4dimethylphenyl)acetate Thymolphthalein

8.4-9.6

colourless to blue

9.4-10.6

colourless to blue

5-(p-Nitrophenylazo)salicylic acid, Na-salt (Alizarin Yellow R) p-(2,4-dihydroxyphenylazo) benzenesulfonic acid, Na-salt 5,5′-Indigodisulfonic acid, di-Nasalt 2,4,6-Trinitrotoluene 1,3,5-Trinitrobenzene Clayton yellow

10.1-12.0 yellow to red

0.1g in NaOH (0.01N, 26.2 cm3) and water (223.8 cm3) 0.1g in NaOH (0.01N, 21.5 cm3) and water (228.5 cm3) 0.04% in EtOH 1% dil. alkali 0.05 g in EtOH (50 cm3) and water (50 cm3) Saturated solution in 50% acetone/ alcohol 0.04 g in EtOH (50 cm3) and water (50 cm3) 0.01% in water

11.4-12.6 yellow to orange

0.1% in water

11.4-13.0 blue to yellow

water

53 54 55 56 57 58 59 60 61 62 63

Preparation

11.5-13.0 colourless to orange 0.1-0.5% in EtOH 12.0-14.0 colourless to orange 0.1-0.5% in EtOH 12.2-13.2 Yellow to amber 0.1% in water



Chapter 8

SMART TEXTILES Ali Akbar Merati Advanced Textile Materials and Technology Research Institute (ATMT), Amirkabir University of Technology, Tehran, Iran

ABSTRACT The smart textile is a convergence of different sciences such as materials, physics, chemistry, electrical engineering, wireless and mobile telecommunication and nanotechnologies. This chapter introduces the phase change materials (PCM), shape memory materials (SMM), chromic materials (color change), optical fibers and conductive materials and their application in the functionalized smart textiles. Then the important key issues for the design of a smart textile system such as working conditions, effective alarm generation, and energy constraints are presented. The components of an electronic smart textile that provide several functions such as sensors unit, network unit, processing unit, actuator unit and power unit are then discussed. The conductive fibers, yarns and fabrics are defined and explain how textile materials and structures can be used as sensors, actuators, communication devices, energy sources and storage tools, and even processors. Finally, the formation of the flexible electrical circuits in smart textile structures and different device attachment methods are explained.

Keywords: Chromic materials, conductive materials, fabric, fiber, phase change materials, shape memory materials, smart textile, yarn

INTRODUCTION Textiles are defined as drapeable structures made of fine and flexible fibers and yarns that have a high length/diameter ratio. Fibers and fabrics have to meet special requirements concerning processability and wearability. In order to be comfortable to wear, the fibers of fabrics have to be fine and elastic. They should be able to withstand handling that is typical 


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for textiles, for example weaving, washing and wrinkling, without damaging functionality. Therefore, fabrics need to have a low mechanical resistance to bending and shearing so that they can be easily deformed and draped. The closer the textiles are to the body, the more flexible and lightweight they have to be. The multifunctional textiles such as fashion and environmental protection, ballistic and chemical protection, flame protection are all passive systems. The smart textiles are a new generation of fibers, yarns, fabrics and garments that are able to sense stimuli and changes in their environments, such as mechanical, thermal, chemical, electrical, magnetic and optical changes, and then respond to these changes in predetermined ways [1-3]. They are multifunctional textile systems that can be classified into three categories of passive smart textiles, active smart textiles and very smart textiles [4]. Smart textiles is a new aspect in textile that is a multidiscipline field of research in many sciences and technologies such as textile, physics, chemistry, medicine, electronics, polymers, biotechnology, telecommunications, information technology, microelectronics, wearable computers, nanotechnology and micro-electromechanical machines. Shape memory materials (SMMs), conductive materials, phase change materials (PCMs), chromic materials, photonic fibers, mechanical responsive materials, intelligent coating/membranes, micro and nanomaterials and piezoelectric materials are applied in smart textiles. The objective of smart textile is to absorb a series of active components essentially without changing its characteristics of flexibility and comfort. In order to make a smart textile, firstly, conventional components such as sensors, devices and wires are being reshaped in order to fit in the textile, ultimately the research activities trend to manufacture active elements made of fibers, yarns and fabrics structures. Smart textiles are ideal vehicle for carrying active elements that permanently monitor our body and the environment, providing adequate reaction should something happen. The smart textiles have some of the capabilities such as biological and chemical sensing and responding, power and data transmission from wearable computers and polymeric batteries, transmitting and receiving RF signals and automatic voice warning systems as to ‘dangers ahead’ that may be appropriate in military applications. Other than military applications of smart textiles, mountain climbers, sportsmen, businessmen, healthcare and medical personnel, police, and firemen will be benefitted from the smart textiles technologies. A smart textile can be active in many other fields. Smart textiles as a carrier of sensor systems can measure heart rate, temperature, respiration, gesture and many other body parameters that can provide useful information on the health status of a person. The smart textiles can support the rehabilitation process and react adequately on hazardous conditions that may have been detected. The reaction can consist of warning, prevention or active protection. After an event has happened, the smart textile is able to analyze the situation and to provide first aid. Wearable electronics and photonics, adaptive and responsive structures, biomimetics, bioprocessing, tissue engineering and chemical/drug releasing are some of the research areas in integrated processes and products of smart textiles. There are some areas that the research activities have reached the industrial application. Optical fibers, shape memory polymers, conductive polymers, textile fabrics and composites integrated with optical fiber sensors have been used to monitor the health of major bridges and buildings. The first generation of wearable motherboards has been developed, which has sensors integrated inside garments and is capable of detecting injury and health information of the wearer and transmitting such

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information remotely to a hospital. Shape memory polymers have been applied to textiles in fiber, film and foam forms, resulting in a range of high performance fabrics and garments, especially sea-going garments. Fiber sensors, which are capable of measuring temperature, strain/stress, gas, biological species and smell, are typical smart fibers that can be directly applied to textiles. Conductive polymer-based actuators have achieved very high levels of energy density. Clothing with its own senses and brain, like shoes and snow coats which are integrated with Global Positioning System (GPS) and mobile phone technology, can tell the position of the wearer and give him/her directions. Biological tissues and organs, like ears and noses, can be grown from textile scaffolds made from biodegradable fibers.

PHASE CHANGE MATERIALS Phase change materials (PCM) are thermal storage materials that are used to regulate temperature fluctuations. The thermal energy transfer occurs when a material changes from a solid to a liquid or from a liquid to a solid. This is called a change in state, or phase. Incorporating microcapsules of PCM into textile structures improves the thermal performance of the textiles. Phase change materials store energy when they change from solid to liquid and dissipate it when they change back from liquid to solid. It would be most ideal, if the excess heat a person produces could be stored intermediately somewhere in the clothing system and then, according to the requirement, activated again when it starts to get chilly. The most widespread PCMs in textiles are paraffin-waxes with various phase change temperatures (melting and crystallization) depending on their carbon numbers. The characteristics of some of these PCMs are summarized in Table 1. These phase change materials are enclosed in microcapsules, which are 1–30 m in diameter. Hydrated inorganic salts have also been used in clothes for cooling applications. PCM elements containing Glauber’s salt (sodium sulphate) have been packed in the pockets of cooling vests [5]. PCM can be applied to fibers in a wet-spinning process, incorporated into foam or embedded into a binder and applied to fabric topically, or contained in a cell structure made of a textile reinforced synthetic material. In manufacturing the fiber, the selected PCM microcapsules are added to the liquid polymer or polymer solution, and the fiber is then expanded according to the conventional methods such as dry or wet spinning of polymer solutions and extrusion of polymer melts. Fabrics can be formed from the fibers containing PCM by conventional weaving, knitting or nonwoven methods, and these fabrics can be applied to numerous clothing applications. Table 1. Phase change materials Phase change material Eicosane Nonadecane Octadecane Heptadecane Hexadecane

Melting temperature C 36.1 32.1 28.2 22.5 18.5

Crystallization temperature C 30.6 26.4 25.4 21.5 16.2

Heat storage capacity in J/g 246 222 244 213 237

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In this method, the PCMs are permanently locked within the fibers, the fiber is processed with no need for variations in yarn spinning, fabric knitting or dyeing and properties of fabrics (drape, softness, tenacity, etc.) are not altered in comparison with fabrics made from conventional fibers. The microcapsules incorporated into the fibers in this method have an upper loading limit of 5–10% because the physical properties of the fibers begin to suffer above that limit, and the finest fiber available is about 2.2 dtex. Due to the small content of microcapsules within the fibers, their thermal capacity is rather modest, about 8–12 J/g. Usually PCM microcapsules are coated on the textile surface. Microcapsules are embedded in a coating compound such as acrylic, polyurethane and rubber latex, and applied to a fabric or foam. In lamination of foam containing PCMs onto a fabric, the selected PCMs microcapsules can be mixed into a polyurethane foam matrix, from which moisture is removed, and then the foam is laminated on a fabric [6]. Typical concentrations of PCMs range from 20% to 60% by weight. Microcapsules should be added to the liquid polymer or elastomer prior to hardening. After foaming (fabricated from polyurethane) microcapsules will be embedded within the base material matrix. The application of the foam pad is particularly recommended because a greater amount of microcapsules can be introduced into the smart textile. In spite of this, different PCMs can be used, giving a broader range of regulation temperatures. Additionally, microcapsules may be anisotropically distributed in the layer of foam. The foam pad with PCMs may be used as a lining in a variety of clothing such as gloves, shoes, hats and outerwear. Before incorporation into clothing or footwear the foam pad is usually attached to the fabric, knitted or woven, by any conventional means such as glue, fusion or lamination. The PCM microcapsules are also applied to a fibrous substrate using a binder (e.g., acrylic resin). All common coating processes such as knife over roll, knife over air, screenprinting, gravure printing, dip coating may be adapted to apply the PCM microcapsules dispersed throughout a polymer binder to fabric. The conventional pad–mangle systems are also suitable for applying PCM microcapsules to fabrics. The formulation containing PCMs can be applied to the fabric by the direct nozzle spray technique. There are many thermal benefits of treating textile structures with PCM microcapsules such as cooling, insulation and thermo regulating effect. Without phase change materials the thermal insulation capacity of clothing depends on the thickness and the density of the fabric (passive insulation). The application of PCM to a garment provides an active thermal insulation effect acting in addition to the passive thermal insulation effect of the garment system. The active thermal insulation of the PCM controls the heat flux through the garment layers and adjusts the heat flux to the thermal circumstances. The active thermal insulation effect of the PCM results in a substantial improvement of the garment’s thermo-physiological wearing comfort [7]. Intensity and duration of the PCM’s active thermal insulation effect depend mainly on the heat-storage capacity of the PCM microcapsules and their applied quantity. In order to ensure a suitable and durable effect of the PCM, it is necessary to apply proper PCM in sufficient quantity into the appropriate fibrous substrates of proper design. The PCM quantity applied to the active wear garment should be matched with the level of activity and the duration of the garment use. Furthermore, the garment construction needs to be designed in a way which assists the desired thermo-regulating effect [7]. Thinner textiles with higher densities readily support the cooling process. In contrast, the use of thicker and less dense textile structures leads to a delayed and therefore more efficient heat release of the

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PCM. Further requirements on the textile substrate in a garment application include sufficient breathability, high flexibility, and mechanical stability. In order to determine a sufficient PCM quantity, the heat generated by the human body has to be taken into account carrying out strenuous activities under which the active wear garments are worn. The heat generated by the body needs to be entirely released through the garment layers into the environment. The necessary PCM quantity is determined according to the amount of heat which should be absorbed by the PCM to keep the heat balance equalized [7]. It is mostly not necessary to put PCM in all parts of the garment. Applying PCM microcapsules to the areas that provide problems from a thermal standpoint and thermoregulating the heat flux through these areas is often enough. It is also advisable to use different PCM microcapsules in different quantities in distinct garment locations.

APPLICATIONS OF TEXTILES CONTAINING PCMS Fabrics containing PCMs have been used in a variety of applications including apparel, home textiles and technical textiles (Table 2) [8]. Phase change materials are used both in winter and summer clothing. PCM is used not only in high-quality outerwear and footwear, but also in the underwear, socks, gloves, helmets and bedding of world-wide brand leaders. Seat covers in cars and chairs in offices can consist of phase change materials. Currently, phase change materials are being used in a variety of outdoor apparel items such as smart jackets, vests, men’s and women’s hats and rainwear, outdoor active-wear jackets and jacket lining, golf shoes, trekking shoes, ski and snowboard gloves, boots, earmuffs and protective garments. In protective garments, the absorption of body heat surplus, insulation effect caused by heat emission of the PCM into the fibrous structure and thermo-regulating effect, which maintains the microclimate temperature nearly constant are the specified functions of PCM contained smart textile. The addition of PCMs to a fabric-backed foam significantly increases the weight, thickness, stiffness, flammability, insulation value, and evaporative resistance value of the material. It is more effective to have one layer of PCM on the outside of a tight-fitting, two layer ensemble than to have it as the inside layer. This may be because the PCMs closest to the body did not change phase. Table 2. Application of PCMs in Textiles [8] Casual clothing: Professional clothing: Medical uses: Shoe linings: Building materials: Life style apparel: Other uses:

Underwear, Jackets, sports garments Fire fighters protective clothing, Bullet proof fabrics, Space suits, Sailor suits Surgical gauze, Bandage, Nappies, Bed linings, Gloves, Gowns Caps, Blankets Ski boots, Golf shoes In proof, In concrete Elegant fleece vests, Men’s and women’s hats, Rain wear Automative interiors, Battery warmers

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PCM protective garments should improve the comfort of workers as they go through these environmental step changes (e.g., warm to cold to warm, etc.). For these applications, the PCM transition temperature should be set so that the PCMs are in the liquid phase when worn in the warm environment and in the solid phase in the cold environment [9]. The effect of phase change materials in clothing on the physiological and subjective thermal responses of people would probably be maximized if the wearer was repeatedly going through temperature transients (i.e., going back and forth between a warm and cold environment) or intermittently touching hot or cold objects with PCM gloves [9]. One example of practical application of PCM smart textile is cooling vest (TST Sweden Ab) [5]. This is a comfort garment developed to prevent elevated body temperatures in people who work in hot environments or use extreme physical exertion. The cooling effect is obtained from the vest’s 21 PCM elements containing Glauber’s salt which start absorbing heat at a particular temperature (28 ºC). Heat absorption from the body or from an external source continues until the elements have melted. After use the cooling vest has to be charged at room temperature (24 ºC) or lower. When all the PCMs are solidified the cooling vest is ready for further use [5]. A new generation of military fabrics feature PCMs which are able to absorb, store and release excess body heat when the body needs it resulting in less sweating and freezing, while the microclimate of the skin is influenced in a positive way and efficiency and performance are enhanced. In the medical textiles field, a blanket with PCM can be useful for gently and controllably reheating hypothermia patients. Also, using PCMs in bed covers regulates the micro climate of the patient. In domestic textiles, blinds and curtains with PCMs can be used for reduction of the heat flux through windows. In the summer months large amounts of heat penetrate the buildings through windows during the day. At night in the winter months the windows are the main source of thermal loss. Results of the test carried out by Pause [10] on curtains containing PCM have indicated a 30% reduction of the heat flux in comparison to curtains without PCM.

SHAPE MEMORY MATERIALS Shape memory materials (SMMs) are able to ‘remember’ a shape, and return to it when stimulated, e.g., with temperature, magnetic field, electric field, pH-value and UV light [11– 15]. An example of natural shape memory textile material is cotton, which expands when exposed to humidity and shrinks back when dried. Such behavior has not been used for aesthetic effects because the changes, though physical, are in general not noticeable to the naked eye. The most common types of such SMMs materials are shape memory alloys and polymers, but ceramics and gels have also been developed. When sensing this material specific stimulus, SMMs can exhibit dramatic deformations in a stress free recovery. On the other hand, if the SMM is prevented from recovering this initial strain, a recovery stress (tensile stress) is induced, and the SMM actuator can perform work. This situation where SMM deforms under load is called restrained recovery [16]. Because of the wide variety of different activation stimuli and the ability to exhibit actuation or some other pre-determined response, SMMs can be utilized to control or tune

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many technical parameters in smart material systems in response to environmental changes – such as shape, position, strain, stiffness, natural frequency, damping, friction and water vapor penetration [11, 12]. Both the fundamental theories and engineering aspects of SMMs have been investigated extensively and a rather wide variety of different SMMs are presently commercial materials. Commercialized shape memory products have been based mainly on metallic shape memory alloys (SMAs), either taking advantage of the shape change due the shape memory effect or the super-elasticity of the material, the two main phenomena of SMAs. Shape memory polymers (SMPs) and shape memory gels are developed at a quick rate, and within the last few years also some products based on magnetic shape memory alloys have been commercialized. Shape memory ceramic (SMC) materials, which can be activated not only by temperature but also by elastic energy, electric or magnetic field, are mainly at the research stage.

Applications of Textiles Containing SMMs There are many potential applications of shape memory polymers in industrial components like automotive parts, building and construction products, intelligent packing, implantable medical devices, sensors and actuators, etc. SMPs are used in toys, handgrips of spoons, toothbrushes, razors and kitchen knives, also as an automatic choking device in small-size engines [17]. One of the most well known examples of SMP is a clothing application, a membrane called Diaplex. The membrane is based on polyurethane based shape memory polymers developed by Mitsubishi Heavy Industries. Polyurethane is an example of shape memory polymers which is based on the formation of a physical cross-linked network as a result of entanglements of the high molecular weight linear chains, and on the transition from the glassy state to the rubber-elastic state [18]. Shape memory polyurethane (SMPU) is a class of polyurethane that is different from conventional polyurethane in that these have a segmented structure and a wide range of glass transition temperature (Tg). The long polymer chains entangle each other and a three-dimensional network is formed. The polymer network keeps the original shape even above Tg in the absence of stress. Under stress, the shape is deformed and the deformed shape is fixed when cooled below Tg. Above the glass transition temperature polymers show rubber-like behavior. The material softens abruptly above the glass transition temperature Tg. If the chains are stretched quickly in this state and the material is rapidly cooled down again below the glass transition temperature the polynorbornene chains can neither slip over each other rapidly enough nor become disentangled. It is possible to freeze the induced elastic stress within the material by rapid cooling. The shape can be changed at will. In the glassy state the strain is frozen and the deformed shape is fixed. The decrease in the mobility of polymer chains in the glassy state maintains the transient shape in polynorbornene. The recovery of the material’s original shape can be observed by heating again to a temperature above Tg. This occurs because of the thermally induced shape-memory effect [18]. The disadvantage of this polymer is the difficulty of processing because of its high molecular weight [15]. Some of the shape memory polymers are suitable for textiles applications (Table 3).

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Polymers Polynorbornene Polyurethane Polyethylene/nylon-6 graft copolymer Styrene-1, 4-butadiene block copolymer Ethylene oxide-ethylene terphethalate block copolymer Polymethylene-1, 3-cyclopentane) polyethylene block copolymer

Physical interactions Original shape Chain entanglement Microcrystal Crosslinkig Microcrystal/Glassy state of polystyrene Microcrystal of PET Microcrystal of PE

Transient shape Glassy state Glassy state Microcrystal Microcrystal of poly(1,4butadiene) Microcrystal of PEO Glassy state/microcrystal of PMCP

Shape memory polymers can be laminated, coated, foamed, and even straight converted to fibers. There are many possible end uses of these smart textiles. The smart fiber made from the shape memory polymer can be applied as stents, and screws for holding bones together. Shape memory polymer coated or laminated materials can improve the thermophysiological comfort of surgical protective garments, bedding and incontinence products because of their temperature adaptive moisture management features. Films of shape memory polymer can be incorporated in multilayer garments, such as those that are often used in the protective clothing or leisurewear industry. The shape memory polymer reverts within wide range temperatures. This offers great promise for making clothing with adaptable features. Using a composite film of shape memory polymer as an inter-liner in multilayer garments, outdoor clothing could have adaptable thermal insulation and be used as protective clothing. A shape memory polymer membrane and insulation materials keep the wearer warm. Molecular pores open and close in response to air or water temperature to increase or minimize heat loss. Apparel could be made with shape memory fiber. Forming the shape at a high temperature provides creases and pleats in such apparel as slacks and skirts. Other applications include fishing yarn, shirt neck bands, cap edges, casual clothing and sportswear. Also, using a composite film of shape memory polymers as an interlining provides apparel systems with variable tog values to protect against a variety of weather conditions.

CHROMIC MATERIALS Chromic materials are the general term referring to materials, which their color changes by the external stimulus. Due to color changing properties, chromic materials are also called chameleon materials. This color changing phenomenon is caused by the external stimulus and chromic materials can be classified depending on the external stimulus of induction. Photochromic, thermochromic, electrochromic, piezochromic, solvatechromic and carsolchromic are chromic materials that change their color by the external stimulus of heat, electricity, pressure, liquid and an electron beam, respectively. Photochromic materials are suitable for sun lens applications [19]. Most photochromic materials are based on organic materials or silver particles. Thermochromic materials change color reversibly with changes

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in temperature. The liquid crystal type and the molecular rearrangement type are thermochromic systems in textiles. The thermochromic materials can be made as semiconductor compounds, from liquid crystals or metal compounds. The change in color occurs at a pre-determined temperature, which can be varied. Electrochromic materials are capable of changing their optical properties (transmittance and/or reflectance) under applied electric potentials. The variation of the optical properties is caused by insertion/extraction of cations in the electrochromic film. Piezochromism is the phenomenon where crystals undergo a major change of color due to mechanical grinding. The induced color reverts to the original color when the fractured crystals are kept in the dark or dissolved in an organic solvent [19]. Solvatechromism is the phenomenon, where color changes when it makes contact with a liquid, for example, water. Materials that respond to water by changing color are also called hydrochromic and this kind of textile material can be used, e.g., for swimsuits.

Applications of Textiles Containing Chromic Materials The majority of applications for chromic materials in the textile sector today are in the fashion and design area, in leisure and sports garments. In workwear and the furnishing sector a variety of studies and investigations are in the process by industrial companies, universities and research centers. Chromic materials are one of the challenging material groups when thinking about future textiles. Color changing textiles are interesting, not only in fashion, where color changing phenomena will exploit for fun all the rainbow colors, but also in useful and significant applications in soldier and weapons camouflage, workwear and in technical and medical textiles. The combination of SMM and thermochromic coating is an interesting area which produces shape and color changes of the textile material at the same time [9].

OPTICAL FIBERS IN SMART TEXTILES Optical fibers are currently being used in textile structures for several different applications. Optic sensors are attracting considerable interest for a number of sensing applications [20, 21] There is great interest in the multiplexed sensing of smart structures and materials, particularly for the real-time evaluation of physical measurements (e.g., temperature, strain) at critical monitoring points. One of the applications of the optical fibers in textile structures is to create flexible textile-based displays based on fabrics made of optical fibers and classic yarns [22]. The screen matrix is created during weaving, using the texture of the fabric. Integrated into the system is a small electronics interface that controls the LEDs that light groups of fibers. Each group provides light to one given area of the matrix. Specific control of the LEDs then enables various patterns to be displayed in a static or dynamic manner. This flexible textile-based displays are very thin size and ultra lightweight. This leads one to believe that such a device could quickly enable innovative solutions for numerous applications. Bending in optical fibers is a major concern since this causes signal attenuation at bending points. Integrating optical fibers into a woven perform requires bending because of the crimping that occurs as a result of weave interlacing. However, standard plastic optical fiber (POF) materials like polymethylmethacrylate, polycarbonate and

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polystyrene are rather stiff compared to standard textile fibers and therefore their integration into textiles usually leads to stiffen of the woven fabric and the textile touch is getting lost [23]. Alternative fibers with appropriate flexibility and transparency are not commercially available yet.

CONDUCTIVE MATERIALS IN SMART TEXTILES Several conductive materials are in use in smart textiles. Conductive textiles include electrically conductive fibers fabrics and articles made from them [24]. Flexible electrically conducting and semi-conducting materials, such as conductive polymers, conductive fibers, threads, yarns, coatings and ink are playing an important role in realizing lightweight, wireless and wearable interactive electronic textiles. Generally, conductive fibers can be divided into two categories such as naturally conductive fibers and treated conductive fibers. Naturally, conductive fibers can be produced purely from inherently conductive materials, such as metals, metal alloys, carbon sources, and conjugated polymers (ICPs). Highly conductive flexible textiles can be prepared by weaving thin wires of various metals such as brass and aluminum. These textiles have been developed for higher degrees of conductivity. Metal conductive fibers are very thin filaments with diameters ranging from 1 to 80 μm produced from conductive metals such as ferrous alloys, nickel, stainless steel, titanium, aluminum and copper. Since they are different from polymeric fibers, they may be hard to process and have problems of long term stability. These highly conductive fibers are expensive, brittle, heavier and lower processability than most textile fibers. Treated conductive fibers can be produced by the combination of two or more materials, such as non-conductive and conductive materials. This conductive textiles can be produced in various ways, such as by impregnating textile substrates with conductive carbon or metal powders, patterned printing, and so forth. Conducting polymers, such as polyacetylene (PA), polypyrrole (PPy), polythiophene (PTh) and polyaniline (PAn), offer an interesting alternative. Among them, polypyrrole has been widely investigated owing to its easy preparation, good electrical conductivity, good environmental stability in ambient conditions and because it poses few toxicological problems [25, 26]. PPy is formed by the oxidation of pyrrole or substituted pyrrole monomers. Electrical conductivity in PPy involves the movement of positively charged carriers or electrons along polymer chains and the hopping of these carriers between chains. The conductivity of PPy can reach the range 102 S cm-1, which is next only to PA and PAn. With inherently versatile molecular structures, PPys are capable of undergoing many interactions. The conductive fibers obtained through special treatments such as mixing, blending, or coating are also known as conductive polymer composites (CPCs), can have a combination of the electrical and mechanical properties of the treated materials [23]. Fibers containing metal, metal oxides and metal salts are a proper alternative for metal fibers. Polymer fibers may be coated with a conductive layer such as polypyrrole, copper or gold [27]. The conductivity will be maintained as long as the layer is intact and adhering to the fiber. Chemical plating and dispersing metallic particles at a high concentration in a resin are two general methods of coating fibers with conductive metals.

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The brittleness of PPy has limited the practical applications of it. The processability and mechanical properties of PPy can be improved by incorporating some polymers into PPy [28, 29]. However, the incorporation of a sufficient amount of filler generally causes a significant deterioration in the mechanical properties of the conducting polymer, in order to exceed the percolation threshold of conductivity [30]. Another route to overcoming this deficiency is by coating the conducting polymer on flexible textile substrates to obtain a smooth and uniform electrically conductive coating that is relatively stable and can be easily handled [31, 32]. Thus, PPy-based composites may overcome the deficiency in the mechanical properties of PPy, without adversely affecting the excellent physical properties of the substrate material, such as its mechanical strength and flexibility. The resulting products combine the usefulness of a textile substrate with electrical properties that are similar to metals or semi-conductors. Due to electron-transport characteristics of Conjugated polymers or ICPs, they are regarded as semi conductors or even sometimes conductors. Due to their high conductivity, lower weight, and environmental stability, they have a very important place in the field of smart and interactive textiles [33]. The conductivity of materials is often affected by several parameters which may be exploitable mechanisms for use as a sensor. Extension, heating, wetting and absorption of chemical compounds in general may increase or decrease conductivity. Swelling or shrinkage of composite fibers of carbon nanotubes alters the distance between the nanoparticles in the fibers, causing the conductivity to change. Fibers containing conductive carbon are produced with several methods such as loading the whole fibers with a high concentration of carbon, incorporating the carbon into the core of a sheath–core bicomponent fiber, incorporating the carbon into one component of a side–side or modified side–side bicomponent fiber, suffusing the carbon into the surface of a fiber. Nanoparticles such as carbon nanotubes can be added to the matrix for achieving conductivity. Semi-conducting metal oxides are often nearly colorless, so their use as conducting elements in fibers has been considered likely to lead to fewer problems with visibility than the use of conducting carbon. The oxide particles can be embedded in surfaces, or incorporated into sheath–core fibers, or react chemically with the material on the surface layer of fibers. Conductive fibers can also be produced by coating fibers with metal salts such as copper sulfide and copper iodide. Metallic coatings produce highly conductive fibers; however adhesion and corrosion resistance can present problems. It is also possible to coat and impregnate conventional fibers with conductive polymers, or to produce fibers from conductive polymers alone or in blends with other polymers. Conductive fibers/yarns can be produced in filament or staple lengths and can be spun with traditional non-conductive fibers to create yarns that possess varying wearable electronics and photonics degrees of conductivity. Also, conductive yarns can be created by wrapping a nonconductive yarn with metallic copper, silver or gold foil and be used to produce electrically conductive textiles. Conductive threads can be sewn to develop smart electronic textiles. Through processes such as electrodeless plating, evaporative deposition, sputtering, coating with a conductive polymer, filling or loading fibers and carbonising, a conductive coating can be applied to the surface of fibers, yarns or fabrics. Electrodeless plating produces a uniform conductive coating, but is expensive. Evaporative deposition can produce a wide range of thicknesses of coating for varying levels of conductivity. Sputtering can achieve a uniform coating with

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good adhesion. Textiles coated with a conductive polymer, such as polyaniline and polypyrrole, are more conductive than metal and have good adhesion, but are difficult to process using conventional methods. Adding metals to traditional printing inks creates conductive inks that can be printed onto various substrates to create electrically active patterns. The printed circuits on flexible textiles result in improvements in durability, reliability and circuit speeds and in a reduction in the size of the circuits. The printed conductive textiles exhibit good electrical properties after printing and abrading. The inks withstand bending without losing conductivity. However, after twenty washing cycles, the conductivity decreases considerably. Therefore, in order to improve washability, a protective polyurethane layer is put on top of the printed samples, which resulted in the good conductivity of the fabrics, even after washing [34]. Currently, digital printing technologies promote the application of conductive inks on textiles.

Applications of Conductive Smart Textile Electrically conductive textiles make it possible to produce interactive electronic textiles. They can be used for communication, entertainment, health care, safety, homeland security, computation, thermal purposes, protective clothing, wearable electronics and fashion. The application of conductive smart textile in combination with electronic advices is very widespread. In location and positioning, they can be used for child monitoring, geriatric monitoring, integrated GPS (global positioning system) monitoring, livestock monitoring, asset tracking, etc. In infotainment, they can be used for integrated compact disc players, MP3 players, cell phones and pagers, electronic game panels, digital cameras, and video devices, etc. In health and biophysical monitoring, they can be used for cardiovascular monitoring, monitoring the vital signs of infants, monitoring clinical trials, health and fitness, home healthcare, hospitals, medical centers, assisted-living units, etc. They can be used for soldiers and personal support of them in the battlefield, space programs, protective textiles and public safety (fire fighting, law enforcement), automotive, exposure-indicating textiles, etc. They can be also used to show the environmental response such as color change, density change, heating change, etc. Fashion, gaming, residential interior design, commercial interior design and retail sites are other application of conductive smart textiles.

DESIGNING THE SMART TEXTILE SYSTEMS Comfort is very important in textiles because stresses lead to increased fatigue. The potential of smart textiles is to measure a number of body parameters such as skin temperature, humidity and conductivity and show the level of comfort through the textile sensors. To keep the comfort of textiles, adequate actuators are needed that can heat, cool, insulate, ventilate and regulate moisture. The use of the smart system should not require any additional effort. The weight of a smart textile system should not reduce operation time of the rescue worker.

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Other key issues for the design of a smart textile system are [35]: 

     

Working conditions – relevant parameters: only relevant information should be provided in order to avoid additional workload; this includes indication of danger and need for help. Effective alarm generation: the rescue worker or a responsible person should be informed adequately on what needs to be done. System maintenance: it must be possible to treat the suit using usual maintenance procedures. Cost must be justified Robustness Energy constraints: energy requirements must be optimized Long range transmission: transmission range must be adjusted to the situation of use. Fighting a fire in a building is different from fighting one in an open field.

A wearable smart textile system basically comprises following components [36]:      

Sensors to detect body or environmental parameters; A data processing unit to collect and process the obtained data; An actuator that can give a signal to the wearer; An energy supply that enables working of the entire system; Interconnections that connect the different components; A communication device that establishes a wireless communication link with a nearby base station.

The main layers concerned with smart clothing are the skin layer and two clothing layers. Physically the closest clothing layer for a human user is an underwear layer, which transports perspiration away from the skin area. The function of this layer is to keep the interface between a user and the clothes comfortable and thus improve the overall wearing comfort. The second closest layer is an intermediate clothing layer, which consists of the clothes that are between the underclothes and outdoor clothing. The main purpose of this layer is considered to be an insulation layer for warming up the body. The outermost layer is an outerwear layer, which protects a human against hard weather conditions. The skin layer is located in close proximity to the skin. In this layer we place components that need direct contact with skin or need to be very close to the skin. Therefore, the layer consists of different user interface devices and physiological measurement sensors. The number of the additional components in underwear is limited owing to the light structure of the clothing. An inner clothing layer contains intermediate clothing equipped with electronic devices that do not need direct contact with skin and, on the other hand, do not need to be close to the surrounding environment. These components may also be larger in size and heavier in weight compared to components associated with underclothes. It is often beneficial to fasten components to the inner clothing layer, as they can be easily hidden. Surrounding clothes also protect electronic modules against cold, dirt and hard knocks.

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Generally, the majority of electronic components can be placed on the inner clothing layer. These components include various sensors, a central processing unit (CPU) and communication equipment. Analogous to ordinary clothing, additional heating to warming up a person in cold weather conditions is also associated with this layer. Thus, the inner layer is the most suitable for batteries and power regulating equipment, which are also sources of heat. The outer clothing layer contains sensors needed for environment measurements, positioning equipment that may need information from the surrounding environment and numerous other accessories. The physical surroundings of smart clothing components measure the environment and the virtual environment accessed by communication technologies. Soldier and weapons camouflage is possible by using chromic materials in outer layer of smart textiles.

SMART FABRICS FOR HEALTH CARE The continuous monitoring of vital signs of some patients and elderly people is an emerging concept of health care to provide assistance to patients as soon as possible either online or offline. A wearable smart textile can provide continuous remote monitoring of the health status of the patient. Wearable sensing systems will allow the user to perform everyday activities without discomfort. The simultaneous recording of vital signs would allow parameter extrapolation and inter-signal elaboration, contributing to the generation of alert messages and synoptic patient tables. In spite of this, a smart fabric is capable of recording body kinematic maps with no discomfort for several fields of application such as rehabilitation and sports [37].

ELECTRONIC SMART TEXTILES The components of an electronic smart textile that provide several functions are sensors unit, network unit, processing unit, actuator unit and power unit. On the smart textile, several of these functions are combined to form services. Providing information, communication or assistance are possible services. Because mobility is now a fundamental aspect of many services and devices, these smart textiles can be used for health applications such as monitoring of vital signs of high-risk patients and elderly people, therapy and rehabilitee, knowledge applications such as instructions and navigation and entertainment applications such as audio and video devices [38]. For communication between the different components of smart textile applications, both wired and wireless technologies are applicable. An applied solution for data transferring is often a compromise based on application requirements, operational environment, available and known technologies, and costs.

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Data Transfer Requirements in Smart Textiles The data transfer requirements can be divided into internal and external. The internal transfer services are divided into local health and security related measurements. Many of the services require or result in external communications between the smart clothing and its environment. Wired data transfer is in many cases a practical and straightforward solution. Thin wires routed through fabric are an inexpensive and high capacity medium for information and power transfer. The embedded wires inside clothing do not affect its appearance. However, wires form inflexible parts of clothing and the detaching and reconnecting of wires decrease user comfort and the usability of clothes [39]. The cold winter environment especially stiffens the plastic shielding of wires. In hard usage and in cold weather conditions, cracking of wires also becomes a problem [39]. The connections between the electrical components placed on different pieces of clothing are another challenge when using wires. During dressing and undressing, connectors should be attached or detached, decreasing the usability of clothing. Connectors should be easily fastened, resulting in the need for new connector technologies. A potential alternative to plastic shielded wires is to replace them with electrically conductive fibers. Conductive yarns twisted from fibers form a soft cable that naturally integrates in the clothing’s structure keeping the system as clothing-like as possible. Fiber yarns provide durable, flexible and washable solutions. Also lightweight optical fibers are used in wearable applications, but their function has been closer to a sensor than a communication medium [40, 41]. The problem of conductive fibers is due to the reliable connections of them. Ordinary wires can be soldered directly to printed circuit boards, but the structure of the fiber yarn is more sensitive to breakage near the solder connections. Protection materials that prevent the movement of the fiber yarn at the interface of the hard solder and the soft yarn must be used. Optical fibers are commonly used for health monitoring applications and also for lighting purposes [42]. Low-power wireless connections provide increased flexibility and also enable external data transfer within the personal space. Different existing and emerging WLAN and WPAN types of technologies are general purpose solutions for the external communications, providing both high speed transfer and low costs. For wider area communications and full mobility, cellular data networks are currently the only practical possibility.

Electrical Circuits in Smart Textile Structures In order to form flexible circuit boards, printing of circuit patterns is carried out on polymeric substrates such as films. Fabric based circuits potentially offer additional benefits of higher flexibility in bending and shear, higher tear resistance, as well as better fatigue resistance in case of repeated deformation. Different processes that have been described in literature for the fabrication of fabric based circuits include embroidery of conductive threads on fabric substrates, weaving and knitting of conductive threads along with nonconductive threads, printing or deposition and chemical patterning of conductive elements on textile substrates. The insulating fabric could be woven, non-woven, or knitted. The conductive threads can be embroidered in any shape on the insulating fabric irrespective of the constituent yarn path

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in a fabric. One of the primary disadvantages of embroidery as a means of circuit formation is that it does not allow formation of multi-layered circuits involving conductive threads traversing through different layers as is possible in the case of woven circuits. Conductive threads can be either woven or knitted into a fabric structure along with nonconductive threads to form an electrical circuit. One of the limitations of using weaving for making electrical circuits is that the conductive threads have to be placed at predetermined locations in the warp direction while forming the warp beam or from a creel during set up of the machine. Different kinds of conductive threads can be supplied in the weft or filling direction and inserted using the weft selectors provided on a weaving machine. Some modifications to the yarn supply system of the machine may be needed in order to process the conductive threads that are more rigid. In most conventional weft knitting machines, like a flatbed machine, the conductive threads can be knitted in the fabric only in one direction, i.e., the course (or cross) direction. In order to keep the conductive element in a knit structure straight, one can insert a conductive thread in the course direction such that the conductive thread is embedded into the fabric between two courses formed from non-conductive threads. Processes that have been employed to form a patterned conductive path on fabric surfaces include deposition of polymeric or nonpolymeric conducting materials and subsequent etching, reducing, or physical removal of the conductive materials from certain regions. Thus, the conductive material that is not removed forms a patterned electrical circuit or a region of higher conductivity. The biggest problem associated with patterning of circuits from thin conductive films (polymeric or metallic) deposited on fabric substrates is that use of an etching agent for forming a circuit pattern leads to non-uniform etching, as some of the etching liquid is absorbed by the threads of the underlying substrate fabric [43-45]. Another problem with deposition of conductive films on fabric substrates is that bending the fabric may lead to discontinuities in conductivity at certain points. There are different device attachment methods like raised wire connectors, solders, snap connectors, and ribbon cable connectors in electronic smart textiles. Soldering produces reliable electrical connections to conductive threads of an electronic textile fabric but has the disadvantage of not being compatible with several conductive threads or materials like stainless steel. Moreover, soldering of electronic devices to threads that are insulated is a more complex process involving an initial step of removal of insulation from the conductive threads in the regions where the device attachments are desired and insulation of the soldered region after completion of the soldering process. The main advantage of employing snap connectors is the ease of attachment or removal of electronic devices from these connectors, whereas the main disadvantages are the large size of the device and the weak physical connection formed between the snap connectors and the devices. Ribbon cable connectors employ insulation displacement in order to form an interconnection with insulated conductor elements integrated into the textiles. A v-shaped contact cuts through the insulation to form a connection to the conductor. Firstly, the ribbon cable connector is attached to the conductive threads in an e-textile fabric and subsequent electronic devices and printed circuit boards are attached to the ribbon cable connector. One of the advantages of employing ribbon cable connectors for device attachment is the ease of attachment and removal of the electronic devices to form the electronic textiles.

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Tao, X. M. (2001). Smart Fibers, Fabrics and Clothing, Woodhead Publishing Limited, England, ISBN 1 85573 546 6. Culshaw, B. (1996). Smart Structures and Materials, Artech House, USA. Seinivasan, A. V., and Mcfarland D. M. (2001). Smart Structures, Cambridge University Press, UK. Schwarz, A., Langenhove, L. V., Guermonprez, P., Deguillemont, D. (2010). A roadmap on smart textiles. Textile Progress 42:2, 99-180 http://www.tst-sweden.com/en, 2013. Pause, B. (2001). New possibilities in medicine: Textiles treated with PCM microcapsules. Lecture No. 627, 10th International Symposium for Technical Textiles, Nonwovens and Textile Reinforced Materials, 7 p. Pause, B. (2000). Tailored to the purpose: Computer-optimized development of thermoregulated active wear. Lecture No. 333. International Avantex-symposium, Frankfurt, Germany, 8 p. Keyan, K., Ramachandran, T., Shumugasundaram, O. L., Balasubramaniam, M., and Ragavendra, T. (2012). Microencapsulation of PCMs in Textiles: a review. Journal of Textile and Apparel, Technology and Management 7(3), 1-10. Mattila, H., (2006). Intelligent textiles and Clothing, Woodhead Publishing Limited, England, ISBN 184569 005 2. Pause, B. (2001). Possibilities for air-conditioning buildings with Phase Change Material. Technical Tex. Int. 44 (1), 38–40. Lendlein, A., and Kelch, S. (2002). Shape-memory polymers. Angew. Chem. Int. 41, 2034–2057. Okano, T., Kikuchi, A. (1996). Intelligent biointerface: remote control for hydrophilic hydrophobic property of the material surfaces by temperature, Proceeding of the third international conference on intelligent materials. Third European conference on smart structures and materials, Lyon, F., Gobin, P. F. and Tatibouët, J. (Ed.). 34–41. Koshizaki, N., Yasumoto, K., Yano, S., Yoshida, H. (1992). Intelligent Functionalities of Composite Materials. Bulletin of Industrial Research Institute, No 127, 99–128. Srinivasan, A. V., McFarland, D. M. (2001). Shape Memory Alloys, Smart Structures. Cambridge University Press, 26–72. Otsuka, K., Wayman, C. M. (1998). Shape memory materials. Cambridge University Press, 203–219, ISBN: 052144487. Mondal, S., Hu, J. L., Yang, Z., Liu, Y., and Szeto, Y. S. (2002). Shape memory polyurethane for smart Garment. Research Journal of Textile and Apparel 6 (2), 75–83. Wang, M., Luo, X., Ma, D. (1998). Dynamic mechanical behavior in the ethylene terephthalate-ethylene oxide copolymer with long soft segment as a shape memory material. European Polymer J., 34(1), 1–5. Mather, P. T., Jeon, H. G., Haddad, T. S. (2000). Strain recovery in POSS hybrid thermoplastic. Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 41, 528–529. Bouas-Laurent, H., Dürr, H. (2001). Organic Photochromism, IUPAC Technical Report. Pure Appl. Chem. 73(4), 639–665.

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[20] Kersey, A. D., Davis, M. A., Morey, W. W. (1993). Quasi-distributed Bragg-grating fiber-laser sensor, Proceedings OFS’9, Florence Italy, postdeadline paper PD-5. [21] Xu, M. G., Reekie, L., Chow, Y. T., Dakin, J. P. (1993). Optical in-fiber grating high pressure sensor. Electron. Lett., 29(4), 398–399. [22] Deflin, E., Koncar, V. (2002). For communicating clothing: The flexible display of glass fiber fabrics is reality. Second International Avantex Symposium, Frankfurt, Germany. [23] Rothmaier, M., Luong, M. P., Clemens, F. (2008). Textile Pressure Sensor Made of Flexible Plastic Optical Fibers. Sensors 8, 4318-4329. [24] Marchini, F. (1991). Advanced applications of metalized fibers for electrostatic discharge and radiation shielding. J. Coated Fabrics 20, 153–166. [25] Omastova, M., Pavlinec, J., Pionteck, J., Simon, F. (1997). Synthesis, electrical properties and stability of polypyrrole-containing conducting polymer composites. Polym. Int. 43(2), 109–116. [26] Thiéblemont, J. C., Brun, A., Marty, J., Planche, M. F., Calo, P. (1995). Thermal analysis of polypyrrole oxidation in air. Polymer 36, 1605–1610. [27] Bashir, T. (2013). Conjugated Polymer-based Conductive Fibers for Smart Textile Applications. PHD Thesis, ISBN: 978-91-7385-814-4. [28] Ruckenstein, E., Chen, J. H. (1991). Polypyrrole conductive composites prepared by coprecipitation, Polymer 32(7), 1230–1235. [29] Truong, V. T., Riddell, S. Z., Muscat, R. F. (1998). Polypyrrole based microwave ab sorbers. J. Mater. Sci. 33(20), 4971–4976. [30] Chen, Y. P., Qian, R. Y., Li, G., Li, Y. (1991). Morphological and mechanical behaviour of an in situ polymerized polypyrrole/Nylon 66 composite film. Polym. Commun. 32(6), 189–192. [31] Gregory, R. V., Kimbrell, W. C., Huhn, H. H. (1991). Electrically conductive nonmetallic textile coatings. J. Coated Fabrics 20(1), 167–175. [32] Heisey, C. L., Wightman, J. P., Pittman, E. H., Kuhn, H. H. (1993). Surface and adhesion properties of polypyrrole-coated textiles. Textile Res. J. 63(5), 247–256. [33] Batchelder, D. N. (1988). Colour and chromism of conjugated polymers. Contemporary Physics 29(1): p. 3-31. [34] Kazani, I., Hertleer, C., De Mey, G., Schwarz, A., Guxho, G., Van Langenhove, L. (2012). Electrical Conductive Textiles Obtained by Screen Printing. Fibres and Textiles in Eastern Europe. 201(90) 57-63. [35] Kiekens, P., and Jayaraman, S. (2010). Intelligent Textiles and Clothing for Ballistic and NBC Protection, Springer, ISBN 978-94-007-0576-0. [36] Ajmera, N., Dash, S. P, Meena, C. R. (2013). Smart Textile. www.fibre2fashion.com. [37] Pacelli, M., Paradiso, R., Anerdi, G., Ceccarini, S., Ghignoli, M., Lorussi, F., Scilingo, E. P., De Rossi, D., Gemignani, A., Ghelarducci, B. (2001). Sensing threads and fabrics for monitoring body kinematic and vital signs. Proceedings of Fibers and Textiles for the Future Conference, Tampere, Finland, 55–63. [38] Tao, X. M. (2005). Wearable electronics and Photonics. Woodhead Publishing Limited, ISBN 1 85573 605 5. [39] Rantanen, J., Impiö, J., Karinsalo, T., Malmivaara, M., Reho, A., Tasanen, M., Vanhala, J. (2002). Smart clothing prototype for the arctic environment. Personal and Ubiquitous Computing 6(1), 3–16.

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[40] Lind, E. J., Jayaraman, S., Eisler, R., McKee, T., (1997). A sensate liner for personnel monitoring applications, 1st International Symposium on Wearable Computers (ISWC). Cambridge, MA, USA, 98–105. [41] Lee, K., Kwon, D. (2001). Wearable master device using optical fiber curvature sensors for the disabled, International Conference on Robotics & Automation. Seoul, Korea, 892–896. [42] http://www.lumitex.com/medical-devices, 22.06.2013. [43] Locher, I., Kirstein, T., Tröster, G. (2002). Electronic Textiles, Proc. of ICEWES Conference, Cottbus, Germany, 1-14. [44] DeAngelis, A. R., Child, A. D., Green, D. E. (1995). Patterned conductive textiles, US Patent 5624736. [45] Kuhn, H. H., Kimbrell Jr., W. C. (1987). Electrically conductive textile materials and method for making same, US Patent 4803096.



Chapter 9

OVERVIEW OF TEXTILES EXCAVATED IN GREECE Christina Margariti*, Stavroula Moraitou and Maria Retsa Textile conservator, Directorate of Conservation of Ancient and Modern Monuments / Hellenic Ministry of Culture, Athens, Greece

ABSTRACT Research was conducted through the Archives of the Hellenic Ministry of Culture and Tourism, the literature, and a questionnaire sent to museums, and regional services of the Ministry in order to provide an overview of the condition of excavated textiles. A preliminary statistical analysis of the data collected identified four types of preservation: 1) in association with a metal present (which for the vast majority of the finds is copper); 2) in association with salts (such as calcium salts); 3) incomplete burning (carbonisation); and 4) inhumation burials. It also showed that only 56% of the finds have received a conservation treatment that has been properly recorded. In addition, there were only three cases where conservators, archaeologists and textile historians had produced a common publication, indicating that collaboration between them was limited. In general, this review showed that, in contrary to the general notion, a considerable number of textiles have been preserved (90), in an excavation context, in Greece.

ABBREVIATIONS AIC CTR ECCO IIC JAIC NATCC UKIC

*

American Institute for Conservation Centre for Textile Research European Confederation of Conservator-Restorer’s Organizations International Institute for Conservation Journal of the American Institute for Conservation North American Textile Conservation Conference United Kingdom Institute for Conservation


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INTRODUCTION Textiles have been indissolubly connected with numerous aspects of human life and culture. They have been records of everyday life conditions, products of technology, social, religious, and cultural symbols, exchangeable commodities, and works of art and crafts, and hence worth conserving as evidence of the evolution of human culture. Conservation is the comprehensively documented action taken by adequately qualified professionals, to diagnose the condition of cultural property in order to retard or prevent deterioration or damage, and to retain its significance as primary evidence, by control of the environment, whether in store, display or transport, and/or treatment of the structure, and/or research that conforms to established legal, ethical and academic practices, in order to maintain it as nearly as possible in an unchanging state, accessible to present and future generations [1,2,3]. Archaeology is a highly esteemed, prolific science, in Greece. Extensive research has been and still is conducted in areas such as, architecture, ceramics, metalsmithing, and sculpting but this is not the case with textiles. There is the general notion in Greece, that survival of textiles in a burial context is rare, a fact that inhibits a comprehensive research. The scope of this paper is, therefore, to identify the current condition of textiles excavated in Greece. The term ‘condition’ is more generally used here, to include the physical condition of the finds as this has been recorded, and the general situation concerning these textiles on issues such as, location, analysis, conservation and publication. This research aimed to determine their present location and storage and/or display environments, whether they had been conserved, whether the finds had been published, and finally to provide the approximate number of excavated textiles retrieved within Greece.

CHRONOLOGICAL TABLE OF TEXTILES EXCAVATED IN GREECE Information was collected from several different sources such as, the General and Sampling Archives of the Hellenic Ministry of Culture, the literature, archaeological journals, symposia and conferences, a questionnaire distributed around the museums and regional services of the Ministry, and personal communication with conservators, archaeologists and textile researchers. The fields included in the table were: 1) Reference Name, according to which the finds are known, for easier reference; 2) Period and Area of Origin, to achieve a chronological order; 3) Type and Date of Excavation, to record whether the finds were from a recent or old and a systematic or rescue excavation; 4) Type and State of Preservation, to identify how textiles have been preserved in Greece, in an excavation context; 5) Type of Fibre/Dye/Other Decoration, to record any information on previous analyses of the finds; 6) Conservation, to present an overview of the conservation of excavated textiles in Greece; 7) Present Location, to locate the finds; 8) Study, and 9) Publication Conservation/Archaeological/Technological, to determine the level of collaboration between conservators, archaeologists and textile researchers in Greece. The finds were put in order by the period of origin, thus putting them in a chronological order, which was thought to be the simplest and most objective way.

Overview of Textiles Excavated in Greece

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The total number of textiles recorded was ninety (90) at the time of writing, hence a considerable number of textiles have been excavated, which is in contrast to the general notion, that textiles do not survive in an excavation context in Greece. Moreover, the number 90 is not representing the actual number of textiles preserved, but the homogeneous groups of textiles that have survived under certain conditions. More often than not, there are indications that the fragments, though numbered as one, come from different textiles. However, the aim of this table was to identify the different cases where textiles have been preserved, rather than the actual number of different textiles. In the following sections approximate percentages are used to present the preliminary statistical analysis results. The percentages are calculated and quoted to the nearest integer according to the ratio of the number of finds falling under the same category to the total number of finds present in the table.

Types of Preservation of Textiles Excavated in Greece Four types of preservation were identified: 1) in association with a metal present (66%); 2) inhumation burials (14%); 3) in association with salts from a ceramic and/or stone container (7%); and 4) carbonisation (8%). High Relative Humidity (RH) values, elimination of oxygen or a combination of the above seem to be the reasons for preservation in inhumation burials. For 5% of the finds the type of preservation is unknown. Note that these are the types of preservation as recorded in the sources. The condition of several of the finds has never been comprehensively studied and assessed. The results are better illustrated in the pie chart (Figure 1).

Figure 1. Pie chart showing the percentages of the types of preservation of textiles excavated in Greece.

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Different Metals Responsible for the Preservation of Textiles Excavated in Greece The cases where textiles have been preserved in association with metals can be further analysed according to the type of metal present. Copper was the metal present in 76% of the cases, gold 5%, iron 5%, lead 5%, silver 2%, combination of metals 5%, and unidentified metal 2% (Figure 2).

Figure 2. Pie chart showing the percentages of the different metals responsible for the preservation of textiles excavated in Greece.

A considerable amount of textiles (76%) have been preserved due to the presence of copper in their burial environment. This may indicate that if copper was present in a burial environment there is high likelihood that any textiles in its proximity would be preserved.

Textile Preservation in Association with Metals The preservation of textiles in association with metals is one of the most important methods of preservation with abundant examples worldwide. Textiles have been recovered from sites all over the world, which have been preserved through their association with metals such as copper, iron, silver or lead [4]. Of particular interest is the fact that these textiles may have been preserved under conditions which would otherwise have detrimental effects on them [5]. The exact mechanisms of textile preservation in association with metal are not yet understood [6]. The process of textile preservation in association with a metal is known as mineralisation. The process of mineralisation begins when the organic fibres of a textile, which is in close contact with a metal object, are gradually replaced by the metal corrosion products [7]. At a molecular level, it means that the atoms of the fibres are replaced by metal ions or the spaces between the molecular chains are filled with metal ion complexes. The progress of this process may terminate at any time or continue until the replacement is complete [8]. In any case, the physical shape of the fibre is preserved [9]. The mineralisation process could be broken down into three stages: 1) the corrosion of the metal, which is dependent on factors such as, the amount of water, oxygen, carbon


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dioxide, micro-organism and organic matter, temperature, salts, acids, and soil porosity. Corrosion is an electrochemical reaction, that is a reaction between negatively (organic fibres) and positively (metal ions) charged atoms [10]; 2) the migration of the metal ions, when they move towards the organic fibre, and; 3) the precipitation of the metal ions on the textile fibre. For precipitation, and finally replacement, to occur the organic fibre must be preserved. Certain metal ions, such as copper, nickel, mercury and lead, act as micro-organisms inhibitors, hence the fibres are not attacked by bacteria [4, 11]. The environmental factors prevailing, the amount of textile fibres and metal present, even the position of the textile in relation to the metal are of crucial importance to the mineralisation of the fibres. Hence, not all fibres, or even the whole fibre, of a textile may be mineralised, if at all, at the same stage. Indeed, Mannering and Peacock [6] when analysing mineralised samples, found that in several cases, areas of the same object had reached different stages of mineralisation. It is possible that the partially replaced fibres are at an intermediate stage of being fully replaced by the corrosion products [8]. The total replacement of the organic matter of the textile fibre by the metal corrosion products results in the formation of a pseudomorph. The term literally describes the formation of an object, which looks like a fibre but chemically speaking, it is not a fibre. Meaning that it retains all the morphological characteristics of the fibre, and in consequence of the textile, but none of the original constructive organic elements is present, since they have been replaced by the inorganic metal corrosion products. The fibre formations in pseudomorphs are solidly filled with inorganic material and have bigger dimensions than their organic predecessors [4,12]. Nevertheless, Gillard et al. [9] when reporting the results of the experiments they conducted indicate that total replacement is rarely achieved and that true pseudomorphs are uncommon. In spite of the fact that the mineralisation process is not fully understood, thus not providing an adequate answer as to why the textiles have been preserved, the excavated finds are evidence of how textiles have been preserved. There is a marked difference in the preservation of textiles in association with metals. There are either positive casts formed, where the metal corrosion products precipitate within the fibre, and negative casts, where metal corrosion products deposit on the fibre surface [4,9,13]. In order for a positive cast to be formed, the concentration of the metal ions needs to be high enough for its biocidal action to be effective, yet low enough for the ions to penetrate the fibre rather than to deposit on its surface in the form of encrustations. Copper has biocidal properties, because of the toxicity of its salts to micro-organisms [7], hence the fibre is preserved long enough to be impregnated by the copper corrosion products. Even small-scale degradation, other than that occurring by micro-organisms, promotes mineralisation, since even the crystalline regions of the fibres are more susceptible to impregnation by copper corrosion products [9]. Thus copper is commonly associated with the formation of positive casts. In certain cases even evidence of the original colour of the fibre has been preserved [14]. Although copper has been found to act as a catalyst in cellulosic degradation, it also forms a barrier around and/or within the fibre, which protects it from the micro-organisms. The kinetics of these contradictory actions of copper have not yet been identified. Nevertheless, it has been suggested that when the biocidal action of the copper corrosion products is predominant, then partially mineralised fibres are formed. In contrast, when the catalysis of cellulose hydrolysis by copper corrosion products is predominant, then pseudomorphs are formed [4,8].

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Lead and silver have been reported to have a similar action to copper in the process of mineralisation. Meaning that the corrosion products of these two metals have biocidal properties and are able to impregnate the textile fibres to form positive casts [6,13,14]. Iron on the other hand, does not have marked biocidal properties and its rate of corrosion is much faster than that of copper. As a result, there is not sufficient time for the iron corrosion products, which are readily formed, to penetrate the fibre before this is degraded by micro-organisms. In addition, Iron (III), which is one of the main forms of iron corrosion products is highly insoluble, thus even harder to penetrate the fibre. Nevertheless, due to the fast rate of iron corrosion there is plenty of time for the corrosion products to precipitate on the surface of the fibre before this is perished due to the action of micro-organisms. Hence iron corrosion products precipitate on the fibre’s surface, forming negative casts [9,10,15]. The fibre inside the cast could be either totally perished or preserved in varying stages of degradation [14]. Whether the imprint on the cast is recognisable depends on the rate of fibre degradation compared to the rate of metal corrosion. In essence, it depends on whether there was sufficient time for the metal corrosion products to encapsulate the fibre before this had decayed to an unrecognisable degree [15]. Only rarely casts which are partly positive and partly negative have been detected on the same object [4, 6].

Textile Preservation in Association with Salts Sodium chloride (common salt) has been reported to preserve skin and cloth from the Iron Age salt mines at Halstatt in Austria due to its property of inhibiting the growth of micro-organisms [16]. Calcium salts from sources such as limestone, shell and bone have been reported to be responsible for the preservation of plants and invertebrates by mineral replacement [17]. Textile Preservation by Carbonisation In carbonisation, similarly to mineralisation, the nature of the textile fibres changes irreversibly, though not from organic to inorganic, but from cellulosic or proteinaceous material to carbon. It is the irreversible chemical reaction of incomplete burning, similar to that of wood becoming charcoal. The carbonised textiles are black and very brittle, but short lengths of fibre may remain virtually intact [16]. Several articles have been found in the literature review, where carbonised textiles are reported. Nevertheless, none of them offers an explanation or even raises hypotheses as to why these textiles have been preserved. Wild [13] presents the case of a 60 AD Roman legionary base in Colchester, where the rebel forces set fire to timber buildings. A mattress was not consumed by the heat, but carbonised. The diamond twill weave is still recognisable, although the fibres are distorted. Excavations at the cities around Vesuvius, buried by the eruption of the volcano in AD 79, have brought many textile fragments to light. These have been preserved in various degrees of carbonisation [18]. Textile Preservation in High Moisture Content and Low Oxygen Levels The growth of micro-organisms is a major factor for the destruction of textiles in burial environments. Low oxygen levels inhibit the growth of micro-organisms providing a favourable environment for the preservation of textiles, and organic materials in general [19].


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In Northern and Central Europe, textiles are usually preserved due to the combination of high moisture and low oxygen levels [13, 16]. In Greece, the low oxygen levels have usually been achieved in combination with a metal present, in the form of a sealed metal vessel that had been preserved intact, and in sealed inhumation burials.

States of Preservation of Textiles Excavated in Greece Four states of preservation were identified: 1) object/s 11% (a complete or incomplete find with a defined shape, even if there are numerous areas of loss); 2) Fragment/s 56% (one or more loose parts of one or more textiles, with no attachment between them); 3) Remains 28% (textile yarns/threads/fibres that are loose and/or deposited on a foreign surface); 4) Traces 2% (imprint of a textile and/or yarns/threads/fibres on another surface); and unknown 3% (Figure 3).

Figure 3. Pie chart showing the percentages of the states of preservation of textiles excavated in Greece.

The majority of the finds have been preserved as fragments. Remains are fewer than fragments and whole objects even less. Preservation in the form of traces, is extremely low. An obvious question is whether the recording methods traditionally used and the tight time limits of especially rescue excavations, are inadequate for the salvation of obscured and extremely vulnerable traces of textiles.

TEXTILE FINDS PRESERVED AS COMPLETE OBJECTS In the case of textile finds preserved as complete objects, the percentage (11%) represents ten case studies.

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Five of the finds have been preserved enclosed in copper vessels, one enclosed in lead, one in gold, two in contact with a copper vessel, and two have been preserved in inhumation burials. It is interesting that the aforementioned finds cover a wide date range from the 8th c. BC to the 15th c. AD. Hence, the time length of the burial does not correspond to the condition of the find. Achievement of favourable conditions is far more important. Seven out of the ten finds that have been preserved as whole objects were found inside sealed metal containers, i.e., in association with a metal in combination with limited amounts of oxygen present. Five out of these seven containers were made of copper. Therefore, the combination of copper with oxygen elimination provides the most favourable environment for the preservation of textiles within Greece.

Types of Fibres Both cellulosic and proteinaceous fibres have been identified. In most of the cases fibre identification has been achieved by the means of an optical microscope or a Scanning Electron Microscope. In one case study TLC analysis confirmed by HPLC analysis identified the remains of wool fibres. In more detail, the types of fibres identified were: cellulosic (20%), flax (23%), cotton (4%), hemp (3%), silk (7%), wool (8%), combination of fibres (8%) and unidentified fibres (27%). These results are better illustrated in the following pie chart (Figure 4). The largest percentage represents unidentified fibres. This indicated that either the majority of the finds have not been adequately analysed or their condition does not allow for conclusive fibre identification.

Figure 4. Pie chart showing the percentages of the types of fibres found in textiles excavated in Greece.


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ASSOCIATING THE TYPE OF FIBRE WITH THE TYPE OF PRESERVATION Some observations were made according to the type of fibre and the type of preservation, and are presented below (Table I). Table 1. Preservation of certain types of fibres according to the type of preservation Type of fibre Cellulosic

Total percentage 20%

Flax

23%

Cotton

4%

Hemp

3%

Silk

7%

Wool

8%

Combination of fibres

8%

Unidentified fibres

27%

Percentage according to type preservation 15% – in association with copper 1% – in association with gold 1% – in association with silver 1% – carbonisation 1% – inhumation burial 1% – unknown 21% – in association with copper 1% – in association with a combination of metals 1% – unknown 2% – in association with copper 1% – in association with gold 1% – carbonisation 3% - in association with copper 2% – in association with copper 4% – inhumation burial 1% – unknown 1% – in association with copper 1% – in association with gold 1% – in association with lead 3% – carbonisation 2% – inhumation burial 5% – in association with copper 2% – in association with salts 1% – carbonisation 8% – in association with copper 3% – in association with iron 1% – in association with silver 3% - in association with salts 3% – carbonisation 7% – inhumation burial 2% - unknown

Cellulosic finds represent 50% of the total, unidentified fibres 27%, proteinaceous fibres 15%, and combination of fibres 8%. Forty-one percent (41%) of the cellulosic fibres have

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been preserved in association with copper and 21% of that is flax fibres preserved in association with copper. There are three possible explanations. First, flax is more resistant than cotton due to its higher proportion of crystalline regions within the fibre. Hence, it has greatest chances of survival in an excavation context [20]. Second, cotton cultivation is believed to have reached Greece through India and Egypt at a later date than flax, hence the use of cotton textiles in ancient Greece was rare [21]. Third, flax is a cellulosic bast fibre. Fibres belonging to that type, such as hemp and nettle, share common morphological characteristics, such as nodular thickening along their length, polygonal cross-sections, thick cell walls and narrow lumens and they occur in bundles [21, 22, 23, 24]. It could be possible that some of the fibres identified as flax were other cellulosic bast fibres. As far as proteinaceous fibres are concerned, they are almost equally divided in silk (7%) and wool (8%). Four percent (4%) of the silk finds have been preserved in inhumation burials. Inhumations are in general alkaline environments due to the body decomposition products. Silk is relatively resistant to alkalis [20], due to the absence of disulphide bonds in its proteins and high crystallinity, i.e., decreased accessibility [9]. Wool on the other hand, is markedly affected by alkalis [20], because they are responsible for the breakdown of the disulphide bonds within the wool proteins [9]. Indeed, only two (2%) of the woolen fibres identified have been preserved in an inhumation burial. There are certain methods of preservation which are mainly associated with unidentified fibres, such as: in association with iron (3%); in association with silver (1%); in association with salts (3%); and inhumation burial (7%). For the cases with the iron and salts, a possible explanation could be that, as mentioned before, they tend to precipitate on the surface of the fibres rather than penetrating them [9,10,15], which would account for severe masking of the fibres’ morphology, hence increased difficulty in identifying them. For the cases of silver and inhumation burials, possibly the preservation of fibres is not as good for their morphological characteristics to be retained, again inhibiting identification.

CONSERVATION Four methods of treatment were identified: 1) First Aid (29%, which is mainly consolidation); 2) Preventive (8%); 3) Interventive (9%); and 4) Combination of treatments (10%). In 44% of the cases no treatment has been applied or this has never been recorded. These results are better shown in a pie chart (Figure 5). A preliminary observation of the type of treatment applied to the finds, according to the date when this was applied and the dates (middle 1990’s) when a more systematic technical examination initiated, revealed the following. Consolidation has been traditionally used as means of First Aid treatment from the first half of the 20th century until the end of the 1990’s. At this point the results of technical examination started being published [e.g., 25,26,27]. However, consolidants may obscure and/or confuse the results of such investigations, and this may have prompted the coincidental change in conservation approach. The first interventive treatments recorded, took place in the first half of the 1950’s and continued through the late 1970’s and 1980s. Another interventive method of treatment has been recorded later in 2000 [28]. Preventive conservation, i.e., the provision of a controlled environment and/or


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appropriate storage, started being applied in the second half of the 1990’s – beginning of 2000’s.

Figure 5. Pie chart showing the percentages of the types of conservation treatments applied to textiles excavated in Greece.

Collaboration Recording the studies and publications of the analysis and/or conservation of the finds afforded the opportunity to make observations on the collaboration between conservators, archaeologists and textile historians, in Greece. Almost 50% of the finds have been studied. Half of that percentage has been studied by conservators in the process of treatment. As far as publications are concerned, 40% of the finds have been published by archaeologists [e.g., 29,30,31], 20% by textile historians [e.g., 26,27,32,33] and only 4% have been published by conservators [e.g., 28]. There are only three joint publications of conservators, archaeologists and textile historians [28,34,35], indicating that collaboration between the aforementioned professionals has been limited but is now growing. It is in the author’s belief that the educational background of a professional is reflected in their conduct. In Greece, archaeology is a highly esteemed science and has been taught at a University level since 1837. On the other hand, the National School of Conservation was founded in 1985 at a Technological and not a University level. Even today this School has not been upgraded to a University level. Moreover, Art History studies have only been available in Greece, at a University level, since 2006. Consequently, in Greece, archaeologists are always in charge of any potential collaboration between these professionals, conservators are more often than not considered to be technicians, and art historians are rare and usually their

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role is taken by the archaeologist. As a result, collaboration between them becomes a thorny issue.

Collaboration between Conservators, Archaeologists and Textile Historians Archaeology is the science that studies the material culture of the past, in order to reconstruct it. Studying the material culture means interpreting the evidence held within objects [36]. In the past, the predominant notion was that very rarely textiles survive in a burial context, therefore archaeological interest in them was limited [37]. At present this situation has changed. An interest of the archaeologists in more social and economic questions along with the fact that a considerable amount of textile finds has been retrieved, has raised the awareness of archaeologists about excavated textiles [38]. Conservators are the professionals responsible for the long-term preservation of objects. To them, the object’s life continues after excavation, it just changes form. It is still considered to be an information recipient and care is taken not to undertake a treatment that would interfere with its new history. Conservation goes beyond the application of the appropriate treatment. The presence of a specialised conservator would not only ensure the welfare of the finds but also aid the yielding of information held within them. Conservation enables, increases and clarifies the interpretation of objects, and this is attributed to two main reasons: One reason is the examination methods used in conservation, which can unlock information held within a degraded object. Odegaard [39] presented a case where the application of technical analysis used in conservation, on extremely fragile, fragmentary painted clay-covered basketry, lead to the recovery of important ethnological information. The second reason lies with the fact that the close contact and continuous observation of the find afforded by the conservation process allows for a level of study otherwise inaccessible. The conservator has the opportunity to analyse and understand the characteristics of the constituent materials of the object and to reveal details in its construction that would otherwise remain concealed. When that is combined with the conservator’s knowledge of the archaeological/historical context of the object it ensures a justified interpretation [36,40]. The earlier a conservator is involved in an excavation project the better, both for the preservation and the interpretation of the finds. Since the conservator is the one responsible for treating and examining, hence interpreting, the fragile excavated finds, it would be of utmost importance for them to have been present at the time when the find was first brought to light. In that way they would be able to record evidence such as, the exact positioning of the find, its condition and the environmental parameters prevailing. Cruickshank et al. [41] argued that considerable information was retrieved by the conservator (Cruickshank) involved in the excavation project of the 1st-3rd century AD Nabataean/Roman cemetery in Jordan, from the initial stage of planning. For the conservator was able to observe the undisturbed graves and textiles within them in-situ, hence a significant amount of information on burial practices was transported back to the conservation laboratory to be combined with the analytical examination results and provide guidance to the treatment decision-making. One could argue that archaeologists are adequately trained to record in detail the way an object was found and its exact position. Nevertheless, the conservator still has to offer additional input. First, they would be able to record the environmental parameters, which would provide necessary evidence for the future treatment and preservation of the actual object. Second, archaeological conservators are trained in lifting the objects in a way that they


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are safe for transport to the laboratory and all information is retained. Third, the combination of the expert knowledge of the archaeologist on the context of the find, with that of the conservator on its materials and condition would ensure the correct completion of the archaeological record, which is the first and very important stage of its interpretation [39]. Mathias et al. [42] added that the examination of the Ferryland site in Newfoundland would be incomplete without the combined input of a conservator, conservation scientists and archaeologists in researching the excavated finds, original documents of the period and other contemporary costumes. As far as the preservation of the finds is concerned, archaeologists do not usually appreciate the sensitivity of their nature, and the fact that although they may have been preserved for thousands of years in burial, the extreme changes in the environmental conditions could lead to their complete destruction in less than a few days even hours. Hence, the services of the conservator are essential when the object is to be treated for either storage or display. Rotroff [43] presented the case of the Agora excavations, conducted by the American School of Classical Studies in Athens (ASCSA). As time passed, the accumulated finds (mainly ceramics and stone) started to deteriorate. This alerted the archaeologists to the involvement of trained conservators at the excavation project, which according to Rotroff’s: ‘meant profound changes in the attitude of archaeologists toward the objects of their study: a sharper awareness of their fragile nature and our responsibility, and ability, through collaboration with conservators, to take decisive action to pass these objects on to future generations intact’ [43]. In the case of excavated textiles, the need for a conservator to be involved in their retrieval is even more pressing. The sensitive, unique, and sometimes obscured nature of excavated textiles are the main reasons for seeking the assistance of a specialist conservator. Textiles preserved in either damp, or very dry and anaerobic conditions are susceptible to rapid deterioration from the moment they are brought to light. As Glover [44] wrote, the only way to suspend deterioration and to retain the value of textiles as archaeological/historic documents, is to seek advice and practical assistance from a specialist textile conservator as soon as possible. There are similar considerations for mineralised textiles, which especially in the form of pseudomorphs, are not only very sensitive to handle, but often not recognisable to the untrained eye of the archaeologist. An adequately trained conservator should be present to identify the mineralised textile, hence preventing its accidental removal from the metal/host object and finally to ensure its safe retrieval and transport to the laboratory [8, 38, 45]. Glover [44] presented two case studies to illustrate how the prompt contribution of a specialised textile conservator would have improved the condition of textile finds dramatically. The first one is that of an excavated burial, where deleterious interventive action was taken by non-specialists. Once lifted, the damp textile was transported to the local Museum to be examined by archaeologists and other specialists. Two weeks passed before it was assigned to a specialist textile conservator (Glover). By that time it had dried and to the conservator’s astonishment it had not only been washed but two quite large triangular pieces had been cut off from its corners for the sake of analysis. One of the pieces bore evidence of selvedge while the other a section of braided edge. Without the removal of these pieces, the outline of the object would have been complete. A textile conservator would have not washed the find unless absolutely necessary, and in that case they would have kept a detailed record

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of the characteristics (such as dimensions and weave count) of the object before treatment. In the case of analysis a textile conservator would be aware of the fact that the same information could be extracted from already detached fragments and/or other damaged areas, and would have never cut pieces from the object. The second case study presented is that of another inhumation burial where the damp textiles excavated were moved to the Conservation Department of the local University for storage. They were folded, wrapped in polythene and refrigerated without first seeking the advice and guidance of a textile conservator. Eight months later, when the textiles were removed from the refrigerator to be opened at the presence of the textile conservator (Glover) they had been extensively attacked by ‘green and fluffy white mould’. A textile conservator would have been prompt in freezing the objects before mould growth; they would have made sure the textiles were not so tightly folded for the centre to cool at very slow rates [44], and would have ensured that a sufficiently low temperature was reached to prevent mould growth. Textile historians are the professionals primarily interested in the analysis and research of textiles. They constantly compare and evaluate the results of the analysis on one object with these from other groups of objects, seeking to create an all round body of knowledge. Hence, they have adapted an inherent hesitation towards conservation remedial treatments, which they, more often than not, consider them to be an obstacle to this retrieval of information. Objects on display in a museum need to be accessible and unaltered, even after conservation treatment, for a textile researcher to be able to retrieve information [38]. Although recording and analysis ideally takes place before conservation, this is not always the case [46] and in addition there are still many questions to be answered in the future, hence an object needs to remain accessible [38]. Excavated textiles, even those in the poorest condition or obscured state of preservation, can yield a substantial amount of valuable information. A specialised textile conservator is the one entrusted with preserving both the tangible and intangible evidence of past history and technology enclosed in textile finds. Archaeologists should appreciate that the sooner a conservator is involved at an excavation the better for the welfare of the finds. Conservators, in turn, should always take care not to inhibit the work of textile analysts and historical researchers by using inappropriate treatments and materials. Apparently good collaboration between conservators, archaeologists and textile researchers is of crucial importance to the welfare, long-term preservation and understanding of excavated finds [47]. There are four ways to aid a successful collaboration between representatives of the three aforementioned professions: the use of a common ‘language’ and terminology, which would enable better understanding between them; joint publications in journals of interest to their professions, which would promote the fact that they are all partners sharing the common goal of preserving material culture and its evidence for future generations; close contact, which would enable the appreciation of each profession’s contribution and restrictions; and continuous dialogue, which would secure the transfer of information between them [38, 41, 43, 46].


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CONCLUSION Compiling a chronological table of textiles excavated in Greece and analysing the information gathered, provided an overview of the present condition of these finds. Ninety (90) different finds were identified, which indicates that in contrary to the general notion, textiles could survive in a burial context in Greece, should favourable environmental conditions prevail. These conditions, which are not unique to Greece, were identified as: in association with a metal present (66%), in association with salts (7%); carbonisation (8%), and inhumation burials (14%). In certain cases (5%) the method of preservation was unknown. The presence of a metal in a burial context was found to be primarily responsible for the preservation of textiles. Different metals have been recorded in association with textiles: copper (76%), lead (5%), silver (2%), gold (5%), iron (5%), and combination of metals (5%). The kind of metal is unknown in very few cases (2%). The high percentage of copper showed that its presence in a burial environment greatly increases the chances of textile preservation, which was in accordance with the findings of the literature review. Excavated textiles in Greece have been found in different states of preservation: object/s (11%), fragment/s (56%), remains (28%), and traces (2%). In certain cases (3%) the state of preservation was unknown. The fact that fewer textiles have been retrieved in the state of remains and/or traces could indicate a lack of experience in identifying textiles in such a poor state of preservation during the excavation process. The actual number of textiles found as whole objects is ten. Seven of them have been preserved by the combination of a metal present and elimination of oxygen. This could mean that the presence of a metal in association with elimination of oxygen provides optimum conditions for the preservation of textiles in a burial context in Greece. Different types of fibres have been identified: cellulosic (50%), proteinaceous (15%), and combination (8%). The majority of cellulosic fibres have been preserved in association with a metal present, whereas the majority of the proteinaceous fibres have been preserved in inhumation burials. This indicated that the former method of preservation is favourable to the preservation of cellulosic fibres, while the latter is favourable to the preservation of proteinaceous fibres, which was in accordance with the findings of the literature review. The small percentage of a combination of different types of fibres preserved (8%), futher indicated preferential preservation of cellulosic and proteinaceous fibres under different conditions. The type of fibre was not identified in certain cases (27%), indicating the lack of comprehensive analysis of textiles excavated in Greece. As far as conservation of the finds is concerned, first aid treatment by the means of consolidation was the usual conduct of practice (29%) up to the late 1990’s / beginning of 2000. The beginning of a more systematic study and analysis of the finds at that period might have been responsible for the discontinuation of this practice. Interventive treatment (9%) was similarly discontinued at the same period, giving way to preventive conservation (8%). The employment of specialist textile conservators by the Hellenic Ministry of Culture at that period, probably affected that change in attitude. The literature review showed that a good and continuous collaboration of conservators, archaeologists and textile historians would be most beneficial to the preservation of the information and physical existence of excavated textiles. The small number (3) and dates (2000; 2011) of joint studies and publications of the aforementioned professionals, indicated

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that their collaboration may have been limited, but is now growing. There are two possible reasons for the limited collaboration: either the interest in excavated textiles is generally low, or these professionals lack a common ground. Open communication, continuous dialogue using a common ‘language’ and joint publications from excavation to conservation, storage, display and analysis, is required between conservators, archaeologists and analysts to secure a successful collaboration. In conclusion, this research showed that a significant number of excavated textiles have survived in Greece, the study of which would greatly contribute to the body of knowledge on archaeology, technological advancements and material culture, and it would be enabled by a good collaboration established between the professionals involved.

ACKNOWLEDGEMENTS To all the conservators and archaeologists of the Hellenic Ministry of Culture who collaborated for this research project.

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[34] Margariti, C., Protopapas, S., Orphanou, V. (2011). Recent analyses of the excavated textile find from Grave 35 HTR73, Kerameikos cemetery, Athens, Greece. Journal of Archaeological Science 38, 522-527. [35] Margariti, C, Kallitsi, N., Petrou, M., Papadaki, A. (2010). Encountering challenges and finding solutions for the display of an obscured archaeological assemblage from Theva, Greece. Conservation and the Eastern Mediterranean 152-157. [36] Lewis, R. (2006). Interpretation in conservation: A rare leather find from an early historic crannog. The Conservator 29, 87-94. [37] Jakes, K.A., Howard III, J.H. (1986). Replacement of protein and cellulosic fibers by copper minerals and the formation of textile pseudomorphs. Historic Textiles and Paper Materials: Conservation and Characterization 277-287. [38] WILD, J.P. (1990). An introduction to archaeological textile studies. Archaeological Textiles, UKIC Occasional Papers 10, 3-4. [39] Odegaard, N. (2002). A fusion of archaeology and conservation: painted clay-covered basketry from the American southwest. JAIC 41 (1), 13-19. [40] Lochead, V. (1990). The conservation of four Egyptian tunics. Archaeological Textiles 41-48. [41] Cruickshank, P., Harrison, A., Fields, J. (2002). From excavation to display: the conservation of archaeological textiles from an AD first-third century cemetery site in Jordan. The Conservator 26, 44-55. [42] Mathias, C., Moffatt, E., Murray, A. (2004). Technical analysis of textile remains from a 17th century English plantation at Ferryland, Newfoundland and Labrador, Canada. Journal of the Canadian Association for Conservation of Cultural Property 29, 26-41. [43] Rotroff, S. (2001). Archaeologists on conservation: how codes of archaeo-logical ethics and professional standards treat conservation. JAIC 40 (2), 137-146. [44] Glover, J.M. (1990). The conservation of medieval and later shrouds from burials in North West England. Archaeological Textiles 49-58. [45] Sibley, L.R., Jakes, K.A., Kuttruff, J.T., Wimberley, V.S., Malec, D., Bajamonde, A. (1989). Photomicrography and statistical sampling of pseudomorphs after textiles. Archaeological Chemistry IV 465-480. [46] Boccia-Paterakis, A. (1996). Conservation: preservation versus analysis? IICArchaeological Conservation and its Consequences 143-148. [47] Brooks, M., Lister, A., Eastop, D., Bennett, T. (1996). Artifact or information? Articulating the conflicts in conserving archaeological textiles. Archaeological Conservation and its Consequences 16-21.



Chapter 10

INNOVATIVE Ag-TEXTILES PREPARED BY COLLOIDAL, CONVENTIONAL SPUTTERING AND HIPIMS INCLUDING FAST BACTERIAL INACTIVATION: CRITICAL ISSUES Sami Rtimi1,*, Cesar Pulgarin1, Rosendo Sanjines2 and John Kiwi3 1

EPFL-SB-ISIC-GPAO, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland 2 EPFL-SB-IPMC-LNNME Ecole Polytechnique Fédérale de Lausanne, Bat PH, Lausanne, Switzerland 3 EPFL-SB-ISIC-LPI, Ecole Polytechnique Fédérale de Lausanne, Bâtiment Chimie, Lausanne, Switzerland

ABSTRACT The bacteria inactivation of E. coli by Ag colloidal loaded cotton and polyester was investigated. Textile surfaces were pretreated by RF-plasma and UVC to introduce organic-polar groups containing oxygen functionalities binding/complexing/chelating Ag-clusters. Since sol-gel films are not mechanically stable, only exhibit low adhesion and can be wiped off by a cloth or thumb, we present in this study the Ag-sputtering of semiconductors and metal films to avoid the lack of reproducibility attained by colloidal preparations on textiles. Films sputtered by the DC-magnetron sputtering (DC) and pulsed direct magnetron sputtering (DCP) were compared with films sputtered by highly ionized pulse plasma power magnetron sputtering (HIPIMS). The amounts of Ag needed to inactivate E. coli by HIPIMS were an order of magnitude lower than films loaded with DC. The more compact microstructure obtained by HIPIMS seems to lead to a significant saving of noble metal compared to the DC/DCP sputtering. The antibacterial kinetics evaluated for the Ag-sputtered films are estimated to be sufficient to decrease

*


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Sami Rtimi, Cesar Pulgarin, Rosendo Sanjines et al. significantly the bacteria in hospital rooms besides precluding the formation of pathogenic biofilms on textile surface. The sputtering by (DC) and surface characterization of TiN, TiON, TiN-Ag and TiON/Ag textiles are reported addressing disinfection in the dark and under light, either solar or actinic. The TiN and TiON films presented semiconductor properties leading to the formation of TiO2. These TiN and TiON textile samples induced bacterial inactivation within acceptable times without leaching of Ag into the natural environment. ZrN/Ag and ZrNO/Ag nanofilms were deposited on textiles by DCP in Ar+N2 and/or O2 atmosphere. These nitride films were more active for E. coli inactivation compared to Zr/Ag-films. ZrO2-Ag2O was formed during the co-sputtering of ZrNO and Ag. Finally, the coupling narrow and wide band-gap semiconductorswas investigated on TaON/Ag sputtered sample. The mechanism of interfacial charge transfer (IFCT) due to the electron injection from the Ag2O conduction band (cb) to the lower laying Ta2O5 (cb) is discussed. A beneficial effect for the e-injection from Ag2O clusters into Ta2O5 is suggested.

Keywords: Textiles pretreatment, sol-gel, sputtering, Ag, Ag-nitrides, Ag-oxynitrides, IFTC

INTRODUCTION Silver has been recognized as antibacterial agent in various material forms: colloids, powders and supported on natural textiles fibers like cotton and artificial fibres like polyester, polyamide and wound-pads, thin polymer films like polyethylene, polypropylene, polyurethane. The silver ion release kinetics and extended operational time and cytotoxicity (biocompatibility) will determine its effective use when deposited on antibacterial surfaces. In this review we address the description/discussion of the preparation of Ag on textile surface by different methods, the evaluation of their antibacterial activity in the dark and under light irradiation and the characterization of the Ag-textile surfaces by up-to-date surface techniques. The content of this review is warranted since silver biocidal surfaces are the strongest growth segment in the medical and health care applications. The advantage of using Ag-disinfection is that it will not cause bacteria to become resistant to antibiotics and that Ag surface will prevent the formation of harmful biofims since this is the main source of human infections. Textiles presenting a faster bacterial inactivation are needed at the present time due to the increasing resistance of pathogenic bacteria to synthetic antibiotics when administered for long-times. If Ag-textiles would be optimized and attain a more widespread use in hospital textiles, gloves, rugs, curtains, medical devices and catheters, an effective reduction or elimination of infections can be expected [1-3]. This review describes the current search for more efficient, stable and adhesive antimicrobial Ag-nanoparticulate films on textiles to preclude the formation of biofilms leading to hospital acquired infections (HAI) [4]. These biofilms remain stable for long periods spreading bacteria by contact in public places or confined to hospital or school-rooms and could only be precluded by Ag-ion release in a slow and steady way by a favorable ionic transfer rate regulated by the ambient environmental conditions. The nanoparticles of Ag exhibit bacterial and fungicidal properties. They can accumulate on the cell wall of bacteria and release Ag-ions that due to their small size penetrate into the cells through the wall porins [5]. Ag-nanoparticles affect the bacteria respiratory enzyme due to the production of reactive oxygen species (ROS) and associated DNA damage leading to

Innovative Ag-Textiles Prepared by Colloidal, Conventional Sputtering ...

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death [6,7,8] and the antimicrobial effect of the potentials of Ag-solutions have been recently reported [9]. The release of Ag-ions from Ag-grafted surfaces involves Ag-oxidation reactions due to the oxygen available to the Ag-clusters, protons, salts and are directly dependent on the Ag-particle size that for large particles is effective only when releasing Agions in sufficient concentrations in a sustained way during relatively long periods [10]. Recently, the advances in Ag-nanoparticle preparations nanotechnology led to Ag nanocrystalline structures with a markedly improved biological value and efficiency. Agformulations in solution or embedded in humid wound-pads pass the Ag-ions/radicals and have been in use since 1920. Silver atoms are in itself no disinfectant and are considered nontoxic to in vivo human cells [11]. Decreasing the Ag particle size increases the particle surface area available for surface reactions to take place over shorter time periods. The large surface of the nano-Ag crystals contain a higher amount of oxidized surface Ag-species, some of them soluble leading to an enhanced disinfectant reactivity. The Ag-nanoparticles will release Ag-ions for days compared to the Ag-salts and complexes releasing in the hours range [12-13]. Sulfadiazine by itself does not show antibacterial action but due to its synergy with Ag+ a slow release from Ag-ions occurs from the sulfadiazine-Ag salt presenting low solubility [14]. Many studies have appeared over the last three decades involving the preparation of colloidal/powder Ag [15-18]. More recently, Ag/TiO2 dispersions or colloids prepared by different routes in the dark and in some cases under light have been leading to a bacterial inactivation [19-21]. When applying solar or visible light Ag2O (bg 1.5-1.7) has been observed to act as a semiconductor enhancing bacterial inactivation [22]. Recently, Ag photoswitching processes by finely divided dispersed Ag 2nm in size has been reported relating the hydrophobic Ag initial surface kinetics when the surfaces changed to super-hydrophilic under light concomitant to E. coli and Staphylococcus aureus inactivation. In this way the contact angle and surface energy were investigated during the light induced and dark reversible process after bacterial disinfection [23]. Recently, some reviews have appeared on the cell killing mechanism by semiconductor TiO2 and by metal nanoparticles on E. coli and other bacteria [24-28]. These reviews report and efficient processes by nanoparticle dispersions leading to the loss of bacterial viability or inducing the lack of bacterial cultivability.

METHODS AND RESULTS RF-plasma and UVC Pre-treatment of Surfaces/textiles Loaded with Colloidal Ag Microbial colonization with the consequent biofilm formation is a widespread complication on implants, catheters and textiles used in hospitals, health facilities and laboratories. Colloidal Ag film deposition on non-heat resistant surfaces attached weakly on the textile surface. The colloidal Ag-deposits were not uniform, hardly reproducible and no heating could be applied to diffuse them into the substrate [29]. This lead us to pre-treat textiles in the presence of residual O2 to introduce O-containing negative polar groups like:

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COO-, -O-O- and other -O-C- containing functionalities. These sites introduce additional bonding functionalities able to attach the Ag found in colloidal suspension. a) Functionalization of fibers by RF-plasma pretreatment: this fabric was pretreated in a RF-plasma cavity (Harrick Corp. 13.56 MHz, power 100 W). Generally for RF-plasma formation low pressures are used to increase the capture length of the electrons generated in the electric field generated in the RF-chamber. Vacuum at 1 torr avoids the collisions between the electrons when allowing the electrons to react with residual O2. The RF–plasma is created when a gas is exposed an electromagnetic field within radio frequencies. In the low temperature plasma the gaseous ions present temperature ranges between ambient and few hundred degrees, but the electrons have transient energies corresponding to high temperature values. The system is not under thermal equilibrium. The activated RF-plasma interacts with oxygen leading to atomic, excited O*, anionic Oand cationic O+, giving rise to carboxyl, per-carboxylic, peroxides, lactam etc able to chelate/complex or/and attach by electrostatic attraction with the partial positive Ag-species. The Ag-salt/colloid are reduced by isopropanol and precipitated by ammonia on the textile surface. Without vacuum, the RF-plasma induces a localized heating breaking intermolecular H-bonds and generating for very short times temperatures > 160°C able to segment the textile [30]. b) Functionalization of fibers by atmospheric or vacuum UVC: the textile polymer surface can also be functionalized by UVC light irradiation using the 185 nm line (6W) from a 25W (254 nm + 185 nm light) low-pressure mercury lamp (Ebara Corp. Tokyo, Japan). UVC activation having a lower energy than the RF-plasma, does not lead to cationic or anionic oxygen species in the gas phase. Only atomic (O) and excited oxygen (O*) species under UVC are obtained. The energy necessary for the O2  2O* reaction is at the wavelength 241 nm (495 kJ/mole). The absence of cationic or anionic oxygen species when pre-treating with UVC lead to a more uniform TiO2 layer of the textile surfaces and has been reported in the literature [30]. Figures 1a and 1b below report the loading of Ag and the bacterial inactivation time on textile pretreated in the UVC cavity and positioned at 3 mm of the UVC source. The O2 cross section is 10-20 cm2 and the molar absorption coefficient O2 (185 nm) ~26M/cm-1 [31]. The cross section of N2 is about 10 times smaller than for O2 at this wavelength. Therefore, the N2(185 nm) would negligible. At 185 nm the extinction coefficients of O2 and N2 are so low, that practically no UVC-radiation is lost in the optical pathway between the light source and the sample even at atmospheric pressures. The control fabric in Figure 1b shows a modest reduction of the number of initial bacteria concentration on the fabric surface due to bacterial adsorption on the textile surface [30]. The inactivation performance was observed to be dependent on the amount of silver on the textile surface. By XPS the Ag2O and AgO species were identified on the cotton surface. Continuing the preceding study, Ag-colloidal clusters were fixed on cotton to investigate the fabric antibacterial kinetics [32]. Figure 2a shows that in the dark bacteria are inactivated by contact with the Ag-cotton surface. The bactericidal activity of the Ag-TiO2-cotton in the dark is shown in Figure 2b. It is readily seen that the addition of TiO2 to the colloid under diffused laboratory light increases the bacterial inactivation time with respect to the Ag-cotton samples.


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inhibition of airborne bacteria (%)

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Figure 1a. Inhibition of airborne bacterial growth by textile fabrics activated by vacuum-UVC as a function of the textile Ag-loading. Total inhibition occurs of E. coli activity at concentrations ≥0.5 g AgNO3/200 ml solution. 4

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(c) Figure 2. (a) E. coli survival on Ag-cotton, samples in the dark. (b). E. coli survival on Ag-TiO2 cotton, samples in the dark. (c). TEM of the Ag-clusters on the cotton textile deposited as described before.

Figure 2c shows the Ag-clusters on the cotton textiles and also in the topmost layers where they have penetrated by diffusion. Figure 2c has been obtained after the cotton sample has been cross-sectioned with an ultra-microtome. Particle sizes 3-10 nm imparted a brownish color to the Ag-cotton presented in Figure 2c. The presence of Ag2O and AgO were detected and identified later by XPS [33]. Leaching of Ag-ion clusters with a minimal dissolution of Ag is responsible for the E. coli inactivation (1-4, 15-16, 23-28).


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Sputtering of Ag-textile Presenting Uniformity, Adhesion and Fast Bacterial Inactivation (i) The Ag-deposition on cotton is important since cotton has the property to adsorb a large amount of moisture making this textile prone to microbial attack. With ambient temperature and humidity, cotton is a nutrient for bacterial and fungal growth. To preclude bacterial growth we reported the preparation of Ag on wound pads by wet impregnation/reduction of AgNO3 to inactivate airborne bacteria induced infections [30,32]. By direct current magnetron sputtering (DC) we sputter Ag-films having a strong adhesion, fast kinetic bacterial inactivation and would not smear under friction [33]. XPS analysis of cotton samples loaded at 15, 60 and 600 s present a surface atomic percentage concentration of 7.31, 23.36 and 37.76 % of Ag, respectively. We used XPS and Auger lines to follow the changes in the oxidation state of Ag [34]. The highest Ag-oxidation state was found after the shortest deposition time of 15s. In this case, the Auger parameter was 725.15 eV and the Agcontent for the cotton sample was low. But at longer deposition times, a significant shift of Auger parameter from 725.15 to 725.65 eV indicates a higher deposition for the AgO at 60s and 600s sputtered samples. The amount of oxidized silver was observed to be similar for samples sputtered during 60s and 600s (Fig. 9c, d) while at the same time the total amount of Ag was almost two times higher after 600s DC-sputtering. This indicates that the Ag-ions are located mainly at the silver interface and provides the evidence that Ag-ions and not Ag0 is responsible for the bacterial inactivation. While the presence of Ag0 and Ag2+ seems to be documented, the assignment to Ag+1 is less clear [35]. The reason for that is that O1s line at 530.71 eV and for this reason cannot be used for clear identification of the Ag-oxidation state. Sputtering from an Ag-target for 60s produced thin semi-transparent coatings with 4-5 layers showing strong adherence, bactericide activity and did not affect the handle or touch of the cotton textile. The Ag wt % Ag/wt cotton to for a bactericide film on the cotton was found to be 0.054% and could be sputtered in 60s, this time is short and shows that Ag-sputtering on cotton makes an economic use of Ag. (ii) In a more recent study [36] the deposition of active, uniform nano-particulate Ag-thin films on polyester textiles by DC-magnetron sputtering (DC) and pulsed DC-magnetron sputtering (DCP) has been reported. The deposition of Ag on the polyester fiber was observed to be function of the type of sputtering used either DC or DCP directly determining the E. coli inactivation kinetics. In the magnetron sputtering chamber the reaction Ar  Ar+ + e- lead in a subsequent steps to the collision of the electron with Ag0: e- + Ag0  Ag+ + 2e-. The Ag0 kick-off a second electron. The Ag ionization increased when higher currents (mA) were applied during the DC or DCP-sputtering. The ratio of Ag+/Ag0 was higher for DCP (up to 10%) than in the case of the DC presenting Ag+/Ag0 ≤ 1% [37]. The shortest E. coli inactivation was attained within 2 hours DCP. The results are shown in Figure 3a. Pulse trains of 3 pulses each of 10 microseconds with a recovery time of 7 ms to avoid overheating of the Ag-target was used during in the DCP mode. When sputtering DC with 300 mA the bacterial inactivation was complete after 5 hours. Samples sputtered by DCP for 160s inactivated E. coli within 2 hours with an equivalent loading of ~1018 atoms/cm2. The threshold Ag-loading by DCP in Figure 3a was attained after sputtering for 20s and led to inactivation of E. coli only after 9 hours.

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Figure 3b. Electron microscopy of Ag-polyester fiber DCP sputtered for 160s at 300 Ma..

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By electron microscopy (TEM) Ag-polyester fibers it was found that Ag sputtered by DCP penetrated more deeply into the polyester fiber compared to DC-sputtering. Figure 3b shows the composite TEM results for an Ag-polyester fiber sputtered by DCP for 160s. The arrow on the lower side in Figure 3b indicates the direction of incidence of the Ag-particles on the polyester in the sputtering chamber. A dark continuous Ag-deposit ~80-90 nm thick was observed. But only 5-15 nm thick Ag-layer was found on the other end. About 65-70% of the full polyester fiber perimeter was covered by a 50-90 nm thick Ag-deposit. The DCP ionenergies are much higher than the DC energies and DCP sputtering ion-energies of 10-100 eV have been recently reported with a small number of ions exceeding 100 eV and electron densities of ~1016 e-/m3 [37]. The E. coli inactivation process has been described to proceed by Ag-ionic states using the ambient kT energy and ambient humidity leads to the formation of highly oxidative radicals HO2° and OH° necessary for E. coli inactivation. The Ag-crystals in air are covered by layer(s) of AgOH and the kT energy at room temperature leads to bacteria oxidation via the surface AgOH groups [38].

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 Figure 4. X-ray diffraction of DCMS and HIPIMS sputtered Ag-polyester fibers under different conditions. For other details see text.

Figure 4 shows the XRD for Ag-nanoparticle films on polyester sputtered by DCP for 20s and 160s. The cluster formation occurs when Ag-atoms bind to other metal-atoms rather than to polyester. The growth of Ag-atoms into clusters at 20s in Figure 4 leads to near spherical but not necessarily crystallographic Ag-clusters [39]. At longer sputtering time of 160s, a steep peak is observed in Figure 4 assigned to the Ag-metal peak at 2=38°. Ag-metal nanoparticles have been reported with dimensions > 1 nm [40]. HIPIMS sputtering

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for 13s at 1A indicate a low Ag-cluster formation in the insert to Figure 4. The Ag-clusters grow into bigger aggregates when sputtered for 75s at 5A, but did not lead to Ag-metal formation. We have not looked in a detailed way in Figure 4 into the effect of the microstructure changes introduced in the Ag-nanoparticles by the HIPIMS sputtering during 75s at 5 A leading to the formation of a 40 nm film compared to a thinner 4 nm film sputtered during only 13s at 1 A. (iii) In a separate study we addressed the DC-magnetron sputtering (DC) by Ag-films on polyester and compared the results obtained with (HIPIMS) for bacterial inactivation [41]. HIPIMS deposition of Ag-films was carried out in a CMS-18 vacuum system from Kurt Lesker Ltd. evacuated to 10-2 Pa by a turbomolecular pump using Ag-target was 5 cm in diameter, 99.99% pure from K. Lesker Ltd. UK. The HIPIMS unit was operated at 100 Hz with pulses of 100 microseconds separated by 10 ms. The HIPIMS short pulses avoid a glow-to-arc transition during plasma particle deposition. The applied power was varied between 1 and 5 A and no glow-to-arc transition was detected during the plasma deposition. The pressure was the same as the one used in the DC chamber. The mass spectrometry measurements were carried out in a Hiden Analytical Ltd PSM003 unit to determine the ion-composition of the ions in the plasma Ar-atmosphere. The polyester used was a polyester Dacron polyethylene-terephthalate; type 54 spun, plain weave ISO 105-F04 used for color fastness determinations. The nominal calibration of the Ag-film thickness on the polyester was carried out on Si-wafers. The film thickness was determined with a profilometer (Alphastep500, TENCOR) as shown in Figure 5a for DC and Figure 5b for HIPIMS samples. Figure 5a shows that DC sputtering applying 0.3 A increases the Ag-deposition rate by a factor of 8 with respect to Ag-deposition at a lower current of 0.05 A. Figure 5b shows that a thinner Ag-coating is deposited within the same times by HIPIMS compared to DC- sputtering shown in Figure 5a. Since the lattice distance between Ag-atoms can be estimated at 0.3 nm, a monolayer of Ag contains ~1015/atoms/cm2. DC sputtering at 0.3 A deposits a coating 100 nm thick after 80s, and if each Ag-layer is about 0.2 nm thick, then the silver deposition rate was ~6x1015 atoms/cm2s.

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Figure 6a presents the results for HIPIMS sputtering at 1A and 2A. HIPIMS sputtering for 3s at 2A lead to the most effective E. coli inactivation having a relatively low Ag-content. The initial CFU decrease in Figure 6a for Ag-polyester at time zero with respect to polyester alone is due to a quasi-instantaneous redox process taking place between Ag and E. coli. The Ag-layer thickness and the % Ag wt/ wt polyester for the samples prepared by HIPIMS at 1 A or 2 A with respect to DC samples Ag-sputtered for 160s was observed. Figure 6b presents the results for the E. coli inactivation with HIPIMS sputtering with 5A. Trace (2) shows that sputtering for 13 s at 5A leads to bacterial inactivation within 5 hours. The threshold polyester Ag-loading was 0.0029% wt Ag/wt polyester. Sputtering times shorter than 13 s did not induce complete bacterial inactivation. HIPIMS sputtering for 37s lead to an Ag-film 20 nm thick with 0.0086 Ag wt% / wt polyester able to inactivate E. coli within 4 hours. DC sputtering for 80s lead to E. coli inactivation within 5 hours. In this case the Ag wt% / wt polyester was 0.118 and the Ag-layers were 105 nm thick. DC-sputtering required >10 times higher loading when compared to HIPIMS and led layers more than 5 times thicker compared to the HIPIMS. This shows the significant saving in Ag-metal and sputtering time introduced by HIPIMS compared to more traditional DC sputtering. Figure 6c presents the trends for the inactivation time of E. coli vs the Ag-layer thickness deposited by DC and HIPIMS sputtering and shows the significant reduction of the Ag-layer thickness required to completely inactive E. coli by HIPIMS compared to DC. Issues related to the basis of Ag and Au and Ag/TiO2 and Ag/SiO2/TiO2 colloidal films have been reported recently by Daoud et al., [42] focusing on self-cleaning issues on cotton, wool and synthetic fibers [43] involving the discussion of mechanism, photocatalytic efficiency and material stability during long operational times. These considerations are also valid for Ag-antibacterial surfaces when addressing the basic science related to Agdisinfection. An active group in Belgrade (Saponjic, Radetic) has recently published consistent work on Ag-sputtering and colloidal deposition on natural and artificial fibers to optimize their antibacterial performance in the dark and under light irradiation [44-47]. Other


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workers are reporting studies on Ag-textiles like Ag-Nylon [48], Ag-cotton [49], and Agcellulose [50]. The search for more efficient, stable and adhesive antimicrobial nanoparticulate films is a valid research topic. These films are directed to preclude the formation of biofilms leading to hospital acquired infections (HAI) [1-4]. Films presenting a faster bacterial inactivation are needed at the present time due to the increasing resistance of pathogenic bacteria to synthetic antibiotics when administered for long-times. These bacterial biofilms remain stable for very long periods on a variety of surfaces spreading bacteria by contact in public places or confined to hospital or schools. To cover heat resistance surfaces with uniform thin antibacterial films has by Physical Vapor Deposition (PVD) where the materials are heated in vacuum until they decompose. The released atoms/species condense on the substrate being this surface at a lower temperature mainly on heat resistant materials. TiO2, Ag, and Cu films from 6 to 50 nm have been reported and these thicknesses have been shown to lead an effective bacterial inactivation under UV and under visible light irradiation. The disadvantages of the PVD deposition approach are the high investment costs, the high temperatures needed precluding film deposition on textiles like the polyester and the amount of heat used requiring costly cooling systems. By spin-coating semiconductor and metals films with a uniform structure have been deposited on a variety of substrates using volatile molecular precursors. By CVD Ag-films have been deposited by Page et al., [50-51] Foster et al., [52] and Dunlop et al. [53]. More recently the application of diverse sputtering methods have become widely spread to deposit thin metal or oxides (by reactive sputtering) on non-heat resistant substrates like textiles or thin polymer films like polyethylene (PE) since these substrates resist temperatures up to about 120°C. The sputtering approach to deposited Ag-antibacterial films has been addresses with the objective to produce surfaces decreasing/eliminating the leaching of Ag from textiles. There is a growing concern that Ag-nanoparticles in commercial textiles will spread the Ag-nanoparticles into the environment. Geranio et al., [54] shows that a significant release of Ag-cations was observed after addition of oxidants to washing formulations of textile containing Ag. This was investigated also after several washing cycles. Since the further environmental chain transformation of these Ag-nanoparticles and their toxicity is not entirely known [55]. Work in this direction addressing the solubility and reactivity of the Agleachates is necessary. Antimicrobial silver films/textiles have been produced by magnetron sputtering processes in chamber where traces of H2O/O2 are available. The crystals of Ag present point defects, crystal impurities and dangling bonds in low or high-density imperfections acting as a pump for elusive Ag-ions able to inactivate bacteria, fungi and algae. Most of the magnetron sputtered Ag-films present an effective antibacterial action with coatings < 1 micron [56]. Sputtering silver textiles research is warranted since it aims to reduce or eliminate the Ag-leaching during washings keeping at the same time the Ag-disinfection performance. Aghospital textiles are in principle able to reduce/eliminate the contamination of public hospitals from E. coli and MRSA. The level found for these bacteria in many UK hospitals is higher than the allowed level for the hospital rooms. For example, the contamination of 105 CFU/cm2 was observed in a diabetic wound dressing. But in the vicinity of the patient, a microbial density of about 102 CFU/cm2 was found. The use of Ag-textiles as described

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above should be sufficient to decrease significantly the bacterial concentration, since we do not deal with a high bacterial concentration [57].

Sputtering of Textiles by TiN and TiN/Ag: Kinetics of the Dark and Light Induced Bacterial Inactivation (i) To avoid environmental Ag-contamination by bactericide surfaces we have sputtered TiN films on polyester and evaluated the bacterial inactivation kinetics. Ti was sputtered in the plasma chamber in N2 atmosphere depositing TiN films loaded on polyester fibers. These films present absorption in the visible region as shown in Figure 7a. A TiN layer of 50 nm sputtered for 3 min under low intensity/actinic visible light led to the inactivation within 120 min of 99.99% of bacteria [58]. XPS measurements were carried out on an AXIS NOVA photoelectron spectrometer (Kratos Analytical, Manchester, UK). The surface atomic concentration was determined from the peak areas using sensitivity factors [34]. Spectrum background was subtracted according to Shirley [59]. The XPS peaks of the Ti-species were analyzed by the spectra deconvolution software (CasaXPS-Vision 2, Kratos Analytical UK). The formation of TiO2 can be understood in terms of: a) the partial oxidation of TiN takes place in the presence of an oxygen source due to the residual H2O vapor in the sputtering chamber at the residual pressure Pr=10-4 Pa. This pressure is representative of about 1015 molecules/cm2, there are sufficient O-radicals available to induce partial oxidation of TiN films and b) the films also oxidize after the deposition when exposed to air and during the sterilization process when autoclaving at 121°C.

Figure 7a. Diffuse reflectance spectroscopy of TiN-polyester for the sputtering times shown in the figure captions.


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Figure 8. X-ray photoelectron spectroscopy (XPS) of the TiN (3 min) in contact with bacteria for 3s: a) at time = 0 min and b) at time 120 min, showing the shift in the deconvoluted peaks after bacterial inactivation.

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Figure 8 presents the TiO2 (Ti2p3/2 doublet) for the polyester when sputtering TiN for 3 min. The peaks in Figure 8a assigned to TiN and Ti2O3 (Ti3+ in the net sense) have been deconvoluted and TiN shows a peak at 455.62 eV, the Ti3+ doublet at 456.22 eV and the the Ti4+ doublet at 458.43 eV. Figure 8b) presents the XPS deconvoluted spectra for the TiN sample at the end of the bacterial inactivation process (120 min). The TiO2 (Ti2p3/2 doublet) BE shifted to 459.01 eV. Peak shifts ≥ 0.2 eV are due to changes in the oxidation states Ti4+/Ti3+ during bacterial inactivation. The shift of the Ti2O3/Ti3+ doublet to 457.13 eV at 120 min reflects an increase in the reduced Ti3+-species at the end of the bacterial inactivation. The surface atomic concentration of the fastest TiN (3min) sample at time zero was determined by XPS as: O1s 10.2%; Ti2p 44.7% N1s 3.5 % and C1s 22.31%. (ii) In a separate study TiN and TiN-Ag nanoparticulate films on polyester induce photocatalytic and catalytic inactivation of E. coli [60]. For TiN-Ag samples, bacterial inactivation was attained within ~15 min. The absorption of the TiN-Ag samples in KubelkaMunk (KM) units was directly proportional to the E. coli inactivation kinetics. The TiN and TiN-Ag thin films have been sputtered onto polyester heating <130°C using two confocal magnetron-sputtering systems. The polyester samples were 2x2 cm in size. Before the deposition of the films, the residual pressure Pr in the sputtering chamber was typically Pr  10-4 Pa. The substrate-to-target distance was fixed at 10 cm. The TiN thin films have been deposited by reactive DC magnetron sputtering (DC) using a 5 cm diameter Ti target 99.99 at. % (Kurt J. Lesker, East Sussex, UK) in an Ar + N2 atmosphere. The total working pressure PT=(PAr+PN2) was fixed at 0.5 Pa and the ratio PN2/PT= 4.5 %. Figure 9 shows the bacterial inactivation of E. coli for TiN/Ag films. The deposition time of the TiN under layer film was fixed at 3 min while the deposited amount of the Ag was tuned by changing the deposition time from 10 s to 30 s. A 15 min irradiation period led to a 3log10 reduction (99.9%) of the initial E. coli concentration as shown in the insert. Complete bacterial inactivation was observed within ~60-90 min. A darker-grey metallic Ag-color was observed on the polyester with increasing sputtering time. Migration/aggregation of the Agparticles leads to stable agglomerates. The dark grey color corresponds to the Ag2O/Ag0 with a band-gap (bg) 0.7-1.0 eV and an absorption edge of ~1000 nm. Figure 10 presents the release of ions from polyester samples sputtered with Ag, TiN-Ag and TiN. For Ag-sputtered samples up to the 8th cycle the level of Ag-release is seen to be 6 and 8 ppb/cm2. In the case of TiN-Ag samples the Ag-release was observed to decrease with the number of cycling down to 5 ppb/cm2. Ag-ions were formed by oxidation of the Agloaded polyester surface in contact with reaction media. The release of Ag-ions > 0.1 ppb has shown significant antimicrobial effect and higher Ag-ions >35 ppb can be toxic to human cells [1]. The TiN polyester samples maintained a release of ~14 ppb/cm2 of Ti-ions. The excellent intrinsic biocompatibility of TiN has been well documented in biomedical applications [51, 61, 62]. A fast bactericidal kinetics and a low cytotoxicity are the two essential requirements for bactericide surfaces and this is referred to the oligodynamic effect [1].

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Figure 9. E. coli survival on TiN-Ag polyester sputtered for different times under light irradiation. Traces (1): TiN-Ag 3 min/ 20s; (2): TiN-Ag 3 min/ 30s; (3): TiN-Ag 3 min/ 10s; (4): TiN-Ag 3 min/ 20s in dark and (5): polyester alone. The inset shows the time for bacterial reduction of 3log10.

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recycling cycles Figure 10. Ion-coupled plasma spectrometry (ICPS) determination of Ag- ions and Ti-ions released during the recycling of a) sample sputtered with Ag for 30s (trace 1), b) TiN-Ag (3min-20s) sputtered sample and c) TiN sample sputtered sample for 3 min (trace 3).

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Figure 11 shows the ratio found for the XPS signals for the oxidative species (C-O) and the reduced initial polyester groups (C=C) during the bacterial inactivation/oxidation on a TiN-Ag (3min-20s) and a TiN sputtered sample. The increase of the surface O is due to the appearance C-OH, C-O-C and carboxyl species as the E. coli inactivation time progresses [63]. At the same time, the total C-content decreases with reaction time due to bacterial inactivation and this is monitored by the progressive decrease of the C-C signals as a function of time. The ratio of the peaks area of the C-C species including the reduced C-forms C=C, C-H) at 285 eV and the deconvoluted oxidized C-forms of C-OH, C-O-C and carboxyl functionalities at 286.1 eV, 287.0 eV and 289.1 eV respectively [64] is plotted a s a function of time in Figure 11. The increase of this ratio C-OH + C-O-C + carboxyl/C-C is shown in traces 1 and 2 up to 180 min.

Figure 11. Ratio of oxidized carbon and reduced carbon (C-O/C=C) on TiN-Ag (3min-20s) and TiN (3 min) during E. coli inactivation under actinic light.

Sputtering of Textiles by TiON and TiON/Ag Composite Antibacterial Surfaces, Testing and Surface Characterization (i) New evidence has been reported for TiON sputtered polyester surfaces activated by sunlight irradiation leading to the accelerated bacterial inactivation in the minute range [65]. The objective of the present study is to report on solar induced bacterial inactivation by sputtered TiON films using a laboratory scale solar simulator. These TiON films avoid the adverse environmental effects caused by Ag leaching out of silver films as reported by Geranio et al., [54].


295

Irradiation of the samples during the bacterial inactivation was carried out with a Suntest cavity provided with Xenon lamp with an emission spectrum between 320 and 700 nm. Figure 12 shows the bacterial inactivation kinetics as a function of the TiON sputtering time. The bacterial inactivation becomes faster at longer sputtering times up to 4 min. Beyond 4 minutes sputtering time the reverse trend is observed in Figure 12 for sputtering times of 5 and 10 min. The slowing down in the bacterial inactivation for samples sputtered above 4 min presenting a 70 nm layer thickness may be due to thicker coatings leading to bulk inward diffusion of the charge carriers diffusing from the TiON decreasing the amount of active sites held on the surface in exposed positions interacting with the bacteria. Besides these considerations, longer sputtering times induce TiON inter-particle growth decreasing the TiON contact surface area with bacteria. A solar simulator for Hereaus GmbH, Hanau, Germany was used to irradiate the samples with an overall power of 92 mW/cm2 with light distribution wavelength distribution resembling solar irradiation emitting at wavelengths between 320-800 nm.

10

6

10

5

10

4

10

3

10

2

10

1

10

0

(7)

E. coli (CFU/ml)

(6)

(1) (2) (3) (4)

0

(1) TiON 4 min (2) TiON 5 min (3) TiON 10 min (4) TiON 3 min (5) TiON 2 min (6) TiON in dark (7) polyester alone

(5)

60

120

180

time (min) Figure 12. E. coli inactivation on TiON sputtered on polyester for: (1) 4 min, (2) 5 min, (3) 10 min, (4) 2 min, (5) 1 min, (6) TiON 4 min in dark and (7) polyester alone and irradiated by a Suntest Xenon lamp (320-700 nm). The reactive gas flow composition: Ar 90%: N2 5%: O2 5% and total P = 0.5 Pa.

E. coli was obtained from the Deutsche Sammlung GmbH (DSMZ) ATCC23716, Germany. The polyester fabrics were sterilized by autoclaving at 121°C for 2h. The 20 µL aliquots of the bacterial culture with a concentration of ~106 CFU mL-1 in NaCl/KCl were placed on the polyester fabric. These polyester samples were placed on Petri dish provided with a lid to prevent evaporation. After each determination, the fabric was transferred into a sterile 2 mL Eppendorf tube containing 1 mL autoclaved NaCl/KCl saline solution. This solution was subsequently mixed thoroughly using a Vortex for 3 min. Serial dilutions were made in NaCl/KCl solution. The 100 µl sample of each dilution was pipetted onto a nutrient

296


agar plate and then spread over the surface of the plate using the standard plate method. Agar plates were incubated lid down, at 37°C for 24h prior to the counting of the bacterial colonies. The bacterial data reported were replicated three times. The statistical analysis of the experimental values was compared by one-way analysis of variance and with the value of statistical significance. Figure 13 shows the TiON plasmon resonance occurring in the UV region in agreement with a recent study recently by Subramaniam et al., [66] The optical absorption of the TiON samples increases with longer sputtering times up to 4, 5 min. Increasing the sputtering times from 1 to 5 min in Figure 13 lead to TiON samples with a higher optical absorption due to the introduction of N-interstitial sites doping the TiO2 with O-vacancies. This in turn leads to a larger amount charge transfer sites in the visible region [67]. Samples sputtered for 4 ad 5 min are seen to present a similar optical absorption indicating saturation of the polyester surface by the sputtered TiON layers. This suggestion seems to be confirmed by the lack of further growth in the optical absorption by the samples sputtered for 10 minutes showing additionally a different shape for the TiON spectra. This is due to the non-linear optics introduced by the high density of TiON layers on the polyester surface not following quantitatively the normal optical absorption increase beyond the saturation concentration [68]. Diffuse reflectance spectroscopy (DRS) was determined using a Perkin Elmer Lambda 900 UV-VIS-NIR spectrometer. The absorption of the samples was plotted in Kubelka-Munk (KM/S) units. 0.8 (4)

(5)

0.6 (3)

KM/S

0.4 (2)

0.2 (1)

0.0

-0.2 200

300

400

500

600

700

Wavelengh (nm) Figure 13. Diffuse reflectance spectra of TiON samples sputtered on polyester for different times: (1) 1 min, (2) 2 min, (3) 4 min, (4) 5 min and (5) 10 min.

By Inductively coupled plasma mass spectrometry (ICP-MS) spectrometry, the K, Naions released by the bacteria within the 40 min inactivation time was determined and the results shown in Figure 14. The K+-ions leak at a relative low concentration through the


297

2.5

2

ions concentrations (ppb/cm )

+

2.0

(1) K -ions release + (2) Na -ions release

Ti-ion concentration (ppb/cm2)

bacterial cell wall membrane becoming more permeable up to 30 min. These K+-ions are known to be important regulators of the cell-wall redox potential. The Na+-ions present at a higher initial concentration leaked at a higher rate up to 40 min due to their smaller size compared to the K+-ions [69]. The cell wall permeability increase of E. coli preceding inactivation occurs within 40 min, the time of bacteria inactivation as shown in Figure 12 [70]. A FinniganTM ICPMS was used for these experiments equipped with a double focusing reverse geometry mass spectrometer presenting an extremely low background signal and high ion-transmission coefficient. The spectral signal resolution for the Na, K and Ti-ions was 1.2x105 cps/ppb and the detection limit of 0.2 ng/L.

Ti-release

4.5

3.0

1.5

1.5

1.0

(2)

0.0 0

2

4

6

8

recycling cycles 0.5 (1) 0.0

10

20

30

40

time (min) Figure 14. Ion-coupled plasma mass spectrometry (ICP-MS) determination of the leakage of 1) K+ and 2) Na+-ions through the E. coli cell wall during bacterial inactivation by a TiON 4 min samples irradiated by a Suntest solar simulator. The insert shows the Ti-ions release during the sample recycling after 1, 3, 5, and 8 E. coli inactivation cycles.

(ii) A further study involving E. coli inactivation on TiON-Ag films sputtered on polyester by DC and DCP has been reported out of our laboratory [71]. A photo-induced charge transfer from Ag2O and TiO2 is suggested for the interfacial charge transfer mechanism (IFCT) between Ag2O and TiO2 formed after the oxidation of the top-most-layers of the sputtered TiON-Ag. Figure 15 shows the atomic deposition rate of TiON films as a function of the O2/N2 ratio. The total pressure PT = (PAr+ PN2 + PO2) was fixed at 0.5 Pa and after optimization the fastest bacterial inactivation kinetics and under a gas flow Ar 90%: N2 5%: O2 5%. Sputtering for 4 min leads to layers ~70 nm thick. This is equivalent to 350 layers each containing 1015 atoms/cm2 being deposited at a rate of ~1.5x1015 atom/cm2s. The TiON was sputtered first for 4 min followed by Ag-sputtering for 30s. The atomic deposition rate was observed to be a function of the O2/N2 ratio.

298


16

2

Atomic rate deposition (atom/cm .s)

9.0x10

16

8.5x10

16

8.0x10

16

7.5x10

16

7.0x10

16

6.5x10

0.0

0.5

1.0

1.5

2.0

2.5

O2/N2 ratio Figure 15. Atomic deposition rate of TiON films on polyester as a function of the O2/N2 ratio. Ar gas flow was 90% at a working pressure 0.5 Pa.

Figure 16. Visual presentation of the samples of sputtered TiON and TiON-Ag textiles within 4 minutes: A) color variation as a function of the distance of the Ti-target and the polyester sample, B) color variation as a function O2/N2 ratio for TiON samples C) color variation of TiON-Ag samples with different Ag wt%/ wt polyester.


299

The colors of the TiON samples sputtered for 4 min are shown in Figure 16, row A. These colors are seen to be a function of O2/N2 ratio. A higher content of O2 has been reported also to increase the biocompatibility of the TiON samples. The samples TiON 4 min sputtered with Ag for 20-40s in Figure 16(B) became darker for TiON samples sputtered for longer times. The wt% Ag /wt polyester of the TiON-Ag of samples sputtered Ag for 20, 30 and 40s are shown in Figure 16(C). Figure 17a presents in the left hand side the almost continuous dark TiON-Ag (4min-30s) deposit on the polyester fiber. The right hand side image with a higher magnification of 100 nm shows the immiscibility of the Ag-dark coating and the TiON coating grey layers. The Ag-particles present sizes between 20-40 nm within a TiON-Ag layer with a width of 70 ± 10 nm. Ag/Ag2O particles of 20-40 nm will not pass through the bacterial cell wall having protein porin pores with a diameter of 1.1-1.5 nm [72]. This confirms once more that Ag bacterial inactivation is due the Ag-ions having sizes <1 nm, and not to the Agnanoparticules.

Figure 17a. Left hand side: Transmission electron microscopy of a TiON-Ag (4min-30s) DC-sputtered sample showing the continuity of the sputtered TiON-Ag layer around the polyester fiber. Right hand side: dense continuous Ag-layers being immiscible with the grey TiON layer. (P=polyester and E=epoxide).

Figure 17b. Surface of the TiON-Ag (4min-30s) sample taken by Bright Field (BF) showing Ti and Ag at the current beam position.

300


Figure 17b shows the image of a TiON-Ag (4min-30s) sample in Bright Field (BF). The immiscibility of the Ag and Ti on the sample surface is readily seen at the current beam position. Figure 18 presents the release of Na+ and K+ during the bacterial inactivation from a TiON-Ag (4 min-30s) sample. The K+-ion exists universally in bacteria regulating the potential for the transfer of-ions across the bilayer membranes. The K-ions leak at a low rate from the bacterial cell as the cell wall becomes more permeable up to 30 min. The Na+-ions in Figure 18 are seen to leak at a faster rate compared to K+-ions due to their smaller size. The rate and pattern of the leaking in Figure 18 is different to the Ti and Ag-leakage reported during bacterial inactivation for the same system in Figure 12. The leakage of K+ and Na+ increases after 30 min due to the more advanced state of decomposition of the cell bacterial envelope [73]. The loss of cell viability is consistent with the decomposition of the cell-wall membrane and the time of the leakage of intracellular K+ and Na+. Cell walls are repaired during the culture of cells on the agar plates. This leads to a different rate of decomposition of the outer cell membrane [74]. The possible mechanism of bacterial inactivation for the TiON-Ag film can be suggested: AgOH on the film surface by contact with air. The AgOH decomposes spontaneously to Ag2O (eq3): 2AgOH  Ag2O + H2O (pk= 2.87)

(3)

This Ag2O is stable at pH 6-7 where the inactivation of E. coli proceeds. Light irradiation photo-activates Ag2O with 1.46 < bg < 2.25 eV (77) as noted next in eq(4): 4.0

(1) Na + (2) K

2


3.5

+

3.0

(1)

2.5 2.0 1.5 1.0

(2)

0.5 0.0

0

10

20

30

40

50

60

time (min) Figure 18. Ion-coupled plasma mass spectrometry (ICP-Ms) determination of the leakage of 1) Na+ and 2) K+- ions through the E. coli cell-wall envelope during bacterial inactivation by a TiON-Ag (4min30s) sample under light.

Innovative Ag-Textiles Prepared by Colloidal, Conventional Sputtering ... Ag2O + light  Ag2O h+ + Ag2O e-

301 (4)

The Ag2O/TiO2 transfer of charges we have to consider the position of the energy bands of Ag2O and TiO2. Under visible light irradiation, the transfer of charge from Ag2O to TiO2 is thermodynamically favorable because the position of the Ag2Ocb at 1.3 eV NHE at pH 0 and the vb of Ag2O +0.2 V NHE at pH 0 [75] lies above the TiO2cb at -0.1 V vs NHE and the vb at +3.2 V. Under light an interfacial charge transfer process (IFCT) may proceed between Ag2O and TiON [75,76]. The Ag2Ocb transfer electrons to the TiO2cb in an energetic favorable process and this will hinder the electron-hole recombination in Ag2O. We suggest that the transfer of Ag2O electrons to O2 due to this increased charge separation plays an important role in the photocatalytic activity leading to bacterial inactivation. We suggest a mechanism in which the Ag2O in eq(1) reacts as shown below in eq(5): Ag2O-  2Ag0 + ½ O2-

(5)

The O2 in eq(5) would promote at later stages reactions (5,6) producing highly oxidative radicals, while the h+ in eq(4) reacts with H2O as noted in eq(6). This reaction runs parallel with eq(5) generating OH° radicals or other highly reactive oxidative radicals by way of the Ag2Ovb h+ (see eq(4)) h+ + H2O  OH° + H+

(6)

2e- + 2H2O + O2  2OH° + 2OH-

(7)

ZrN/Ag Textiles and ZrNO/Ag Composite Antibacterial Textiles; Design, Sputtering, Testing, and Characterization Ag-ZrN films were deposited on polyester by direct current pulsed magnetron sputtering (DCP) in Ar+N2 atmosphere. ZrN on the polyester surface interacts with Ag leading to AgZrN films. These composite films were more active in E. coli inactivation compared to the Ag-films by themselves. Sputtering Zr in N2 atmosphere presented no antibacterial activity by itself when applied for short times < 1 min. Figure 19 shows an E. coli inactivation time of 1.5 h on Ag/Zr polyester sputtered for 20s presenting a wt %Ag / wt polyester of 0.0105 and a Zr wt% / wt polyester of 0.0012 as determined by XRF The pattern of trace 5 in Figure 19 indicates that E. coli inactivation is a complex process. This is sample presented the optimal ratio of Ag wt/Ag particle size. The Ag-sites held in exposed positions active in the E. coli inactivation were above other sputtering formulations. Ag sputtered alone as a control experiment in Figure 19 indicates an E. coli required an inactivation time of ~9 h. Figure 20 shows that for samples sputtered > 20s, the E. coli inactivation kinetics became larger compared to samples sputtered for times above 20s since the Ag-agglomerates becomes bigger but the catalytic activity per exposed atom decreased due to the Ag-agglomeration process. At times < 20s, there was not enough Ag on the polyester to mediate the E. coli inactivation as detected on the polyester by the X-ray fluorescence data (XRF).

302


Figure 21 presents the contact angle for different Ag-ZrN samples on Si-wafers. No polyester was used for the contact angle measurements since the water droplet disappeared at zero time. Figure 21 shows that samples sputtered for 5 s at 50 mA presented a contact angle of 64.4° at time zero. This contact angle decreased with the contact time on the Si-wafer surface due to the hydrophobic to hydrophilic transition ending up after15 min and leading to an hydphobic-hydrophilic type of surface. The second row in Figure 21 shows that Ag-ZrN samples become more hydrophobic at time zero after 20s sputtering (initial contact angle of 73.3°). A contact angle of 101° was observed at time zero for 80 s sputtered samples, since the samples became more hydrophobic due to the higher amount of Ag on the Si-wafers.

Figure 19. E. coli inactivation by a Ag-ZrN confocal sputtered DCP catalyst in an Ar 10% N2 gas mixture and applying 300 mA.

Figure 20. Inactivation time of E. coli on Ag-ZrN polyester as a function of the deposition time by DCP sputtered at 300 mA.


303

Ag-ZrN, 50 mA, 5s

0 min: 64.4

10 min: 43.8

15 min: 36.7

10 min: 46.2

15 min: 25.9

10 min: 63.6

15 min: 42.1

Ag-ZrN, 50 mA, 20s

0 min: 77.3 Ag-ZrN, 50 mA, 80s

0 min: 101.0

Figure 21. Contact angle (CA) for Ag-ZrN composites on polyester.

(ii) In a more recent study [77] the co-sputtering of ZrNO and Ag2O was seen to enhance the E. coli bacterial inactivation kinetics compared to the sequential sputtering of ZrNO and Ag addressed above when sputtering ZrN-Ag composites. The amounts of Ag-ions released during bacterial inactivation were < 5 ppb/cm2 and well below the Ag cytotoxic levels. Since no cytotoxicity was introduced during the bacterial inactivation process when a ZrNO-Ag sputtered with Zr for 90s and Ag for 10s in an N2+O2 atmosphere, the disinfection was seen to proceed within 45 min through an oligodynamic effect. Figure 22 presents the sample DRS spectra in Kubelka-Munk units. The UV-vis reflectance rough data cannot be used directly to assess the absorption of the loaded polyester because of the large scattering contribution of polyester to the reflectance spectra. Normally it is assumed a weak dependence of the scattering (S) on the wavelength when taking DRS spectra. The KM/S values in Figure 22 allow the correlation of the spectral intensity of the ZrNO-Ag co-sputtered and of the ZrNO samples spectra with the bacterial inactivation kinetics. The increase in reflectance in the co-sputtered spectra compared to the sequentially sputtered layers in Figure 22 is due to the different microstructure of the ZrNO-Ag photocatalyst in both cases as shown next in Figure 23 by TEM. The red shifted absorption in the nanoparticles of ZrNO-Ag leads to a red tail in the DRS spectra of the nanoparticles in Figure 22 at ~400 nm due to the localized surface resonance of the Ag-plasmons. Gunawan et al., [23] recently reported that the oxidation of Ag0 to Ag2O (Ag+) is a reversible reaction increasing the surface plasmon resonance. The electron microscopy (TEM) of ZrNO-Ag (90 s) co-sputtered sample is discussed next. Figure 23 presents the TEM of a co-sputtered ZrNO-Ag (90 s) sample on polyester. In the left-hand side the Zr and Ag are shown to be immiscible when co-sputtered on the polyester fibers. The right-hand side in Figure 23a shows the Zr and Ag-nanoparticles contrasted by high angular annular dark field (HAADF). The sizes of the ZrO2 and Ag

304


nanoparticles in the co-sputtered ZrNO-Ag (90 s) sample were respectively 80-130 nm and 815 nm. (1) ZrNO-Ag cosputtered for 150 s (2) ZrNO-Ag cosputtered for 90 s (3) ZrNO-Ag cosputtered for 60 s (4) ZrNO-Ag cosputtered for 40 s

3 (1)

KM/S

2 (2)

1

(3) (4)

0 0.75

(1)

(1) ZrNO sputtered for 150 s (2) ZrNO sputtered for 90 s (3) ZrNO sputtered for 60 s (4) ZrNO sputtered for 40 s

(2)

KM/S

0.50 0.25

(3) (4)

0.00 200

300

400

500

600

700

800

Wavelengh (nm) Figure 22. Diffuse reflectance spectra for ZrNO and ZrNO-Ag sputtered on polyester for times as indicated in the Figure legends.

Figure 23. Left-hand side: Transmission electron microscopy of a co-sputtered ZrON-Ag (90 s) sample (amplification 28k) Right side: the same sample in high angular annular dark field (HAADF) representation.


305

Due to its size, the Ag-nanoparticles are not able to penetrate to bacteria core through the bacterial porins with diameters of 1-1.3 nm and only Ag-ions are able to diffuse through bacterial porins leading to DNA damage and finally to bacterial inactivation [72,77]. Figure 24 shows the Ag- and Zr-ions concentrations released during the reuse of ZrNOAg (90 s) sputtered samples. The Ag-ions release during 8 cycles was < 5 ppb/cm2, which is below the allowed cytotoxicity levels of 35-90 ppb/cm2 for Ag[79]. Therefore, the bacterial inactivation mediated by ZrNO-Ag (90 s) sample does not introduce cytotoxicity but proceeds through an oligodynamic effect comprising fast bacterial inactivation kinetics and acceptable cytotoxycity [1]. The surface atomic percentage concentration of elements in the ZrNO-Ag (90s) sputtered samples after being contacted 3s with bacteria were: O1s 8.8%; N1s 2.3%; C1s 54.9%; Zr3d 2.8% and Ag3d 35.4%. These percentages did vary less than 10% during the 45 min reaction leading to the total bacterial loss of viability. Therefore, the rapid destruction of decomposition products during the photocatalysis allows for repeated bacterial inactivation by the ZrNO-Ag (90s) sputtered samples.

TaON and TaON/Ag Composite Antibacterial Surfaces This study reports the design, preparation, testing and surface characterization of uniform films deposited by sputtering Ag and Ta on polyester in the presence on N2 and O2 to evaluate the E. coli inactivation. Co-sputtering for 120s Ta and Ag in the presence led to the faster E. coli inactivation by a TaON/Ag sample within ~40 min under visible light irradiation. A mechanism of interfacial charge transfer (IFCT) from the Ag2O conduction band (cb) to the lower laying Ta2O5 (cb) is suggested. The TaON/Ag sample microstructure was characterized by contact angle (CA) and by atomic force microscopy (AFM) [78]. 7.5

2


(1) Zr ions (2) Ag ions

6.0

4.5

(1) (2)

3.0

1.5

0.0

0

2

4

6

8

reusing cycles Figure 24. Ion-coupled plasma mass spectrometry (ICP-MS) determination of Ag-ions and Zr-ions released from a co-sputtered ZrNO-Ag (90 s) sample within the E. coli loss of bacterial viability.

306


The bacterial inactivation becomes faster for increasing TaN-sputtering times. Figure 25a shows that sputtering TaN for 120 s inactivated bacteria within 300 min. Figure 25a, trace 5) shows that in the dark no bacterial inactivation on TaN/Ag-polyester. TaN/Ag shows a faster bacterial inactivation compared to TaN films and inactivate E. coli within 120 min for a 120s co-sputtered sample. Figure 25a, traces 3) shows bacterial inactivation for TaN/Ag surfaces co-sputtered for 60s. Since the E. coli inactivation time for samples sputtered for 120s becomes shorter, a 60s sputtering time did not deposit sufficient TaN/Ag layers or did not allow a full light absorption of the incident visible light. A sample of TaN/Ag co-sputtered for 120 shows an inactivation time of 120 min. The co-sputtered TaN/Ag (150 s) sample (Figure 25a, trace 2) is seen to inactivate E. coli at longer times compared to the TaN/Ag co-sputtered sample for 120 s (Figure 25a, trace 1). This is due probably to: a) bigger Ag-clusters hindering the diffusion of charges between TaN and the Ag layers, b) a decrease in the number of surface catalytic sites available for bacterial inactivation, and c) an excess of Ag acting as recombination centers for the photo-induced charges on the sample surface. Figure 25b shows the bacterial inactivation kinetics on TaON/Ag-polyester under O2/N2/Ar atmosphere. A 6log10 (99.99%) reduction in the bacterial concentration was observed within ~40 min for the TaON/Ag co-sputtered sample for 120s. Sequential sputtering of Ta and Ag lead to a slower bacterial inactivation than the co-sputtered samples as shown in Figure 25b, trace 4). The shorter bacterial inactivation kinetics reported on Figure 25b compared to Figure 25a can be rationalized considering that reactive sputtering in the presence of O2 introduces in the TaN ionic metal-oxygen species in a matrix of covalent metal-nitrogen bonds [80]. The polarity introduced by these metal-oxygen species is due to the van der Waals forces comprising: permanent dipoles, induced dipoles and hydrogen bonds. The surface energy of the TaON-Ag surfaces (Figure 25b) is higher than the one available on the TaN/Ag (Figure 25a) surface due to the presence of ionic Ag-O metal oxygen species. Figure 2c shows that Ag sputtered on polyester does not lead to complete bacterial inactivation even after 6 h of irradiation. Figure 25d shows that TaON samples sputtered on polyester for 120 s inactivated bacteria within 90 min. This is two times longer than the time required by TaON/Ag due to an interfacial charge transfer between Ag and TaON. E. coli inactivation time as a function of the TaON/Ag layer thickness showed that a 130 nm coating leads to the shortest bacterial inactivation. For very thin TaON/Ag thicknesses below 50 nm, the microstructure of the film seems not to be effective in inducing fast bacterial inactivation kinetics. Figure 26a shows the atomic force microscopy (AFM) for a sputtered TaON (120 s) sample. Non-uniform TaON grains with sizes of 40-60 nm are observed. Figure 26b shows the AFM image for a co-sputtered TaON/Ag (120 s) sample with grain sizes of 70-100 nm. The root mean square (rms) roughness for the samples TaON and TaON/Ag were respectively 2.2 and 2.7 nm. An increase in roughness leads to higher contact angle reducing the polarity and the total surface energy. Increased sample rugosity allows for a better adhesion of the Ag-ions leading to the bacterial inactivation [28,29].


b)

a) 6

6

10

5

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4

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3

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2

10

10

E. coli (CFU/ml)

(5)

5

10

4

10

3

10

(4)

2

10

(3)

(2)

(1)

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(4) 10

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(3)

(1) (2)

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10

10

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60

120

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10

300

0

60

120

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E. coli (CFU/ml)

240 (6)

300 d)

(5)

5

10

4

10

3

3

10

10

Ag sputtered on polyester for 120 s in dark Ag sputtered on polyester for 20 s Ag sputtered on polyester for 30 s Ag sputtered on polyester for 60 s Ag sputtered on polyester for 120 s

2

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1

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(1)

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240

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10

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60

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Figure 25. E. coli inactivation on TaN, TaN/Ag, TaON and TaON/Ag sputtered on polyester for different times under light (360-700 nm) with an output of 4 mW/cm2. 25a: (1): TaN/Ag co-sputtered for 120 s, (2): for 150 s, (3): for 60 s, (4): TaN sputtered for 120 s and (5): TaN/Ag co-sputtered for 120s in dark, 25b (1): TaON/Ag co-sputtered for 120 s, (2): for 150 s, (3): for 60 s, (4): TaON/Ag sequential sputtered for 120 s TaON / 40 s Ag and (5) TaON/Ag co-sputtered for 120 s in dark. 25c: Ag sputtered on polyester for different times under light. 25d: (1): TaON for 120 s, (2): TaON for 150 s, (3): TaON for 60 s, (4): TaON for 20s, (5): TaON sputtered on polyester for 120 s in dark and (6) polyester alone irradiated under visible light.

The contact angles (CA) with TaON and TaON/Ag polyester as a function of time after the bacterial inactivation are shown in Figures 27a and 27b. The TaON sample after 2s shows a CA of 80° and after 6s of 12°. The water droplet disappeared after 10s. This means that the TaON-sample becomes completely hydrophilic after 10s and eliminates any hydrophobic residues left by bacterial inactivation. A water droplet on the polyester alone was observed to disappear by contact with the fabric. Although the polyester is hydrophobic, the polyester has a high amount of void areas/porosity promoting water penetration through the polyester microstructure. The sputtering TaON decreases the void areas leading to water penetration and concomitantly increasing the sample hydrophobicity. The amount of O2 plays a role in the contact angle of the surface. Studies on nitrides/oxynitrides have reported that O2 photo-adsorption introduces highly polar and electronegative groups compared to N2 changing the electro-negativity and electron density of nitrides [78,79].

308


Figure 26. Atomic force microscopy for polyester samples: a) sputtered with TaON for 120s time and b) co- sputtered TaON/Ag for 120 s.

Figure 27b shows the CA of the water droplet on the surface of co-sputtered TaON/Ag polyester samples. A slower decrease of the CA with time was observed on the TaON sample in Figure 6a. The CA varied from an initial value of 108° at 10s to 14° within 300s and disappears completely after 310s. The surface energy of Ta2O5 controls the surface CA. The addition of Ag increases the hydrophobicity in the TaON/Ag film surface leading to a longer to attain complete hydrohilicity. The photo-induced interfacial charge transfer from the Ag-layers to the TaON layers will be discussed in this section. Visible light is absorbed by the narrow band semiconductor Ag2O up to 880 nm and the wideband semiconductor Ta2O5 absorbs UV-light < 310 nm (4 eV). In Figure 28, a mechanism for electron injection for the charge transfer from Ag2O into Ta2O5 is suggested. This mechanism considers the potential energy of the semiconductor bands. When the sputtered Ag layer is exposed to air, the water vapor in the air leads to the formation of surface AgOH. The AgOH has been reported to decompose spontaneously to Ag2O as shown before in eq(3). The electron injection from Ag2O to the Ta2O5 is thermodynamically favorable. The Ag2Ocb at -1.3 eV NHE lays above the Ta2O5 cb at 0.4 eV NHE. The potential 1.7 eV difference in provides a considerable driving force inducing a fast electron injection from Ag2O into Ta2O5. The Ag2O transfers the majority of the electrons to the Ta2O5cb hindering


309

the e-/h+ recombination in Ag2O. The values for the potentials for the cb for both semiconductors are only indicative, since in quantum size nanoparticles, the band energy shifts have been reported to higher potentials [80]. The reductive character in the quantum size Ag2O particles proceeds at a higher energy level than -1.3 eV NHE.

80°

108°

12°

94°

0°

14°

0°

Figure 27. Contact angle water-droplets as a function of contact time for: a) TaON sputtered on polyester for 120s and b) TaON/Ag co-sputtered on polyester for 120 s.

Under visible light irradiation Ag2O gives raise to the charge separation Ag2O + visible light  h+ + e-

(8)

Ag2O + e-  2Ag0 + O-

(9)

Figure 28. Scheme for the photoinduced interfacial charge transfer (IFCT) from Ag2O to Ta2O5 under visible light irradiation.

310

Sami Rtimi, Cesar Pulgarin, Rosendo Sanjines et al. Ag2O + e-  2Ag0 + 1/2O2

(10)

The cbe- become available to reduce oxygen in eq.(9). The photo-induced electron eq.(10) lead to silver atoms and additionally produce O2- eq(11): e- + O2  O2°-

ACKNOWLEDGMENTS We thank the EPFL for financial support of this work and COST Actions MP1106 and MP1101for interactive discussions during the course of this study.

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[5] [6] [7] [8] [9]

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Chapter 11

FUNGAL DETERIORATION OF AGED TEXTILES Katja Kavkler1,*, Nina Gunde-Cimerman2,3, Polona Zalar2 and Andrej Demšar4 1

Restoration Centre, Institute for the Protection of Cultural Heritage of Slovenia, Ljubljana, Slovenia 2 Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia 3 Centre of Excellence for Integrated Approaches in Chemistry and Biology of Proteins (CIPKeBiP), Jamova, Ljubljana, Slovenia 4 Faculty of Natural Sciences and Engineering, University of Ljubljana, Ljubljana, Slovenia

ABSTRACT Preservation of historical objects is of the utmost importance for future generations, as such objects have great social, historical, cultural and educational value. However, the preservation of organic materials often causes problems, as those involved can have little knowledge of biological decay. Fungal contaminations in particular can alter the appearance, and the structural and mechanical properties of an object, which can consequently prove difficult to conserve or to return to its former state. Most museums are aware of the importance of the maintenance of the correct environmental conditions in storage rooms, such as low temperature and low relative humidity. However, some fungi can still thrive under such conditions, and thus result in long-term contamination and severe damage to materials. Some fungi can also remain viable in a dormant phase. The present chapter describes an interdisciplinary approach for mycologists, textile scientists, and art restorers to better understand the impact of fungi on historical textile objects. The diversity and frequency of occurrence of different fungal species for each selected material (cotton, linen, silk, wool) is here investigated, and the available literature is reviewed. Additionally, there is often a lack of complete information about the history of many objects, and a limit to the sample size that can be available for analysis. On this basis, the impacts of selected fungal species are further examined here *


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Katja Kavkler, Nina Gunde-Cimerman, Polona Zalar et al. by inoculation of pure cultures on artificially prepared laboratory samples, with incubation in a controlled environment. Cotton is used as a representative of cellulose material, and wool as a representative of proteinaceous material, and these are analysed using non-destructive analytical methodologies, including tensile tests, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. An overview of the textile changes detected at the levels of the surface morphology and the supermolecular structure of these textile fibres is thus presented. It can be concluded that in comparison to non-aged textiles, aged textiles are at greater risk when exposed to fungal contaminations, and so they require additional care at the conserving institutions. As changes in the structure and properties of textile fibres increase with longer incubation periods after fungal contamination has occurred, museum workers need to regularly examine stored objects for uncommon stains or visible fungal growth. As well as such visual inspections, nano- and microtechnologies need to be implemented as new standards of damage documentation.

INTRODUCTION Conservation of objects that define our cultural heritage is the main aim of museums and related institutions. This work is of great importance, as the objects can have social, historical, cultural and/or educational value [1]. Cultural heritage is a crucial source of the common identity for mankind. Specifically in Europe, the cultural development through the centuries has left a heritage that is nowadays often kept in indoor and outdoor facilities at archaeological sites and museums. Artwork textiles are usually preserved and stored in museums, and these are common to all human societies, and represent an important aspect of the cultural heritage. Historical textile objects that are conserved in museums include clothing, accessories, furnishings, tapestries, decorations, and many more. Although these were used by people in historical times, they were not designed to last a long time, and thus often only a few pieces have remained in their original state from different historical periods. More objects have remained preserved since the baroque times than from earlier times, while few conserved objects are recovered from several-thousand-year-old archaeological finds. Therefore these are precious, and they need to be conserved for future generations, without allowing major changes to the materials, or to their appearance and mechanical characteristics. Deterioration of materials is an unavoidable part of the life-cycle of preserved objects, although people working in the field of conservation of cultural heritage attempt to interrupt, or at least to slow down, this process. Fungi are the most significant invaders of materials, and they can cause major changes as a consequence of their growth. The aim of the present chapter is to better define the influence of fungi on textile materials, from the perspective of three different fields of science: textile sciences, mycology, and conservation. To present this interdisciplinary approach, this chapter is divided into four main sub-chapters, which include: (i) an introduction to the theme; (ii) the fungal deterioration of museum textiles; (iii) an analysis of laboratory textile samples that have been artificially inoculated by fungi; and (iv) short concluding remarks.

Fungal Deterioration of Aged Textiles

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2. FUNGAL DETERIORATION OF MUSEUM TEXTILES 2.1. Fungi on Historical Textiles Objects stored and displayed in museums and in similar institutions have different histories and are therefore in different states of preservation. In the several decades, or maybe hundreds of years, of their existence, they have been subjected to the influences of different and various external factors, such as UV irradiation, oscillations in temperature and relative humidity, mechanical and chemical damage, and (micro)biological influences. As organic polymers, textile objects are prone to deterioration through different processes that can occur during long-term storage, due to the above-mentioned external factors. All of these factors can cause oxidation, hydrolysis, polymer-chain scission, and breaking of intramolecular bonds [2-5]. Through these processes, objects lose their value as historical specimens, and can finally completely disintegrate. Oxidative processes and hydrolysis of the polymers in natural fibres result in the breakage of intermolecular and intramolecular bonds, and this facilitates the penetration of microbes or their enzymes. The above-mentioned changes influence the structure of a fibre and can allow its decomposition by enzymes that are secreted by different types of microorganisms [6,7]. Organic materials are especially affected. Fungi represent one of the most important risk factors for degradation and damage of textile objects that are part of our cultural heritage (e.g., museum artifacts), as they are important decomposers of textile fibres of different origins (i.e., plant, animal) and they can attack all kinds of macromolecules, such as cellulose and protein, and even synthetic fibres [2]. Cellulosic fibres are supposed to be very sensitive, whereas proteinaceous fibres, especially silk, tend to be more resistant to microbial attack [2, 8, 9]. Fungi are transmitted via spores. For their germination and further growth, spores need a source of nutrition and oxygen, and appropriate temperatures and humidity. The growth of fungi is the most important aspect here, and it involves secretion of enzymes into the fibres and absorption of the resulting degraded products through the hyphae [10,11]. The degradation of textiles by fungi can be the result of different processes, which include: (i) various enzymes can breakdown the macromolecules, and subsequently metabolise the products; (ii) fungi also produce various kinds of primary and secondary metabolites, such as acids, oligopeptides, dyes and volatile organic compounds, and these can damage textiles or change their appearance; (iii) fungi can cause physical disruption of the material via hyphal penetration; and (iv) fungi can increase the water retention of a material, subsequently allowing other microbes to colonise it. In summary, fungal colonisation not only leads to an unpleasant mouldy odour, but also to changed appearance, pigmentation and texture, and/or altered mechanical and structural characteristics, which will reduce the historical value of an object [1,2,12,13]. Fungi that can infest cultural heritage objects have been relatively well documented over the last decades, and particularly those involved with stone, wood, paintings and paper biodeterioration (reviewed by [14]). However, there are only a few reports on fungi that can cause deterioration of historical textiles [9,15-20]. Amongst these studies, there are also a few reports on fungal species on archaeological textiles [17,18,20] and historical textiles [9,16,17], and recently also on synthetic textiles stored as museum exhibits of modern times

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Katja Kavkler, Nina Gunde-Cimerman, Polona Zalar et al.

[2]. Fungi have mainly been isolated from cellulosic substrates. Fungal genera reported in these studies have included: Alternaria, Aspergillus, Chaetomium, Ctenomyces, Fusarium, Memnoniella, Myrothecium, Neurospora, Penicillium, Scopulariopsis and Stachybotrys [1619]. Most of these can grow on historical cellulosic fibres; however, Aspergillus, Chrysosporium, Ctenomyces, Fusarium, Penicillium, and Trichoderma have been reported from historical proteinaceous fibres [17,19], and dermatophytic fungi (Trichophyton and Microsporum) from historical wool [19]. To the best of our knowledge, only a few investigations have been performed on fungal deterioration of historical textiles. These have mainly been part of more extensive investigations of historical and archaeological textile objects [17,18,21-24]. Only a limited number of investigations have been carried out on buried contemporary materials [20,25,26]. The fungi that have been isolated belong mainly to xerophilic species of the genera Aspergillus and Penicillium. Additionally Cladosporium species have been commonly isolated, as well as Alternaria spp., Chaetomium spp. and Trichoderma spp. (Table 1). Table 1. Cultural heritage objects infected by fungi and organised according to substrate material, as an overview of the literature. The period of the origin is given, if known Object COTTON Wooden statue in textile dress Embroidered napkin FLAX Painting on canvas with a paper patch on the back Painting on canvas Painting on canvas (original canvas)

Painting on canvas (original canvas) Painting on canvas (original canvas) Painting on canvas (original canvas) Painting on canvas (lining) Painting on canvas (lining) Painting on canvas

Date

Fungal species

Literature source

1850

Penicillium chrysogenum

[15]

1906

Aspergillus versicolor

[15]

Unknown

white filamentous hyphae

[15]

Unknown Mid-19th century

[15] [15]

1729

Alternaria sp., Penicillium corylophilum Penicillium corylophilum, Penicillium bialowizense, Aspergillus proliferans, Cladosporium tenuissimum, Penicillium crustosum Penicillium cf. corylophilum

17th century

Chaetomium globosum

[15]

1821

Penicillium chrysogenum

[15]

Unknown

Penicillium palitans

[15]

Unknown

Aspergillus sydowii, Aspergillus clavatus, Penicillium chrysogenum Penicillium chrysogenum

[15]

Unknown

[15]

[15]

319

Fungal Deterioration of Aged Textiles Object

Date

Fungal species

Literature source

(lining) Coptic and Egyptian textiles

Unknown

Aspergillus sp., Penicillium sp., Chaetomium sp., Alternaria sp., Trichoderma sp. Chaetomium sp.

[16]

Alternaria alternata, Alternaria sp., Aspergillus candidus, Aspergillus sp., Aspergillus versicolor, Aureobasidium pullulans, Cladosporium cladosporioides, Cladosporium sp., Cladosporiun herbarum, Drechslera sp., Epicoccum purpurascens, sterile mycelium, Penicillium cyclopium., Penicillium sp., Rhizopus stolonifer, Trichoderma viride, Ulocladium chartarum, Ulocladium oedemansii, Ulocladium sp. Penicillium chrysogenum

[24]

Mid-20th century

Cladosporium cf. cladosporioides

[15]

End of 19th or beginning of 20th century End of 19th or beginning of 20th century

Aspergillus versicolor

[15]

Fomes fomentarius, Penicillium chrysogenum

[15]

WOOL Military coat Coptic textiles

20th century Unknown

[15] [16]

Bedouin belts

Unknown

Cladosporium cf. cladosporioides Aspergillus sp., Penicillium sp., Chaetomium sp., Alternaria sp. Aspergillus sp., Chaetomium sp., Pencillium sp.

Archaeological remains in Georgia Painting canvasses from Serbia

Unknown

Painting on canvas HEMP Painting on canvas

16th century

SILK Embroidery

Embroidery

Unknown

[18]

[22]

In the framework of the studies performed by the authors of this chapter, the most frequently occurring species has been Penicillium chrysogenum, as isolated from seven different objects of various historical periods – from Roman times to the 20th century – and of different fibre compositions – cellulosic and proteinaceous. P. chrysogenum secretes proteases [27] as well as cellulases [28]. The second-most frequently occurring species has been Cladosporium cf. cladosporioides, as isolated from both cellulosic and proteinaceous substrates that originate from the 19th and 20th centuries. C. cladosporioides has been reported for its cellulolytic [29] and proteolytic [30] activities, and for its secretion of large amounts of succinic acid [31], all of which can cause hydrolytic degradation. Species belonging to the

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genus Cladosporium represent an important threat for historical objects, due to its ability to survive relatively unfavourable conditions, such as low temperatures and low humidity [32]. The third and fourth most frequently occurring species are the cellulolytically active Aspergillus clavatus and Penicillium corylophilum [33,34], which have both been isolated from cellulosic objects: A. clavatus from cotton and flax, and P. corylophilum only from flax (Table 1).

2.2. Environmental Conditions in Institutions Storing Historical Textiles The environmental conditions in the storage and exhibition rooms of museums are of great importance for the conservation of objects of high cultural and historical value [9]. Objects stored in buildings where conditions cannot be controlled are endangered and need to be either preventively protected (e.g., chemical protection) or cured after infection. For archaeological objects, the problem is even greater, as these objects have been exposed to numerous environmental and microbial degradation factors for a long time [35]. Museum guidelines on storage conditions, which to some extent diminish these degradation processes, have been known for decades. They include controlled temperature (from 20 to 25 °C), and relative humidity (from 45% to 50%) [4,36]. Application of these conditions in many instances does not suffice, however, as they do not prevent growth of many fungi, and particularly airborne and xerotolerant fungi [37,38]. Additionally, reduction of the relative humidity to below 45% can dry out stored materials, which can become brittle as a consequence [4]. In summary, biodeterioration has to be controlled with additional precautions, which include expensive air-filtering systems [9]. As mentioned above, fungal growth is related to the appropriate environmental conditions; i.e., high room temperature and humidity, especially in non-ventilated storage areas [7]. Storage conditions in the institutions selected for a study of biodeteriorated historical textiles in Slovenia are mainly uncontrolled [15]. Generally, all of the objects investigated in our recent study [15] were until recently exposed to inappropriate conditions. The most extreme case is the Slovene Museum of Christianity, where the storage rooms are in an attic of a convent and the conditions changed according to the seasonal weather. In spite of these adverse conditions, only a relatively small number of the objects investigated was infected by fungi [15], which indicates that fungal infections are not exclusively connected to environmental conditions. The objects might have become infected before the acquisition by museums, as observed in the case of a painting [15]. In some museums with controlled environmental conditions, the surfaces of objects are cleaned before moving them to renovated storage rooms, to prevent further fungal growth, but this does not destroy fungal spores, which remained viable and germinated on solid laboratory medium. According to these cases, it can be concluded that storage of objects under the appropriate conditions (20 to 25 °C, 45% to 50% relative humidity); [4,36] can temporarily prevent active fungal growth, although this can be reactivated as soon as the objects are exposed to humid and warm conditions again. In the case of xerotolerant species of the genera Aspergillus and Penicillium, environmental conditions have less important roles, as these fungi do not need high relative humidity [2,39]. Therefore, lowering of the relative humidity in storage rooms is not a


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sufficient measure, especially keeping in mind that historical textiles need to be kept in environments that are humid enough to prevent them becoming brittle.

2.3. Influences of Substrate Type The main constituents of most of infected objects are cellulosic fibres, and the most infected cellulosic material is flax (Table 1). The possible reasons include a higher content of non-cellulosic substances; e.g., hemicelluloses, pectins and pentosans make up 15% of flax, in comparison to 5% of cotton [2,40], and the more complete supermolecular structure of cotton in comparison to flax. Additionally, the objects made from flax include mainly paintings that are stored or displayed in religious institutions where there is no control of the environmental conditions, and often in contact with easily degradable materials, such as protein glues [15]. Surprisingly, many objects composed of wool and silk fibres are also infected by fungi (Table 1). One of the species that has been isolated from wool is C. cladosporioides, which to the best of our knowledge, has not been isolated previously from wool. Within the study in the Slovene museums, half of the objects made from silk that were analysed were infected. The species isolated were Aspergillus protuberus, Fomes fomentarius and P. chrysogenum [15]. According to the previous literature, only A. niger has been reported so far from silk objects [17,41]. Rare fungal infections of silk objects are due to silk being the natural fibre that is most resistant to biodeterioration [2]. As the sericin that is susceptible to biodeterioration is mainly removed during processing, the remaining resistant fibroin becomes susceptible only when exposed to light, heat or bacterial growth [41]. Many objects are composed of additional organic materials that can promote fungal growth [19, 42]. In particular, non-fibrous protein (e.g., animal glues, which are used as sizing of paintings) are easily affected by fungi [19]. Indeed, many of the objects we investigated recently were paintings, where the textile carrier was in contact with other organic materials. Some of these were identified using Fourier transform infrared (FTIR) spectroscopy, as proteins, acrylic resins, and organic calcium salts.

2.4. Structural and Mechanical Properties of Historical Textiles Infected by Fungi The main structural changes due to fungal inestation that have been determined from biodeteriorated textiles in previous reports were loss of tensile strength and/or weight, and visual changes [16,20,43]. The methods already used for chemical and physicochemical analyses of the raw materials and other components of archaeological and historical textiles have included optical microscopy, scanning electron microscopy, inductively coupled plasma mass spectrometry, attenuated total reflection FTIR spectroscopy, dispersive and Fourier transform Raman spectroscopy, and atomic absorption spectroscopy, as well as high-pressure liquid chromatography for colour analyses [17,44,45]. However, due to limited sample sizes, and therefore limited choice of analytical methods, as well as insufficient information regarding the history of selected objects, satisfactory interpretation of the results is often difficult.

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Figure 1. Representative scanning electron microscopy photograph of canvas painting RCS01, showing extensive mycelium growth covering the surface of the flax fibres (magnification, 1900×).

In our recent study on biodeteriorated historical textiles from Slovene museums and religious institutions, various objects were selected for analysis of their structural and mechanical properties after suspected fungal infections. These objects varied in terms of their age, composition, purpose of use, history of use, and storage conditions (Table 1). FTIR and Raman spectroscopy were used for the analysis of the structural properties of the fibres, and scanning electron microscopy for determination of mechanical damage to the fibres [15]. These analyses were performed on textile materials that were taken as loosened fibres or threads, or pieces of fabric. In general, they show that fungal growth was mostly limited to the surface of the fibres (Figure 1), and did not influence their inner structure. Analysis of the structural properties of infected textile fibres showed the most intensive changes in the cellulosic fibres, and especially the flax fibres, and less distinctive structural changes to proteinaceous materials. For the structural changes analysed using FTIR and Raman spectroscopy, the spectra of contemporary unaffected textiles were compared with those of inoculated and non-inoculated historical fibres from the museums and religious institutions. The Raman spectroscopy was used to assess the skeletal and supermolecular structure of the cellulosic fibres [46]. When analysing historical samples, a strong luminescent background can disturb the analysis, especially when analysing bast fibres, which contain more non-cellulosic substances than cotton [47]. This luminescence can be caused by non-cellulosic materials in fibres, by fungal hyphae, or by deterioration products on the surface of the materials analysed [48]. In several cases, only the two strongest bands could be identified specifically (at 1096 cm-1 and 1122 cm-1), which are typical of asymmetric and symmetric vibrations of glycoside bonds, respectively [49]. By using prolonged exposure to low laser power (known as the ‘signal quenching’ method), the quality of the spectra was improved, thus allowing their better interpretation, to obtain further information on the structures of the specimens selected. In the most deteriorated samples, there were two bands in the Raman spectra, at 435 cm-1 and 520


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cm-1, that are typical of crystalline cellulose [50], and these completely disappeared. Fewer bands in the region between 300 cm-1 and 600 cm-1, which are typical of different ring vibrations [49], is an indication of cellulose deterioration [44]. The most visible changes in the spectra of flax fibres were observed for a painting, which was on the reverse side, with the sample visibly covered with mycelia (Figure 1) [46]. Although the strong luminescent background made interpretation of the spectrum difficult, the decreased ratio between the two most intense bands at 1096 cm-1 and 1122 cm-1 (Figure 2) was indicative of the hydrolysis of cellulose chains and the scission of glycoside bonds [45].

Figure 2. Comparison of the Raman spectra bands in the region between 950 cm-1 and 1250 cm-1 of the reference flax sample (dotted line) and the sample of the inoculated canvas (RCS01; solid line), which was severely affected by fungal growth.

FTIR spectroscopy is another efficient method that enables observations of changes that have occurred at the molecular and supermolecular scale (e.g., depolymerisation, crystallinity), as caused by either fungi or other external influences. FTIR spectroscopy measures the vibrations of the molecular bonds of functional groups. When used as FTIR micro-spectroscopy, this has a microscope attached to the IR source in transmission mode, and changes throughout the whole thickness of a fibre can be identified [51]. Our recent FTIR micro-spectroscopy revealed changes in the spectra of cellulose fibres, while no structural changes were observed for the inoculated proteinaceous fibres (Table 1). Several spectral features also showed decreases in the cellulose crystallinity in both inoculated and nonaffected samples, primarily as a decrease in the bands at 1430 cm-1 (typical of CH2 and OCH vibrations, and intramolecular hydrogen bonds;) [3,52], 1371 cm-1 (COH and HCC vibrations of cellulose and hemicellulose) [3], and 1335 cm-1 (OH and CH2 vibrations) [53]. This was seen in the cotton and flax specimens, along with a shift in the bands at 1430 cm-1 and 1111 cm-1 (asymmetric vibrations of glycoside rings) [52] in the flax specimens (Figure 3). In the spectra of the objects composed of bast fibres, a band at 1735 cm-1 was observed, which is typical of carbonyl bonds [54], and probably arose as a consequence of depolymerisation [55]

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due to fungal infection. Using these selected analytical methods, this enabled us to reveal and qualify the extent of the changes arising from the deterioration of the fibres, although they did not allow the clear attribution of the causative external factors, such as fungi, temperature, humidity and/or time.

Figure 3. Comparison of the FTIR spectra of different flax samples (a-e) in the region typical of crystalline cellulose vibrations. The peaks at 1430 cm-1, 1371 cm-1, 1335 cm-1 and 1111 cm-1 (from left) are indicated (arrows).

Additional information can be obtained using attenuated total reflection FTIR spectroscopy, which enables the analysis of only the surface properties of the fibres. In two flax painting-canvass samples, two bands at 1335 cm-1 and 1316 cm-1 were joined into a single peak at 1320 cm-1 as a consequence of the cellulose deterioration [56]. As well as the qualitative interpretation of the spectra, FTIR spectroscopy also provides (semi)quantitative analysis [52,57]. As the intensities of certain bands change according to the crystallinity of the cellulose, height ratios can be used as a cellulose crystallinity index. Nelson and O'Connor [57] indicated two band ratios as measures of the Total Crystallinity Index (TCI) (ratio of the bands at 1372 cm-1 and 2900 cm-1), which expresses the overall arrangement of the cellulose macromolecules, and the Lateral Order Index (LOI) (ratio of the bands 1430 cm-1 and 900 cm-1), which indicates the crystallinity. However, researchers still differ in their views as to the use of these two ratios [58-60]. In our study of inoculated textiles from Slovene museums and religious institutions, in most cases the TCI was lower for bio-deteriorated samples than for non-infected samples (Figure 4) [51], while the LOI, which can be affected by alkaline treatment of materials, did not give any clear results.


325

Figure 4. Total crystallinity indices of (A) hemp, (B) flax and (C) cotton samples.

3. IN VITRO TESTS OF FUNGAL DETERIORATION OF NATURAL TEXTILES Due to their cultural importance and conservation, historical textiles are endangered by extensive sampling. To understand and to explain the processes of deterioration caused to historical textiles by different fungal species, laboratory samples can be prepared under controlled conditions. Fabrics can differ in composition and structure, and can be either freshly prepared or artificially aged. In our study, the materials were selected according to the composition of the museum objects investigated [21]. On this basis, cotton and wool fabrics were selected for laboratory experiments. Cotton was selected as representative of a cellulose material, as the second most often occurring fibre type among historical textile objects, and as the most often used natural fibre in the world nowadays [61]. The selection criterion for wool fabric was as representative of proteinaceous material, which is less resistant to fungal infection than silk [2]. Both of the selected fabric types were neither dyed nor sized, to minimise possible influences of added materials. Half specimens of each fabric type were

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artificially aged at increased temperature (80 °C) and relative humidity (65%), as previously shown using different analytical techniques [21]. Six different fungal species were selected for inoculation, four of which are those most often isolated from historical textiles. The most frequently occurring species were A. clavatus, C. cf. cladosporioides, P. chrysogenum and P. corylophilum. Two additional species, Hypoxylon fragiforme and F. fomentarius, were included due to their wood-degrading abilities. The inoculation of samples and the experimental set-up was described in detail in [21,62]. The specimens were incubated for either 8 weeks or 20 weeks, and later autoclaved to prevent further deterioration. The samples were analysed using scanning electron microscopy, Raman spectroscopy, and FTIR, with tensile strength tests performed on a tensile testing machine.

3.1. Molecular and Supermolecular Structures and Mechanical Properties of Contemporary Non-aged and Artificially Aged Cotton and Wool Specimens, inoculated with Selected Fungal Species 3.1.1. Cotton Fungal growth on cotton samples differed according to the species inoculated. Mycelia were already observed by the naked eye after eight weeks of incubation in all cases, but particularly with C. cf. cladosporioides, F. fomentarius and H. fragiforme inoculations, while after 20 weeks, the mycelia had spread throughout the samples in almost all cases. Scanning electron microscopy was used for observation of the morphological changes to the fibre surface. Prolonged incubation led to more damage, which was more obvious in artificially aged samples than in non-aged samples. The most extreme damage was observed with C. cf. cladosporioides in both aged and non-aged samples. Longitudinal cracks are typical of cellulosic fibres that are exposed to microbial influences [26], and breaks were seen in brittle amorphous regions of the fibres [63] (Figure 5). As the cellulolytic activity of this fungus is relatively low [64], the high amounts of secreted succinic acid [31] was probably responsible for the deterioration seen. The least invasive fungal species were F. fomentarius and P. chrysogenum. F. fomentarius belongs to primarily lignolytic white rot fungi [65], while P. chrysogenum is known for its strong cellulolytic activity [66]. Nevertheless, only occasional longitudinal creases were observed. The structural properties of the surface layers of the textiles investigated were analysed using Raman and FTIR spectroscopies. Molecular and supermolecular changes in the cotton fibre structure were more clearly visible in samples incubated for the longer time, and with the aged samples. Using FTIR spectroscopy, there were no structural changes seen at eight weeks for the non-aged samples and the artificially aged samples inoculated with A. clavatus, C. cf. cladosporioides and F. fomentarius, which are all known for their weak cellulolytic activity [29,65]. As with the Raman spectroscopy, changes in the cotton structure were visible, and with the scanning electron microscopy, changes to surface morphology were observed. It can therefore be concluded that A. clavatus, C. cf. cladosporioides and F. fomentarius do not influence the functional groups and depolymerisation of cellulose chains in the early stages of deterioration of cotton fibres [21].


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Figure 5. Representative scanning electron microscopy photograph showing a crease and a broken fibre in a non-aged cotton sample inoculated with C. cf. cladosporioides, after 20 weeks of incubation (magnification 1500×).

Figure 6. Comparison of Raman spectra of a reference non-aged cotton sample (a), and a non-aged cotton sample inoculated with C. cf. cladosporioides (b). The bands at 435 cm-1, 520 cm-1, 1096 cm-1, 1122 cm-1 and 1180 cm-1 are indicated (arrows).

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Figure 7. FTIR spectra of an artificially aged reference cotton sample (a), and an artificially aged cotton sample inoculated with F. fomentarius (b). The shift at 1430 cm-1 and the joining of two bands with a new peak at 1320 cm-1 are indicated (vertical dotted lines).

When compared to reference samples, the fewest visible differences in the Raman spectra were seen with H. fragiforme and both of the Penicillium species. For H. fragiforme and P. corylophilum this was as predicted, [67], while this behaviour was not expected for P. chrysogenum. The Raman spectra of the inoculated samples after 20 weeks of incubation showed decreased crystallinity and depolymerisation in the cotton fibres. For most of the spectra analysed, there was a decrease in the band at 435 cm-1 relative to the band at 457 cm-1, which indicates cellulose deterioration and a decrease in the crystallinity [50]. Both of these bands are typical of the CCC and CCO vibrations of glucose rings [49,50]. The most visible changes appeared in the non-aged specimens inoculated with C. cf. cladosporioides (Figure 6). Another sign of a crystallinity decrease [68] was the decrease in the band at 380 cm-1 (CCC vibrations of glucose rings) [49] for the non-aged specimens inoculated with H. fragiforme and P. corylophilum. The ratio between the bands at 1096 cm-1 and 1122 cm-1 [45,49] increased in the non-aged specimens inoculated with A. clavatus, C. cf. cladosporioides and H. fragiforme, as well as for the artificially aged samples inoculated with C. cf. cladosporioides, as a consequence of the deterioration of the cellulose chain [49,69]. For samples inoculated with C. cf. cladosporioides, deterioration of the cellulose was observed as decreased intensity of the band at 1380 cm-1 (CH2 bending and skeletal vibrations) [70,71], and as the joining of the band at 1057 cm-1 with that at 1034 cm-1, which are typical of CO vibrations of secondary and primary alcohols, respectively [48]. The FTIR analysis showed that in most cases the band at 900 cm-1, which is typical of βglycoside bonds [52], broadened, and its intensity increased as a result of cellulose deterioration. For non-aged samples inoculated with H. fragiforme and for the artificially aged samples inoculated with P. chrysogenum, the band at 900 cm-1 decreased, as a sign of


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increased crystallinity of the samples. Increased crystallinity in these samples was also confirmed by an increase in the band at 1372 cm-1, which is typical of COH and HCC vibrations of cellulose and hemicellulose [3,72]. For all of the other inoculated specimens, the band at 1372 cm-1 decreased due to a decrease in the crystallinity. This decrease in crystallinity was seen for the non-aged samples inoculated with A. clavatus and H. fragiforme, as well as for the non-aged and artificially aged samples inoculated with F. fomentarius (Figure 7). Here there was a shift of the band at 1430 cm-1 to lower wavenumbers, which is typical of CH2 and hydrogen bond vibrations [52,73]. The deterioration of the cellulose in the cotton fibres inoculated with F. fomentarius and the decrease in crystallinity also results in the joining of the bands at 1335 cm-1 and 1316 cm-1, which are typical of OH and CH2 [56] and COH and HCC vibrations [3], respectively; these then showed a single band with a peak at 1320 cm-1 [56,74] (Figure 7). Depolymerisation of cellulose in cotton fibres was confirmed also with the Raman spectroscopy, as a decrease in the band at 520 cm-1 (CCC vibrations of glucose rings and glycoside bonds) [44] for non-aged and artificially aged samples inoculated with C. cf. cladosporioides and A. clavatus, and aged samples inoculated with P. corylophilum. This shows that P. corylophilum can degrade previously deteriorated cellulose, although it is not a typical cellulolytic species. Even clearer signs of depolymerisation were seen by the appearance of a band in the region between 1710 cm-1 and 1750 cm-1 in the FTIR spectra. This band is typical of vibrations of carbonyl groups [54,73,74]. Here, the depolymerisation of the cellulose chains is caused either by hydrolysis or by oxidation [54,55,75], which leads to the appearance of carbonyl groups at the depolymerised ends of the cellulose chains. Although carbonyl bands mainly occur around 1730 cm-1, they were observed at higher wavenumbers in the spectra of samples inoculated with P. corylophilum, due to changes in the hydrogen bonding as a consequence of the deterioration [76]. The intensity of the band increased with longer incubation times (Figure 8). In spectra inoculated with H. fragiforme, the carbonyl band had already appeared after eight weeks of incubation, whereas in the samples inoculated with C. cf. cladosporioides and P. corylophilum, the carbonyl band occurred only after 20 weeks of incubation. It should be noted that none of these three species has strong cellulolytic activity [64,67]. On the basis of the FTIR and Raman spectroscopy analyses of these inoculated samples, it can be concluded that most of the fungi caused depolymerisation of the sample, and a decrease in the crystallinity, which means that the fungi influenced the crystalline regions of the cotton fibres. A few features suggested that certain fungi attack the amorphous regions first. The luminiscence seen in some of the Raman spectra (non-aged samples inoculated with F. fomentarius and P. chrysogenum, as well as artificially aged samples inoculated with C. cf. cladosporioides and F. fomentarius) is a consequence of hyphae or deteriorated cellulose on the surface of the fibres [48], which makes the interpretation of the spectra more difficult, as the low intensity bands completely disappear into this background. The mechanical properties of selected samples of the cotton specimens inoculated (i.e., weft yarns of the fabric) were analysed in terms of their tensile behaviour. The stress–strain curves of these cotton yarns were monitored over the whole deformation range (from the beginning of the deformation, until the break). The tensile behaviour of the cotton yarns during this tensile analysis depended on the yarn properties (e.g., linear density, twist), as well as on the fibre properties (e.g., degree of polymerisation, intramolecular bonding, macromolecule orientation). Changes in the tensile properties occurred as a consequence of

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changes in both the yarn and the fibre structures. Here, as all of the cotton specimens were from the same textile material with the same initial textile properties, conclusions about the structural changes to the cotton fibres can be drawn from the results of the tensile analysis. Therefore, the differences in the tensile properties between the samples might be related to the changes in the fibre structures as a consequence of the aging of the cotton specimens and the inoculation of the samples with different fungi. The initial parts of the stress–strain curves showed their initial resistance to stretching (initial modulus) [21].

Figure 8. FTIR spectra of an aged cotton reference sample (a), and samples inoculated with C. cf. cladosporioides and incubated for 8 weeks (b) and 20 weeks (c). The band around 1730 cm-1, which is typical for carbonyl group vibration, is indicated (arrow).

Figure 9 shows the stress-strain curves of the non-aged and artificially aged samples inoculated with C. cf. cladosporioides. Comparisons of the stress–strain behaviours of the non-inoculated aged and non-aged reference cotton specimens showed that the artificial ageing resulted in severe changes to the tensile properties of the cotton yarns analysed. These were seen as much lower breaking elongation, slightly lower breaking stress, and higher elastic modulus. These changes in the tensile properties of the aged samples can be attributed to the depolymerisation of the cellulose macromolecules and the higher crystallinity, as observed by the spectroscopic methods. The aging significantly influenced the structure of the cotton fibres, and consequently also the stress–strain behaviour, such that the stress–strain curves were much lower for the aged samples than for the non-aged samples [21]. In all of the inoculated samples tested, there was a distinctive rise in the resistance to stretching, which was seen as a steep rise at the beginning of the curve when compared to the reference samples. The higher initial modulus of the yarn can be attributed to the fungal growth between the fibres of the yarn, which can act as a yarn filler that increases the initial modulus. The lower breaking strain, and in some cases the lower breaking stress, can be attributed to the depolymerisation of the cellulose macromolecules in the fibres of the yarn,


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while the higher initial modulus of the yarns was due to the depolymerisation of the cellulose macromolecules in the fibres, which can form greater numbers of intermolecular bonds. This phenomenon can be seen at the beginning of the stress–strain curves as a higher initial modulus, and in some cases, also as a relatively high specific breaking stress and lower breaking strain. When the initial modulus of the non-aged samples was compared with that of the artificially aged samples, it could be seen that the initial modulus of the non-aged samples was higher compared to that of the aged samples. This behaviour can be explained by the much more severe degradation of the fibres in the aged samples, compared to the non-aged samples. In the aged samples, the fibres were already degraded to such an extent that the ‘filling’ effect of the fungi on the yarn was overcome. The factors affecting the stress–strain behaviour of the non-aged and the inoculated samples acted synergistically. These were: depolymerisation of the cellulosic macromolecules in the cotton fibres, the filling effect of the fungi between the fibres in the yarn, and the C. cf. cladosporioides secretion of succinic acid [21].

Figure 9. Stress-strain curves of (A) a non-aged sample inoculated with C. cf. cladosporioides, and (B) an artificially aged sample inoculated with C. cf. cladosporioides. Each panel shows the reference sample (a) and samples incubated for 8 weeks (b) and 20 weeks (c).

3.1.2. Wool For the wool samples, the infection with fungi was barely visible on the surface of the samples. Deeper inspection of the material revealed more widespread mycelia between the yarns of the fabric. The growth of all of the fungal species was also less intense on the wool samples, in comparison to the cotton, in agreement with the literature data [2]. The least intensive growth was observed with A. clavatus and P. chrysogenum, and the most intensive with C. cf. cladosporioides,. Most of the wool fibres analysed remained undamaged after inoculation with the fungi, and especially the non-aged fibres. The frequency of occurrence and the intensity of the surface morphological changes increased with the time of incubation. The most frequent change was damage to the scales (Figure 10a), which already started during the processing in the non-inoculated samples. The most intensive changes, which were seen as damaged scales, longitudinal creases, fibrillation, and breaks, were observed with the non-aged samples inoculated with H. fragiforme. In the non-aged samples inoculated with C. cf. cladosporioides and F. fomentarius, there were some longitudinal creases seen.

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Figure 10. Scanning electron microscopy photographs of deteriorated wool fibres. (A) Non-aged fibres inoculated with P. chrysogenum, showing surface damage. (B) Artificially aged sample inoculated with C. cf. cladosporioides, showing severe deterioration of cortical cells. (C) Artificially aged sample inoculated with A. clavatus, showing a break in a fibre.

More surface changes were observed for the aged samples, where all of the fungal species grew more intensively than on the non-aged samples. For example, C. cf. cladosporioides completely destroyed the cuticle and cortex fibrils (Figure 10b), and caused breaks in the fibres (Figure 10c). It was not possible to analyse these wool fibres with Raman spectroscopy, as the luminiscent background of the infected samples was so strong that no spectral bands could be seen. FTIR analysis anabled the evaluation of the intensity of the wool deterioration, by comparing the intensity and positions of the amide I and II bands in the FTIR spectra [77]. No clear changes were seen in the FTIR spectra of the inoculated wool samples, which indicated that the fungi selected did not cause any intensive changes to the peptide bonds. The only exception was an artificially aged sample that was inoculated with F. fomentarius, which secretes proteases [78], with a decrease in the amide II band (1540 cm-1) (Figure 11). This band is typical of the HN and CN vibrations [79], and it is sensitive to the molecular conformation [80]. Its decrease is a consequence of changes in H-bonds, the steric arrangement of the proteins, and the changes in the supermolecular structure [81].


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Figure 11. FTIR spectra of an artificially aged wool reference sample (a) and an artificially aged wool sample inoculated with F. fomentarius (b). In the amide II region (arrow) there is a slight decrease in the band of the inoculated sample.

For the non-aged samples inoculated with F. fomentarius and P. chrysogenum, as well as for the artificially aged samples inoculated with A. clavatus, H. fragiforme and P. corylophilum, a carbonyl band was observed after 20 weeks of incubation (Figure 12). This appeared mainly as a shoulder, which suggests that the depolymerisation process had just started. Carbonyl bands are a consequence of oxidation of polypeptide chains, which leads to crosslinking and interruptions to the macromolecules [81]; this can cause brittleness of the fibres and less resistance to mechanical influences [63]. Carbonyl groups occur mainly on depolymerised chain ends [82]. As the band occurred in samples inoculated with the various fungal species, the depolymerisation is probably not directly connected with the fungal proteolytic activities. Deterioration of polypeptide chains can be observed as a decrease in the band at 1450 cm1, which is typical of skeletal CC vibrations [83]. This decrease in the 1450 cm-1 band was seen for non-aged samples inoculated with P. corylophilum. In the region between 1170 cm-1 and 1000 cm-1, the vibrations of oxidised cysteine residues can be seen at 1075 cm-1 for CysO and at 1120 cm-1 for Cys-O2 [82]. The appearance of the 1075 cm-1 band is a consequence of keratin oxidation [84]. This decreased in the non-aged samples inoculated with A. clavatus, which shows that the deterioration of cysteine and its oxides leads to the formation of cysteic acid [83]. The intensity of the amide III band (1235 cm-1) decreased only for the non-aged sample inoculated with A. clavatus, which showed the more ordered structure of the molecules [82]. According to the literature, A. clavatus secretes proteases [85] and attacks the amorphous regions first.

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Figure 12. FTIR spectra of an artificially aged wool reference sample (a) and an artificially aged wool sample inoculated with H. fragiforme (b). The carbonyl band is indicated (arrow).

The mechanical properties of selected samples of the inoculated wool specimens (weft yarns of the fabric) were also analysed according to their tensile behaviour. The stress–strain curves of these wool yarns were monitored over the whole deformation range (from the beginning of the deformation, until the break). Figure 13 shows the stress–strain curves of these non-aged samples inoculated with P. corylophilum and artificially aged samples inoculated with P. chrysogenum. Different fungal species affected different mechanical properties of the wool fibres. The fungi did not influence the mechanical properties of the wool fibres to any large extent, and especially in the non-aged samples, the differences from the reference samples were small. Comparison of the stress–strain behaviour of the non-inoculated aged and non-aged reference wool samples was seen as lower breaking elongation, slightly lower breaking stress, and higher elastic modulus for the artificial ageing. These changes in the tensile properties of the aged samples can be attributed to the depolymerisation of the macromolecules and the higher number of intermolecular interactions. The changes caused by aging of the wool fibres was the same as for the cotton fibres, but to a lesser extent. In the non-aged samples inoculated with P. corylophilum, the breaking strain was only a little lower than with the reference sample. The breaking stress significantly decreased after eight weeks of incubation, and then increased after 20 weeks of incubation (Figure 13a). In the aged samples inoculated with P. chrysogenum, the breaking stress increased after both the shorter and longer incubation times (Figure 13b). The stress–strain behaviour of all of the inoculated samples showed that the initial modulus and breaking strain are lower compared to the reference sample. The changes related to ageing, inoculation and incubation appear to be as a consequence of the lower crystallinity and the higher number of intramolecular interactions [63].


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Figure 13. Stress-strain curves of (A) non-aged samples inoculated with P. corylophilum, and (B) artificially aged samples inoculated with P. chrysogenum. Each panel shows the reference sample (a) and samples incubated for 8 weeks (b) and 20 weeks (c).

CONCLUSION This chapter has focused on fungal deterioration of historical and modern, aged and nonaged, textiles through an interdisciplinary approach. The review of the literature and our analyses performed on historical textiles stored in several Slovene museums and religious institutions reveal that the history of each artefact has to be carefully considered, as many factors can influence the structure and properties of historical materials, from the growing and processing of the fibres, and the making and application of the object, to the storage conditions. The combination of these factors can change the fibre properties in terms of the physical and chemical structures, thus affecting further the chemical changes, and promoting

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microbial infestation. Biodeterioration of historical textile objects is most often caused by fungi, which do not necessarily change the structure and properties of the fibres to any large extent; however, they can nevertheless have a considerably effect on the visual image of the object, and most importantly, pose a latent danger to later fungal reactivation and growth. The analysis performed on the diversity of the fungal species that can contaminate historical textiles cannot be linked to certain historical periods and institutions, as the same genera were isolated from historical objects that originated from different periods and environments. However, the genera Alternaria, Aspergillus, Chaetomium, Cladosporium, Penicillium and Trichoderma were most often the infecting agents in our analysis of historical textile objects, as they were repeatedly isolated. These can thus be considered as ubiquitous ‘museum mycoflora’. The structural, surface and mechanical properties were also analysed for historical textiles, as contemporary non-aged and artificially aged textiles, composed of cotton and wool, and inoculated with the six selected species of fungi. The structural and morphological changes were more pronounced for the cellulosic than proteinaceous textiles. The most intensive changes in the structure (e.g., depolymerisation, decrease in crystallinity) and the mechanical properties (e.g., breaks in the fibres, tensile properties) of the cellulosic fibres were caused by C. cf. cladosporioides, while they were least affected by P. chrysogenum. Wool fibres showed their greatest deterioration with H. fragiforme, and their least with A. clavatus and P. corylophilum. The most pronounced surface changes in the cellulosic fibres were longitudinal creases between the fibrils, while for the wool fibres, the surface scales were mostly damaged. At the level of the structural changes, depolymerisation, and disordering of the macromolecular structures of the fibres, this occurred for both cellulose and proteinaceous fibres. The intensity of these changes increased with the prolonged incubation time following the fungal infection, and with the aging of the samples. Those in charge of taking care of historical textiles (e.g., curators, conservators) must be aware of the possible influences of fungi on the visual, mechanical and structural properties of these objects. The best measure is prevention, so storage of the objects in environments with low humidity and cool temperatures, with regular ventilation of the rooms. As infections with different fungal species can nevertheless occur and cause different structural changes, it is important to correctly identify the infecting fungal species, to take appropriate curative measures.

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Chapter 12

DURABILITY OF FUNCTIONALIZED TEXTILES BY MICROCAPSULES Lucia Capablanca, Pablo Monllor, Pablo Díaz and Maria Ángeles Bonet* Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Alcoy, Spain

ABSTRACT Nowadays textiles are required to have extra properties, they should offer active functionality. Microcapsules applied on textiles have become a way of modifying textiles properties. Microencapsulated products can be applied on fabrics by impregnation, bath exhaustion, foam, spraying and coating. The most extended industrial application is by padding. To paste microcapsules to fabrics, they should be in contact with a bath, which contains microcapsules, resin and water. The resin allows the microcapsules adhesion to the fabrics´ fibers because no affinity between them. Textiles in their useful life are submitted to washing, drying, ironing, abrasion, etc. These processes affect the stability of microencapsulated products. The aim of the textile industry is to achieve greater permanence of microcapsules on fabrics. In this chapter we study microcapsules useful life on plain fabrics applied by impregnation. Washing treatments allow us to study the behavior and permanence of the microencapsulated commercial products on fabrics. The aim of this work is to provide to the textile industry a study about the microcapsules behavior on washing treatments in order to ensure the major durability of microcapsules. Scanning electron microscopy (SEM) has been used in order to determinate the quantity of microencapsulated products that remains on fabrics after washing treatments. We concluded that washing treatments affect the microcapsules stability and permanence. To sum up, we can indicate that depending on the washing treatment conditions microcapsules behavior can differ from one fabric to other.

*

E-mail: [email protected]

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1. INTRODUCTION Nowadays textiles are required to have extra properties; they should offer active functionality, and in recent years some textiles have come to be known as smart textiles. It is very common to think that smart textiles contain electronic devices, but this is not necessarily so. The term smart textile refers to textiles that are able to react when an external effect is present. Nanotechnology processes are present into the textile field. One of these processes involves encapsulated nanoparticles or nanoproducts, know as microcapsules. Microencapsulated products are very common in some fields, such as pharmacy [1-19], cosmetics [20-25], food [26-40], insecticides [33,41-43], adhesives [44,45], medicine [8,23], and the textile industry has recently incorporated them into their products. They are used by the more developed countries into textiles to confer new properties and added value, for example into medical and technical textiles. It has encouraged the industry to use microencapsulation processes as a means of imparting finishing and properties on textiles which were not possible or cost-effective using other technologies [46]. Textile manufacturers are demonstrating an increasing interest in the application of durable fragrances and skin softeners to textiles [42,46,47]. Other potential application include insect repellents, dyes, vitamins, antimicrobials, phase change materials and specific medical applications, antibiotics, hormones, and other drugs [42,46-54]. Microcapsules present an active core, which is protected by means of an external polymer. The composition of microencapsulated products can be different because they are made of different shell materials and diverse core materials. The core material will define the use, i.e., medicine, food, etc. The cosmetic industry uses fragrances in liquid cores, and although they can be used in aromatherapy, they are not as important as in medicine. The nature of the shell is considerably wide nevertheless, it is not common to find reactive polymers that can react with fibers surface. The effect of microcapsules is usually measured by the presence of a property such as odor measurements when flavors are encapsulated. Nevertheless, some properties such as hydration, antibacterial, insect repellents, etc., can’t be tested without analytical methods. Some characterization techniques have been applied in order to study microcapsules products, presence and state [42,46,47,49,55-60]. Fragrance encapsulation is one of the applications of microencapsulation technology in the textile sector. Microencapsulation technology allows us an opportunity that can flavor its durability on fabrics. Some papers have been published on fragrance microcapsules [42,46,47,61-64], where they were studied in relation to their final use on textiles or other materials and their effect. When microcapsules are applied to textiles, commonly used shells are not reactive; otherwise, they would stick together. As a result of that chemical stability, no chemical reaction can be applied between microcapsule and fiber. Thus, in order to improve durability to washing or handle some auxiliary products, it is required to join microcapsules to the fiber surface [42], they are usually based on acrylic, polyurethanes or silicone resins [65]. Knowing there is not enough affinity between microcapsules and fibers, a resin is needed to adhere them to the fiber and a mechanical process to help microcapsules to get into the fabric. In the textile sector the most extended microcapsules industrial application is by

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padding; however commercial brands suggest some recipes depending on the procedure mainly padding or bath exhaustion, although foam is also an application system. In all application processes, the control of variables is essential to achieve increased deposition and retention of microencapsulated products on fabrics. Fabric structure is an important parameter to consider in the microcapsules application on fabrics [66]. Furthermore application procedure, bath composition, fibers nature (hydrophobic vs hydrophilic character), cross section, fabric weight and fabric wave, are variables to consider in the application of microencapsulated products into textile substrates [67,68] in order to ensuring the stability and durability of microencapsulated. Textiles in their useful life are submitted to washing, drying, ironing, abrasion, etc. These processes affect the stability of microencapsulated products [68-70]. The aim of the research is to evaluate the durability of fragrance microcapsules deposited on plain fabrics. Normalized washing treatments have been carried out on fabrics with an active substance to evaluate their effects on the maintenance of fabrics conditions and the state of commercial products. Scanning electron microscopy (SEM) has been used to check their presence, surface distribution, preferred join position in textile fibers and washing effects.

2. EXPERIMENTAL 2.1. Materials Lavender fragrance microcapsules were supplied by COLOR CENTER (Tarrasa, Spain). The wall material was melamine formaldehyde. An acrylic resin was applied in order to bond the microcapsules to the fabric, also supplied by COLOR CENTER. The plain fabrics used were a 100 % cotton twill 210 g/m2, which have been chemically bleached with peroxide in an industrial process.

2.2. Fabric Treatment Fragrances microcapsules were applied to the surface of the fabrics by impregnation. An acrylic resin was used as a binder. For the process, a horizontal foulard (2608 TEPA foulard; Barcelona, Spain) was used. Bath treatment was composed of 10g/L of resin and 60g/L of commercial microcapsules, it had been studied previously [68]. Pick-up (bath absorption) obtained was about 90-95%. All the samples were thermally dried and fixed in a scale pin stenter at 110ºC for 10 min in an air forced heater (WTC BINDER 030;Wisconsi, USA). Previously, it has been demonstrated that this temperature was high enough to polymerize the binder without evaporating the fragrance [69].

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2.3. Washing Treatment Washing treatments were applied in order to study microcapsules behavior and durability. One of them was carried out in a Heraeus Linitest; Frankfurt, Germany applying the standard ISO 105 C10. Samples were dried on a horizontal surface. The other was carried out in a Domestic Washing Machine Fagor Innova; Guikuzpoa, Spain applying the standard ISO 6330. Samples were dried on a horizontal surface according to the standard. All samples were examined by scanning electron microscopy (SEM) (Phenom Microscope FEI Company, Hillsboro, OR, USA) after 1 and 10 washing cycles.

2.4. Organoleptic Analysis Qualitative and subjective analysis, for implementation is not available or used no standardized method or instrumental technique. Organoleptic analysis is always performed by specialists in order to counter the results. In turn, these results are corroborated by scanning electron microscopy in order to ascertain the presence or absence of microencapsulated products between the fabrics fibers. This analysis is performed in fabrics after being subjected to washing cycles. After drying is checked if fabrics off the scent used as active material or if it is necessary to appreciate that rub aroma. If the fabric contains microcapsules the friction will cause membrane rupture and the release of the active ingredient.

2.5. Instrumental Techniques In order to observe fabric surface, a scanning electron microscopy (Phenom Microscope FEI Company, Hillsboro, OR, USA) was used. Each sample was fixed on a standard sample holder and sputtered with gold and palladium.

3. RESULTS 3.1. Application Procedure Figure 1 shows a SEM microphotograph of cotton fabric with microcapsules applied by impregnation. It was not possible quantify microcapsules presence using this technique. SEM only allowed us to observe the fabrics surface detecting the microcapsules presence, location and condition. It can be observed that microcapsules have a spherical shape with the fragrance inside. In the same commercial product there are microcapsules with different sizes. Microcapsules tend to be in the grooves that forming the kidney section of the cotton fibers. Resin presence can be observed in SEM micrographs. If the encapsulated fragrance is applicated only onto a substrate and dried, the microcapsules could be lost during a hot, wet,


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frictional washing because there is no affinity between the microcapsules and the fabric. The resin enables to fix the microcapsules to the fabric.

Figure 1. Cotton fabric with microcapsules.

3.2. Washing Effect

Figure 2. SEM micrographs of cotton fabrics with microcapsules and after one washing cycle. Cotton fabric with microcapsules. Cotton fabric after 1 washing cycle ISO 105 C10. Cotton fabric after 1 washing cycle ISO 6330.

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It can be observed in Figure 2 that larger microcapsules have lost the core partially, and cannot be observed as spheres. A previous work [70] demonstrated that larger microcapsules are washed out of the fabric more quickly (in the first washing cycles) than the smaller microcapsules that remain on the fabric for more washing cycles. Moreover, larger microcapsules deflate rather than smaller microcapsules. After five washing cycles (Figure 3) the microcapsules presence decreases on the fabric. Washing cycles affect the microcapsules stability.

Figure 3. SEM micrographs of cotton fabrics after five washing cycles. Washing process according to ISO 105 C10. Washing proces according to ISO 6330.

In Figure 3 the SEM images from ISO C10 (linitest machine) and from ISO 6330 (domestic washing process) are compared, it can be observed differences between the number and the state of microcapsules that remaining on the fabrics. Resin remains on the cotton fibers after five washing cycles. When the standard ISO 6330 is used less microcapsules were observed between cotton fibers and most have lost their spherical shape and therefore the fragrance inside. These microcapsules do not provide any property to the cotton fabric. Washing cycles with standard ISO 6330 are the most similar to those made at home with textiles.

3.2.1. Organoleptic Analysis In Figure 1 it can be observed that microcapsules tend to be in the grooves that forming the kidney section of the cotton fibers. Microcapsules located at these positions will be more protected against washing action. If one compares the results of organoleptic analysis between washing processes it can be observed again differences. These differences are shown in Table 1. Table 1 shows the organoleptic analysis results, "Yes" has been typed when it is necessary to rub the fabric to appreciate the fragrance and “No” when appreciated the fragrance without rub. Before the analysis, fabrics with microcapsules have been washed (1, 5 or 10 washing cycles) according to the standards and dried.


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Table 1. Results of Organoleptic Analysis, cotton fabric with microcapsules Washing Cycles 1 5 10

ISO C10 No No No

Standards ISO 6330 No Yes Yes

Organoleptic analysis results coincide with the micrographs of Figure 3. After five washing cycles, in the cotton fabric washed according to ISO 6330 (domestic washing) is necessary to rub the fabric to appreciate the fragrance. In Figure 3b it can be observed less microcapsules between cotton fibers. Microcapsules located in the grooves that forming the kidney section of the cotton fibers are more protected from the washing action and retain their spherical shape with the fragrance inside after five washing cycles. Rub action breaks the membrane and the fragrance can be appreciated. Cotton fabrics washed according to ISO C10 maintain the fragrance without rubbing after five and ten washing cycles. Washing conditions influence the microcapsules permanence and stability.

CONCLUSION The present study compares the stability and durability of microcapsules on plain fabrics surfaces after washing treatments. Certain differences can be observed. The number of microcapsules that remain on the fabrics after washing cycles is different depending on the washing process. When the standard ISO 6330 is used, less microcapsules were observed between cotton fibers and it is necessary the rub action to appreciate the lavender fragrance after five and ten washing cycles. After 5 and 10 washing cycles according to ISO C10 we can confirm some odor intensity remained on fabrics. This means that there are small microcapsules partially filled on the fabric, the active material is still on the fabric and we can appreciate the odor without the rubbing action. Washing process according to the standard ISO 6330 is stronger than standard ISO C10, therefore, it affects microcapsules stability and permanence. Washing cycles with standard ISO 6330 are more similar to those made at home with textiles. Process conditions and substantial quantities of products are parameters to consider in order to ensure the stability and durability of microencapsulated products. Regardless of the standards used, the continuous washing cycles affect the microcapsules durability to fabrics, thus, optimizing product baths is necessary to achieve textile articles with a long life.

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Chapter 13

NEW APPROACHES AND APPLICATIONS ON CELLULOSIC FABRIC CROSSLINKING Eva Bou-Belda, Maria Ángeles Bonet, Pablo Monllor, Pablo Díaz, Ignacio Montava and Jaime Gisbert Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Alcoy, Spain

ABSTRACT Shrinkage and wrinkling are the major undesirable properties of cotton fabric. Those fibers are generally treated with crosslinking agents to further provide new properties to cotton fabric such as durable press property. Generally, in a cross-linked cotton fabric, cellulose chains are bridged across through chemical reaction with certain compounds. Cellulose cross-linking can be traced back more than eighty years and is still being actively researched. In this paper, literature on cotton cross-linking was reviewed from the past to the present. In this paper, possibilities offered by these type of acids in the textile, the experimental techniques used to characterize the treated fabric, new approaches and applications are discussed.

Keywords: Polycarboxylic acids, durable press, cotton, fabric, crosslinking

INTRODUCTION Cellulosic textiles are finished in order to improve their properties, dimensional stability and crease resistance play a considerably important role. These properties can be satisfactorily achieved by crosslinking agents, which react with hydroxyl groups of cellulose fibers. Esterification between polycarboxylic acids and cotton cellulosic has been investigated since 1960’s [1, 2]. 

Corresponding author: Maria Bonet. Departamento de Ingeniería Textil y Papelera, Universitat Politécnica de València, Plaza Ferrandiz y Carbonell s/n, 03801 Alcoy, Spain. E-mail: [email protected].

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Eva Bou-Belda, Maria Ángeles Bonet, Pablo Monllor et al.

Some finishing treatments such as wrinkle-free, wrinkle-resistant and crease recovery confer very important properties to cotton fabrics. There are many cross-linking agents which are effective to this type of textile finishing, these have been studied for years in the past, such as urea/formaldehyde, melamine/formaldehyde, tetramethyllolacethylenediurea, dimethyleneurea and dimethyloldihydroxyethylene-urea (DMDHEU) [3, 4]. Although dimethyloldroxylethyleneurea was the most widely reactant for the production of durable press garments, its use resulted in fabrics that were chlorine retentive and also prone to some degree of yellowing [5]. N-methylol agents have long been used by the textile industry as durable press finishes producing wrinkle-resistant cotton fabrics. However, as they release formaldehyde either from treated fabrics or during finishing processes, their use in textile industry is limited. Formaldehyde has been identified to have impact on human health and the environment. For this purpose, in recent years extensive efforts have been made to develop polycarboxylic acids (PCAs) as new crosslinking finishing agents for cotton fabrics to replace the traditional reagents [5]. Over the past few years, there has been an attention on application of nanoparticles with crosslinking agents to impart other properties to the fabric, such as antimicrobial, flame retardant, water repellency or UV protective. In this work, literature on cellulosic fabric crosslinking have been reviewed from the past to the present. Publications refer to the possibilities which can offer these type of acids in the textile product, the experimental techniques used to characterize the treated fabric, new approaches and applications are discussed.

POLYCARBOXYLIC ACIDS AGENTS Some of the most used and studied in different works are reviewed briefly. Citric acid (CA), is a tri-functional carboxylic acid known as a cost-effective and environmentally friendly cotton crosslinking agent but it was not satisfactory with its performance due to its tendency to discolor the treated fabric. Among the various effective polycarboxylic acids, 1,2,3,4-butanetetracarboxylic acid (BTCA) has proved to be the most efficient cross-linking agent for cotton fabrics [6, 7]. Esterification of cotton cellulose with BTCA in order to form crosslinking is believed to proceed through a mechanism involving formation of an intermediate cyclic anhydride, which reacts with the cellulosic hydroxyl to complete the ester linkage. [5] Peng et al. [8] suggested the combination of maleic acid (MA) and sodium hypophosphite as a formaldehyde-free and cost-effective durable press finishing system with superior fabric strength retention. Yang et al. [9] found that acid maleic was less effective than 1,2,3,4butanetetracarboxylic acid (BTCA) due to the low mobility of the anhydride intermediates to access the cellulosic hydroxyl during a curing process. For this reason, some works suggested the combination of maleic acid with another polycarboxylic acid, for example citric acid or the combination of maleic and itaconic acid. Research has been done by Yang et al. in 2001 [10] on the effectiveness of poly itaconic acid (PITA) synthesized in an aqueous solution and ITA polymerizing in situ for crosslinking cellulose and imparting wrinkle resistance to the cotton fabric.

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They reported that despite the fact that the tensile strength loss of the cotton fabric crosslinked by ITA polymerizing in situ is very similar to that cross-linked by PITA applied as a polymer, ITA is more effective in esterifying cotton cellulose. In 2003 [11], they reported that the cotton fabric treated with ITA, lost more tensile strength than that treated with PITA due to cellulose degradation and the tensile strength loss caused by cross-linking for PITA treated fabric is significantly higher than that for ITA treated fabric. This was believed to be due to more concentrated cross-linkages formed on the nearest surface of the fabric treated with PITA. Succinic acid (SUA) is used as a crosslinking agent as well. For example, Chen Chi Che et al. [12] used succinic acid as crosslinking agents in the presence of nanometer TiO2 as catalyst under the irradiation of UV light whose wavelength is 254 nm. They found that the carboxylic acid group of succinic acid can be photo-reduced to form the aldehyde group. The crystalline structure of SUA adsorbed on nanometer TiO2 particles can be changed under UV irradiation. The photo-reduction of succinic acid in the presence of nanometer titanium dioxide solved in water under UV irradiation can increase the values of conductivity and improve the creation of free radicals. In this study they suggested that the crosslinking reactions were due to the reaction between aldehyde group from succinic acid and the hydroxyl group on cellulose and the reaction between free radical of succinic acid and the free radical of cellulose. The stress concentration caused by crosslinks and the damage caused by the photo-reduction are the main factors to decrease the tensile strength of the treated fibers. In a previous work [13], we evaluated the yellowing of the treated samples with different acid. We could observe whiteness index differences, which were compared with the untreated cotton fabric´s whiteness. We could observe different behaviour depending on the acid used. Using PCA as a crosslinking agent for cotton causes fabric yellowing. This yellowness can be increased by the increase of curing temperature and acid concentration, however, when BTCA and SA-treated cotton are used it can be obtained a gradual decrease in whiteness index. It could be noticed that while untreated sample´s whiteness decreases exponentially as the curing temperatures increases, the same sample treated with BTCA or SA showed a reduction in yellowness at higher temperatures above at 170ºC.

EXPERIMENTAL TECHNIQUES FTIR Yang et al. [14] indicated, using FTIR, that PCA esterifies cellulose in two steps: the formation of a 5-membered cyclic anhydride intermediate to form an ester linkage [14-16]. In another research these authors used FTIR and Fourier transform Raman spectroscopy to study the formation of cyclic anhydride intermediates by BTCA and other polycarboxylic acids. The reaction between cellulose and BTCA with catalyst and high cured temperatures. They found that BTCA and other polycarboxylic acids in a crystalline state start to form 5membered cyclic carboxylic anhydride when the temperature reaches the vicinity of their melting point with the exception of bifunctional acids, which form cyclic anhydrides at temperatures much higher than their melting point.

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Intermolecular hydrogen bonding between carboxylic acid prevents the formation of the cyclic anhydride intermediates at lower temperatures [17]. Authors to confirm the crosslinking reactions of different PCAs on cotton use FTIR spectroscopic studies. The formation of ester crosslinking between the hydroxyl groups of PCAs can be witnessed in the spectra of PCAs treated fabrics. For example, Figure 1 shows the spectra of the BTCA cotton treated samples studied in a previous work [18]. The spectra of untreated cotton fabric was compared with the one from the treated fabric with 80 g/L of BTCA and 40 g/L of catalyst. An FTIR spectrum of untreated sample shows absorption in the region 3010-3750 cm-1 due to the hydroxyl groups present in the cotton fabric. Spectra of the BTCA treated fabric sample shows absorption in the band 1725 cm-1 due to the ester carbonyl groups formed (which confirm the covalent bond between the cellulose and BTCA) [14].

Scanning Electron Microscope Some researches such as Lam et al. [3] examined the surface morphology of cotton specimens by the scanning electron microscope (SEM). The untreated sample’s picture shows the normal spiral structure of the cotton sample, which was clearly defined (Figure 2). Treating the cotton samples with 5% BTCA evidenced a damaged surface as shown in Figure 3. Figure 4 illustrates the SEM image of the cotton sample treated with 10% BTCA in the presence of 10% SHP. 0,6

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2100 Wavenumber (cm‐1) CO_210

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Figure 1. Infrared spectra of the untreated and treated samples.

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Absorbance

0,4


Figure 2. SEM image of control cotton sample by YL Lam et al. [3].

Figure 3. SEM image of cotton sample treated with 5% BTCA [3].

Figure 4. SEM image of cotton sample treated with 10% BTCA and 10% SHP [3].

359

360


It was obvious that fibers were severely damaged when 10% BTCA was applied to the cotton samples. It was concluded that the surface was damaged after undergoing the treatment and the deterioration of fibers might be caused by the attack of BTCA at extremely low pH value, i.e., pH 1–2.

Whiteness Index Another experimental technique used is the spectrophotometer applied in order to compare objectively samples whiteness index. In a previous study [13], cotton fabric´s yellowing was studied when different carboxylic acids were used at high temperature. The study was conducted with four acids: 1,2,3,4-butane-tetracarboxilyc acid (BTCA), citric acid (CA), maleic acid (MA) and succinic acid (SA) and different response were obtained depending on the acid used. Using carboxylic acids as a crosslinking agent for cotton causes fabric yellowing. This yellowing can be increased by the increase of curing temperature and acid concentration, but if BTCA and SA-treated cotton are used, it can be obtained a gradual decrease in whiteness index.

Wrinkle Recovery Angle In the past, workers studied the relationship between cotton fabric strength and the chain lengths of crosslinking agents [19-23]. In 2000, Yang and Wei [24] studied the relationship between fabric´s tensile strength loss and the molecular structures of crosslinking agents. Crosslinking between cellulose molecules causes stiffening of the cellulosic macromolecular network and fiber embrittlement thus, reducing the mechanical strength of the treated cotton. Authors used a linear tetracarboxylic acid (BTCA) and a cyclic one (CPTA) to treat cotton at different concentrations and different temperatures, and compare the tensile strength loss from the crosslinked fabric as a function of wrinkle recovery angle (WRA). It was also compared the tensile strength loss of cotton treated with DMDHEU and DHDMI. Results indicate that BTCA is more effective as a crosslinking agent for cotton cellulose and imparts higher levels of wrinkle resistance to the treated cotton than CPTA. The relationship between tensile strength loss and wrinkle recovery angle for the cotton treated with BTCA and CPTA is essentially equivalent. Cottons treated with DMDHEU and DHDMI showed the similar phenomenon. Therefore, all the studies evaluated indicate that the tensile strength loss of crosslinked cottons fabric is independent of differences in the molecular structure and reactivity of the crosslinking agents.

Thermal Analysis In order to investigate the effect of performed treatment on cellulose pyrolysis process, thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out by several researches. For instance, Lessan et al. [25] studied the effect of SHP and nano TiO2 as a novel flame retardant for cotton fabric.


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Some analysis including char length, char yield, LOI, TGA and DTA were studied in order to evaluate flame retardant properties from treated samples. They concluded that the presence of phosphorus deposited on the SHP treated samples is the most effective parameter in the char forming and decreasing the treated fabrics´ flammability. Furthermore, nano TiO2 is an effective compound in increasing the char formation. Moreover, the performed treatment helps to form more non-flammable char residue and increases char formation after heating. Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were employed to investigate the thermal decomposition from the treated samples.

NEW APLICATIONS Flame Retardant Polycarboxylic acids are able to reduce the flammability of cotton as reported by Blanchard and Graves [26]. For example, phosphorus-containing oligomers of maleic acid reduce flammability through increases of char formation in cotton. The combination of an insaturated bifunctional acid, for example maleic acid, and a phosphorus-containing inorganic compound, such as sodium hypophosphite, can reduce the flammability of cotton fleece [27]. Other polycarboxylic acids like succinic acid, tartaric acid, citric acid and 1,2,3,4butanetetracarboxylic acid have been used as flame retardant. These polycarboxylic acids in combination with sodium hypophosphite reduce the flammability of cotton fabrics [26, 27]. The most successful and effective durable flame retardant systems of cellulosic textile are based on phosphorus-containing and nitrogen-containing compounds. The mechanism of flame retardancy in these systems is based on cellulose crosslinking, making more char and preventing the formation of undesirable levoglucosan and flammable volatiles [28]. The phosphorus-nitrogen synergism plays an important role in these compounds [29]. Dehabadi et al. [30] use polyamino carboxylics acids (PACAs) and their combination with sodium hypophosphite (NaH2PO2) as a novel flame retardant finishing for cotton fabrics. To evaluate its flammability 45º flammability test and differential scanning calorimetry were used.

Antimicrobial Property Chitosan is the deacetylated derivative of chitin, which is the main component of the shells of crustaceans such as shrimps, crabs and lobsters [31]. Large quantities of chitin are produced as a byproduct of the seafood industry. Chitosan has been found to inhibit the growth of microbes in a large body of work that has been extensively reviewed by Lim and Hudson [32]. The antimicrobial mechanism is not clear but is generally accepted that the primary amine groups provide positive charges which interact with negatively charged residues on the surface of microbes. Such interaction causes extensive changes in the cell surface and cell permeability, leading to leakage of intracelular substances.

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This antimicrobial ability, coupled with its non-toxicity, biodegradability and biocompatibility, is facilitating chitosan’s emerging applications in food science, agriculture, medicine, pharmaceuticals and textiles. The prime focus for chitosan as an antimicrobial treatment has been on cotton. Ancient works, indicated that the antimicrobial effect was potent against a range of microbes, but the finishing was not durable at all. To improve durability, chitosan has been crosslinked to cotton using chemicals such as dimethyloldihydroxyethyleneurea (DMDHEU), citric acid, 1,2,3,4-butanetetracarboxylic acid (BTCA) or glutaric dialdehyde [33, 34]. Eltahlawy et al. [33] demonstrated that cotton fabrics treated with two different crosslinking agents BTCA and Arcofix NEC (low formaldehyde content) in the presence of chitosan provide the cotton fabrics a durable press finishing and antimicrobial properties by chemical linking of chitosan to the cellulose structure. Orhan et al. [35] used citric acid and BTCA to improve the effect antimicrobial of the cotton fabric and Chung et al. [36] used Citric acid (CA) and chitosan as durable press and antimicrobial finishing agents on cotton fibers. They showed that cotton fabric treated with no more products than CA shows antimicrobial properties and strength retention improvement is higher when CA is used with chitosan.

Grafting of Micro and Nano Particles on Fabric Polycarboxylic acids are used to improve the adhesion of nano and micro particles onto cotton fabric, thereby to increase washing durability. It is known that carboxylic acids could esterify with cellulose–OH, and also could co-condense with Si–OH groups, leading to the formation of interfacial ester bonds. When one of the carboxylic acid groups in polycarboxylic acid binds to cellulose with ester bond, there would still be free carboxylic acid group(s) available to form ester bonds with Si–OH [37]. As a result, polycarboxylic acids could act as “ester-bridge” to connect cellulose and heterogeneous silica functional layer. Huang et al. [38] used different polycarboxylic acids to fix hydrophobic cellulose fabric finished by sol–gel method combining SiO2 nanoparticles and with hexadecyltrimethoxysilane modification. They concluded that among various polycarboxylic acids, BTCA gave the best performance. One of the main disadvantages of using film-forming binders in application of microcapsules onto textile materials is possible hindrance of the active substances release. To avoid this problem, microcapsules can be covalently linked onto textile substrate by using bi/ polyfunctional crosslinking reagents. The most agent crosslinking used in the literature is BTCA. Badulescu et al. [39] used BTCA with cyanamide (CA) and N,Ndicyclohexylcarbo-diimide (DCC) as catalyst and shown that esterification between BTCA, ethylcellulose microcapsules and hydroxyl groups of cellulose can occur simultaneously. The same authors linked supramolecular compound (β-cyclodextrin) onto cotton cellulose via grafting or crosslinking with BTCA [40].

Water Repellency Fluorocarbon resin is the most effective treating agent for making fabrics water repellant [41].


363

To improve the washing durability of water repellency, some cross-linking agents are usually used along with the water repellent agents. Montazer [42] applied BTCA, with the optimum concentration of 5 g/L, and different concentrations of fluorocarbon agent for water repellent finishing of cotton fabrics. BTCA is confirmed to be an effective cross-linking agent with sodium hypophosphite (SHP) catalyst for washing durability improvement of cotton fabrics treated with fluorocarbon resin. It has been reported that the water repellency of the sample treated with fluorocarbon resin and 8% BTCA is higher than the sample treated only with fluorocarbon resin [43]. This kind of difference can be seen especially after fifty washing cycles and subsequent heat treatments [5].

CONCLUSION In years past, significant progress has been made in introducing cross-linking nonformaldehyde agents to cotton fabrics in order to obtain a durable press fabric, being BTCA the most used as it is one of the more efficient PCAs. To study the mechanism of the reaction between the PCA and cellulose FTIR is used. Moreover, this technique is used to study and evaluate the effectiveness of the crosslinking agent used. Nowadays, this type of finishing is being studied by many researchers as we have shown in this work due to the fact that they provide new properties to the cellulosic fabric, such as flame retardant and antimicrobial. Moreover, these acids are used to improve the adhesion of nano and micro particles onto cotton fabric, thereby to increase washing durability.

REFERENCES [1] [2]

[3] [4] [5] [6] [7] [8]

Rowland, S. P., Brannan, A. F. (1968). Mobile ester Cross Links for Thermal Creasing of Wrinkle- Resistant Cotton Fabrics. Textil. Res. J. 38, 634-642. Rowland, S. P., Welch, C. M., Brannan, A. F., Gallagher, D. M. (1967). Introduction of Ester Cross Links into Cotton Cellulose by a Rapid Curing Process. Textil. Res. J. 37, 933-938. Lam, Y. L., Kan, C. W., Yuen, C. W. M. (2010). Wrinkle-resistant finishing of cotton fabric with BTCA- the effect of co-catalyst. Text. Res. J. 81(5), 482-493. Welch, C. M. (1988). Tetracarboxylic Acids as Formaldehyde-Free Durable Press Finishing Agents. Text. Res. J. 58, 480-486. Harifi, T., Montazer, M. (2012). Past, present and future prospects of cotton crosslinking: New insight into nano particles. Carbohy. Polym. 88, 1125-1140. Yang, C. Q., Wang, D. (2000). Evaluating ester cross-linking of cotton fabric by a polycarboxylic acid using acid–base titration. Text. Res. J. 70, 615–620. Yang, C. Q., Lu, Y., Lickfield, G. C. (2002). Chemical analysis of 1,2,3,4 butanetetracarboxylic acid. Text. Res. J. 72, 817–824. Peng, H., Yang, C. Q., Wang, S. H. (2002). Non-formaldehyde durable press finishing of cotton fabrics using the combination of maleic acid and sodium hypophosphite. Carbohy. Polym. 87, 491–499.

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Eva Bou-Belda, Maria Ángeles Bonet, Pablo Monllor et al. Yang, C. Q. (1998). Nonformaldehyde Durable Press Finishing of Cotton Fabrics by Combining Citric Acid with Polymers of Maleic Acid. Text. Res. J. 68, 457-464. Yang, C. Q. (2001). FTIR Spectroscopy Study of Ester Crosslinking of Cotton Cellulose Catalyzed by Sodium Hypophosphite. Text. Res. J. 71(3), 201-206. Yang, C. Q., Hu, G., Lickfield, G. C. (2003). Cross-linking cotton with poly(itaconic acid) and in situ polymerization of itaconic acid: Fabric mechanical strength retention. J. Appl. Polym. Sci. 87, 2023–2030. Chen, C. C., Chyung-Chyung, W. (2006). Crosslinking of cotton cellulose with succinic acid in the presence of titanium dioxide nano-catalyst under UV irradiation. J. Sol-Gel Sci. Techn. 40, 31–38. Bou, E., Bonet, M., Monllor, P., Montava, I. (2011). Cotton yellowing by polycarboxylic acids. International scientific conference. Annals of the university of Oradea ISSN 1843-813X. Yang, C. Q. (1991). FT-IR Spectroscopy Study of the Ester Crosslinking Mechanism of Cotton Cellulose. Textil. Res. J. 61, 433-440. Yang C. Q. (1993). Infrared spectroscopy studies of the cyclic anhydride as the intermediate for the ester crosslinking of cotton cellulose by polycarboxylic acids. I. Identification of the cyclic anhydride intermediate. J. Polym. Scie. Part A: Polym. Chem. 31(5), 1187–1193. Yang, C. Q., Wang, X. (1996). Infrared spectroscopy studies of the cyclic anhydride as the intermediate for the ester crosslinking of cotton cellulose by polycarboxylic acids. II. Comparison of different polycarboxylic acids. J. Polym. Scie. Part A: Polym. Chem. 34, 1573-1580. Gu, X., Yang, C. Q. (1998). FT-IR and FT-raman spectroscopy study of the cyclic anhydride intermediates for esterification of cellulose: I. Formation of anhydrides without a catalyst. Res. Chem. Intermed. 24(9), 979-996. Bou, E., Monllor, P., Bonet, M. A., Diaz, P. (2012). Crosslinking analysis of cotton fabrics with 1,2,3,4 butanetetracarboxilic acid and influence of the alkaline laundering. Congress Annals of University of Oradea. ISSN 1843-813X. Campbell, H. J., Francis, T. (1965). The cross-linking of cotton cellulose by aliphatic dicarboxylic acids, Textile Res. J. 35, 260-270. Gagliardi, D. D., Shippee, F. B. (1959). Epoxy resin blended finishes for white cotton, Text. Res. J. 2594-65. Hurwitz, M. D., Conlon, L. E. (1958). Dialdehydes as cotton cellulose cross-linkers. Text. Res. J. 28, 257-262. Segal, L., Timpa, J. D. (1953). The effects of a formaldehyde pad-bake-cure process on cellulose molecular chain length and physical properties of cotton fabrics. Text. Res. J., 1953, 44638-4,74. Tesoro, G. C. (1962). Cross-Linking of cellulose with polyfunctional sulfones under anhydrous conditions. Text. Res. J. 32, 189-201. Yang, C. Q., Wei, W. (2000). Mechanical strength of durable press finished cotton fabric part II: comparison of crosslinking agents with different molecular structures and reactivity. Text. Res. J. 70(2), 143-147. Lessan, F., Montazer, M., Moghadam, M. B. (2011). A novel durable flame-retardant cotton fabric using sodium hypophosphite, nano TiO2 and maleic acid. Therm. Acta 520, 48–54.


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[26] Blanchard, E., Graves, E. (2005). Improving flame resistance of cotton/polyester fleece with phosphorus base polycarboxylic acids. AATCC Review 5(5), 26-30. [27] Wu, X., Yang, C. (2008). Flame retardant finishing of cotton fleece fabric: part III—the combination of maleic acid and sodium hypophosphite. J. Fire Scie. 26, 351–368. [28] Gaan, S., Sun, G. (2009). Effect of nitrogen additives on thermal decomposition of cotton. J. Analyt. Appl. Pyrolysis 84, 108-115. [29] Yang, C., Wu, W., Xu, Y. (2005). The combination of a hydroxy-functional organophosphorus oligomer andmelamine-formaldehyde as a flame retarding finishing system for cotton. Fir. Mater. 29, 109–120. [30] Dehabadi, V. A., Buschmann, H. A., Gutmann, J. S. (2012). Flame-retardant finishing of cotton fabrics using polyamino carboxylic acids and sodium hypophosphite. Fire Mater. 129, 155-158. [31] Rinaudo, M. (2006). Chitin and Chitosan: Properties and Applications, Progr. Polymer Sci. 31, 603–632. [32] Lim, S. H., Hudson, S. M. (2003). Review of chitosan and its derivatives as antimicrobial agents and their uses as textile chemicals. J. Macromol. Sci. Polymer Rev., 43, 223–269. [33] El-Tahlawy, K. F., El-Bendary, M. A., Elhendawy, A. G., Hudson, S. M. (2005). The antimicrobial activity of cotton fabrics treated with different crosslinking agents and chitosan. Carbohydr. Polymer, 60, 421–430. [34] Zhang, Z. T., Chen, L., Ji, J. M., Huang, Y. L., Chen, D. H. (2003). Antibacterial properties of cotton fabrics treated with chitosan. Text. Res. J., 73, 1103–1106. [35] Orhan, M., Kut, D., Gunesoglu, C. (2009). Improving the antibacterial activity of cotton fabrics finshed with triclosan by the use of 1,2,3,4-butanetetracarboxylic acid and citric acid. J. Appl. Polym. Sci., 111(3), 1344-1352. [36] Chung, Y.-S., Lee, K. K., Kim, J. W. (1999). Durable press and antimicrobial finishing of cotton fabrics with a citric acid and chitosan treatment. Text. Res. J. 68 (10), 772775. [37] Yang, C. Q., (1991). Characterizing ester crosslinkages in cotton cellulose with FT-IR photoacoustic spectroscopy. Text. Res. J., 61, 298–305. [38] Huang, W., Xing, Y., Yu, Y., Shang, S., Dai, J. (2011). Enhanced washing durability of hydrophobic coating on cellulose fabric using polycarboxylic acids. Appl. Surf. Scie. 257(9), 4443–4448. [39] Badulescu, R., Vivod, V., Jausovec, D., Voncina, B. (2008). Grafting of ethylcellulose microcapsules onto cotton fibers, Carbohy. Polym. 71, 85–91. [40] Voncina, B., Majcen-LeMarechal, A. (2005). Grafting of cotton with β-cyclodextrin via poly(carboxylic acid). J. Appl. Polym. Sci. 96(4), 1323–1328. [41] Li, Z. R., Fub, K. J., Wang, L. J., Liuc, F. (2008). Synthesis of a novel perfluorinated acrylate copolymer containing hydroxyethyl sulfone as cross-linking group and its application on cotton fabrics. J. Mater. Process. Techn. 205, 243–248. [42] Montazer, M. Water repellent finishing of cotton fabrics (Thesis) Leeds University. [43] Xu., W., Shyr, T. (2001). Applying a non-formaldehyde cross-linking agent to improve the washing durability of fabric water repellency. Text. Res. J. 71, 751–754.



Chapter 14

WRINKLE RESISTANT AND COMFORT FINISHING OF COTTON TEXTILES Vahid Ameri Dehabadi* and Hans-Jürgen Buschmann Deutsches Textilforschungszentrum Nord-West gGmbH, Universität Duisburg-Essen, NETZ / DTNW GmbH, Duisburg, Germany

ABSTRACT The Cotton fiber is the most important fiber in the apparel industry, since it can readily absorb moisture. Cotton made clothes are the most comfortable garments. However, easy wrinkling of cotton fabrics is their main disadvantage. Therefore, wrinkle resistant cotton is one of the consumer’s demands in the textile market and durable press finishing is still an interesting field in chemical processing textiles. On the other hand, there is always an increasing request for those clothes and garments with high specifications and more performance, such as easy-care garments and more comfort. Durable press (DP) or easy care finishing is the special treatment to defeat the easy wrinkling of cotton textiles. This process provides resistance against shrinkage and improved wrinkle recovery to cellulosic textiles. The mechanism of durable press finish is inhibition of easy movement of the cellulose chains via crosslinking with appropriate resins/polymers. During this finishing process other molecules can be simultaneously bonded to improve the wear comfort. In this chapter, after presenting a short historical background of DP finishing, the general strategies and the most recent advances of easycare finishes will be discussed.

Keywords: Cotton, easy-care, comfort, finishing

INTRODUCTION Finishing is a process to add extra value such as fashion aspects and new functions into the textile materials. In other words, the aim of finishing is completing the fabric’s *

Corresponding author: E-mail: [email protected].

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performance through providing special functions, such as anti-microbial activity, odourresistance and easy-care. In contrast to the traditional usage of textiles, which are restricted to their primary performances as covering and protecting of the human body against environmental influences, finishing brings extra values and functions in a direct response to market demand. For instance, it has been always a growing request for wrinkle-free apparel, known also as wrinkle resistant, easy-care, durable press or easy-ironing clothes. Among the fibers used in apparels, cotton fabrics show the most problems with wrinkling. The main cause of easy wrinkling of cotton originates from its chemical/physical structure. As a matter of fact, crushing of fabrics during use and care generates wrinkles. By considering the chemical structure of cellulose – as the main component of cotton – we can see lots of hydrogen bonds between molecular chains (see Figure 1). Water or moisture absorption during washing and wearing (from environment or body perspiration) by hydroxyl groups of cellulose chains leads to the easy moving of the molecular chains in amorphous and intermediate (non-crystalline) regions of cellulose (see Figure 2). Then, cellulose chains will be newly arranged and fixed by the hydrogen bonds between the adjacent hydrogen groups [1].

Figure 1. Hydrogen bonds between cellulose chains.

Figure 2. Moving of cellulose chains in amorphous and non-crystalline regions of cotton (right) due to the deformation and new-formation of hydrogen bonds (left).

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Wrinkle Resistant and Comfort Finishing of Cotton Textiles

Therefore, inhibiting the movement of cellulose chains by crosslinking of with resins/polymers is the appropriate way to overcome this problem [2-3]. The crosslinking agents can be principally divided into two main groups: formaldehyde-based chemicals (the oldest crosslinkers) and formaldehyde-free compounds.

PRIMARY EASY CARE FINISHING AGENTS BASED ON FORMALDEHYDE RESINS N-methylol compounds, namely urea-formaldehyde or melamine-formaldehyde (see Figure 3), were introduced as the primary easy-care finishing agents at the end of 1920s [4-5]. In 1947 dimethylolethylen urea compounds, in particular N, N´-dimethylol-4,5dihydroxyethylen urea (DMDHEU), were employed as the main crosslinking agents [6-7]. DMDHEU as the final product of the reaction between urea, glyoxal and formaldehyde reacts with the cellulose and form a crosslinking net [8-11] (Figure 4). O

O

C HO

H2C

HN

NH

C

CH2 OH

H3C

O

H2C

HN

NH

CH2 O

A

H NCH2OCH3 N CH3OCH2N

N(CH2OCH3) 2

N

N NCH2OCH3

N

H

(CH3OCH2)2N

N N(CH2OCH3) 2

N

H

B

Figure 3. Resins of urea-formaldehyde (A) and melamine-formaldehyde (B). O

O

C Cell

OH

+

HOH2C

N

N

CH2OH

HO

C

C

OH

H

H

A

+ 2H2O - 2H2O

C Cell

O

H2C

N

N

CH2 O

HO

C

C

OH

H

H

B

Figure 4. Reaction of DMDHEU (A) with cellulose and resulting crosslinked cellulose (B).

Cell

CH3

370


H C C H

H C C3H6

O O

O

glyoxal

C H O

glutaraldehyde

Figure 5. Chemical structures of glyoxal and glutaraldehyde.

The main problem of the above-described compounds was release of formaldehyde during washing and use. Formaldehyde has lots of potential hazards: it can irritate mucous membranes, cause teary eyes, cough, headache and difficulties in breathing. Furthermore, eczema and allergic responses may be evoked through direct contact of skin with the textiles containing of high levels of [12-15]. Due to the release of formaldehyde during production of easy care textiles with DMDHEU or even during the storage and use of the treated cotton fabrics N-methylol compounds, since 1960s it has been tried to develop the formaldehyde-free easy care agents or the finishes with low amount of formaldehyde release [16-17].

PRIMARY FORMALDEHYDE-FREE EASY CARE FINISHING AGENTS The early formaldehyde-free compounds were nitrogen-free finishes, including aldehydes such as glyoxal and glutaraldehyde (see Figure 5) [18-19]. Apart from high costs of glyoxal and glutaraldehyde, application of these compounds on cotton textiles cause more strength loss (in comparison to N-methylol compounds), yellowing and discoloring the fabric [20-22]. Acetals such as 2,5-dimethoxyfuran, 2,3-dihydroxy-1,1,4,4-tetramethoxybutane, 3,4dihydroxy-2,5 dimethoxytetra-hydrofuran, and glyceraldehyde dimethylacetal have been used as formaldehyde-free crosslinking agents. Treatment of cotton textiles with acetals reduces the fabric strength dramatically and therefore they are not applied in industrial scales [23-26]. Reaction products of amides and aldehydes, mainly N, N´-dimethyl-4,5dihydroxyethxylen urea (DMeDHEU) or 4,5-dihydroxy-2-imidazolin (see Figure 6) have been considered as effective formaldehyde-free finishes, which produce enough easy-care performance with a good durability against washing [26-27]. O C H3CN HO

NCH3

C

C

H

H

OH

Figure 6. Chemical structure of N, N´-dimethyl-4,5-dihydroxyethxylen urea (DMeDHEU).

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CURRENT TREND IN EASY-CARE IN EASY-CARE FINISHING OF FINISHING COTTON FABRICS Polycarboxylic Acids Among the formaldehyde-free crosslinking agents for providing wrinkle resistant textiles and considering the limits of the primary finishes in practical applications (yellowing of textiles, reduce of tensile strength and in some cases high costs of chemicals), it can be said that polycarboxylic acids are the most promising compounds [28-33]. The benefits of finishing with polycarboxylic acids are: high quality crosslinking, high fabric strength retention and good durability against laundering [34-37]. The presence of at least three carboxylic groups in polycarboxylic acids is necessary to create an acceptable wrinkle-resistant effect on cotton textiles. Therefore, 1, 2, 3, 4butanetetracarboxylic acid (BTCA), citric acid (CA) and succinic acid (SUA) (see Figure 7) are the most conventional polycarboxylic acid [38-43]. Except from BTCA, the other mentioned polycarboxylic acids have some limitations in practice and BTCA shows the best results [44-48]. Cotton fabric is crosslinked by polycarboxylic acids through the formation of 5- or 6member cyclic anhydride intermediates and finally esterification of the hydroxyl groups in the cellulosic chains (see Figure 8) [49-51]. In Figure 9 formation of the cyclic dianhydride intermediate of BTCA and final esterification of cellulose chains is shown [52]. HO

O

O

HO

HO

OH O

O

O

O HO

OH

O

OH O OH

OH

O

OH

BTCA

SUA

CA

Figure 7. Chemical structure of the conventional polycarboxylic acids used for easy-care finish of cotton textiles: 1,2,3,4-butanetetracarboxylic acid (BTCA), succinic acid (SUA) and citric acid (CA). R1 O

R1 O HC

HC

C

C

OH

OH

R2 O

Polycarboxylic acid

HC

R1 O

C

- H2O

O HC

C

R2 O

Cyclic anhydride

+ HO

Cell

HC

C

O

Cell

HC

C

O

H

R2 O Polycarboxylic acid bonded to cellulose through ester linkage

Figure 8. Esterification of cellulose chains by polycarboxylic acids via formation of cyclic anhydride intermediates.

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Vahid Ameri Dehabadi and Hans-Jürgen Buschmann O HO

O

HO

O

O HO OH - H2O

O O

O O

O

+ H2O

+Cell

CH2OH

Cell

H2C

O CH2 Cell

O

O O

O

OH

O

OH

O a

b

c

Figure 9. Crosslinking of cellulose (c) with BTCA (a) via formation of cyclic anhydride intermediate (b).

Application of a proper catalyst accelerates the esterification reaction and reduces the time and temperature of process. Several catalysts have been used and their advantages and disadvantages were studied by researchers. Most of the used catalysts belong to the sodium salts of phosphoric acids, such as sodium hypophosphite (NaH2PO2), monosodium phosphate (NaH2PO4), disodium phosphate (Na2HPO4), and trisodium phosphate (Na3PO4) [29, 46, 5354]. It has been shown that sodium hypophosphite (NaH2PO2) is the best catalyst for the crosslinking of cotton with polycarboxylic acids, especially BTCA. By application of sodium hypophosphite in durable press finishing of cotton highest levels of durable press rating and wrinkle recovery angle, reduction in cure temperature, increase of tensile strength retention and the most satisfactory whiteness are obtained [54-60]. The action mechanism of sodium hypophosphite as catalyst in reaction of polycarboxylic acid and cellulose is shown in Figure 10 [51, 60]. Beside to the phosphorus catalysts, nonphosphorus catalysts have been also investigated, including aromatic N-heterocyclic compounds such as imidazole and its derivatives to improve the retention of mechanical properties of the treated fabric [61], base catalysts such as sodium carbonate and tertiary amines to minimize degradation of treated cotton fabric, and other compounds like mono- or disodium salts of α-hydroxy acids such as tartaric, malic, or citric acid [33]. In addition to the role of catalyst in easy care finish of cellulosic textiles, pH value of finishing bath and the molecular weight of polycarboxylic acid have an important effect in final result. The number of ester linkages and the effectiveness of the bonded polycarboxylic acid molecules decrease by increase of pH from 1.5 to 5.5. As a matter of fact, by decrease of the pH the number of cyclic anhydride intermediate increases. In the other words, forming of cyclic anhydride is accelerated by increase the concentration of proton in the finish bath [6263]. Polycarboxylic acids with lower molecular weights cause easy mobility of cyclic anhydride intermediate to access hydroxyl groups of cellulose chains [39-40,64]. R1 O HC

R1 O O

C O

HC

C

R2 O

+

H

P

HC

C

P

HC

C

ONa OH

H

ONa

R1 O

R2 O

H

Cell

OH

HC

C

O

HC

C

OH

O

Cell +

H

P

H

ONa

R2 O

Figure 10. Crosslinking of cellulose by polycarboxylic acids in the presence of sodium hypophosphite as catalyst.


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High cost, requirement of large amount of catalystsand loss of the mechanical strength are general limits of finishing with the conventional polycarboxylic acids [65-66]. The last progress in polycarboxylic acids, we can mention to polyamino carboxylic acids (PACAs) [67-68]. PACAs can be easily synthesized by carboxylation of polyvinylamine (PVAm) or polyethyleneimine (PEIm), via reaction of the primary amino groups (Figure 11a) with halocarboxylic acids, such as bromoacetic acid (Figure 11b). The resulting substance can esterify the hydroxyl groups in cellulose and make crosslinking net (Figure 12). PACAs have less negative impact on tensile strength and whiteness of the cotton compared to the conventional polycarboxylic acids such BTCA and citric acid [67-68]. On the other hand, cotton finished with PACAs shows biostatic properties [69], and has a better dyeability due to the presence of the free amino groups [70]. PACAs in a combination with sodium hypophosphite reduce the flammability of the cotton, as well [71].

Figure 11. Synthesis of polyaminocarboxylic acids (b) via carboxylation of polyvinylamine (a) with bromoacetic acid under alkaline condition.

Figure 12. Covalent crosslinking of cellulose chains with PACAs.

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Ionic Crosslinking Agents Another approach to impart wrinkle resistance effect is ionic crosslinking, in which a preionized cotton fabric (either cationic or anionic) can adsorb an opposite charged substance and form a crosslinking net [72]. For instance, a precationized cotton fabric can be crosslinked with a citric acid [73]. In Figure 13, cellulose is precationized with 3-chlorohydroxypropyl trimethyl ammonium chloride (CHTAC) and then crosslinked in the presence of citric acid. OH Cell

O

O

CH2 CH

CH2 N (CH3)3 Cl +

HO OH O

OH O

Cell

CH2 CH

CH2 N (CH3)3 OOC

CH2 + HCl

HOOC

C

OH

HOOC

CH2

Figure 13. Ionic crosslinking of cotton precationized with 3-chloro-hydroxypropyl trimethyl ammonium chloride (CHTAC) in the presence of citric acid. H3C

CH3 H3C

Si O

CH3 H3C

Si O

NH3

 H

Si O



O

Si

Si O 

OH

CH3

Si O

O

O COO

CH3 H3C

H3C

Si O

O

CH3

O

CH3 NH3 CH3

H

O





Cotton or CMC fabric Figure 14. Crosslinking of cellulose using an aminosilicone softener with partially protonated amino groups on negatively charged cotton (e.g., carboxymethylated cotton-CMC).


375

Using of an aminosilicone softener with partially protonated amino groups on negatively charged cotton (e.g., carboxymethylated cotton), wrinkle resistant and soft-hand effects will be simultaneously created [74] (see Figure 14). Two basic reactions occur between amino-silicones and cellulose chains in cotton: the ionic interaction between protonated amino groups of in amino-silicone molecule and negatively charged cotton, and self-polymerization of silicone molecules through their respective reactive groups. Incorporation of amine functional silicone softeners in the ionically crosslinked cotton includes coulomb and dipole-dipole forces, hydrogen bond, van der Waals interaction and ether crosslinking. The nitrogen atoms in amino-silicone molecule are protonated under acidic condition. The negatively charged carboxymethylated cotton (CMC) and the positively charged amino-silicone make a crosslinking when these groups are localized at two adjacent cellulose chains.

Nanotechnology in Easy-Care Finish of Cotton Textiles The first use of nanotechnology – particularly nanoparticles – in easy care finish of cotton textiles is employing of titanium dioxide (TiO2) nanoparticles as catalyst to improve the wrinkle resistance properties of silk fabrics treated with maleic anhydride as crosslinking agent [75]. Nanoparticles of titanium dioxide have been used as photo catalyst for finish of cotton with polycarboxylic acids: BTCA, maleic acid, succinic acid and citric acids [76]. The action mechanism of nanoparticles of titanium dioxide can be explained in this way: electron of TiO2nanoparticles is excited at the valence bond under UV radiation with a wavelength lower than 400 nm for a few microseconds (µs) and moves to the surface of the nanometer particles and therefore water molecules and hydroxyl ions can be reduced by this process (known as photo reduction) [77]. As a result, the carboxylic acid groups and vinyl double bond of the polycarboxylic acids react with the cellulose molecules (crosslinking) [78]. In the case of crosslinking with polycarboxylic acids, e.g., succinic acid, and nanoparticles of titanium dioxide, the mechanism of reaction can be supposed as following (see Figure 15): the molecules of succinic acid are adsorbed on the surface of the nanoparticles and exposed to the UV photo-reduction under to form free radicals of succinic acid (Figure 15a) and an aldehyde group (Figure 15b). The contact between the succinic acid’s free radicals and the cellulose molecules complete the crosslinking reaction (Figure 15c). Another well-known technique in nanotechnology is sol-gel processes, which involve the hydrolysis of inorganic precursors such as organo-silicates, organo-titanates-aluminates, etc. and forming a 3D molecular network [79]. Finishes based on sol-gel technique have been investigated to improve performance of cotton finished with polycarboxylic acids [79]. Cotton can be finished in two steps with BTCA, sodium hypophosphite and TEOS (tetraethoxysilane)/GPTMS (glycidylpropyloxytrimethoxysilane)-based solutions with different amounts of GPTMS [80]. Dry wrinkle recovery angle can be fairly improved; meanwhile abrasion resistance increases greatly.

376


2 HOOC

CH2 CH2 COOH

HOOC

CH2 CH COOH

HOOC

CH2 CH2 CHO

+

H

(a)

H2O2

(b)

TiO2, H2O UV irradiation

Cell

TiO2

OH

Cell

O

+

H

+

(c)

UV irradiation

COOH Cell

O

+

HOOC

CH2 CH

COOH

Cell

O

CH

(d)

CH2 COOH O Cell

OH

+

OHC

CH2 CH2 COOH

H

Cell

C

CH2

+

H2O

(e)

CH2 COOH

Figure 15. Crosslinking of cellulose with succinic acid catalyzed by nanoparticles of titanium dioxide under UV irradiation.

Figure 16. Chemical structures of the different cyclodxetrins and their dimensions.


377

Comfort Finishing of Cotton Textiles Due to their chemical structure cotton fabrics easily adsorb water molecules. Therefore, the consumer judges the comfort of cotton fabrics high. However, due to the permanent contact of the textile with the human skin also the organic sweat components are incorporated within the cellulosic fiber. Due to the coincidence of humidity and the adsorbed organic substances from the sweat microorganism decompose these organic substances. This may result in some unpleasant odour released from the textiles. It is also well-known that textile materials act as reservoir for odour adsorbed from the neighborhood. These substances e.g., tobacco smoke are slowly released. To achieve a permanent fresh impression the desorption or release of substances from the textile have to been avoided. This effect can be realized by the use of cyclodextrins. Cyclodextrins are formed during the enzymatic degradation of starch. They are polysaccharides built from six to eight (α=6, ß=7, γ=8) D-glucose units. The D-glucose units are covalently linked at the carbon atoms C1 and C4.. The glucose units form a torus shaped molecule with a cavity. In these cavities guest molecules can be enclosed. Cyclodextrins are already used in pharmaceutical and cosmetic applications [81]. The chemical structures of the different cyclodextrins are given in Figure 16. Unfortunately the cyclodextrin molecules do not show any affinity to any fibre material. Thus, a permanent fixation of the cyclodextrins on cotton fibers has to be done using chemical reactions. A cyclodextrin derivate with a reactive group (e.g., the monochlorotriazinyl group) is able to react with the hydroxyl groups of a cotton fiber [82-83]. Since the hydroxyl groups of the cotton and of the cyclodextrin molecules behave chemically nearly identical any crosslinking reaction can be used for the permanent fixation of cyclodextrins on the cotton fiber. Using bifunctional or polyfunctional reactants cyclodextrins have already successfully bound on cotton fibers [84-88]. Thus, it is very simple to combine an easy care finishing with an additional wearing comfort.

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[48] Yang, C., Xu, L., Li, S. & Jiang, Y. (1998). Nonformaldehyde durable press finishing of cotton fabrics by combining polymers of maleic acid with citric acid. Text. Res. J., 68(6), 457-464. [49] Trask-Morrell, B., Andrews, B. K. & Graves, E. (1990). Spectrometric analysis of polycarboxylic acids. Text. Chem. Color., 22(10), 23. [50] Welch, C. (1990). Durable press finishing without formaldehyde. Text. Chem Color., 22(5), 13. [51] Gillingham, E., Lewis, D. & Voncina, B. (1999). An FTIR study of anhydride formation on heating butane-tetracarboxylic acid in the presence of various catalysts. Text. Res. J., 69(12), 949-955. [52] Sauperl, O. & Ribitsch, V. (2009). Cotton cellulose 1,2,3,4-butanetetracarboxylic acid (BTCA) crosslinking monitored by some physical-chemical methods. Text. Res. J., 79(9), 780-791. [53] Trask-Morrell, B. & Andrews, B. (1992). Thermoanalytical ranking of catalysts for use with polycarboxylic acids as durable press reactants. Text. Res. J., 62(3), 144-150. [54] Brown, R. & Tomasino, C. (1991). Catalysis of 1,2,3,4-butanetetracarboxylic acid in the durable press finishing of cotton. In Book of Papers, 1991 ATTCC International Conference, Research Triangel Park, NC: American Association of Textile Chemists and Colorists, 168-185. [55] Welch, C. & Peter, J. (1997). Mixed polycarboxylic acids and mixed catalysts in formaldehyde-free durable press finishing. Text. Chem. Color., 29(3), 22-27. [56] Morris, C., Morris, N. & Trask-Morrell, B., (1996). Interaction of mesobutanetetracarboxylic acid with phosphorus containing catalysts for esterification crosslinking-linkage of cellulose. Ind Eng Chem Res., 35(3), 950-953. [57] Yang, C. (2001). FTIR spectroscopy study of ester crosslinking of cotton cellulose catalyzed by sodium hypophosphite. Text. Res. J., 71(3), 201-206. [58] Lammermann, D. (1992). New possibilities for non-formaldehyde finishing of cellulosic fibers. Melliand Textilber., 3, 274-279. [59] Wei, W., Yang, C. & Jiang, Y. (1999). Nonformaldehyde durable press garment finishing of cotton slacks. Text. Chem. Color., 31(1), 34-38. [60] Gu, X. & Yang, C. (2000). FTIR spectroscopy of the formation of cyclic anhydride intermediates of polycarboxylic acids catalyzed by sodium hypophosphite. Text. Res. J., 70(1), 64-70. [61] Choi, H., Welch, C. & Morris, N. (1993). Nonphosphorus catalysts for formaldehydefree DP finishing of cotton with 1,2,3,4-butanetetracarboxylic acid. Text. Res. J., 63(11), 650-657. [62] Yang, C. (1993a). Effect of pH on nonformaldehyde durable press finishing of cotton fabric: FT-IR spectroscopy study: part I: ester crosslinking. Text. Res. J., 63(7), 420430. [63] Yang, C., (1993b). Infrared spectroscopy studies of the effects of catalysts on the ester crosslinking of cotton cellulose by polycarboxylic acids. J. Appl. Polym. Sci., 50(12), 2047-2053. [64] Yang, C. & Wang, X. (1998). The formation of five membered cyclic anhydride intermediates by polycarboxylic acids studied by the combination of thermal analysis and FT-IR spectroscopy. J. Appl. Polym. Sci., 70(13), 2711-2718.


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[65] Bhattacharyya, N., Doshi, B. & Sahasrabudhe, A. (2003). Cost effective catalyst for polycarboxylic acid finishing. Text. Chem. Color., 31(6), 33-37. [66] Sircharussin, W., Ryo-Aree, W., Intasen, W. & Poungraksakirt, S. (2004). Effect of boric acid and BTCA on tensile strength loss of finished cotton fabrics. Text. Res. J., 74(6), 475-480. [67] Ameri Dehabadi, V., Buschmann, H. J. & Gutmann, J. S. (2012). Durable press finishing of cotton fabrics with polyamino carboxylic acids. Carbohydr. Polym., 89(2), 558-563. [68] Ameri Dehabadi, V., Buschmann, H. J. & Gutmann, J. S. (2013). Neue Möglichkeit zur Hochveredlung cellulosicher Textilien. Melliand Textilber., 1, 29-31. [69] Ameri Dehabadi, V., Buschmann, H. J. & Gutmann, J. S. (2013). Study of Easy care and biostatic properties of finished cotton fabric with polyamino carboxylic acids. J. Text. Inst., 104(4), 414-418. [70] Ameri Dehabadi, V., Buschmann, H. J. & Gutmann, J. S. (2013). Pretreatment of cotton fabrics with polyamino carboxylic acids for salt-free dyeing of cotton with polyamino carboxylic acids. Color. Technol., 129, 155-158. [71] Ameri Dehabadi, V., Buschmann, H. J. & Gutmann, J. S. (2012). Flame retardant finishing of cotton fabrics using polyamino carboxylic acids. Fire Mat ahead of print. DOI: 10.1002/fam.2170. [72] Hashem, H., Hauser, P. & Smith, B. (2003). Wrinkle recovery for cellulosic fabric by means of ionic crosslinking. Text. Res. J., 73(9), 762-766. [73] Hebeish, A., Hashem, M., Abdel-Rahman, A. & El-Hilw, Z. (2006). Improving easy care nonformaldehyde finishing performance using polycarboxylic acids via precationization of cotton fabric. J. Appl. Polym. Sci., 100(4), 2697-2704. [74] Hashem, M., Ibrahim, N. A., El-Shafei, A., Refaie, R. & Hauser, P. ( 2009). An ecofriendly - novel approach for attaining wrinkle-free/soft-hand cotton fabric. Carbohydr. Polym., 78(4), 690-703. [75] Wang, C. & Chen, C. (2005). Physical properties of the crosslinked cellulose catalyzed with nanotitanium dioxide under UV irradiation and electronic field. Appl. Catal. A Gen., 293, 171-179. [76] Chen, C. & Wang, C. (2006). Crosslinking of cotton cellulose with succinic acid in the presence of titanium dioxide nano-catalyst under UV irradiation. J. Sol-Gel Sci. Technol., 40, 31-38. [77] Nazari, A., Montazer, M., Rashidi, A., Yazdanshenas, M. & Moghadam, M. (2010). Optimization of cotton crosslinking with polycarboxylic acids and nano TiO2 using central composite design. J. Appl. Polym. Sci., 117(5), 2740-2748. [78] Wang, C. & Chen, C. (2005). Physical properties of crosslinked cellulose catalyzed with nano titanium dioxide. J. Appl. Polym. Sci., 97(6), 2450-2456. [79] Mahltig, B. & Textor, T. (2008). Nanosols and textiles. Singapore: World Scientific Publishing. [80] Huang, K., Yang, K., Lin, S. & Lian, W. (2007). Antiwrinkle treatment of cotton fabric with a mixed sol of TEOS-TTB/DMDHEU. J. Appl. Polym. Sci., 106(4), 2559-2564. [81] Szejtli, J. (1988). Cyclodextrin Technology. Dordrecht, Kluwer. [82] Denter, U. & Schollmeyer, E. (1996). Surface modification of synthetic and natural fibres by fixation of cyclodextrin derivatives. J. Incl. Phenom Macrocyclic Chem., 25, 197-202.

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[83] Schmidt, A., Knittel, D., Buschmann, H. J. & Schollmeyer, E. (2001). Verfahren zur Herstellung von reaktiven Cyclodextrinen, ein damit ausgerüstetes Material und deren Verwendung. DE, Patent No. DE 10155781. [84] Buschmann, H. J., Knittel, D. & Schollmeyer, E. (1991). Hochveredlung von Baumwolle in Anwesenheit von Cyclodextrinen zur Einlagerung von Duftstoffen. Melliand Textilber., 72, 198-199. [85] Reuscher, H. & Hirsenkorn, R. (1996). BetaW7MCT – New ways in surface modification. J. Incl. Phenom Macrocyclic Chem., 25, 191-196. [86] Martel, B., Weltrowski, M., Ruffin, D. & Morcellet, M. (2002). Polycarboxylic acids as crosslinking agents for grafting cyclodextrins onto cotton and wool fabrics: Study of the process parameters. J. Appl. Polym Sci., 83, 1449-1456. [87] Voncina, B. & Le Marechal, A. M. (2005). Grafting of cotton with β-cyclodextrin via poly(carboxylic acid). J. Appl. Polym. Sci., 96, 1323-1328. [88] Kulke, T. (2007). Aqueous liquid compositions of reactive cyclodextrin derivatives a finishing process using the said composition. s.l. Patent No. EP1499644.



Chapter 15

EVALUATION OF PHYSICAL AND THERMAL COMFORT PROPERTIES OF COPPER/ALGINATE TREATED WOOL FABRICS BY USING ULTRASONIC ENERGY Muhammet Uzun* 1

Institute for Materials Research and Innovation, University of Bolton, Bolton, UK. Department of Textile Engineering, Faculty of Technology, Marmara University, Goztepe, Istanbul, Turkey

2

ABSTRACT The aim of this study is to treat wool fibre based woven fabric with sodium alginate and copper sulphate by using ultrasonic energy, and then test and analyse the treated fabric’s physical and thermal comfort properties including: tensile properties, abrasion behaviour, flexural rigidity, and thermo physiological properties. The fabrics were immersed in 5%, 10% and 15% w/v copper solution and subsequently the fabric specimens were subjected to 10 min and 20 min ultrasonic energy treatment. The results clearly demonstrated that the wool fabric was successfully treated with the copper and the coated fabrics showed significant changes as compared to their untreated forms. The tensile strength of the treated fabrics was strongly affected by the volume of copper in the solution. The abrasion test was performed for up to 50.000 rubs due to the standard test method and there were no considerable differences between the untreated and the treated fabrics. The treatment lowered the flexural rigidity values. The fabric’s thermal conductivities and thermal resistances were increased significantly after the treatment. It was also observed that the conductivity of the fabrics increased gradually. Furthermore, the treated fabrics had lower thermal absorbtivity values. The treated fabrics showed considerably lower water vapour permeability compared to the untreated fabrics. The ultrasonic energy application times did not affect any of the measured fabric properties significantly.

*

E-mail: [email protected] and [email protected].

384

Muhammet Uzun

Keywords: Wool fabric, alginate, copper treatment, thermal comfort, physical properties, ultrasonic energy

INTRODUCTION Recently, there have been a number of studies carried out detailing the converting of conventional textile materials to novel smart, responsive and high value-added products. The textile surface structure of the fabric can be modified by appropriate chemical method for the required functions and features. A wide range of smart products have been successfully commercialised which include fire-retardant fabrics, waterproof fabrics, biomedical applications such as silver treated wound dressings. Some coated products have been developed to minimise the risk of the bacteria which occurs in a hospital environment. To prevent forming of reservoirs of bacteria, surfaces such as bed rails, bedside tables and door handles, must be cleaned and disinfected properly. However, some bacteria now have the ability to survive even after thorough treatment with disinfectant [1]. Thus there is a greater need for biocidal surfaces to help reduce cross-contamination. This has led researchers to investigate antimicrobial agents such as copper to produce biocidal surfaces. Copper has been identified as being effective against a broad spectrum of microorganisms such as Clostridium difficile [2], Escherichia coli O157:H7 [3], Influenza A(H1N1) [4], Listeria monocytogenes [5], and methicillin-resistant Staphylococcus aureus. Sodium alginate can form a hydrophilic gel when in the presence of divalent cations such as copper (Cu2+) via a unique ion exchange mechanism whereby the sodium ions attached to the carboxyl groups on the uronic acid monomers are exchanged by the copper ions, which subsequently cross-links the alginate chains together, forming a crystalline structure [6]. A number of studies have shown that the ultrasonic energy has many advantages over alternative treatment methods such as superior cleaning, a reduction in the textile processing time, and reduced energy and chemicals [7-9]. Thermo physical comfort has been described as the garment’s ability to keep the wearer dry whilst maintaining body temperature, even when the wearer is subject to varying surrounding temperatures and humidity. The thermal comfort properties of a textile fabric are advantageous characteristics for the end-product [10-12]. The comforts of a garment mainly depend on its thermal properties, water vapour permeability and air permeability [13, 14]. Garment comfort characteristics are based on fibre types (natural, synthetic), yarn production method (ring, open-end), yarn properties (count, twist), fabric structures (woven, knitted, nonwoven), fabric’s physical features (thickness, warp-weft number) and also textile finishing process (bleaching, dyeing), etc [15-17]. In this study, a novel technique of incorporating copper into100% wool fabric using sodium alginate, cupric sulphate and ultrasonic energy has been effectively established. The main idea is to take advantage of alginate’s unique ion exchange mechanism to form copper alginate soaked wool fabric by incorporating ultrasonic energy. In order to investigate the effect of the copperon the wool fabric, three different concentrations (5%, 10% and 15%) of cupric sulphate solution were prepared and the fabric specimens were soaked for two hours and then the fabrics were subjected to 10 min and 20 min of ultrasonic energy. The untreated (control, 0%) and the treated fabrics were tested and analysed for tensile properties, abrasive properties, flexural rigidity, thermo physiological properties including; thermal conductivity, thermal resistance, thermal absorbtivity, water vapour permeability, and heat loss. Analysis of

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Evaluation of Physical and Thermal Comfort Properties …

variance (ANOVA) was employed to determine the significance of the tested properties for assessing the statistical significance of the differences between i) the untreated and the treated fabrics; ii) ultrasonic energy application times; and iii) dry and wet states of the comfort test results.

MATERIALS AND METHODS Materials 100% plain wool fabric was purchased from the UK market. The plain weave, being the fundamental weave, was chosen as the fabric structure where each filling yarn passes successively over and under each warp yarn, alternating each row. The fabric dimensional properties were tested and the results are given in Table 1. Sodium alginate, MANUCOL ® DH, was obtained from Ashland Ltd., U.K., (formerly ISP) (SA, medium viscosity 40-90 mPas (1%), M: G ratio 61/39). Copper (II) sulphate, pentahydrate was obtained from Fisher Bioreagents Ltd., U.K. Table 1. Dimensional property of wool based woven fabric

Fabric

Area density Thickness (gm-2) (mm) 171 0.5

Bulk density (gm-3) 0.343

Warp no. (per cm) 28

Weft no. (per cm) 19

Figure 1. Plain woven fabric structure.

Methods Copper/Alginate Treatment 20cm ×20cm fabric specimens were prepared and the specimens were fully immersed into the sodium alginate solution (2.5% w/v) for 24 h and then they were rinsed thoroughly with distilled water. After rinsing, the fabrics were then bathed in the copper sulphate solutions of different concentrations, (5%, 10% and 15% (w/v)) for two hours. Ultrasonic energy was applied to the fabrics under a 25ºC bathing temperature at different application

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times, 10 and 20 min. For the ultrasonic application, the ultrasonic bath (Bamdelim Sonorex Digital, UK 10P, 220 volt and 205 watt) was employed using a 10×10% power. The treated fabrics were rinsed three times in distilled water and finally, the fabrics were left to dry at room temperature for 24 h.

Tensile Properties The specimens were prepared in 20cm length x 5cm width in both weft and warp direction of the fabrics. The specimens were then mounted in the grips of an Instron universal tester 3300, UK, with 100 mm gauge length and 300mm/minute extension rate. Five measurements were carried out for each fabric combinations and the mean values of the readings were calculated. Abrasive Testing The abrasion test was performed with Martindale Abrasion and Pilling Tester M235/3, USA, using the established standard Martindale abrasion test method. The abrasive wear testing determines the resistance to abrasion of textile fabrics. The measurement of the resistance to abrasion of textile fabrics relies on several parameters such as the mechanical properties of the fibres, the dimensions of the fibres, the structure of the yarns, the construction of the fabrics, the type and kind of finishing material etc. The fabric specimens were cut using press cutters into circular specimens of 38mm diameter and placed on the specimen holder. The test was performed while applying a pressure of 9kPa, and the machine speed was maintained at 50 rubs per minute. After performing every 5000 rubs, the specimens were inspected for abrasion. Flexural Rigidity Testing The stiffness depending on bending length and flexural rigidity of fabrics were done using Shirley stiffness tester, UK, in accordance with BS 3356:1961. The test specimen size was prepared in 25mm width and 200mm length. Three specimens in warp directions and three weft directions were tested and the mean values were calculated. Thermo Physiological Testing The thermophysiological properties of the woven fabrics were determined by using an Alambeta instrument (Sensora Instruments, Czech Republic). The Alambeta instrument provides values for thermal conductivity, thermal resistance (insulation) and thermal absorbtivity (warmth-to-touch), fabric thickness and thermal diffusion. The test instrument was used to conclude the transient and steady state thermophysical properties of the fabrics. The specimen’s size of 20cm ×20cm were prepared and placed in between two plates. The heat flow through the fabric due to the difference in temperature between the bottom measuring plate (at ambient temperature) and the top measuring plate which is heated to 40ºC. The thermal absorbtivity of the textile structure is a measure of the amount of heat conducted away from structure surface per unit time [18-20]. The test was performed on dry and wet specimens. The wet specimens were wetted with 0.2mL of water on the centre of the fabrics and allowed 4 min of thermal recovery before testing. For each side (front and back side of fabric) of the untreated and treated fabric measurements were made, and the mean values of the measured parameters were calculated.


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Water vapour permeability and the resistance to evaporative heat loss of the fabrics were tested using the Permetest instrument (Sensora Instruments, Czech Republic). This instrument is based on a skin model, which simulates dry and wet human skin in terms of its thermal feeling. The instrument uses the same principle as specified in ISO 11092 developed by Hohenstein Institute, Germany, whereby a heated porous membrane is used to simulate sweating skin. The heat required for the water to evaporate from the membrane, with and without a fabric covering, is measured [18].

RESULTS AND DISCUSSION Tensile Properties of Wool Fabrics The tensile properties of the fabrics are presented in Table 3. The tensile test results of the warp and weft direction of the fabrics were found to be different. It can be seen in Figure2 the warp directions of treated fabrics lost their tensile strength properties gradually when the copper volume increased. On the other hand, it is shown in Figure3 that the copper treatment had different impact on the tensile properties in weft direction. Table 2. Tensile properties of the treated and untreated wool fabrics Copper Concretions

Warp

Weft

0% 5% 10% 15% 0% 5% 10% 15%

10 min 20 min Tensile strengthBreaking extensionTensile (N) (mm) (N) 341 5.4 341 263 8.5 261 253 6.9 263 170 6.4 177 257 7.9 252 348 6.9 342 366 6.7 366 143 6.9 156

strengthBreaking extension (mm) 5.4 7.2 6.2 7.2 5.9 6.4 7.2 6.2

The tensile strength of warp direction for the untreated (0%) fabric was 341 N which was the highest strength value compared to the treated fabrics and 15% copper treatment applied fabric had the lowest tensile strength of 170 N. It can be observed that the copper treatment has a noticeable impact on the tensile strength in warp direction of the wool fabrics. Moreover, comparing the data sets by analysis of variance “ANOVA” demonstrates that the difference between the untreated and the copper treated ones is statistically significant (F ratio = 25.08 > F critical = 5.93; α = 0.01). In both 10 min and 20 min ultrasonic energy application times, the tensile strength values of copper treated fabrics were much lower than their untreated counterparts. Furthermore, the effect of the ultrasonic energy application times on the tensile properties did not find to be significant (F critical = 7.39 > F ratio = 0.023; α = 0.01). The breaking extension of the warp direction was increased by the copper treatment. For the all cases, the copper treated fabrics had higher breaking extension compared to the untreated fabric.

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Figure 2. Tensile strength properties of warp direction.

Some variations were observed in tensile strength results of weft direction. The fabrics that were treated with 5 % and 10 % copper solution, improved the tensile strength in the weft direction significantly (F ratio = 119.1 > F critical = 5.95; α = 0.01), nevertheless; 15% copper treatment decreased the tensile strength of weft considerably. 10 % copper treated fabrics for both application times, 10 min and 20 min, had 366 N which was the highest tensile strength value compared to all the tested combinations. Conversely, 15% copper treated fabric had the lowest tensile strength (143 N) in this study. Besides, the effect of the ultrasonic energy times on the tensile properties in weft direction was not found to be noteworthy and ANOVA analysis showed that the differences are not statistically significant (F critical = 13.75 > F ratio = 5.11E-05; α = 0.01). The breaking extension values decreased with 10 min application time and increased with 20 min time.

Figure 3. Tensile strength properties of weft direction.


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There are two scenarios that could explain this decrease. The first scenario, the tensile strength could be affected because of the interaction between the metal ions and the polymer structure. The metal ions could cause the fibres to become more brittle and this can have a negative impact on the physical properties of the fibre. The second scenario could be that the presence of silver could make the fabrics more dry which also could cause a reduction in the tensile behaviour. These findings require further in-depth study, in order to establish the true impact of silver and how it can cause a decrease in fabric tensile properties. Wasif and Laga treated cotton fabric with nanosilver and they found that silver treatment decreased the tensile strength of the fabrics [24].

Abrasive Test Results The plain woven woollen fabric’s resistance to abrasion were tested and compared for a total of 35 fabrics (5 controls, 30 treated fabrics with different copper volume). Each tested specimen was inspected to analyse its abrasion behaviour after every 5.000 rubs. After the initial 50.000 rubs, none of the fabrics exhibited any sign of damage or wear. This result indicates that all the fabrics were not subject to significant abrasion after 50.000 rubs; however, 15% copper treated fabrics showed some minor weak points. Overall there were no considerable differences found between the treated and untreated fabrics after 50.000 rubs. This study proves that there is no noteworthy difference between the particular amounts of copper alginate treated wool fabrics and control fabric.

Figure 4. SEM photograph (100×) of treated fabrics A) 0%, B) 5%, C) 10% and D) 15%.

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Flexural Rigidity Test Results The flexural rigidity is the ratio of the small change in bending moment per unit width of the material to the corresponding small change in curvature: Flexural rigidity; G = M X C3 X 9.807 X 10-6inµNm

Eq. (1)

where: C = bending length (mm); M = fabric mass per unit area (g/m2). The flexural rigidity values of the untreated and the treated fabrics are given in Table 3. The higher flexural rigidity of fabric can be caused by the compactness of the structures which affects the freedom of movement during bending. This reduction in freedom of movement is an undesirable property for clothing. Lower flexural rigidity value is preferred for apparel fabrics [21]. In all cases, the flexural rigidity values of the fabrics decreased after the copper treatment. This decrease increases gradually with higher copper volumes. The fabrics which were treated with 15% copper solution had the lowest flexural rigidity values. This could be attributed to the surface deformation of the wool fabrics by the copper treatment. The ultrasonic energy application times did not have any significant impact on the flexural rigidity properties. Table 3. Average values of weft and warp flexural rigidity of woven fabrics (µNm) 0% 6.03 5.99

10 min 20 min

5% 5.87 5.89

10% 5.55 5.62

15% 5.17 5.25

Thermal Comfort Properties Table 4. Thermal comfort properties of untreated and treated wool fabrics in dry state

10 min

20 min

0% 5% 10% 15% 0% 5% 10% 15%

Thermal conductivity (W/mK×10-3) 32.4 33.8 33.7 35.1 33.1 34.2 34.5 35.5

Thermal resistance (W-1K m2×10-3) 25.4 57.6 67.4 77.8 26.5 60.1 71.3 82.1

Thermal absorbtivity (W m-2 s 0.5 K -1) 129 87.5 83.1 78.8 129 85.1 81.3 77.1


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Table 4 and 5 show the thermal conductivity, thermal resistance and thermal absorbtivity for dry and wet states of fabrics, respectively. The thermal properties of the fabrics were measured using an Alambeta instrument. The wet state was investigated separately due to the importance of fabric application areas and to determine wet performance of the treated fabrics. Table 5. Thermal comfort properties of untreated and treated wool fabrics in wet state

0% 10 min. 5% 10% 15% 0% 20 5% min. 10% 15%

Thermal conductivity (W/mK×10-3) 53.1 61.7 64.8 65.7 53.9 61.6 65.6 66.1

Thermal resistance (W-1K m2×10-3) 15.0 29.5 39.2 50.9 17.1 30.9 40.1 51.7

Thermal absorbtivity (W m-2 s 0.5 K -1) 289 229 218 179 289 220 213 180

Thermal Conductivity of Woven Fabrics in Dry and Wet State The thermal conductivity basically gives the amount of heat, which passes from 1 m2 area of tested structure through the distance 1 m within 1 s and create the temperature difference of 1 K. The thermal conductivity can be calculated by using the following expression [22,23], λ = Q/ Fτ×ΔT/σ in Wm-1 K-1

Eq. (2)

where: Q = amount of conducted heat, F = area through which the heat is conducted, τ = time of heat conducting ΔT = drop of temperature, σ = fabric thickness The thermal conductivity results are presented in Table 4 and Table 5 for dry and wet states, respectively. The thermal conductivity values ranged from 32.4 to 35.5 Wm-1 K-1 in its dry state and 53.1 to 65.6 Wm-1 K-1 in its wet state. The copper treatment increased the thermal conductivity of the wool fabric in dry and wet states for all the test combinations (Fig.5). 15% copper treated fabric had the highest thermal conductivity values in its dry and wet states. Moreover, comparing the data sets by analysis of variance “ANOVA” demonstrates that the difference between the untreated and the copper treated ones is

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statistically significant (F ratio = 130.9 > F critical = 16.69; α = 0.01). The fabrics which were subjected to 20 min of ultrasonic energy had slightly higher conductivity than those applied for 10 min. The application times were found to have an inconsiderable effect on the thermal conductivity of wool fabrics (F critical = 8.10 > F ratio = 1.86; α = 0.01). In wet state, the fabrics exhibited higher conductivity values than dry state and the difference is statistically significant (F ratio = 291.16 > F critical = 9.33; α = 0.01).

Figure 5. Thermal conductivity (λ) of woven fabrics in dry and wet state (W/mK×10-3).

Thermal Resistance of Woven Fabrics in Dry and Wet States The thermal resistance of the fabrics depends on thickness and thermal conductivity value. The thermal resistance has to be known due to the fabrics application areas and seasons. For the winter garments, it is higher resistance value is preferred. The resistance is expressed by the following relationship. R(m2kW-1) = h(m)/λ inW-1K m2×10-3

Eq. (3)

where: h = fabric thickness λ = thermal conductivity The thermal resistance values of dry and wet states are given in Table 4 and Table 5, respectively. The resistance results are also illustrated in Fig.6. The resistance of the fabrics ranged from 25.4 to 82.1 W-1K m2×10-3 for the dry state and from 15.0 to 51.7 W-1K m2×103 for the wet state. The differences between the groups were found to be highly significant (F ratio = 51323.7 > F critical = 16.69; α = 0.01). As seen in F values (F critical = 8.09 > F ratio = 0.14;

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α = 0.01) the ultrasonic application periods did not have significant effect on the resistance properties of the fabrics. In wet state most of the fabrics had up to two times lower values of thermal resistance than dry state. The difference between dry and wet states is considerable and it is statistically significant (F ratio = 9.76> F critical = 9.33; α = 0.01). The fabric’s thermal resistance behaviour improved gradually with the copper treatment and the application times also affect the measured property positively.

Figure 6. Thermal resistance (r) of woven fabrics in dry and wet state (W-1K m2×10-3).

The percentage recovery of the fabrics after 4 min of wetting is presented in Table 6. Any textile fabrics which have a 75% recovery value can dry quicker than any lower % values. All the fabric combinations had lower than 75% percentage recovery value after 4 min of wetting. Only 15% copper treated fabric had slightly higher percentage recovery values in comparison to the rest of the fabrics. The ultrasonic treatment did not have any significant effect on the tested recovery values. Table 6. % recovery after 4 min wetting (%)

10 min. 20 min.

0% 59.1 64.5

5% 51.2 51.4

10% 58.2 56.2

15% 65.4 62.9

Thermal Absorbtivity of Woven Fabrics in Dry and Wet States ‘Warm-cool’ feeling (thermal absorbtivity) of fabric is one of the prior characteristics for textile garments and this feature is the first sensation that is felt when any customer touches the garments, this is a kind of heat transfer between the skin and the fabric surface. A fabric’s

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‘warm-cool’ characteristic can be modified during the textile finishing processes. Lower thermal absorbtivity causes a warm feeling and a diametrically higher thermal absorbtivity value tends to give a cooler feeling. The thermal absorbtivity is calculated by the following equation. b =√ λ×ρ×c in Ws1/2 m-2 K-1

Eq. (4)

where: λ = thermal conductivity; ρ = fabric density; c = specific heat of the fabric. The treated fabrics had lower thermal absorption values in comparison with the untreated fabrics, furthermore; the treated fabric’s absorbtivity slightly decreased when they were treated with 20 minutes of ultrasonic energy (Table 4, Table 5 and Figure7). The differences between the untreated and the treated fabrics were found to be significant (F ratio = 1657.1 > F critical = 16.69; α = 0.01). The 15% copper treated fabric had the lowest absorbtivity value. The copper treatment increases the warm feeling of the fabrics due to the lower absoptivity. Important differences in thermal absorbtivity of the fabrics were observed when the specimens were wetted with 0.2 ml of water and the statistical analysis showed that there is a significant differences (F ratio = 69.59 > F critical = 9.33; α = 0.01). The thermal absorbtivity values of fabrics in their wet states are considerably higher than the dry state fabrics. The ultrasonic application times were found to be insignificant (F critical = 21.20 > F ratio = 0.33; α = 0.01).

Figure 7. Thermal absorbtivity (b) of woven fabrics in dry and wet state (W m-2 s 0.5 K -1).


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Water Vapour Permeability and Resistance to Evaporative Heat Loss (Permetest) The water vapour permeability (WVP) depends on the water vapour resistance which indicates the amount of resistance against the transport of water through the fabric structure. The amount of water present in a garment (which has crucial importance in the degree of comfort) must be minimal. The relative WVP is expressed using the following formula. WVR = Qs(Wm-2)/Q0(Wm-2)×100in %

Eq.(5)

where; Qs = the heat flow with the fabric specimen Q0 = the heat flow without the fabric specimen The WVP and resistance to evaporative heat loss results are summarized in Table 7. The study of WVP was performed by using Permetest instrument. According to the test results there are noticeable differences between the untreated and the treated fabrics, all the treated fabrics had reduced WVP value compared to the untreated counterparts. It can be clearly seen that the copper treatment enhances WVP properties of the wool fabrics and ANOVA results showed that it is of significant level (F ratio = 262.1 > F critical = 7.59; α = 0.01). The ultrasonic energy treatment times did not have any determinable influence on the WVP property of the fabrics (F critical = 13.75 > F ratio = 0.009; α = 0.01). Table 7. Water vapour permeability (%) and Resistance to evaporative heat loss (m2Pa W-1)

10 min. 20 min.

Water vapour permeability (%) 0% 5% 10% 15% 63 49 47.9 40.7 64 50 48.9 41.5

Resistance to evaporative heat loss (m2 Pa W-1) 0% 5% 10% 15% 2.8 4.8 5.2 6.1 2.9 5.0 5.2 6.3

As seen in Table7, the copper treated fabrics had higher resistance to evaporative heat loss values than the untreated fabric. The treated fabric’s resistance to evaporative heat loss values increased gradually and the change is statistically significant (F ratio = 582.8 > F critical = 7.59; α = 0.01). The ultrasonic energy treatment times did not have any considerable effect on the fabric heat loss values (F critical = 13.75 > F ratio = 0.016; α = 0.01).

CONCLUSION Copper is considered as an antimicrobial agent with useful medical applications in order to develop protection against the risk of the bacteria which occurs hospital environment. In this study, the physical and thermal comfort properties of 100% wool fabric coated with sodium alginate via a copper sulphate interaction, incorporating with ultrasonic energy has

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been studied. The coated fabrics demonstrated lower tensile strength values and it was found that the differences between the control and the treated fabrics were statistically significant. The coating did not have considerable effect on the abrasive properties of the fabrics up to 50.000 rubs, however; the fabrics which were treated with 15% copper volume had some weak points after the 50.000 rubs, nevertheless; the fabrics was not abraded. The flexural rigidity of the coated fabrics was lower than the control fabric. The fabric’s thermal conductivities were changed after the treatment. The fabrics coated with copper had higher thermal conductivities in comparison with the control fabrics for the both dry and wet states. The thermal resistance of the coated fabrics was found to be significantly higher than the control fabrics. The coated fabrics have lower thermal absorbtivity values when compared to the control fabrics. In the wet state, the thermal absorbtivity is considerably higher than in the dry state for all cases. According to the Permetest results, the differences between the control and the coated fabrics are considerable. The coated fabrics had reduced water vapour permeability. Heat loss increased when the fabrics are coated with copper. In general, the ultrasonic energy application times have no significant effect on most of the tested properties.

ACKNOWLEDGEMENTS The author would like to thank Dr. India Rose Sweeney and Dr. Vijay Parikh for supports during the project.

REFERENCES [1] [2]

[3]

[4]

[5]

[6] [7] [8]

Russell, A.D. (1999). Bacterial resistance to disinfectants: present knowledge and future problems. Journal of Hospital Infection 43, 57-68. Weaver, L., Michels, H.T., Keevil, C.W. (2008). Survival of Clostridium difficile on copper and steel: futuristic options for hospital hygiene. Journal of Hospital Infection 68, 145-151. Noyce, N.O., Michels, H., Keevil, C.W. (2006). Potential use of copper surfaces to reduce survival of epidemic methicillin-resistant Staphylococcus aureus in the healthcare environment Journal of Hospital Infection 63, 289-297. Noyce, J.O., Michels, H.T., Keevil, C.W. (2007). Inactivation of Influenza A virus on copper versus stainless steel surfaces. Applied and Environmental Microbiology 2748– 2750. Wilks, S.A., Michels, H.T., Keevil C.W. (2006). Survival of Listeria monocytogenes Scott A on metal surfaces: Implications for cross-contamination. International Journal of Food Microbiology 111, 93-98. Grant, G.T., Morris, E.R., Rees, R.A., et al. (1973). Biological Interactions between polysaccharides and divalent cations: The egg-box model. FEBS Letter 32, 195-98. Sun, D., Guo, Q., Liu, X. (2010). Investigation into dyeing acceleration efficiency of ultrasound energy. Ultrasonic 50, 441-446. Akalin, M., Merdan, N., Kocal, D., Usta, I. (2004). Effects of ultrasonic energy on the wash fastness of reactive dyes. Ultrasonic 42, 161-164.

Evaluation of Physical and Thermal Comfort Properties … [9]

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[11] [12] [13] [14] [15] [16] [17]

[18] [19] [20]

[21] [22]

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Uzun, M., Patel, I. (2010). Mechanical properties of ultrasonic washed organic and traditional cotton yarns. Journal of Ach. in Materials and Manufacturing Engineering 43(2), 608-612. Hes, L. (2008). Non-destruction determination of comfort parameters during marketing functional garment and clothing. Indian Journal of Fiber and Text. Research 33, 239245. Kawabata, S. (2000). A guide line for manufacturing ideal fabrics. International Journal of Clothing Sciences and Technology 12, 134-140. Lee, C.V., Ly, N.G. (1995). Heat and moisture transfer in textile assemblies. Textile Research Journal- Part 1. 65(4), 203. Milenkovic, L., Skundric, P., Sokolovic, R., Nikolicl, T. (1999). Comfort properties of defence protective clothing. The Scientific Journal Facta Universitatis 1(4), 101-106. Watkins, D.A., Slater, K. (1981). The moisture vapour permeability of textile fabrics. Journal of Textile Institute 72, 11-18. Li, Y. (2001). The science of clothing comfort. Textile Progress 31 (1/2), 1-135. Wan, X., Fan, J., Wu, H. (2009). Measurement of thermal radiative properties of penguin down and other fibrous materials using FTIR. Polymer Testing 28, 673-679. Majumdar, A., Mukhopadhyay, S., Yadav, R. (2010). Thermal properties of knitted fabrics made from cotton and regenerated bamboo cellulosic fibres. International Journal of Thermal Science 49, 2042- 2048. Pereira, S., Anand, S.C., Rajendran, S., Wood, C. (2007). A study of the structure and properties of novel fabrics for knee braces. Journal of Industrial Textiles 36, 279-300. Alambeta Measuring Device: Users’ Guide Version 2.3, Sensora Instrument Liberec, Company Brochure. Splendore, R., Dotti, F., Cravello, B., Ferri, A. (2010). Thermo-physiological comfort of a PES fabric with incorporated activated carbon-Part 1: Preliminary physical analysis. International Journal of Clothing Science and Technology 22(5), 333-341. Saville, B.P. (1999). Physical testing of textiles, first ed., Woodhead, Cambridge. Frydrych, I., Dziworska, G., Bilska, J. (2002). Comparative analysis of the thermal insulation properties of fabrics made of natural and man-made cellulose fibres, Fibres&Textiles in Eastern Europe 40-44. Hes, L., Mangat, M.M. (2010). The effect of industrial washing on thermal comfort parameters of denim fabrics. 7th International Conference-TEXSCI, September 6-8, Liberec, Czech Republic Wasif, A.I., Laga, S.K. (2009). Use of nano silver as an antimicrobial agent for cotton. AUTEX Research Journal 9, 5-13.



Chapter 16

HEMP FIBERS: OLD FIBERS – NEW APPLICATIONS Mirjana Kostic1, Marija Vukcevic*1, Biljana Pejic1 and Ana Kalijadis2 1

Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia 2 Laboratory of Physics, Vinca Institute of Nuclear Sciences, University of Belgrade, Belgrade, Serbia

ABSTRACT Hemp (Cannabis sativa) was most likely the first plant cultivated by mankind for its textile use. Currently, the interest in hemp is focused on its use as a raw material for the production of environmentally friendly clothes, technical textiles and composite materials. The increased production of hemp fibers in textile industry brings the considerable amount of waste in the form of short and entangled fibers. The cost of waste disposal can be minimized by recycling the waste in the way of producing useful lowcost products. Following the general trend of finding low-cost and easily available adsorbent, waste short and entangled hemp fibers were utilized as a heavy metal biosorbents. Due to the specific structure and heterogenous chemical composition (cellulose, hemicelluloses, lignin, pectin), short hemp fibers as biosorbent offer an effective way to decrease Pb2+, Cd2+ and Zn2+ ion concentration in wastewaters. The influence of hemp fiber chemical composition on their heavy metal ions sorption potential, were assessed by evaluating the water and metal ions uptake capacities of differently modified hemp fibers. The process of heavy metal ions biosorption on short hemp fibers was clarified by mathematical model development. Proposed mathematical model provides a better insight into phenomena of different ions transport through porous fiber matrices, and possibility of optimization of the complex process of biosorption. This is from great importance in the case of using short hemp fibers as filter material for removing the heavy metal ions from polluted water. Furthermore, there is a growing interest in using different type of waste biomass for production of carbon materials as a sorbents for water purification. From that aspect, short and entangled hemp fibers were used as low-cost precursor for production of carbon materials. Chemical modification of hemp fibers, prior to carbonization, affects the specific surface area, amount of surface *

Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia, E-mail: [email protected].

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Mirjana Kostic, Marija Vukcevic, Biljana Pejic et al. oxygen groups and morphology of carbonized hemp fibers. Furthermore, activation of carbonized materials with potassium hydroxide improves sorption properties of carbonized hemp fibers by increasing the specific surface area (up to 2192 m2/g) and amount of surface oxygen groups. Due to the good adsorption properties toward heavy metals and pesticides, carbonized and activated hemp fibers were successfully used as a sorbent for the purification of water polluted with pesticides and heavy metals. Also, activated hemp fiber sorbent used for analyte preconcentration in the solid-phase extraction procedure (SPE) for pesticide analysis in water samples, showed even higher efficiency in pesticides preconcentration than expensive commercial cartridges. Sorption process of heavy metal ions and structural parameters of carbonized hemp fibers were described by upgrading already proposed mathematical model. A good agreement between model prediction and the experimental data indicates that the proposed mathematical model can be used for optimization of heavy metal ions adsorption process by correlating the model parameters to the carbonized hemp fibers performances.

Keywords: hemp fibers, chemical modification, biosorption, carbonization and activation, mathematical modeling

INTRODUCTION Hemp (Cannabis Sativa), an old and controversial plant, was harvested by the Chinese 8500 years ago. Hemp was most likely the first plant cultivated by man kind for its textile use. However, the decline of hemp began in 1925, when hemp was included in the prohibition list due to its hallucinogenic properties, which resulted in an almost total ban of the plant. Also, chemical fibers and their intensive development after the Second World War had an influence on the total textile fiber situation characterized by the significant elimination of natural fibers from textile products. Among the fibers, which suffered the most, were flax, hemp, wool and silk. Such situation was caused by relatively cheep, simple and efficient chemical fibers production technology and foremost by the possibility of their adaptation to the existing technologies. However, in the 1990s, due to the exhaustion of major organic chemicals resources (coal, gas, oil) necessary for chemical fibers production, the attention was paid to the renewable and biodegradable raw materials. At this point, production of hemp fiber is experiencing a renaissance again. After quite a long period of intensive application, synthetic fibers, created to replace natural fibers, are today considered inferior to natural ones, especially in respect to comfort and ecological properties. From this point, the total substitution of natural with synthetic fibers is not desirable. These facts, together with limits in the yield of cotton, the main comfort providing fibers, were main reasons for the beginning of an unexpected, worldwide return to almost forgotten bast fibers, among them hemp [1-5]. Intensive growth of world population imposes the need for comfortable, biodegradable, biocompatible and ecological fibers. Textile fibers and textile materials are in continuous contact with consumer bodies during their use and comfort of clothing materials, among the other things, implies hygienic materials with good sorption properties and low values of electric resistance. As a textile fiber, hemp fiber has the specific properties, namely aseptic properties, high absorbency and hygroscopicity, good thermal and electrostatic properties, as well as good UV protection properties and lack of any allergenic effect, that make them different from other fibers. However, high quantity of noncellulosic components in hemp

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fibers (hemicelluloses, lignin, pectin and waxes) and impurities negatively influence further fiber processing and fiber properties (fineness, elasticity, evenness, and sorption properties). In order to make them finer, cleaner, softer, and more suitable for processing on machines of higher efficiency than traditional hemp machines, numerous chemical, mechanical, enzymatic and combined treatments of hemp fibers are applied which are mostly directed towards elimination of hemicelluloses, lignin and pectin. Modification of hemp fibers has to be performed in such way that attaining the desired goal is not followed by decreasing the most important positive properties of hemp fiber, especially very important comfort properties of fibers – their relation to water (vapor or liquid) and low static electricity charges, which defines their physiological properties [1,6-11]. The increased production of hemp fibers in textile industry brings the considerable amount of waste in the form of short and entangled fibers. The cost of waste disposal can be minimized by recycling the waste in the way of producing useful low-cost products. Following the general trend of finding low-cost and easily available adsorbent, waste short and entangled hemp fibers were utilized as a heavy metal biosorbents. Due to the specific structure and heterogenous chemical composition, short hemp fibers as biosorbent offer an effective way to decrease Pb2+, Cd2+ and Zn2+ ion concentration in wastewaters [12]. Furthermore, short and entangled hemp fibers can be used as low-cost precursor for production of carbon materials, as a sorbent for water purification [13].

HEMP FIBERS CHEMICAL COMPOSITION Technical (multi-cellular) hemp fibers, obtained from hemp plant, are characterized with extremely complicated microstructure and heterogonous chemical composition. Generally, hemp fibers contain about 67.0 - 78.3 % cellulose, 5.5 - 16.1 % hemicelluloses, 0.8 - 2.5 % pectin, 2.9 - 3.3 % lignin, and some fats and waxes in the fibers [12,14]. The main component of hemp fiber structure is cellulosic macromolecule. Cellulose is a natural polymer consisting of D-anhydro-glucoside repeating units held together by β-(1,4)glycosidic linkages at C1 and C4 position [15]. The degree of polymerization (DP) is around 10,000 [16]. Each repeating unit contains three hydroxyl groups, which have ability to form intramolecular and intermolecular hydrogen bond within the same cellulose chain and the surrounding cellulose chains. In that way, chains tend to be arranged parallel and form a crystalline supermolecular structure, with regions of high order, i.e., crystalline regions, and regions of low order, i.e., amorphous regions. Then, bundles of linear cellulose chains (in the longitudinal direction) form a microfibril which is oriented in the cell wall structure [17]. Cellulose is insoluble in most solvents and has a low accessibility to acid and enzymatic hydrolysis [14]. Unlike cellulose, hemicelluloses comprise a group of polysaccharides composed of different monosaccharide units, such as combination of 5- and 6-carbon ring sugars. Hemicelluloses are derived mainly from chains of pentose sugars, and act as supportive matrix for cellulose microfibrils. Hemicelluloses differ from cellulose in three aspects. Firstly, they contain several different sugar units whereas cellulose contains only 1,4-β-Dglucopyranose units. Secondly, they exhibit a considerable degree of chain branching containing pendant side groups giving rise to its noncrystalline nature, whereas cellulose is a

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linear polymer. Thirdly, DP of hemicelluloses is around 50–300, whereas that of native cellulose is 10–100 times higher than that of hemicelluloses. Among the most important sugar of the hemicelluloses component is xylose. In hardwood xylan, the backbone chain consists of xylose units which are linked by β-(1,4)-glycosidic bonds and branched by α-(1,2)glycosidic bonds with 4-O-methylglucuronic acid groups [17]. In addition, O-acetyl groups sometime replace the OH groups in position C2 and C3. For softwood xylan, the acetyl groups are fewer in the backbone chain. However, softwood xylan has additional branches consisting of arabinofuranose units linked by α-(1,3)-glycosidic bonds to the backbone. Hemicelluloses are very hydrophilic, soluble in alkali, and easily hydrolyzed in acids [14]. Lignin is a hydrocarbon polymer with a complex three-dimensional structure and very high molecular weight, consisting of both aliphatic and aromatic constituents. Lignin is covalently linked with xylans in the case of hardwoods and with galactoglucomannans in softwoods. The basic chemical phenylpropane units of lignin (primarily, syringyl, guaiacyl and p-hydroxy phenol) are bonded together by a set of linkages to form a very complex matrix. This matrix comprises a variety of functional groups, such as hydroxyl, methoxyl and carbonyl, which impart a high polarity to the lignin macromolecule [15,17,18]. Lignin has been found to contain five hydroxyl and five methoxyl groups per building unit. It is believed that the structural units of lignin molecule are derivatives of 4-hydroxy-3-methoxy phenylpropane. Lignin is totally amorphous and hydrophobic in nature. It is totally insoluble in most solvents and cannot be broken down to monomeric units. It is not hydrolyzed by acids, but soluble in hot alkali, readily oxidized, and easily condensable with phenol [19-22]. Pectins are complex polysaccharides consisting mainly of esterified D-galacturonic acid resides in an alpha-(1-4) chain. Pectins may also contain rhamnogalacturonan II side chains containing other residues such as D-xylose, L-fucose, D-glucuronic acid, D-apiose, 3-deoxyD-manno-2-octulosonic acid and 3-deoxy-D-lyxo-2-heptulosonic acid attached to poly-α-(1 4)-D-galacturonic acid regions [23]. D-galacturonic acid residues form most of the molecules, in blocks of 'smooth' and 'hairy' regions. The molecule does not adopt a straight conformation in solution, but is extended and curved ('worm like') with a large amount of flexibility. The `hairy' regions of pectins are even more flexible and may have pendant arabinogalactans. The carboxylate groups tend to expand the structure of pectins as a result of their charge, unless they interact through divalent cationic bridging (their pKa of about 2.9 [24] ensuring considerable negative charge under most circumstances). Methylation of these carboxylic acid groups forms their methyl esters, which take up a similar space but are much more hydrophobic and consequently have a different effect on the structuring of the surrounding water. The properties of pectins depend on the degree of esterification, which is normally about 70 %.

STRUCTURE AND MORPHOLOGY OF HEMP FIBERS The hemp fibers are characterized with cross section complexity and specific surface morphology. It can be considered as composites of hollow cellulose fibrils held together by a lignin and hemicelluloses matrix. The cell wall in a fiber is not a homogenous membrane. Structure of hemp fibers is presented in Figure 1. Each fiber has a complex, layered structure consisting of a thin primary wall which is the first layer deposited during cell growth


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encircling a secondary wall. The secondary wall is made up of three layers and the thick middle layer determines the mechanical properties of the fiber. In the secondary cell wall, the cellulose molecules are synthesized by enzymes that float around in the cell membrane, spinning off primary fibrils of about 5 nm in diameter, each containing about 40 molecules. These primary fibrils are assembled into microfibrils of about 20–40 nm in diameter, which have hemicelluloses decorating the outside. These hemicelluloses act as the connection between the microfibrils, creating the primary structural network. Lignin can be deposited within this network in two ways: either as isolated lumps (when it acts to limit the movement of the microfibers, thus increasing stiffness by steric hindrance) or (later) as a continuous matrix, which then supplements and presumably replaces the hemicelluloses in importance as a linker of the cellulose microfibrils The hydrophobic lignin network affects the properties of other network in a way that it acts as a coupling agent and increases the stiffness of the cellulose/hemicelluloses composite [25].

Figure 1. Structure of hemp fibers.

Complex structure and heterogeneous chemical composition of hemp fibers are the crucial factors that affect their specific characteristics. As a textile fiber, hemp possesses a range of extraordinary properties as: antimicrobial properties, extremely quick absorption of humidity accompanied with quick drying, good thermal and electrical properties (increased heat of sorption and low static electricity charges), outstanding tenacity (50–90 cN/tex), lack of allergenic effects, biodegradability and protection against UV radiation [3,26-28]. However, high quantity of noncellulosic components in hemp fibers (hemicelluloses, lignin, pectin and waxes) and impurities negatively influence further fiber processing and fiber properties (fineness, elasticity, evenness, and sorption properties). In order to make them finer, cleaner, softer, and more suitable for processing on machines of higher efficiency than traditional hemp machines, numerous chemical, mechanical, enzymatic and combined treatments of hemp fibers are applied which are mostly directed towards elimination of hemicelluloses, lignin and pectin. The predominant task in preparing hemp fibers for further

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fiber processing is to remove these noncellulosic components with improving fiber properties and without damage to the fiber cellulose [2,6-11].

CHEMICAL MODIFICATION OF HEMP FIBERS The most commonly used methods for hemp fiber modification are different chemical treatments, such as: alkaline, oxidative, silane, benzoylation, acetylation of natural fibers, etc. [29]. The appropriate chemical treatment is generally selected regarding the future hemp fiber usage and desired characteristics. This chapter will be focused on using alkaline and oxidative treatments for hemp fibers modification.

Alkaline Treatment Alkaline treatment or mercerization is one of the commonly used chemical treatments of natural cellulose fibers. Mercerization is usually carried out in the presence of NaOH, KOH and LiOH, and by varying the chemical agent concentration, temperature and time of treatment. The alkaline treatment with 17.5 % NaOH at room temperature, leads to changes in the chemical composition: the level of hemicelluloses removal from hemp fibers is high, while lignin content is almost unchanged. Content of hemicelluloses decreases up to 70 % in relation to unmodified fibers. In contrast to hemicelluloses, lignin shows low reactivity during the alkaline treatment, mainly because of strong carbon–carbon linkages and aromatic groups and rings, which were very resistant to chemical attack. Changes in chemical composition occurred during the alkaline treatment affects the structure of lignocellulosic fibers. The main structural modification is the disruption of hydrogen bonding in the network structure which induces the cellulose depolymerization and increases the amorphous cellulose content at the expense of crystalline cellulose. Additionally, alkaline treatment increases the amount of cellulose exposed on the fiber surface and thereby increase the surface roughness [8,10,12,30]. The NaOH usage affects the swelling of lignocellulosic fibers, during which the natural crystalline structure of the cellulose relaxes. Native cellulose (i.e., cellulose as it occurs in nature) shows a monoclinic crystalline lattice of cellulose I, which can be changed into different polymorphous forms through chemical or thermal treatments. The type of alkali and its concentration will influence the degree of swelling, and hence the degree of lattice transformation into cellulose II [31-33]. Sodium hydroxide treatment results in a higher amount of swelling, due to formation of new Na–cellulose I lattice with relatively large distances between the cellulose molecules. Additionally, the sodium hydroxide promotes the ionization of the hydroxyl group to the alkoxide [15]. The OH-groups of the cellulose are converted into ONa-groups, expanding the dimensions of molecules. Subsequent rinsing with water will remove the linked Na ions and convert the cellulose to a new crystalline structure, i.e., cellulose II, which is thermodynamically more stable than cellulose I. In contrast to other alkalis which produce only partial lattice transformation, NaOH can cause a complete lattice transformation from cellulose I to the cellulose II. The alkali solution influences not only the


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cellulosic components inside the plant fiber but also the noncellulosic components (hemicelluloses, lignin, and pectin) [2,8,12].

Oxidative Treatments The usage of different oxidative agents in order to modified hemp fibers become one of the significant chemical treatments. The factors that may influence the hemp fibers characteristics during the oxidative treatments are concentration and type of oxidative agent, time and temperature of treatment. The most significant change emerged as a result of oxidative treatment, is selective removal of lignin accompanied by decrease in amounts of hemicelluloses, pectines and waxes. Removal of lignin and hemicelluloses induce the fibrillation of hemp fibers which is accompanied by changes in physical and chemical characteristics. The hemp fibers major component, cellulose, which is a polyhydric alcohol, is very sensitive to oxidizing media. The chemical structure of cellulose is altered in a way that hydroxyl groups are oxidized into the corresponding carbonyl structures, i.e., an aldehyde at C-6 and ketone at C-2 and C-3, or carboxyl moiety (at C-6). Oxidation can also be accompanied by a change in the carbon skeleton of the cellulose backbone: a carbon-carbon bond cleavage between C-2 and C-3, for instance, allows for the introduction of aldehyde or carboxyl structures also at C-2 and C-3, which otherwise would not be possible. Cellulose degradation (chain cleavage) often accompanies the oxidation, but is actually caused by subsequent reactions and not by the oxidation itself [15]. Oxidative treatment of lignocellulosic fibers can be carried out through the selective or non-selective cellulose oxidation.

Selective Oxidation Frequently applied procedures for selective cellulose oxidation are TEMPO and periodate treatment. TEMPO oxidation process implied conversion of glucans by the system 2,2’,6,6’tertramethylpiperidine-1-oxyl (TEMPO) / sodium hypochlorite / potassium bromide [15, 34]. This reaction takes place through the selective oxidation at C-6 of the anhydroglucose units to carboxylic groups via the intermediate aldehyde stage, finally producing water soluble polyglucuronic acids. The nitroxyl radical affects the oxidation from the alcohol to the aldehyde oxidation state, while the hyperbromide generated in situ from hypochloride and bromide performs the further oxidation of the aldehyde to the carboxylic acid. TEMPO oxidation is usually accompanied by a drastic change of the molecular weight, due to βelimination starting from C-6 aldehyde. This oxidative process is carried out around pH 1011, since at lower pH hypochlorite becomes an overly aggressive and non-selective oxidant, and TEMPO reactivity is decreased. The selective oxidation of hemp fibers, using TEMPO, introduces new functionalities, removes lignin and hemicelluloses, and improves sorption properties of hemp fibers. By changing the parameters of the oxidation (HClO concentration and treatment time), it is possible to obtain hemp fibers with a different amount of cation exchange functions (0.09 to 0.80 mmol of carboxylic groups per gram of fibers). Amount of cation exchange functions into the fibers depends directly on the time of modification, as well as concentration of oxidizing agents [35]. Another type of selective oxidation is periodate oxidation [15,36]. This type of cellulose oxidation induces bond cleavage between C-2 and C-3 of the anhydroglucose units with

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concomitant introduction of aldehyde functionalities at those two positions. The reaction is thought to proceed via a cyclic diester of per-iodic acid with geminal hydroxyls, which subsequently undergoes an intramolecular redox process with simultaneous C-C bond cleavage according to a concerted mechanism. The reaction is quite selective for cellulosics as the only geminal hydroxyls available at C-2 and C-3 of the anhydroglucose units.

Non-Selective Oxidation Non-selective oxidation of hemp fibers is usually performed by permanganate, peroxide and chlorite treatments. Hydrogen peroxide and potassium permanganate are well known bleaching agents, capable of oxidizing low molecular impurities on natural fiber surfaces, thus obtaining not only greater whiteness but also eventual surface cleaning and oxidation of available functional groups of fibers [37]. In the area of hemp fibers modification, the treatments with chlorine derivatives take precedence. The most frequently used chlorine derivatives are chlor-dioxide and sodium chlorite. Depending of the concentration of oxidizing agent used and treatments parameters, hemp fiber can be fibrillated in that level to obtain the fibrils of micro and nano dimension. Chlorine derivatives (NaClO2) usage in the hemp fibers modification induced the fibrillation and decrease in the fiber diameter from 22-25 μm, for unmodified fiber, to 5-90 nm, for oxidized fibers [38,39]. This fiber diameter decrease is a result of lignin oxidation followed by its degradation and thereby decreases in hemp fibers lignin content. The sodium chlorite modification is commonly used after the sodium hydroxide or sodium periodate treatments. Sodium periodate selectively oxidizes the C-2 and C-3 hydroxyl groups of cellulose into cellulose dialdehyde, which on further reaction with sodium chlorite in the presence of acetic acid forms dicarboxylic groups at C-2 and C-3 position. Hemicelluloses, which consist mainly of pentoses, may react with sodium periodate in a similar way to cellulose. On the other hand, lignin (phenyl propane-based polymer) may be oxidized by the sodium periodate and sodium chlorite. Sodium periodate oxidation of lignin results in demethylation of methoxy groups of lignin and formation of Ph-OH groups, while sodium chlorite oxidation causes benzene ring cleavage and formation of dicarboxylic groups [40]. As it is shown, chemical treatments used for hemp fiber modification leads to changes in chemical structure of cellulose and accompanying compounds and thereby to the changes in hemp fiber structure and morphology. These changes directly affect the hemp fiber properties, such as: physical, mechanical and sorption properties.

INFLUENCE OF SODIUM HYDROXIDE AND SODIUM CHLORITE CHEMICAL TREATMENTS ON HEMP FIBERS CHEMICAL COMPOSITION The alkaline and oxidative treatments used for hemp fiber modification [12,41,42] are schematically presented in the Figure 2.

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Figure 2. The scheme of hemp fiber chemical modification.

The chemical compositions of modified hemp fibers and those of the control, unmodified sample, weight loss and fineness are given in Table 1. From the obtained results, it is obvious that during hemp fibers treatment with 17.5 % NaOH hemicelluloses were progressively removed, their content decreased for approximately 70 % in relation to unmodified fibers. Lignin content decreased slightly, because of its low reactivity. Namely, degradation of lignin during the alkaline treatment is impeded by the presence of strong carbon–carbon linkages and other chemical groups such as aromatic groups, which are very resistant to chemical attack [10]. On the other hand, treatment of hemp fibers with 0.7 % NaClO2 progressively removed lignin for about 50 % in relation to unmodified fibers. It has to be mentioned that, in this case, the content of hemicelluloses in modified hemp fibers decreased for about 17 %. During both types of hemp fibers modification, noncellulosic component content in modified fibers decreased in relation to unmodified hemp fibers, proportionally to the increase of modification time. Removing different amounts of hemicelluloses and lignin by chemical modification changed both chemical and physical properties of hemp fibers. The severity of the treatment is generally characterized by weight loss. Loss in weight, as result of chemical treatment (Table 1), in both cases increased with the increase of time of treatment. Also, the alkaline treatment of hemp fibers results in higher weight loss, in comparison to the sodium chlorite treatment. Additionally, as result of removing noncellulosic substances, hemp fibers acquired a high level of divisibility, which determines important properties of hemp fibers – their fineness (Table 1). Hemicelluloses removal leads to higher extent of fiber liberation than lignin removal; fiber fineness was reduced from 21.5 tex for unmodified to 1.8 tex for H45 sample. Table 1. The chemical composition, weight loss and fineness of unmodified and modified hemp fibers

Sample C H5 H45 L5 L60

α-Cellulose content (%) 78.15 80.59 79.70 80.03 79.15

Hemicelluloses Content Removed (%) (%) 10.72 4.69 56.25 3.59 66.51 8.89 17.07 8.99 16.14

Lignin Content (%) 6.06 5.66 5.41 4.09 3.09

Removed (%)

Weight loss (%)

6.60 10.73 32.51 49.01

8.15 9.90 4.16 6.17

Fineness (tex) 21.5 4.2 1.8 9.2 8.0

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STRUCTURAL CHANGES INDUCED BY CHEMICAL MODIFICATION OF HEMP FIBERS

Figure 3. SEM images of unmodified and modified hemp fiber samples: a) C, b) L5, c) L60, d) H5 and e) H45.

Changes in hemicelluloses and lignin content which are result of chemical treatment by alkaline or sodium chlorite, have influence on hemp fibers structure (surface pore structure, morphology and crystallinity) and sorption properties [12]. Changes in fiber surface and structure can be ascribed not only to the decrease of lignin or hemicelluloses content, but also to the location of these components in the hemp fiber. Lignin is located in the middle lamellae and secondary wall of hemp fibers and with pectins can be more or less strongly associated with the cellulose microfibrils. During the oxidation treatment lignin is selectively removed, resulting in more homogenous middle lamella due to the gradual elimination of micro-pores and the less rigid cell wall. Removal of lignin is accompanied by fibrillation and formation of new capillary spaces in inter-surfacial layer between completely or partially separated elementary fibers. In the other hand, hemicelluloses are deposited in amorphous areas of fiber structure and occupy spaces between the fibrils in primary and secondary walls. When the hemicelluloses were gradually removed, by alkaline treatment, inter-fibrillar regions become less dense and rigid and thereby make the fibrils more capable for rearrangement [2,6,10]. Removal of hemicelluloses and lignin from hemp fibers were followed by peeling of their surface and fiber fibrillation. The SEM photographs of unmodified (sample C) and modified (samples L5, L60, H5 and H45) hemp fibers surfaces, are presented on Figure 3. Surface of unmodified hemp fibers is relatively uneven and fibril bundles within the fiber seems to be embedded in resinous substances (matrix of hemicelluloses, lignin and some pectins) (Figure 3a). Through the progressive removal of lignin, surface peeling of fibers is very intensive and roughness of fiber surface was increased (Figure 3b and 3c). After the alkali treatment, there was uneven surface peeling in various areas along the fiber (Figure 3c and 3d). Also, both treatments lead to liberation of elementary fibers, which is slightly more pronounced in the case of alkaline treatment.


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EVALUATION OF TENSILE PROPERTIES AND FLEXIBILITY OF UNMODIFIED AND MODIFIED HEMP FIBERS In order to obtain usable strength information many aspects of hemp fiber’s morphology should be considered. As a natural bast fiber, hemp shows great variation in fiber diameter even within a single fiber. The fiber surface appears relatively rough and uneven, with small fibrillar ends pointing away from the surface. Due to these irregularities, there are large variations in breaking strength data and assessing tensile strength is a multidimensional problem. Measuring tenacity of single fibers gives the most precise results, but the process is laborious and time-consuming. Many fibers should be tested to obtain representative values, because of wide variations in the tenacity of single fibers (coefficient of variation range up to 30 % after 200 tested fibers [2]). Keeping in mind the all above mentioned, it is reasonable to measure the tenacity of fiber bundles, which give average values. However, an important effect must be taken into consideration: the fibers with shortest elongation will break first, decreasing the size of the bundle cross-section. This effect results in too low tenacity values. For better understanding of this effect, different fineness bundles (bundles containing different number of fibers) and different lengths should be tested. The bundle tenacities decrease with reducing of bundle fineness and increasing test length. These are consequence of two reasons. First, the fiber strength is related to the number of weak places along the axis in the bundle. Second, with increased test length, the number of fibers held only at one end will increase. In order to obtain numeric values which require much less time and skill, and, in the same time, permit good description and comparison of the tensile properties of unmodified and modified hemp fibers, as result of investigated influence of measuring conditions on the tensile properties of hemp fibers, an original method based on the use of tenacity of 500 tex fiber bundle extrapolated to zero-test length was developed and applied by Kostic and co-workers [2]. It is very important to note that values obtained for flat bundle tenacity extrapolated to the zero test length show a high correlation with values measured on single fibers. The bundle strength of unmodified and modified hemp fibers is shown in Table 2. Presented results show the decrease in tensile strength of the modified hemp fibers with increasing time of treatment, which is more pronounced for the alkali treated samples. This pronounced drop in tenacity of alkali treated hemp fibers can be explained by the removal of hemicelluloses accompanied by swelling and shrinkage of the ultimate cells, which result in some disorientation of the fibrils. Such a loss in fibrillar orientation is mainly responsible for the observed significant decrease in tenacity, as well as a poor and ineffective stress transfer among disoriented fibrillar network. The same decrease in tenacity of chemically textured fibers was also observed during chemical texturing of jute fibers by Mukherjee and coworkers [43]. Hemp fibers oxidation induce only slight drop in tensile strength which is the consequence of the middle lamella homogenization. The both oxidative and alkali treatment yielded higher flexibility of modified than unmodified fibers (Table 2). Changes in flexibility with certain treatments reflect changes in chemical composition (part-removing of lignin and other noncellulosic substances) and structure (fibrils rearranging) [2].

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Mirjana Kostic, Marija Vukcevic, Biljana Pejic et al. Table 2. Mean tenacity and flexibility of unmodified and modified hemp fibers

Samples C H5 H45 L5 L60

Tenacity (cN/tex) 23.97 12.35 8.11 20.69 17.68

Flexibility (cm) 3.51 5.48 7.13 7.00 6.92

INFLUENCE OF HEMICELLULOSES AND LIGNIN REMOVAL ON VOLUME ELECTRIC RESISTANCE OF HEMP FIBERS Unmodified hemp fibers have exceptionally low electric resistance in comparison with other natural and synthetic fibers [44]. Data obtained during the experiments (Figure 4) showed that with increase of modification times (i.e., degree of hemicelluloses and lignin removal), the volume electric resistance of all samples of modified fibers increased in comparison with the volume electric resistance of unmodified fibers. Increase of volume electric resistance of hemp fibers modified with sodium hydroxide (i.e., hemicelluloses removal) was higher than for fibers modified with sodium chlorite (i.e., lignin removal). Values of volume electric resistance, at standard relative humidity (65 %), were 34–285 times and 3–3.5 times higher for hemp fibers modified with alkali and chlorite, respectively, than for unmodified fibers. In the case of lower relative humidity, increase of volume electric resistance for modified hemp fibers in comparison to unmodified fibers is more pronounce. Volume electric resistance of alkali modified fibers for all modification time, at 45% relative humidity, was about 57–58 % higher in comparison with values obtained for the same samples at 65 % relative humidity (Figure 4). Volume electric resistance for samples, from which lignin was gradually removed, was higher about 56–66 % at 45 % relative humidity than at 65 % relative humidity (Figure 4). This can be explained by influence of relative humidity on partly ionization of water molecules, which were around the fibers, and neutralization of electric charges on fibers surface by these molecules. Furthermore, according to literature data [45,46] moisture and amorphous regions of the fibers are the most important factor in determining their resistance. Hemp fibers with higher moisture content and greater amorphous fraction, i.e., hemp fibers from which hemicelluloses were removed (H5 and H45), have higher volume electric resistance in comparison with unmodified or fibers from which lignin was removed gradually (L5 and L60) [30]. This indicates that electric resistance of hemp fibers is mainly determined by their chemical composition, i.e., content of noncellulosic substances, namely hemicelluloses. Furthermore, detailed comparison of the results from the literature [44] for cotton, viscose, flax and hemp shows that they are in reasonable agreement with the assumption that the low electric resistance values of hemp fibers are consequence of deposited noncellulosic substances (i.e., hemicelluloses, lignin). Obtained results show that hemp fibers with good levels of the comfort properties are acquired as a result of the noncellulosic substances removal.


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Figure 4. Dependence of volume electric resistance on relative humidity of unmodified and modified hemp fibers.

SURFACE PROPERTIES OF UNMODIFIED AND CHEMICALLY MODIFIED HEMP FIBERS The alteration of hemp fibers chemical composition also affects specific surface area and the amount and accessibility of functional groups present at the hemp fiber surface. Table 3 summarized the values of specific surface area, amount of carboxyl, Q(COOH), and carbonyl, Q(COH), groups, as well the pH values of the point of zero charge for all, unmodified and modified, samples. Although, hemp fiber samples do not have a developed specific surface area (Table 3), pronounced fibrillation induced by longer oxidative and alkali treatment leads to specific surface area increase. Both chemical treatments used, at first, remove the accompanying components from the fiber surfaces, which lead to the liberation of the functional groups, and increasing their amount. Therefore, samples L5 and H5, obtained by shorter treatments, have increased amount of functional groups (Table 3). On the contrary, samples L60 and H45 contain reduced amount of functional groups, compared to L5 and H5. As the hemicelluloses and lignin contain a considerable amount of functional groups, pronounced removal of these components by increased modification time, as in the case of samples L60 and H45, leads to decrease in the amount of functional groups. Additionally, the influence of chemical modification on the acid-base behavior of tested hemp fiber samples was examined through the PZC determination. Point of zero charge pH is a pH of the solution at which the overall observed charge on the hemp fibers surface is zero. When the sorbent is kept in a solution having pH less then pHPZC, the protonation of functional groups occurs and the sorbent behaves as positively charged. At this point functional groups repel the positive ions. An increase in pH above pHPZC makes the functional groups deprotonated, they act as negative species and attracts and binds positive ions. The PZC pH values of the short hemp fiber samples were found to be in the range

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between 3.8 for L5 and 4.6 for L60 (Table 3). These results are in agreement with the amount of surface functional groups hence the highest amount of acidic functional groups leads to the more acidic surface of short hemp fiber sample. Furthermore, for all tested samples the PZC is below pH 5.0, demonstrating the predominantly negative surface charges that will attract the positive ions, i.e., hemp fibers can be used as a sorbent for metal ions [41]. Table 3. Surface characteristics of short hemp fiber samples Sample

SBET (m2/g)

C L5 L60 H5 H45

0.236 0.217 0.312 0.185 0.258

Amount of functional groups (mmol/g) Q(COOH) Q(CHO) Q(COOH)+Q(CHO) 0.535 0.052 0.587 0.606 0.031 0.637 0.525 0.021 0.546 0.571 0.048 0.619 0.527 0.071 0.598

pHPZC 4.4 3.8 4.6 4.1 4.3

DEGREE OF SWELLING AND WATER RETENTION CAPACITY OF HEMP FIBERS Lignocellulosic fibers are, generally, hygroscopic and have an affinity to water. Water is able to permeate into the non-crystalline portion of cellulose and all of the hemicelluloses and lignin. Thus, through adsorption and absorption, aqueous solution comes into contact with a very large surface area of different cell wall components [12,47]. Accessibility of the cell wall components to aqueous solutions is very important for the adsorption from aqueous solutions, and can be assessed by determining the degree of fiber swelling and water retention value. The degree of fiber swelling yields information on the extent of areas accessible to aqueous solutions within hemp fiber. Changes in the degree of fiber swelling of modified hemp fibers reflect changes in chemical composition, crystallinity and pore structure. According to the literature [12], oxidized and alkali modified hemp fibers swell faster than unmodified. Maximum swelling of unmodified hemp fibers is attained after 10 min from immersing in water, while all modified hemp fibers attained maximum swelling already after 5min. Also, from the results presented in Table 4, it is evident that the degree of swelling of all modified samples is higher in relation to the unmodified hemp fibers. The increase of the degree of swelling of hemp fibers modified with 17.5 % NaOH is the most likely consequence of removing the hemicelluloses from interfibrillar regions, followed by swelling and shrinkage of ultimate cells, which result in some disorientation of the fibrils and changes of amorphous and crystalline regions ratio, in favor of amorphous ones [8,12]. Also, during alkaline treatment of hemp fibers, lignin content decreased for 7–11 % (Table 1), which together with the removal of fats and waxes, influences to a certain degree the increase of modified hemp fibers swelling. The degree of swelling of hemp fibers samples H5 and H45 is higher for 77 % and 130 %, respectively, in relation to the unmodified fibers. The increase of degree of hemp fiber swelling with the increase of time of treatment is very pronounced, and can be explained by removing the hemicelluloses and hydrophobic components during the alkaline treatment. Once when hemicellulosic components have been progressively removed, interfibrillar regions become less dense and less rigid, which with the greater content of

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amorphous regions enable easier penetration of larger quantity of water molecules into hemp fiber structure. The degree of swelling of hemp fiber samples treated with 0.7 % NaClO2 samples, L5 and L60, is higher for about 68 % and 78 %, respectively, in relation to the unmodified fibers. In hemp fibers modified with 0.7 % NaClO2 progressive removal of lignin occurred mostly in the middle lamella. The decrease of lignin content for almost 50 % and of hemicelluloses for approximately 17 % influenced changes in hemp fiber structure; these changes influence an increase of degree of swelling in relation to the unmodified fibers. In this case the duration of hemp fiber treatment did not influence the change of degree of swelling to a large extent. It can be noted that the degree of swelling of oxidized samples, is lower in relation to the alkali treated fibers degree of swelling. That could be ascribed to the fact that in this case a greater part of hemicelluloses remained in the interfibrillar regions and their densities have not been reduced as in fibers treated with 17.5 % NaOH, which caused more difficult penetration of water molecules in these regions [8,42]. Table 4. Degree of swelling (DS), water retention (WRV) and iodine sorption values (ISV) for unmodified and modified hemp fibers Sample C H5 H45 L5 L60

DSeq (%) 35.61 54.17 70.48 51.27 53.17

ISV (mg/g) 69.09 58.72 44.91 252.2 212.4

WRV (%) 59.67 72.41 78.42 60.67 50.67

When hemp fibers are immersed in water they swell and imbibe considerably more water than they are capable to hold. The total water holding capacity of a fiber can be estimated by determining water retention values. All water absorbing and holding surfaces, cracks, and cavities are included with the water retention measurement. Water retention values for all samples tested are shown in Table 4. Compared to the unmodified samples, the alkali treatment (hemicelluloses removal) yielded the same or lower water retention values. Hemp fiber sample H5 has an almost unchanged water retention capacity in relation to unmodified fiber (sample C). With an increase of modification time, water retention value decreases so that the sample H45 has approximately 15 % lower water retention value in relation to the unmodified sample. The decrease of water retention value of hemp fibers modified with 17.5 % NaOH with an increase of modification time is a consequence of structure changes, i.e., changes in the size and number of pores and microcracks in fibers during their modification. It is also worth to mention that this treatment reduces the content of hydrophilic components, hemicelluloses and pectins. The effect of lignin removal on water retention value was significant, since removing about 50 % of lignin results in 20 % more water kept by modified hemp fibers in comparison with unmodified fibers. The higher water retention values of hemp fibers with lower lignin content can be explained by lignin removal from the middle lamella followed by fibrillation. Occurred fibrillation increased the roughness of hemp fiber surfaces and induced new capillary spaces in inter-surfacial layer between completely or partially separated fibers within the modified technical hemp fiber [8,13,42]. The iodine sorption value is empirical measure of cellulose accessibility to aqueous solutions in the fiber amorphous areas due to the fact that the mechanism of iodine sorption

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differs from water sorption, i.e., three-iodide ions (built up when an iodide ion is added to an iodine molecule) are preferentially adsorbed in a monomolecular layer, whereas additional water molecules are bound to the water monomolecular layer by hydrogen bounds. Therefore, the iodine sorption value is inversely proportional to the fiber crystalline phase (crystallinity index-CrI) [48]. The obtained data showed that hemicelluloses removal increased the iodine sorption of H5 and H45 samples for more than two times, compared to unmodified fibers (sample C). On the other hand, after the removal of lignin from hemp fibers by chlorite treatment (samples L5 and L60), value for iodine sorption decreased for 15-35 %, compared to sample C (Table 4). This suggests that removing the hemicelluloses leads to an increase in the amorphous area in the structure of hemp fiber, while the progressive removal of lignin leads to increased crystallinity index.

INFLUENCE OF CHEMICAL COMPOSITION OF HEMP FIBERS ON THEIR CAPILLARITY Capillary properties of hemp fibers may have importance when selecting the use of end products. Good capillarity of fibers can be of advantage in products in which a good absorption capacity and/or speed is needed. Also it allows the fiber to absorb moisture, liquids, lubricants, finishes, and stem, permitting faster bleaching, dyeing, impregnating, etc. [49,50]. Capillarity can be defined as the macroscopic movement of a fluid system under the influence of their own surface, difference in pressures and interfacial forces. Equilibrium will happen when the capillary action is balanced by gravity, that is, by the weight of the raised liquid [50]. The evaluation of capillarity of fibers depends to a large extent on the measuring conditions. Also, as a natural bast fiber, hemp showed great variation in chemical composition and fiber diameter even within a single fiber. For this reason, several series of experiments have been done using different number of fibers (single fibers and fiber bundles) and wetting liquid (0.1 % aqueous solution of eosin (viscosity 1.03 x 10-3 Pa s) and transformer oil (viscosity 28.84 x 10-3 Pa s)). The wetting liquids were chosen based on their different polarity and affinity towards hemp fibers. Measuring capillarity of single hemp fibers gives the high coefficient of variation [8] because of the fact that hemp fiber as a natural bast fiber, showed great variation in fiber diameter even within a single fiber, and the fiber surface appeared relatively rough and uneven, with small fibrillar ends pointing away from the surface. These irregularities affect the liquid front movement, i.e., the flow in a capillary space may stop when geometric irregularities allow the meniscus to reach an edge and flatten. From the data presented in Table 5 it is evident that the value of equilibrium height (heq) of capillary rise is different for single fibers and fiber bundles, but the tendency is the same. The increase of heq in the hemp fibers bundles, in relation to the single fibers, is caused by an additional capillary effect, which appears as a consequence of interfacial capillary forces formed between fibers within the bundle. Taking this in consideration and in order to obtain numeric values which permit good description and comparison of the capillarity of unmodified and modified hemp fibers, it is very important to prepare fiber bundles in the same manner, which will minimize influence of fibers alignment and spaces between fibers in

415


the bundle on the obtained results. The applied capillary rise method provides the collective measurements of simultaneous wetting of the fiber surface, liquid uptake in the pore structures – capillary penetration, adsorption on the fiber surface, and liquid absorption within the fibers [50]. The sorption of the liquid into the fibers can cause their swelling, reduce capillary spaces into the fibers and close smaller pores, and complicate kinetics. Influence of chemical composition changes on the fiber capillarity can be misinterpreted if the effects of sorption into the fibers are overlooked. By the removing hemicelluloses and lignin, the fiber bulk structure and moisture sorption (Table 5) were changed, and it is expected that both untreated and treated fibers have different swelling tendency [8]. In order to quantify the individual contributions of wettability, sorption properties and pore structure to liquid transport and retention properties of hemp fibers, two series of experiments using different wetting liquids: 0.1 % aqueous solution of eosin and transformer oil, were set up. Transformer oil was selected because it has no affinity towards hemp fibers and under these measuring conditions the rise of the liquid can be attributed only to capillary effect caused by the fiber surface properties and fiber micro-porosity. Results of capillary rise in single fiber and fiber bundles of unmodified and modified hemp fibers are shown in Table 5. Evidently, the capillary rise is strongly enhanced by fiber modification (i.e., hemicelluloses and lignin removal). According to the literature [8], in the case of eosin solution, the equilibrium value is attained up to 2000 s, and for transformer oil up to 120 s. The capillary rise of eosin solution for modified fibers is increased in relation to initial fibers. The oil capillary rise in modified fibers also manifests a trend of growth, in relation to unmodified fibers. For the aqueous solution of eosin, it is obvious that we have sorption of the liquid into the fibers and fibers swelling, leading to reducing capillary spaces into the fibers and higher capillary pressure in smaller pores, i.e., higher equilibrium capillary rise of water in comparison with transformer oil [8]. The capillary principles dictate that the distance of liquid advancement is greater in a smaller pore because of the higher capillary pressure, smaller pores are filled first and are responsible for the liquid front movement, i.e., the smaller the pore radius, the equilibrium height is greater, and the more time is needed for liquid to reach the equilibrium height. Considering presented results, together with the capillary principles, it is obvious that gradual removal of lignin leads to faster liquid spreading in fibers facilitated by small, uniformly distributed and interconnected pores. Table 5. Capillary rise data for single hemp fibers and fiber bundles and moisture content of unmodified and modified hemp fibers

Sample C H5 H45 L5 L60 *

0.1 % eosin heq (mm) s.f. 8.8 29.2 40.4 29.6 29.4

f.b. 28.4 49.4 43.6 62.0 76.4

s.f. – single fiber; f.b. – fiber bundle.

Oil heq (mm) s.f. 9.8 13.2 24.8 25.0 35.8

f.b. 17.0 17.6 30.4 22.4 40.4

Moisture content (%) 8.40 8.76 9.22 7.17 6.91

416


From the liquid capillary rise height time dependence, coefficient of capillary diffusion can be determined on the basis of the general wettability relationships [51], as it is described below. In the equilibrium, the maximum height heq of the front of capillary rise is defined by

heq 

2    coseq   g  RS

(1)

where γ is the surface tension and ρ the density of the liquid, Rs the average static radius of pores, g the acceleration due to gravity (9.81 m/s2), and heq is the equilibrium, static contact angle, which is generally smaller than the dynamic contact angle. At the beginning of the process, when the height reached by the liquid – h is much smaller than heq, the hydrostatic pressure can be neglected and h2 is proportional to time

h2  D  t

(2)

where the slope D presents the coefficient of capillary diffusion, directly related to the average equivalent radius of the capillaries in porous fiber structure, chemical composition of fiber surface and physico-chemical characteristics of the liquid [51]. In the case when h is close to heq, the hydrostatic pressure cannot be neglected and by introducing the approximation that θ = θeq, the following equation is obtained:

heq  ln

h

heq

eq

 h

h

RD2    g t 8 

(3)

where RD is the average hydrodynamic radius of pores, and η the liquid viscosity. This equation can be presented, as [51] suggested, in a simplified form

H  C t

(4)

Graphical presentation of the function H = f(t) is the straight line with the slope C being dependent only on the size of the capillaries in fibers and to the nature of the liquid. As the measure of validity of the assumption θ = θeq the following ratio can be used:

R

cos D  cos eq 2  C  heq

(5)

This ratio is always smaller than 1, because of the fact that θ is generally larger than θeq. By processing of obtained data, i.e., the liquid capillary rise height vs. time up to the equlibrium height is reached, through Eqs. (2), (4), and (5), and drawing corresponding curves, all three parameters of wettability (D, C and R) were determined. The coefficient of capillary diffusion D is clearly affected by the removing either hemicelluloses or lignin. For modified hemp fibers, the value of coefficient D significantly increases in relation to the unmodified fibers, and this increase is more pronounced in the case

417


of fibers with lower lignin content. The results of coefficient C, that can be made equal to the wetting rate, are spread in a range from 0.02 to 1.26 mm/s (Table 6), suggesting some influence of the lignin and hemicelluloses removal on the wetting rate of modified hemp fibers. It is also obvious that the increase of coefficient C of modified hemp fibers, in relation to the unmodified fibers, is much smaller in the case of hemicelluloses removal than lignin removal. Table 6. Values of coefficients D, C and R for unmodified and modified hemp fibers Sample C H5 H45 L5 L60

0.1 % eosin D (mm2/s) 1.03 5.49 1.68 13.82 25.37

C (mm/s) 0.02 0.07 0.03 0.16 0.25

R 0.91 0.79 0.77 0.69 0.66

Oil D (mm2/s) 4.55 7.45 12.89 15.46 17.42

C (mm/s) 0.27 0.49 0.39 1.26 0.34

R 0.49 0.43 0.54 0.27 0.64

The trend of coefficients D and C of hemp fibers modified with sodium hydroxide listed in Table 6 most likely can be ascribed to the greater influence of structural changes in hemp fibers, in comparison to the changes in the hemicelluloses content. The R values, mostly range from 0.7–1.0, confirm well enough the validity of assumption θ = θeq in the case of wetting with eosin solution, while the values of R are lower and more scattered in the case of transformer oil. From results obtained, it is clear that changing hemp fiber chemical compositions alter its porous structure and capillarity properties. These changes can be ascribed not only to the decrease of lignin or hemicelluloses content, but also to the influence of the location of these components in the hemp fiber structure. Treatments directed towards modification of fiber surfaces bring about changes of pore diameter and of the contact angle, both of them influencing variation of capillary rise heights and capillary diffusion coefficients. These changes are more pronounce in the case of lignin removal and impose the conclusion that gradual removal of hemicelluloses most likely induces smaller changes of the fiber surface than gradual removal of lignin. This circumstance can be explained by the facts that removed hemicelluloses were located in the inter-fibrillar regions inside ultimate cells and that lignin which was partly removed with 0.7 % NaClO2 fulfilled the middle lamella joining ultimate cells. Also, reason for this probably lies in the fact that when hemp fibers are treated with 17.5 % NaOH, hemicelluloses are progressively removed, making the interfibrillar regions less dense and rigid and thereby make the fibrils more capable to rearrangement. The removal of hemicelluloses is accompanied by swelling and shrinkage of ultimate cells, which result in some disorientation of the fibrils and texturing of hemp fibers [2,6,10]. In the case of lignin removal, occurred fibrillation induced new capillary spaces in inter-surfacial layer between completely or partially separated fibers within the technical modified hemp fiber. Due to fibrillation increased the roughness of hemp fiber surfaces can promote wetting by decreasing apparent contact angle, even the intrinsic wettability of the fibers remains the same. From the other side, when hemp fibers are treated with 0.7 % NaClO2 and lignin is removed gradually; the middle lamella joining the ultimate cells is expected to be more homogenous due to the gradual elimination of micro-pores, while the

418


ultimate cells themselves are affected only slightly. According to the literature [6,10] there is no appreciable loss in molecular orientation in delignificated hemp fibers.

BIOSORPTION OF HEAVY METAL IONS FROM AQUEOUS SOLUTIONS BY SHORT HEMP FIBERS The increased production of hemp fibers brought about an increase in the amount of waste, namely shives, short and entangled fibers. Due to the good sorption properties of hemp fibers, it is very convenient to use these waste fibers as biosorbents. The biosorbents have proved to be an efficient alternative to conventional sorbent [52-57]. The term “biosorbent” includes the usage of dead biomass (such as fibers, peat and rice hulls) as well as living plants and bacteria as sorbents. Biosorbents represent cheap filter materials often with high sorption affinity and capacity, and they are already available in most places. Some types of biosorbents are broad range with no specific priority of metal ion bonding, while others can be specific for certain types of metal ions. There are some limitations pertaining to the usage of living organisms as sorbents, e.g., they cannot function at low pH level, or at toxic levels of metal ions, while plant fibers on the contrary are chemically and physically more robust [52,53,58]. Hemp fibers consist mainly of cellulose, hemicelluloses, lignin, some pectin and extractives (fat, waxes, etc.). Strong bonding of metal ions by carboxylic (primarily present in hemicelluloses, pectin and lignin), phenolic (lignin and extractives) and to some extent hydroxylic (cellulose, hemicelluloses, lignin, extractives and pectin) and carbonyl groups (lignin) often involves complexation and ion exchange [12,42]. Biosorption is not restricted to one sorption mechanism only, but comprises several mechanisms such as ion exchange, chelation, precipitation, sorption by physical forces, and ion entrapment in inter- and intrafibrillar capillaries and spaces of structural lignin and polysaccharide networks. Therefore, biosorption of heavy metal ions by lignocellulosics is affected by several factors such as initial pH, initial metal ion concentration, contact time, temperature, fiber pretreatment, etc. [12]. The pH value of the heavy metal ions solution is one of the key parameters that may influence sorption process. The pH of the biosorption medium affects the solubility of metal ions and the ionization state of the functional groups of the hemp fibers. Because of high proton concentration at lower pH, heavy metal biosorption decreases due to the positive charge density on metal binding sites (i.e., hydrogen ions compete effectively with metal ions in binding to the sites) and at a low pH, of almost 2.0, all binding sites may be protonated, thereby desorbing all originally bounded metals from the fibers. The negative charge density on the fiber surface increases with increasing pH due to deprotonation of the metal binding sites. The metal ions then compete more effectively for available binding sites, which increase biosorption. The high sorption levels for the short hemp fibers between pH 4.0 and 5.5 indicate that a high affinity for Pb2+, Zn2+ and Cd2+ predominates in this pH region, with maximum sorption at pH 5.5 [12]. Biosorption capacity is also affected by concentration of the metal ions in the sorption medium, and the time of contact between biosorbent and metal ions solution. Maximum metal ions uptake of unmodified (C) and modified hemp fibers (H5, H45, L5 and L60) increases approximately 4 times, with increase of the initial metal ion concentration from 0.05 to 0.2


419

mmol/L [12]. The biosorption of Cd2+, Pb2+ and Zn2+ ions is very fast in the beginning, since approximately more than 80 % of ions are sorbed in the first 5 minutes, after which sorption process slows down and the amount of sorbed metal ions do not change significantly with an increase in contact time. The generally fast sorptions indicate that reactions at outer surfaces are important [12]. Also, the total uptake capacity of Cd2+ and Zn2+ ions is increased by hemp fibers modification (i.e., the separate removal of hemicelluloses and lignin), while at the same time the total uptake capacity of Pb2+ ions is almost unchanged. The maximum sorption capacity of 0.078 mmol/g for all tested ions was obtained for sample L60 (Figure 5). Data obtained from modification experiments indicated that modification with sodium chlorite (i.e., removal of lignin) resulted in better improvement in biosorption capacities compared to alkali modification. This can be explained by the domination of sorption at outer surfaces of fibers, as we mentioned earlier, and increased the roughness of hemp fiber surfaces and induced new capillary spaces in inter-surfacial layer between completely or partially separated fibers due to the removal of lignin from the middle lamella, followed by fibrillation. Also, sodium chlorite oxidation of residual lignin that caused benzene ring cleavage and formation of dicarboxylic groups [40] should not be neglected. Taking in consideration all above mentioned and complexity of the structure and composition of hemp fibers, a simple relation between the lignin and hemicelluloses contents and the sorption capacity could not be demonstrated. The results of the total uptake capacity of Cd2+, Pb2+ and Zn2+ ions for non-competitive conditions indicate that all samples exhibit capacities which are influenced by the investigated metal ion, but these differences are significant only at the highest ions concentration (0.2 mmol/L). This is because the ratio of the initial quantity of metal ions moles to the available binding sites is low at lower concentration and subsequently the sorption is less dependent on metal ion affinity. The exception is the sodium chlorite modified sample (L60) with the same affinity for Cd2+, Pb2+ and Zn2+ ions. The selectivity of unmodified and modified hemp fibers for metal ions is more pronounced and can be easily seen in the case of simultaneous biosorption of the ternary mixture, in which three metal ions compete for a limited number of binding sites (Figure 5). The biosorption capacities of hemp fibers in the presence of the ternary mixture were lower for Cd2+ and Zn2+ ions than those for noncompetitive conditions, and almost the same for Pb2+ ions. Also, an increase in metal ions concentration from 0.1 to 0.2 mmol/L in the competitive conditions caused about a twofold increase in the total uptake capacity of Pb2+ ions, while the total uptake capacities of Cd2+ and Zn2+ ions stayed almost unchanged (Figure. 5). The order of the affinity for competitive conditions was as follows: Pb2+ >Cd2+ >Zn2+ [12]. The maximum uptake capacity and efficiency of metal ions removal from the ternary mixture was obtained for the sample L5. Nevertheless, it can be noted that sorption capacity of all tested samples is proportional to the amount of functional groups (see Table 3). This suggests that amount of hemp fibers acidic functional groups have dominant influence on the metal ions biosorption, since they act as an active cites for adsorption. Beside the amount and accessibility of functional groups, the process of biosorption is also influenced by their surface distribution i.e., surface homogeneity [41].

420


Figure 5. Total heavy metals uptake capacity of unmodified and modified hemp fibers.

For the better understanding of biosorption process, sorption equilibrium data were treated with Langmuir and Freundlich adsorption isotherms. In order to calculate isotherm parameters, the linear regression analysis was the most commonly used method. However, linearization of such data distorts the experimental error, and the suitability of isotherm models to describe experimental data, is determined only on the marginal differences between correlation coefficients. Therefore, the non-linear form of Langmuir and Freundlich adsorption isotherms were used for isotherm parameters calculation, and the model which is best supported by experimental data is selected by model selection criteria e.g., Akaike information criterion (AIC). AIC is able to answer the question: which model is better for mathematical description of experimental data. On the bases of the results presented in Table 7 we can conclude that shorter time of modification, favor higher values of adsorption capacity and greater homogeneous distribution of active sites for adsorption on the surface of hemp fiber. For all tested samples values of 1/n were less than unity which indicates that the biosorption of zinc on short hemp fibers is a chemical process. This also suggests that biosorption of zinc is predominantly occur through the ion exchange reaction on the functional groups. Adsorption kinetic data obtained using zinc ions as a model of heavy metal ion were analyzed by pseudo-first and pseudo-second order kinetic models, and the best fitting model is chosen using Akaike information criterion [41]. In order to determine the rate-controlling

421


step in the overall process of biosorption, kinetic data were examined by intraparticle diffusion model. The values of the equilibrium amount of zinc adsorbed calculated by pseudo-first and pseudo-second order models, are compared with the experimental data (Table 8.). The calculated values were fitted with the experimental data by minimizing the squared magnitude of the residuals of the amount of zinc adsorbed. The optimal model parameters: qe.cal and k1 for the pseudo-first, and qe.cal and k2 for the pseudo-second order models, obtained by this fitting procedure, have enabled the best comparison with the experimental data. The values of the model parameters, Akaike information criterion and the standard deviation are shown in Table 8. These results show that biosorption of zinc ions on all tested short hemp fiber samples predominantly follows the pseudo-second order kinetic model indicating that adsorption/binding of zinc ions on hemp fibers is mediated by chemical forces rather than physical forces of attraction. Table 7. Corrected Akaike information criterion, standard deviation and Langmuir and Freundlich isotherm parameters for zinc ions adsorption on unmodified and modified hemp fibers samples Sample C L5 L60 H5 H45

Langmuir Q0 (mg/g) 8.0 8.3 7.1 8.1 7.4

b (l/mg) 0.200 0.164 0.322 0.226 0.231

AICc 3.317 6.474 -2.166 5.169 4.109

std 0.135 0.365 0.053 0.333 0.254

Freundlich 1/n Kf 0.390 2.100 0.470 1.606 0.331 2.300 0.420 2.101 0.381 2.046

AICc 5.487 6.995 5.679 6.085 3.362

std 0.253 0.328 0.3228 0.393 0.211

Table 8. Corrected Akaike information criterion, standard deviation and kinetic parameters obtained by pseudo-first order and the pseudo-second order kinetic models for zinc ions adsorption on unmodified and modified hemp fibers samples, for initial zinc ion concentration of 0.1 mmol/l Sample C H5 H45 L5 L60

Pseudo-first order k1, (min-1) qe. cal, (mg/ g) 0.30 2.210 0.20 2.500 0.21 2.378 0.28 2.431 0.30 2.353

AICc -1.352 1.281 1.051 -0.141 -0.206

std 0.147 0.265 0.257 0.190 0.181

Pseudo-second order k2, (min-1) qe. cal, (mg /g) 0.51 2.195 0.40 2.479 0.38 2.400 0.42 2.453 0.55 2.350

AICc -8.336 -5.168 -8.308 -4.548 -6.027

std 0.027 0.054 0.026 0.057 0.029

qe. exp, (mg /g) 2.193 2.454 2.393 2.505 2.444

In order to investigate the diffusion mechanism during the biosorption process, experimental data was tested by the intraparticle diffusion model. Figure 6 shows the plots of qt versus t1/2 for sample H5 and for zinc initial concentrations of 0.1 and 0.2 mmol/dm3.

422


Figure 6. Intraparticle diffusion plots of the zinc ions onto sample H5 at various initial zinc ions concentration.

The initial stage, addressed to external surface adsorption is quite fast, which is expected in the well shaken system. The second step is assigned to moderate intraparticle diffusion while final slow step corresponds to the equilibrium adsorption process, where the intraparticle diffusion starts to slow down due to the extremely low solute concentration in solution. The rates of adsorption observed at different stages of the process indicated that the adsorption rate was initially very fast and then slowed down as time progressed. Obtained multi-linearity in the intraparticle diffusion curves and the fact that the second and the third linear part of the curves did not pass through the origin, suggests that the intraparticle diffusion is not the only rate-controlling step in the overall adsorption process. As the external mass transport is much faster than the diffusion of heavy metal ions through the fibers, the adsorption rate mainly depends on the diffusion of metal ions through the porous structure of hemp fibers and adsorption at interior active sites. In order to describe the mechanism of adsorption and ion transport from water solution through the hemp fibers, mathematical model has been developed [42] and used for modeling the heavy metal ions adsorption on hemp fibers.

(CD

MATHEMATICAL MODELING OF HEAVY METAL IONS , ZN2+AND PB2+) BIOSORPTION BY CHEMICALLY MODIFIED SHORT HEMP FIBERS

2+

Mathematical model that describes phenomena of different ions (Pb2+, Cd2+ and Zn2+) transport through the porous fiber matrices was developed to determine the profile of heavy metal ion concentration in fibers and optimize the biosorption of heavy metal ions by short hemp fibers. Since the hemp fibers sample L5 showed the highest efficiency in heavy metals removal [12], the mathematical model was developed based on the adsorption results obtained for this fiber sample.


423

Mathematical model, formulated for the phenomenological description of the biosorption of metal ions from the aqueous solution by the fibers, is based on the second Fick’s low, and represents the modification of the model developed by Medovic et al. [59]. Diffusion process into the fibers was approximated as mass transport process in the very long cylindrical body with radius R. The model of biosorption process describes the change of metal ions concentration in swollen fibers. The last one is due to the fact that the fiber swelling process is much faster than the biosorption of the ions based on our experimental observation. Maximum swelling of fiber sample L5 was attained already after less than 5 min while the highest sorption efficiency for all the three ions from mixture was attained after 60 min [12]. The experimental data of ion concentrations in solution are introduced into the model in order to: (1) determine the effective diffusion coefficient for metal ions within the fibers and (2) predict the profiles of heavy metal ion concentration within the fibers. Balance equation of metal ion concentration change in the fiber is:

1   CF r , t   CF r , t  r  Deff  r  r  t r 

(6)

where:

CF r, t  is ion concentration difference, i.e., C F r, t   C F eq  C F r, t  , C F r, t  is local ion concentration, CF eq is the equilibrium ion concentration, Deff is effective diffusion coefficient of ions in fibers. Deff corresponds to the Stokes-Einsteind diffusion coefficient for the diluted systems (the single ion solutions). In the case of the concentrated system (the aqueous ion mixture) it represents the temporally averaged collective diffusion coefficient. Balance equation of metal ion concentration change in the solution is:

VS

CS t   CF r , t     Deff   t r  

Peff r R

where:

CS r, t  is ion concentration difference, i.e., C S t   C S t   CSeq ,

CS t  is ion concentration in the solution,

(7)

424


C S eq is the equilibrium ion concentration in the solution,

VS is volume of the solution, Peff is the effective interface between fibers and the solution, i.e.,

Peff 

2VF ( R is the radius of already swollen fiber, V F is total volume of the already R

swollen fibers). The boundary conditions for sorption of metal ions from the solution to the fibers are: 1) At t  0 , the initial concentration of metal ion in the solution is CS 0  CS 0 . 2) At t  0 , the initial concentration of metal ion in the fibers for r  R is

C F R, 0  C S 0 .

3) At every t the concentration of metal ion in the fibers for r  R is equal to

C F R, t    t  C S t  , where parameter  t  represents the effectiveness of

sorption. 4) The initial value of parameter

 is  0  1 based on the condition (1).

5) At t  t eq (where the equilibrium time for sorption of metal ions was t eq  60 min

 

the equilibrium concentration of metal ion in solution is C S t eq  C S eq .

 

6) At t  t eq the equilibrium concentration of metal ion in fibers was C F t eq  C F eq (where

C F eq 

the

C

S0

equilibrium

 C Seq  VS VF

ion

concentration

in

fibers

is

equal

to

).

Model balance equation, Eq. (6) is solved analytically by Fourier’s dividing of the variables and using Bessel functions. The general solution of Eq. (6) determines the profile of the metal ion concentration within the fibers. It is expressed as:

CF r, t   CF eq  e  t C1 J 0 ra   C2 N 0 ra  2

(8)

Where:

J 0 ra and N 0 ra  are the Bessel functions, while the parameter a is equal to a

2 Deff

,


425

Deff is the effective diffusion coefficient of metal ions through the fibers,

2 is the specific rate of changes of metal ions concentration. Only the Bessel function J 0 ra  



1  ra    2 k 0 k!  2 

2k

has the exact value for r  0 equal

to J 0 0  1 . On that base, we formulate the particular solution of Eq. (6) as:

 ra 2 ra 4 ra 6  2 C F r , t   C F eq  e  t C1 1     4 64 2304  

(9)

where C1 is the constant which is determined starting from the boundary condition (2) and Eq. (9). The value of C1 is expressed as:

C1 

C Feq  C S 0

(10)

Ra 2  Ra 4  Ra 6 1 4

64

2304

After introducing Eq. (10) into Eq. (9) for r  R we obtain:

C F R, t   C F eq  C Feq  C S 0  e   t 2

(11)

The temporal change of the ion concentration in the solution is expressed from Eq. (11) and the boundary condition (3) as:

C S t    t 

1

The parameter

 C F eq  C Feq  C S 0  e  t  2

(12)

 t  is expressed in accordance with the boundary condition (4). It is

formulated as:

C Feq  C Feq  C S 0  e   t 2

 t  



C S 0  C S 0  C Seq  1  e  t 2



(13)

After introducing Eq. (13) into Eq. (12), following relationship for the concentration of metal ions in the solution is expressed:

426




C S t   C S 0  C S 0  C Seq  1  e   t 2



(14)

Eq. (9) is in the accordance with the boundary conditions 1 and 6. After introducing Eqs. (9), (10) and (12) into Eq. (7) we obtain:

R R 3a 2 R 5a 4   VS C S 0  C Feq  2 16 384  2 4 Peff C Feq  C S 0  Ra   Ra   Ra 6 1 4 64 384

(15)

Effective diffusion coefficient is obtained from Eq. (15) for all experimental conditions using iterative procedure. The procedure is expressed by introducing the error function from Eq. (15) as:

R R 3a 2 R 5a 4   VS C S 0  C Feq  2 16 384   a   2 4 Peff C Feq  C S 0    Ra 6 Ra  Ra  1   4 64 384

(16)

The optimal value of diffusion coefficient is calculated from the condition

2  a  / a aeff  0 such that Deff  2 . a a eff

Mathematical model enables the estimation of metal ion effective diffusion coefficient value and the prediction of the change of the metal ion concentration in the fiber as the function of time and fiber radial distance (profiles of metal ions concentration in fiber). The model prediction values of ion concentration in solution are calculated from Eq. (14). The predicted values are fitted with the experimental data by non-linear least-squares regression, minimizing the squared magnitude of the residuals of the heavy metal ion concentrations in solution. The experimental data and model prediction of Pb2+ ion concentration in single ion solution, the initial ion concentration 0.1 mmol/L, are shown in Figure 7. The similar agreement between experimental data and model prediction of ion concentration in solution for Zn2+ and Cd2+ in the single ion solutions and for all three ions in the ternary mixture was obtained (data not shown here). The optimal model parameter 2 obtained by this fitting procedure that enables the best agreement with the experimental data is given in Table 9. The values of the model parameter 2 are introduced into Eq. (15) in order to estimate the corresponding values of the effective diffusion coefficients. The effective diffusion coefficients are calculated using the iterative procedure described by Eq. (16) and given in Table 9. Additionally, the equilibrium ion concentrations in fibers (CFeq) obtained as a model prediction are shown in Table 9.

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Figure 7. The change of Pb2+ ion concentration in single ion solution during the biosorption obtained by experiment and by mathematical model.

Table 9. Value for effective diffusion coefficient (De), specific rate of changes the concentration of metal ions (2) and equilibrium ion concentration in fibers (CFeq) for Cd2+, Pb2+ and Zn2+ ions in the single ion solutions and ternary mixture of ions Metal ion Cd2+ Zn2+ Pb2+

Single ion solution Deffx1012 2 2 (m /s) (min -1) 10.10 0.179 10.80 0.228 22.80 0.419

CFeqx10-3 (mmol/m3) 16.87 16.35 16.00

Ternary mixture of ions Deffx1012 2 2 (m /s) (min -1) 9.40 0.131 9.45 0.199 9.71 0.205

CFeqx10-3 (mmol/m3) 14.10 12.90 16.00

Both, specific rate of changes the concentration of metal ions (2) and effective diffusion coefficient (Deff) in the single ion solution have the highest value for the lead ions. The effective diffusion coefficient value is affected by thickness of the metal ions solvation layer in aqueous solution, ion-ion (same and different species of ion) and ion-fiber interactions, the surface microporosity and oxidized hemp fibers structure. In the aqueous solution metal ions are surrounded by solvation layer, whose thickness affects the ion transport through the solution. Ions with smaller radius have thicker solvation layer [60], therefore their transport toward the biosorbent surface is slower. Consequently, the diffusion coefficient of these ions is smaller. Also, in the single ion solution initial concentration of metal ions is low enough that mutual ion interaction can be neglected, so the ions keep the solvation layer when entering the fibers. Considering fact that the dimension and share of the interfibrillar spaces in the fiber structure is much higher than the dimension and share of micropores, microcavities and microcracks, further transport of ions through the fiber can be approximated with the transport through the interfibrillar spaces. The interfibrillar spaces are filled with a solution so it can be assumed that the ions keep almost unchanged salvation layer during the transport. Therefore, the ion transport through the fiber and effective diffusion coefficient is affected by

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thickness of the solvation layer. Lead ions that have larger radius compared to cadmium and zinc, and thinner solvation layer, need the shorter time to reach the hemp fibers surface. This is in agreement with the highest value for the lead ion diffusion coefficient in the infinite diluted solution (D0(Pb2+)=10.00x10-10 m2/s, D0(Cd2+)=7.19x10-10 m2/s, D0(Zn2+)=7.10x10-10 m2/s), obtained from the literature [61,62]. In the case of ternary mixture lead ion also has the highest effective diffusion coefficient, but in this case the values of Deff are similar for all three examined ions. Though the initial concentration of each metal ion was the same as in the single ion solution, there were a three times more particles. This is the reason for an intensive collision between the same and different type of ions, during the transport of these ions through the solution and fiber. As a consequence of the mutual interactions, ions lose solvation layer and change the path of transport. Mechanism of ions transport was partially changed compared to the single ion solution, and now it mostly depends from the efficiency of collision. Lead ions have the highest effective diffusion coefficient in both cases. Therefore, lead ions faster reach the surface of the hemp fiber then other two ions, and have a priority of deposition in micropores and microcracks of fibers and penetration into interfibrillar space in fibers structure. Sorbed lead ions can represent the steric obstruction for sorption of other ions. In the next step of mathematical modeling, calculated values of effective diffusion coefficient are introduced into Eq. (9) to determine concentration profiles of heavy metal ions in fiber: for the single-ion solutions and for the mixture of all three ions in solutions. The profiles of zinc ion concentrations in fibers are shown in Figure 8. The similar trend of ion concentration in fibers was obtained for lead and cadmium ions [42]. Effectiveness of sorption (model parameter α), given by Eq (13), could be explained as the measure of biosorption efficiency in regard to increased ion concentration in fibers (Figure 9).

Figure 8. Profile of Zn2+ ions concentration in the fibers depending on time of biosorption for the single ion solution and ternary mixture.


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Figure 9. The dependence between the effectiveness and time of sorption for the single ion solution and ternary mixture.

The biosorption of metal ions depends on: (1) the transport phenomena within the fibers and (2) the resistance effects which arise as the result of the electrostatic interactions between ions within the fibers. The effectiveness of sorption (α(t)) represents the influence of both processes. The effectiveness of sorption (α(t)) is primarily influenced by the transport of ions within the fibers in first 15 min (regime I). However, the resistance of the further transport of metal ions within fibers increases with the increase of the ion concentration in fibers. The resistance of the transport of metal ions within the fibers dominantly influences the biosorption in next 45 min (regime II). During the regime I effectiveness of sorption is higher for the lead ions then for cadmium and zinc, in both single ion solution and in mixture of ions. In the single ion solution the effectiveness of sorption is changed in regime II in favor to the cadmium and zinc ions. On the other hand, effectiveness of sorption value retained the same order for all three ions (Pb2+>Cd2+>Zn2+) in the mixture during the both regime. The effectiveness of sorption of Cd2+ and Zn2+ ions is higher for the single ion solution then for the mixture of ions, while for Pb2+ ion is the similar in both cases. As it is explained earlier [12], in the competitive condition (mixture of ions) short hemp fibers have a best affinity towards lead ions. Therefore, effectiveness of sorption for lead ions will have the similar value in both single ion solution and in the mixture of ions. In the same time, the effectiveness of sorption for Cd2+ and Zn2+ will decrease in the mixture of ions. Proposed mathematical model provides a better insight into phenomena of different ions transport through porous fiber matrices. Consequently, this model may be considered useful in the optimization of the complex process of biosorption. This is from great importance in the case of using short hemp fibers as filter material for removing the heavy metal ions from polluted water.

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HEMP FIBERS WASTE AS A PRECURSOR FOR CARBON MATERIALS Carbon materials with high surface area and pore volumes can be prepared from a variety of carbonaceous materials such as coal, coconut shell, wood, agricultural or industrial wastes. In the recent years, there is a growing interest in utilization of the low-cost and abundantly available waste materials and biomass as precursors for the preparation of carbon materials [63]. The usage of the waste materials represents a special way of recycling and producing useful products. At the same time the cost of waste disposal are minimized. Additionally, carbon sorbents obtained from waste can be used for water purification by removal of specific pollutants, like dyes [64-66], heavy metals [67-69], pesticides [70,71] and phenols [72]. The possibility of using different type of biomass has already been tested for production of the carbon materials [63,65,72-80]. Among other biomass types, Reed and Williams [81] have used hemp fibers for obtaining activated carbon. Hemp fiber is a lignocellulosic material that contains celluloses, hemicelluloses and lignin which are rich in carbon, and therefore presents a good precursor for carbon materials production.

CARBONIZATION OF CELLULOSIC MATERIALS Celluloses based carbon materials are obtained by controlled thermal decomposition of celluloses in the inert atmosphere and undergoes through the two phases. During the pyrolysis of celluloses, that represents the first phase and ends around 400 oC, the large amount of different compounds (CO, CO2, H2O and resinous products) are released. Therefore the weight loss is very high and obtained carbonaceous material contains 60 – 70 % of carbon. Carbonization represents the second phase with the ending temperatures over the 900 oC. During the carbonization the defect graphitic structure is formed and the carbon content is increased over the 90 %. Although the full mechanism of carbonization of cellulose is not understood completely, a summary of some of the chemical aspects of the process given by Bacon and Tang [82] is shown in Figure 10. The pyrolysis of cellulose is controlled mainly by two predominant reactions, dehydration and depolymerization (cleavage). Physical desorption of water is the first processes during pyrolisys, and take place between 25 and 150 oC, followed by dehydration of the cellulosic unit which continues between 150 and 240 oC. The dehydration reaction stabilizes the cellulose structure: during the dehydration, elimination of the hydroxyl groups results in double bonds, conjugated double bonds, and subsequently, in an aromatic structure. The polymeric structure is basically retained through dehydration and at this temperature range weight loss is usually limited to the evaporation of water. Degradation of native cellulose fibers starts at 200 oC and ends around 380 oC, under inert atmosphere. Although the physicochemical processes taking place during the transformation of cellulose into carbon are complex, it is certain that depolymerisation of the macromolecular chains produces a variety of oxygenated compounds. This leads to the major mass loss of the solid residue through the production of volatile substances. Based on the molecular stoichiometry (C6H10O5)n the theoretical carbon yield of carbonization process of cellulose structure is 44.4 %. However, the actual yield is only between 10 and 30 %. During


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the depolymerisation of the macromolecular chains, the carbon content is decreased due to releasing of carbon monoxide (CO) and carbon dioxide (CO2), aldehydes, organic acids and tars [83].

Figure 10. Mechanism of celluloses controlled thermal decomposition, proposed by Bacon and Tang [82].

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Carbonization is the second step of controlled thermal decomposition of celluloses and represents the conversion of depolymerized structure into graphite-like layers through the repolymerization. Depolymerization to monosaccharide derivatives occurs through the thermal cleavage of the glycosidic linkage and ether bonds which is followed by decrease in degree of polymerization. These derivates are re-polymerized by forming condensed, aromatic structures and releasing gases containing non-carbon atoms (O, H). Subsequently, in the temperature range of 400 – 900 oC, the carbonaceous residue is converted into a more ordered carbon structure. The heat treatment up to 900 oC, under an inert atmosphere, leads to formation of semi-ordered carbonaceous structures. Further heating, above 900 oC, initiate graphitization, and generally amorphous carbonaceous structures converts to a turbostratic carbon structure containing graphene layers. A remarkable feature is that the carbon structure formed via pyrolysis retains some memory of the starting structure through the entire process [83]. Additionally, characteristics of obtained carbon materials depend of the carbon precursor structure and parameters of carbonization process [13].

THE INFLUENCE OF PREPARATION PROCESS PARAMETERS ON THE CARBONIZED HEMP FIBERS SURFACE CHARACTERISTICS Chemical modification of short hemp fibers prior to carbonization was used to examine the influence of carbon precursor chemical structure and morphology on carbonized material characteristics. The amount of hemp fibers structural components, especially lignin, hemicelluloses and cellulose, may affect surface characteristics of carbonized materials, especially specific surface area and amount and nature of surface functional groups [84]. In order to obtain a row material with different characteristics, short hemp fibers were chemically modified as it is described in the literature [12]. The progressive removal of the hemicelluloses was brought by treating the fibers with 17.5 % NaOH solution, while the lignin was progressively removed by treating hemp fibers with 0.7 % NaClO2. The samples obtained by chemical modification along with the original (as received) hemp fiber were then carbonized at 1000 oC under constant nitrogen flow (150 cm3/min), with the heating rate of 5 oC/min. The isothermal time at maximum carbonization temperature was 30 min. After carbonization, five samples denoted Ch1, ChL5, ChL60, ChH5 and ChH45 (as it is shown on the Figure 11), were obtained [13]. The changes in both chemical and structural properties of the hemp fibers incurred as a result of alkali and oxidative chemical treatment are already explained in this Chapter. After carbonization all samples retain fibrous structure of the precursor fibers. Compared to the carbonized hemp fibers obtained from unmodified fibers (Ch1, Figure 12a), the carbonized hemp fibers modified prior to the carbonization (ChL5, ChL60 and ChH5, Figure 12b, 12c and 12d)) are characterized by visible surface fibrillation. In the case of sample ChH45 (Figure 12e) the fibrillation is even more pronounced. The amount of lignin, hemicelluloses and cellulose in the carbon precursor affects the specific surface area of carbonized materials [84]. Lignin has been found to be effective in creating pores, as evident from the work by Kennedy et al. [85]. Furthermore, the BET surface area was found to be highest for the carbon materials obtained from carbon precursors with highest lignin content [81]. In view of that, short hemp fiber modified by removing the

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lignin, after carbonization gave samples ChL5 and ChL60 with lower specific surface area (Table 10) [13].

Figure 11. The scheme of carbonized hemp fibers production.

Figure 12. SEM photographs of carbonized hemp fibers: a) Ch1, b) ChL5, c) ChL60, d) ChH5 and e) ChH45.

Table 10. Specific surface area and amounts of CO and CO2 evolving surface oxygen groups of carbonized short hemp fibers samples Sample Ch1 ChL5 ChL60 ChH5 ChH45

SBET (m2/g) 518.5 428.6 388.6 425.9 573.5

CO evolving groups (mmol/g) 1.718 2.641 4.364 3.513 2.054

CO2 evolving groups (mmol/g) 2.192 0.812 1.851 1.119 0.613

CO + CO2 (mmol/g) 3.910 3.453 6.215 4.632 2.667

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During the alkali treatment of origin short hemp fibers, the crystal structure of cellulose, named as cellulose I (Cell I), is transformed in to cellulose II (Cell II) [31,32]. The polymorphic transformation of Cell I to Cell II depends on alkali concentration and the time of treatment [33]. In the chemical treatment used for obtaining the carbon precursor for sample ChH45 the concentration of NaOH and the time of treatment was high enough to provide appropriate conditions for this polymorphic transformation. This transformation of cellulose I in to more reactive cellulose II is probably the reason for high specific surface area of sample ChH45 [13]. Surface oxygen complexes on carbon materials can be quantified by temperatureprogrammed desorption (TPD), as they decompose upon heating by releasing CO and CO2. TPD peaks of CO and CO2 at different temperatures are related to the bond strength of the specific oxygen groups. Thus, the position of the peak maximum at a defined temperature corresponds to a specific oxygen complex at the surface. For example, CO2 is released by decomposition of carboxylic groups at 373–673 K or lactone groups at 463–923 K. Both CO and CO2 peaks originate from the decomposition of carboxylic anhydrides in the temperature range of 623–900 K. Phenols, ethers, carbonyls and quinones give rise to CO at 973–1253 K [86-89]. The quantities of CO and CO2 released during the TPD experiments correspond to the total amount of oxygen groups present at the carbonized hemp fibers samples surface (Table 10). For all samples modified prior to carbonization amount of CO evolving groups increase while amount of CO2 evolving groups decrease compared to sample Ch1. It is interesting that sample ChL60 has the highest amount of surface oxygen groups and sample ChH45 the lowest, which are totally opposite to the values of their specific surface area. Also, the extension of the oxidation treatment time leads to the increased amount of the surface oxygen groups, while the extension of alkali treatment time leads to the reduced amounts of the functional groups.

Figure 13. The scheme of activated hemp fibers production.

Specific surface area and the amount of surface oxygen groups can be increased by activation of carbon material surface [13,86]. Activation of carbonized hemp fibers using different amounts of potassium hydroxide, as activating agent, is schematically presented in


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Figure 13. During the activation process, decomposition of KOH molecules is followed by gasification process under high temperature: 2KOH → K2O+H2O H2O+C → CO+H2 Stronger activation, i.e., increased ratio of KOH, open up the porous structure and increases specific surface area up to 673 m2/g for sample ACh1 and 2192m2/g for sample ACh2 [13].

Figure 14. TPD spectra of carbonized short hemp fibers samples: (a) CO and (b) CO2 desorption profile.

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Potassium hydroxide activation increases the amount of both CO and CO2 evolving groups with increased amount of KOH used. TPD profiles of CO and CO2 evolution for all tested samples are shown in Figure 14. The TPD spectra of CO2 desorption profiles of all tested samples show an intensive peak at relatively high temperature (from 890 K to 1073 K). For the sample ACh2 this peak is most intensive and shifted to the higher temperatures. It can be noted that activation process as well as the increased amount of activating agent increase the intensity of the peak and shifts it to the higher temperature, which suggests the stabilization of surface oxygen groups. For all tested samples, CO desorption profiles have a maximum at the temperature which coincides with the maximum in CO2 desorption profile indicating the existence of anhydride groups, which decompose upon heating by releasing both CO and CO2. The increase of this peak area, with increased amount of KOH used for activation, suggest that high amount of anhydride groups on the surface of activated hemp fibers samples is probably consequence of the KOH activation process [86].

CARBONIZED AND ACTIVATED HEMP FIBERS APPLICATION AS SORBENT MATERIALS The possibility of producing carbon materials with high specific surface areas, microporous structure, high adsorption capacity and degree of surface reactivity brings the variety of application for these materials. The carbonaceous materials have been proved to be effective sorbents for removal of metal ions as well as their complexes. Their large sorption capacity is linked to well develop internal pore structures, a large specific surface area, and the presence of a wide spectrum of surface functional groups [87]. In the past decade, there is a growing interest in using different type of biomass for production of carbon materials [68,69,90], as a low cost and ecologically acceptable alternative to activated carbon. Carbonized hemp fibers obtained by carbonization of origin and chemically modified waste hemp fibers was used as an efficient, low-cost sorbent for heavy metals removal. Sorption properties of carbonized hemp fiber samples tested through the heavy metal ions adsorption are presented in Figure 15. The increase of the heavy metal ions initial concentration leads to the increase of the adsorbed equilibrium amount. For the initial concentration of 50 mg/dm3 all samples obtained by chemical modification of carbon precursor have similar sorption capacity, which are considerably higher compared to the sample obtained by carbonization of unmodified precursor (Ch1). With increasing the initial concentration up to 100 mg/dm3, the sample Ch1 shows the lowest sorption capacity for lead ions, while its sorption capacities toward cadmium and zinc ions have comparable values. Also, obtained results (Figure 15) suggest that changes in carbon precursor morphology, caused by chemical treatment, affect the sorption process and sorption capacity of examined samples.


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Figure 15. Sorption capacity of carbonized hemp fiber toward a) Cd2+, b) Pb2+ and c) Zn2+.

In order to connect sorption process of heavy metal ions with structural parameters of carbonized hemp fibers (CHF), mathematical model previously developed for prediction of heavy metals biosorption, and described in this Chapter, was upgraded. For this purpose adsorption of lead ions, which is proved to be the most concurrent ion during the adsorption from the mixture of heavy metal ions [91], was used. Since, transport of ions depends on ion concentration in water solution and structure of fibers, model consideration included two successive steps: analysis of ion transport from water solution through CHF and characterization of CHF structure. For ion transport analysis, developed model was upgraded [92] by introducing the damping coefficient that quantifies the influence of fibers morphology and surface porosity on ion transport, while ion transport through the porous matrices is characterized by the effective diffusion coefficient. Additionally, structure of carbonized hemp is described by: the pore volume as function of pore diameter, the porosity and the average tortuosity. Effective diffusion coefficient, damping coefficient and the lead ion concentration profile within the carbonized hemp fibers, obtained as results of proposed mathematical model, give the insight in the mechanism and the rate of adsorption process, while average tortuosity connected the sorbent structure and ions transport through the sorbent. Figure 16 shows the correlation between model prediction and experimental data obtained for lead ions concentration within the sample Ch1.

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Figure 16. Correlation between model prediction and experimental data obtained for lead ions concentration within the sample Ch1.

As it was shown in Figure 16, model prediction is well fitted with the experimental data for the initial concentration up to 200 mg/dm3. With further increase of initial ion concentration in solution data obtained by model prediction and experiment starts to differ, but remaining in good correlation. A good agreement between model prediction for both structural and ion transport model parameters and the experimental data, indicates that the proposed mathematical model can be successfully used for optimization of heavy metal ions adsorption process. Different carbon materials have been widely used as sorbents in the solid phase extraction (SPE) which is an efficient and economical sample preparation technique for preconcentation of the target analyte. This method has been previously applied to the determination of many pesticides in natural water and crops due to its substantial advantages such as providing higher concentration factors, decreasing sample preparation time, reducing costs, and requiring less solvent [93,94]. Following the standard SPE procedure, carbonized and activated hemp fibers described previously in this chapter were used as a sorbent in the solid-phase extraction for pesticide analysis in water samples. Extracts, obtained after SPE procedure, were analyzed by liquid chromatography–tandem mass spectrometry technique. The pesticides belonging to the different chemical classes as triazine (atrazine, simazine, propazine), neonicotinoid (imidocloprid, acetamiprid, thiamethoxam), carbamate (carbofuran, methomyl), organophosphate (monocrotophos, dimethoate, malathion, acephate), hydroxyanilide (fenhexamid), diacylhydrazine (tebufenozide) and phenylurea (linuron) were chosen. The method recoveries obtained using carbonized hemp fibers as a sorbent in SPE procedure is presented in Table 11 and Figure 17.

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Table 11. Recoveries of selected pesticides obtained using different carbonized hemp fibers as SPE cartridges

Pesticide Thiamethoxam Monocrotophos Imidocloprid Acetamiprid Tebufenozide Fenhexamid *

Ch1 ChL5 Recovery (%) (RSD (%)) 62.9 (0) 93.1 (8) 14.3 (11) 57.2 (17) 64.2 (7) 88.8 (19) 61.9 (14) 105.8 (12) 61.4 (10) 95.3 (1) 40.4 (13) 71.1 (0)

ChL60

ChH5

ChH45

90.7 (13) 73.9 (0) 95.2 (7) 87.6 (15) 100.7 (15) 84.3 (0)

89.5 (5) 37.8 (20) 95.2 (7) 89.4 (0) 91.7 (12) 62.5 (3)

91.9 (2) 70.7 (10) 85.3 (7) 96.0 (18) 86.2 (1) 81.8 (13)

RSD – relative standard deviation.

Sample Ch1 could not be used as a sorbent for SPE cartridges due to low recoveries (under 70 %). Carbonized hemp fibers modified prior to the carbonization can be used for preconcentration of few pesticides: thiamethoxam, imidocloprid, acetamiprid, tebufenozide and fenhexamid. Additionally, samples ChL60 and ChH45 can be used for preconcentration of monocrotophos. Activated hemp fibers sample ACh1 can be used for preconcentration of all examined pesticides except for methomyl, imidocloprid, linuron and fenhexamide (Figure 17). Activated sample ACh2, can be used for all examined pesticides except for acephate, methomyl, linuron and fenhexamide. Recoveries obtained for activated samples are comparable with those obtained for commercial cartridges [13]. In the case of acephate, dimethoate, simazine, carbofuran, propazine, malation and tebufenozide recoveries obtained by activated hemp fibers was even better than those obtained with commercial cartridges.

Figure 17. Recoveries of selected pesticides obtained using activated hemp fibers as SPE cartridges.

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Comparing the results obtained in the SPE experiments with the surface properties and morphology of the carbonized and activated samples, it can be noted that the best SPE efficiency was achieved with activated hemp fibers samples with the highest specific surface area and the amount of surface oxygen groups.

CONCLUSION The research summarized in this chapter represents an attempt to explain the influence of chemical modification on hemp fibers structure and consequently on their properties. Hemicelluloses and lignin removal, induced by oxidative and alkaline treatment, affects the fiber structure and improves the fiber properties that are of great importance for their usage for clothing, working and protection textile materials. The influence of hemp fiber chemical composition on their heavy metal ions sorption potential, were assessed by evaluating the water and metal ions uptake capacities of differently modified hemp fibers. The process of heavy metal ions biosorption on short hemp fibers was clarified by mathematical model development. Proposed mathematical model provides a better insight into phenomena of different ions transport through porous fiber matrices, and possibility of optimization of the complex process of biosorption. Also, chemical modification of hemp fibers, prior to carbonization, affects the specific surface area, amount of surface oxygen groups and morphology of carbonized hemp fibers. Furthermore, activation of carbonized materials with potassium hydroxide improves sorption properties of carbonized hemp fibers by increasing the specific surface area (up to 2192 m2/g) and amount of surface oxygen groups. Good sorption properties of short hemp fibers, obtained as the waste material from textile industry, and therefore their very low price in comparison with commercial sorbents highly recommends their use for purification of wastewater. On the other hand, short hemp fibers represent an attractive low cost precursor for carbon material production. Due to the good adsorption properties toward heavy metals and pesticides, carbonized and activated hemp fibers were successfully used as a sorbent for the purification of water polluted with pesticides and heavy metals. Also, activated hemp fiber sorbent used for analyte preconcentration in the solid-phase extraction procedure for pesticide analysis in water samples, showed even higher efficiency in pesticides preconcentration than expensive commercial cartridges.

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Chapter 17

TEXTILES USING ELECTRONIC APPLICATIONS Marica Starešinič, Andrej Javoršek and Dejana Javoršek University of Ljubljana, Faculty of Natural Sciences and Engineering, Ljubljana, Slovenia

ABSTRACT Textiles, from fibers to fabric, with integrated special electronics are more and more used as special materials in newly developed smart clothing. Simple systems are based on electronic elements integrated in pockets and connected with soft wires, while in more developed systems, conductive fibers are used to connect sensors, processors, LED lighting, photovoltaic cells, communication elements and more. Hybrid systems, with permanently integrated electronics, are developed with the elements that are washable and can be used in extreme weather conditions. Different microcontrollers (ATMEL ATmega, ATtiny etc.) used in the products of wearable electronics – LilyPad Arduino, are already available. These textiles can be used as protective clothing due to their material properties for heat, fire, increased visibility and UV protection. For such a protection, electronic sensors can be integrated in combination with integrated batteries and photovoltaic cells that generate electricity, which is stored in batteries. Special fibers can generate power when in motion or when exposed to light and this can be used for the power or reversed, to light the integrated OLED lights. Such textiles can be used in all kinds of activities in different terrain and weather conditions as sports and free time activities as well as in different accidents, natural or transportation, to save lives. These technologies are also used in medicinal applications, when the clothing with integrated sensors can measure patient’s conditions and transmit the data to doctors. In this chapter, textile applications with integrated electronic elements are presented on several examples. The safety vest that was presented at the LOPE-C conference in Frankfurt, with integrated photovoltaic cells and LED lights, can be used in conditions for better visibility on roads and in the case of accidents. Another example is textiles with integrated microcontrollers in the combination with different sensors, e.g., temperature or light, as well as LED lights, which enable numerous combinations of their usage, for protection or decoration, or simply for the color/lighting effect. The integration of a

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Email: [email protected].

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Marica Starešinič, Andrej Javoršek and Dejana Javoršek custom made printed circuit board and designed program for a different action of LED is represented. The research shows that the knowledge from various fields, e.g., textiles, chemistry, electronics and programming, can lead to the creation of textile applications with electronic elements.

Keywords: Wearable electronics, LED light, microcontroller, printed circuit boards

INTRODUCTION Smart textiles, from fibers to fabrics, with integrated special electronics are nowadays used to develop smart clothing. In this paper, some examples for future designs and development are presented, as well as the safety vest that was presented at the LOPE-C conference in Frankfurt with integrated photovoltaic cells and LED lights. Smart textiles are, by definition, textiles which respond to the changes in the environment as a result of mechanical, thermal, chemical or electromagnetic influences [1]. Interactive textiles [2] represent textiles that have built-in into their structure the elements to control (sensors, switches, communication components, batteries). Most commonly, these elements control the health care functions (pulse, temperature, blood sugar etc), enable communication or represent the security and entertainment systems, as well as they allow the power supply thereof. The development of textiles with electronic components can be subdivided into: –

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Simple systems: electronic components are incorporated into pockets sewn-in or attached over soft cables and should be removed before cleaning, e.g., LED lighting devices; Hybrid systems: the elements are a part of permanent fabrics, woven or embroidered, using conductive yarns; Complete integration: the elements are integrated, using the fibers with special properties that act as electronic textiles (sensors etc).

The functions [3] of textiles using electronic applications are: – Passive functions: as a result of material properties, they can sense the environment (sensors); – Active functions: as a result of installed sensors, they can act to the environment – actuators, and can work to supply energy (work actively to changes in temperature hot/cold), for protection (inflatable elements for protection against impact, missiles), protection from water – floating clothing, increased active visibility, communication – a cry for help, protection from hazardous substances, chemicals, gas, alarm and protection against radiation, measurement of vital signals (pulse, temperature etc), integrated antennas for communication and embedded components for the photovoltaic generation of electricity for the operation – independent of batteries.

Textiles Using Electronic Applications

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Embedded components that measure the heart function and enable monitoring of the user throughout the day, the data being transferred to a medical institution, are already used for medical purposes. After the surgery, patients wear clothing with integrated elements of control, thus allowing the movement and they avoid the pain for the installation of measurement probes for their medical condition control. For communication [4], the developed elements can be washed and are a part of the clothing, where they operate as touch screens (touch-pad), are flexible, lightweight, durable and allow interactivity. Smart textiles, which include safety clothing, are materials that allow the installation of a variety of technologies, e.g., various electronic components, in clothing. Such fabrics permit the perception of the environment and thus the adaptation to different conditions. The main functions enabled in smart textiles are integrated sensors [5] that measure vital functions (medical textiles), enable communication, processing and storage of data, acquisition and transmission of energy (including PCM materials – Phase Change Materials) [6]. Electronic components can be fitted directly into textile fibers, e.g., conductive materials and conductive textile fibers, diodes, transistors and photovoltaic fibers. Current electronic components prepared on a silicon base are not flexible whereas the new elements developed on the base of organic polymers are. The fibers that are made from materials which convert light into electricity or electricity is the result of the fiber movement [7] enable the production of electricity. The energy is stored in batteries and when necessary, it powers the built-in OLED lighting. At MIT (Massachusetts Institute of Technology), dyes have been developed for the print of solar cells [8] on different materials, including textiles.

USE OF SMART TEXTILES Smart textile [9] products have been used in various fields, as smart textiles SFIT – Smart Fabrics and Interactive Textiles, as wearable technology (wearable tech), and as interactive textiles. The areas of application range from the clothing for personal protection, e.g., work clothes for special environments, for the protection of the health of workers and for the protection in extreme sports in a variety of environments (hot, cold, wet, dry etc). Smart textiles are intended for everyday use, heated/cooled clothing, for entertainment (clubs, concerts, public events) and special effects with fashionable elements such as built-in lighting, changing colors, as well as for communication. Many of these technologies are being used or planned for use for the elderly who need active assistance or protection in everyday life (control and communication – garments with wearable physiological sensors) in order to reduce the costs of care and treatment. The research is conducted in the areas of direct installation in the clothing, enabling easy maintenance (washing) and increased generation of energy or lower consumption to operate. Energy can be produced on the basis of photovoltaic cells that can be a part of the garment – as a fashion accessory or using piezo crystals, based on the movement of MEMS (MicroElectronic Mechanical Systems). It also works in the field of storage and use of heat energy that is released in the movement – walking user. For all these cases of energy generation, it is

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Marica Starešinič, Andrej Javoršek and Dejana Javoršek

necessary to develop more storage options to be able to use printed batteries that are smaller and can be incorporated into products. All of the above results in increased consumption and increased amount of post-consumer textile waste. Development can take place in the direction of one time use – large quantities of waste, or multiple uses – problems of maintenance, but less waste. The ecology [10] of smart textiles is still at the beginning, which means that there is still a lot of work to be done and the need for deciding whether to use better and more expensive organic materials or recycled towards the development of smart textiles. Of course, these problems are also the opportunity for smaller companies which could focus on the development and manufacture of tailor-made eco-smart clothes. This could lead to the development of products with high added value, with added knowledge and the use of novel developed materials. In today’s world, when electronics become a part of clothing, with embedded microcontrollers and variety of sensors (e.g., temperature or light) and LED lighting, endless combinations for use in both protective and decorative purposes are allowed. Microcontrollers that can be washed, which is their major advantage, allow various connections between the LED elements that can be programmed for any application, which is extremely important for the use in textiles. On the market, there are different microcontrollers (e.g., ATMEL ATmega, ATtiny etc) which can be used in the products of wearable electronics, e.g., LilyPad Arduino [11]. By using these microcontrollers, different applications can be developed, with custom made circuits with arbitrary shape and at reduced price. In our research, the design of printed circuit boards and programs for different behaviors of LED lighting (gradual or simultaneous switched LED lighting) was performed [12]. The final product represents a warning-decorative LED light arrow that lights up differently. The research showed that the knowledge in the field of textiles, chemistry, electronics and programming contributes to the manufacture of high quality applications that in addition to textile components also includes the elements of electronics.

EXAMPLES OF SMART TEXTILES PLED Dress Clothes are changing every day, not only on the basis of fashion trends, but also to follow the research in the field of technology, new materials and innovations from other fields. Predicting the future has never been easy, people have predicted flying cars, peace, a diseasefree world etc – which has not (yet) happened, while nobody foresaw the use of mobile phones, 3D printed food and invisible clothes. At fashion events, we can see clothing equipped with the LED technology and micromotors that change dimensions and act as a light show. Chalayan [13] presented hightech dresses that transform on the body and translated them into wearable, commercially viable pieces. The models, when walking, activated the application at the collar and the fabric unraveled to reveal an entirely different look. Figure 1 shows the clothes illuminated by LED lights, which is interesting from the design point of view.


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Figure 1. Dress with integrated PLED (Polymeric Light Emitting Diode) (Source: Museum of Science and Industry in Chicago, online: http://www.crunchwear.com/cute-circuit-galaxy-led-dress). Cute Circuit Galaxy LED Dress.

Figure 2. Schematic drawing of photovoltaic fiber.

Figure 3. Photovoltaic fibers [17] and single fiber [18].

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Figure 4. Printing dress and detail of keyboard.

For the production of such garments, fabrics with special properties are necessary, e.g., photovoltaic fibers [14], which act as photovoltaic cells for generating electrical energy. Figure 2 shows a scheme of such fibers. Fibers can under the influence of light, wind or rain generate electric potential energy and act as a hybrid photovoltaic-piezoelectric device. Hybrid films are constructed by depositing an organic photovoltaic cell on a commercial PVDF film, while hybrid fibers are developed by depositing an organic solar cell on a piezoelectric [15] polymer fiber. When the hybrid film/fiber is subjected to mechanical vibrations from the wind, rain or tide, the piezoelectric part produces an electrical voltage that is converted to a constant DC voltage by a rectifier. The photovoltaic part of the hybrid film produces constant DC voltage from the solar energy. Electrical energy can then either be used online or stored in a battery. These materials are now available as an energy harvesting device for the use in various e-textile [16] applications. Materials can be fitted on textiles as added materials on the surface or integrated as a part of the material itself, e.g., photovoltaic fiber [19]. An interesting example of this technology is the printed dress which acts as a screen “Printing Dress” [20]. The dress integrates different technologies. It consists of three main parts of the upper corset and a skirt. The corset has fitted four elements LilyPad Arduino 11, a USB port for connecting to a laptop computer, keyboard, a built-in corset and wires to connect. The skirt is made up of a material with incorporated aluminum wires and hangs over the projector which projects images directly onto the skirt. Each time the user presses a key, it communicates with the processor to display the animation typewritten text on the skirt. In Figure 4, the dress [21] is presented. The dress is presented as a prototype of the concept and application of printed electronics in the clothing purposes. The experience will contribute to the creation and development of smart clothing. Nowadays, the dress can be used as a tool to communicate or tweet.


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Safety Vest In the more and more changing climate on the planet, we have to be able to work and travel in the most challenging situations. The weather pattern can change very fast from hot to cold, from draught to floods, so there is a need for the clothing to protect us. The advances in new textiles and printed electronics on flexible substrates can together offer some interesting possibilities. The OE-A association (Organic Electronic Association, Germany), organizer of LOPE-C, presented an international competition for student projects in order to present the possibilities of using printed electronics, they offered a set of elements that had to be assembled in working demonstrator. Safety clothing – the safety vest presented in Figure 5, with printed solar cells on the back and LED lights was developed at our department. The generated energy was stored in the built-in battery and when necessary, the LED lights that are on the back can be used. The basic concept (cf. Figure 6) is to use polymer solar cells to generate the power that is stored in the built-in batteries and used for better visibility on the roads or in nature. The polymer solar cells (Konarka), batteries and LED (Light Emitting Diode) lights are linked by the special built-in softwire, the switch, battery and operation button being in the pocket. In the sunlight, solar cells convert light into electricity, the energy is stored in the batteries and when it gets dark, the LED lights, which are integrated on the back, give light. Previous applications based on reflection, in our case the LED, give light in the dark. LED lights are semiconductor diodes that emit light under the influence of electricity. Photovoltaic cells are the elements that unlike LED lights emit electricity when under light. Unlike past examples of safety clothing that acted on the principle of reflective elements [22] embedded in clothing, our safety vest in Figure 5 has built-in LED lights that are powered by photovoltaic cells. Figure 7 presents the details of the links which are located in the inner side. The basic elements consist of polymer photovoltaic solar cells, LED lighting and batteries. The safety vest represents the beginning of the research in the field of clothing and the added value represented by the elements of printed electronics. Photovoltaic polymer cells printed on a flexible substrate are suitable for the use on textile substrates.

Figure 5. Safety vest on model of conference LOPE-C 2011.

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Figure 6. Basic concept and developed model.

Figure 7. Integration of polymer photovoltaic solar cells, LED lighting and batteries.

Figure 8. Power plastic photovoltaic cells.


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Decorative Arrow with Custom Made Printed Circuit Board In addition to the development of high-tech fabrics for the manufacture of sports clothing [23], it is always possible to achieve better sports results with the incorporation of different elements into fibers and fabrics, which is becoming more and more popular. Some of these elements are microcapsules. Back in the early 1980s, NASA developed the technology for embedding microencapsulated phase change materials into textiles for their temperature control [24], [25]. In the printing and graphic arts industry, the microcapsules are used for pharmaceutical and medical purposes, in cosmetic and food industries, for agricultural products, as well as in the chemical, textile and construction industries, biotechnology, photography, electronics and waste management [26, 27, 28]. In addition to the microcapsules integrated into fibers, there can be different electronic elements, interlacing for the protective or decorative purposes. Electronic components can be fitted directly into textile fibers (hybrid systems) or integrated in pockets connected via flexible cables, e.g., batteries connected to LED lights (simple systems) [29]. Different integrated sensors can be used for a variety of medical purposes, e.g., for the control of respiration or the measurement of respiratory signals [30]. One study presented the usage of sensors and a printed circuit board embedded in textiles, which enables the detection of the changes in the basic life functions for infants, e.g., breathing and heart rate [31], while another study improved the integration of sensors and electronics into textiles enabling the control of the ECG combined with wireless communication [32]. Ultrasonic sensors in combination with a printed circuit board in textiles can be used to detect the obstacles in helping people with impaired vision [33]. The sensors are small, use little power, can be installed internally and can be washed. Embedded microcontrollers, in combination with a variety of sensors (e.g., temperature or light sensors) and LED lighting, can be programmed and used for any purpose. Their advantage lies in the fact that they can be washed, which is for the use in textile applications extremely important. On the market, there are different microcontrollers available (e.g., ATMEL ATmega, ATtiny etc), which are used in the products of wearable electronics such as LilyPad Arduino 11. LilyPad Arduino was designed and developed by Leah Buechley in collaboration with the company SparkFun Electronics. Wearable electronics LilyPad consist of different components (LED light, processor board, light sensor etc). LilyPad electronics are well suited for prototypes and unique design products, while their size (processor board is approx. 50 mm in diameter and approx. 3 mm in thickness) and price make them unsuitable for the mass production or very small items. Some researchers design their own printed circuit boards, while others use LilyPad Arduino microcontrollers, e.g., for an immediate determination of the pH value of the sweat that is excreted in sporting activities. In that case, Arduino controls the operation of LED lights that change color according to the measured pH value of the sweat [34, 35]. The advantage of self-made decorative-protective applications is that they are made as a separate element which can be integrated into various garments or fashion accessories, that they are affordable, and their size and purpose is adjusted to the application. Another example of our work presents a design of wearable electronics that consists of LED lights, a processor, circuit board and custom written program for different behaviors of these LED lights (gradually or simultaneously switched LED lights). The final product represents a warning-decorative arrow shaped with LED lights that light up differently.

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Figure 9. Printing template of circuit board.

Figure 10. Printed circuit board.

Figure 11. Insertion of electronic components a) side view, b) back view.


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Figure 12. Soldering.

For that case, a printed circuit board was designed using the program EAGLE (Easily Applicable Graphical Summary Layout Editor) from CadSoft, in which we made a printed circuit diagram which represents the logical symbols and signs of electronic components and their connections. In Figure 9, the printing template of the circuit board is represented. The manufacturing of a printed circuit board (cf. Figure 10) was followed by the drilling of holes for the insertion of electronic components (cf. Figure 11) and solder (cf. Figure 12) electronic components into the pre-prepared printed circuit board. The software that is run by a microcontroller was designed in the C programming language in the program Arduino 11 1.0 and is shown in Table 1. Figure 13 presents the operation of LED lights for the final application – warning-decorative arrow. The presented program code allows a gradual or simultaneous ignition of LED lights. In Figure 14, the final product is presented. The advantages of our applications are that they still present the most inexpensive option of the relevant microcontroller – in our case ATtiny13 – and a precise adjustment for the desired final product with a manufactured printed circuit board is allowed. The presented application (cf. Figure 14) can be used for various purposes, e.g.: – – – –

for clothing (sportswear, roller skaters and cyclists on the road, for sports activities in low-light conditions, as well as for clothing for entertainment in nightclubs), for fashion accessories (brooch, add-on bag), for warning safety margin for pets on walk and for marking and identification of luggage when traveling.

Possible uses depend only on the imagination of the users. The advantage of the application is in the fact that it can be washed, which is especially for sportswear of extreme importance and it is only necessary to remove the battery before washing. Due to the battery, such products are not suitable for use under water, whereas if the application is well protected with waterproof elements, it can be used in the case of water sports, or in other extreme wet conditions.

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Marica Starešinič, Andrej Javoršek and Dejana Javoršek Table 1. C program code for microcontroller #include uint32_t GUT = 0; uint32_t STEP_DELAY=0; uint8_t U=0; void setup() { DDRB = 0b00011111; // all ports on the controller are output PORTB=0x00; // when initialized all ports turned off } void loop() { GUT=millis(); // assignment of system time if(GUT-STEP_DELAY>300){ // delay for 300 ms before next step if (U < 5){ // during first five steps turn on the port with corresponding number PORTB |= _BV(U); U++; // increase step } else if(U == 5){ // in step 5 PORTB = 0x00; // turn off all ports U++; // increase step } else if(U == 6){ // in step 6 PORTB=0xff; // turn on all ports U++; // increase step } else if(U == 7){ PORTB = 0x00; // turn off all ports U++; // increase step } else if(U == 8){ PORTB=0xff; // turn on all ports U++; // increase step } else if(U == 9){ PORTB = 0x00; // turn off all ports U++; // increase step } else if(U == 10){ PORTB = 0b00010001; // turn on first and fifth port U++; // increase step } else if(U == 11){


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PORTB = 0b00011011; // turn on first, second, fourth and fifth port U++; // increase step } else if(U == 12){ PORTB = 0xff; // turn on all ports U++; // increase step } else{ PORTB = 0x00; // in the last step turn off all ports U=0; // reset step to the firs one } STEP_DELAY=GUT; // set the time of step delay } }

Figure 13. Operation of warning-decorative arrow; a)–f) turning on additional two LED lights at the same time in five steps; A) and C) all LED lights are turned off; B), D) and F) all LED lights are turned on; E) gradually turning on four LED lights (two from front and two from back).

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Figure 14. Warning-decorative arrow.

In our case, we used only LED lights as the integral part of the application, while for other applications, a variety of sensors can be used. Examples are the sensors for sensing different lighting conditions in the environment or temperature sensors, force sensors, flex sensors etc.

CONCLUSION Clothes are changing every day, not only due to fashion trends, but also to follow the research in the field of technology, new materials and innovations. Predicting the future has never been easy, people have predicted flying cars, peace in the world without diseases etc – which has not (yet) happened, while nobody foresaw the use of mobile phones, 3D printed food and invisible clothes. At fashion events, clothing equipped with the LED technology and micromotors that transform dimensions and act as a light show are nowadays presented. Some of the materials shrink under the influence of temperature; consequently, when our surroundings get warmer, we no longer need to turn up the sleeves, since they roll up themselves. Development takes place in the direction of specific materials that can be cut with ordinary tools, and can protect against electromagnetic and infrared radiation. For medical purposes, the materials containing nanocapsules with colors that burst in the presence of infection with bacteria have been developed and with the use of UV light, doctors can quickly check for the presence of infection, as clothes change color. Furthermore, textile products are being developed that can detect the presence of infection on the skin which has been burned faster than enabled by the standard tests, which is especially important in the therapy for children. For safety purposes, the presented safety vest can be used in difficult conditions as it has integrated power-lighting system (photovoltaic cells-batteries-lights), hence making the user independent. The designed printed circuit board in combination with LED lights can be shaped into decorative-protective applications of different sizes with an optional LED lights effect, e.g., special lighting effects.


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For the production of these quality applications, in addition to textile components with integrated electronics items, we must combine the knowledge of textiles, chemicals, electronics, programming and ultimately, of ecology. The research in this area is opening up new possibilities for the development of new products in combination with the technologies in various fields.

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[16] Hadimani, R. L., Bayramol, D. V., Sion, N., Shah, T., Qian, L., Shi, S. & Siores, E. (2013). Continuous production of piezoelectric PVDF fibre for e-textile applications. Smart Materials and Structures, 22 (7), 075017. [17] Szondy, D. (2012). New type of optical fiber could be used in photovoltaic fabric, etext type. http://www.gizmag.com/solar-cell-fabric/25367. [18] Lee, M. R., Eckert, R. D., Forberich, K., Dennler, G., Brabec, C. J., Gaudiana, R. A. (2009). Solar power wires based on organic photovoltaic materials. Science, 324, 232. [19] Krebs, F. C. (2006). Fabrication and processing of polymer solar cells: A review of printing and coating techniques. Solar Energy Materials & Solar Cells, 90, 1058–1067. [20] The Printing Dress, Microsoft Research, e-text type. (2012). http://research. microsoft.com/pubs145919/Theprintingdress.pdf. [21] Small, S. M., Roseway, A. (2012). The printing dress: You are what you tweet, Microsoft corporation, e-text type. http://research.microsoft.com/pubs/149519/the_ printing_dress.pdf http://hlt.media.mit.edu/publications/buechley_DIS_10.pdf. [22] Safety Smart Gear, e-text type. (2011). http://www.safetysmartgear.com. [23] Nusser, M. & Senner, V. (2010). High-tech textiles in competition sports. Procedia Engineering 2 (2), 2845–2850. [24] Mondal, S. (2008). Phase change materials for smart textiles – An overview. Applied Thermal Engineering, 28 (11–12), 1536–1550. [25] Nelson, G. (2001). Microencapsulation in textile finishing. Review of Progress in Coloration, 31(1) 57, 64. [26] Staresinic, M., Šumiga, B. & Boh, B. (2011). Microencapsulation for textile applications and use of SEM image analysis for visualisation of microcapsules. Tekstilec, 54 (4/6), 80–103. [27] Fanger, G. O. (1974). Microencapsulation: A brief history and introduction. Vandegaer J. E. (Ed.), Microencapsulation – processes and applications, Plenum Press, New York, London, 1–20. [28] Boh, B., Knez, E. & Staresinic, M. (2005). Microencapsulation of higher hydrocarbon phase change materials by in situ polymerization. J. Microencapsulation, 22, 715–735. [29] Staresinic, M. (2011). Izdelava prototipa varnostnega oblačila “Safety Vest”. Tekstilec 54 (10–12), 238–244. [30] Huang, C. T., Tang, C. F., Lee, M. C. & Chang, S. H. (2008). Parametric design of yarn-based piezoresistive sensors for smart textiles. Sensors and Actuators A: Physical, 148 (1), 10–15. [31] Jourand, P., De Clercq, H. & Puers, R. (2010). Robust monitoring of vital signs integrated in textile. Sensors and Actuators A: Physical, 161 (1–2), 288–296. [32] Coosemans, J., Hermans, B. & Puers, R. (2006). Integrating wireless ECG monitoring in textiles, Sensors and Actuators A: Physical, (130–131), 48–53. [33] Bahadir, S. K. (2012). Wearable obstacle detection system fully integrated to textile structures for visually impaired people, Sensors and Actuators A: Physical, (179), 297– 311. [34] Benito-Lopez, F., Coyle, S., Byrne, R., Smeaton, A., O’Connor, N. E. & Diamond, D. (2009). Pump Less Wearable Microfluidic Device for Real Time pH Sweat Monitoring, Procedia Chemistry, (1), 1103–1106.


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Chapter 18

TEXTILES FOR CARDIAC CARE Narayanan Gokarneshan, Palaniappan P. Gopalakrishnan, Venkatachalam Rajendran and Dharmarajan Anita Rachel NIFT TEA College of knitwear fashion, Tirupur, India

ABSTRACT This chapter highlights the developments in textile materials used for cardiac care. Blood flow has been analyzed through a polyester vascular prosthesis. Woven bifurcated vascular prosthesis has been developed that has good biocompatibility. The mechanical behavior of knitted vascular graft has been analyzed. Weaving technique has been developed for making small diameter blood vessels that are found very useful in cardiovascular surgeries. A fabric prosthesis has been manufactured that is expected to respect haemo-dynamics, with a central opening, and that is associated with good fatigue resistance for long-term durability. Research has been focused to study the long term fatigue behavior of woven polyester fabrics of different yarns and construction factors to find whether they are suitable for heart valve replacement. Recent developments have focused on developing a stent that minimizes the occurrence of retenosis (blocking of artery). Weft knits have found suitability as stents for arterial implants, and have proved to be more advantageous than their metallic counterparts.

Keywords: Artery, Hemodynamic, Grafts, Prosthesis, Stent

1. INTRODUCTION The textile materials have found varied technical applications and medical textiles is one such emerging area. This chapter specifically focuses on the technological advances with regard to development of textiles for cardiology purpose. A good deal of research has been reported over the past decade and this has revolutionized the surgical procedures in cardiac care. Experimental studies on blood flow have enabled to design better artificial textile 


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prosthesis. Bifurcated prosthesis has been woven adopting 3D weaving technique, and the prosthesis so woven is found to be versatile in its function. The underlying technology has been highlighted. Textile implants have saved millions of people, but they are not yet perfect because of the complexity of arterial biology and textile mechanics. Biocompatibility has been achieved but the problems of compliance and resistance to the blood flow remain. Textile vascular prosthesis made of polyester have been used in crimped form and these exhibit better mechanical properties and resist deformation, and thereby show promise. Technology has been developed for weaving small diameter blood vessels that would render vascular surgery successful. Grafts of desired size can be engineered and their properties predicted. A textile heart valve manufacturing process has been developed, consisting of forming a fabric tube in a concentric way. The process minimizes fabric deformation, especially in the zones that will experience the greatest stress when the valve is functioning. This work already shows that the textile material can be used to manufacture a tricuspid heart valve with performance that is close to that expected for such kinds of replacement prostheses. Recent research trends indicate that one can use to develop criteria for designing a fabric most highly suited for use in heart valve application.

2. ANALYSIS OF BLOOD FLOW IN POLYESTER PROSTHESIS 2.1. Review of the Earlier Prostheses Types During the earlier days progress in vascular surgery has been closely linked to the use of synthetic woven and knitted prostheses. Textile vascular prostheses made of Polyethyleneterapthalate (PET), which was porous, had been used as substitutes. This permitted good clinical performance with regard to satisfactory tissue ingrowths and biostability. The first generation of textile prostheses consisted of hand sewn woven structures. Such devices exhibited practical difficulties after implantation due to lack of compression resistance and tendency to kink. Thus crimping (imparting waviness) was suggested to give the grafts radial resistance and longitudinal compliance. The crimping had been obtained by fixation of an “accordion” pleat deformation, permitting easier implantation of prosthesis and allowing the surgeon to control the longitudinal tension. Crimping also improved the resistance of the prosthesis to kinking when crossing the knee and, also to external compression. The graft was tunnelised subcutaneously.

2.2. The Analysis Method Blood flow has been analyzed in impregnated polyester prostheses commonly used in vascular surgery [1]. Gelatin and collagen are generally used to make the prosthesis impermeable. Experimental investigations have been carried out to assess the impact of their crimping on the flow. Flow velocity profiles measured with a laser doppler anemometer reveal that crimping yields to decrease in flow velocity, particularly near the surface of the prosthesis.

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This has been followed by a numerical simulation of the blood flow in vascular prosthesis using specific computer code, which adopts finite element method. The flow has been investigated in both stationary and pulsatile cases, considering the most crucial physical parameters of the blood namely, relative density and viscosity. In literature, haemodynamics has been widely associated with pathological effects related to the vascular wall [2, 3].

2.3. Discussions and Findings of the Study Experimental measurements and numerical simulations of the blood flow in textile prostheses characterized by the wavy form of their wall under steady and pulsatile regimes have revealed the presence of two distinct zones: an undisturbed central zone that preserves the properties of the Poiseuille flow, and a disturbed zone near the wall characterized by recirculation of the fluid inside crimping associated with very low velocities and shear stress. These perturbations linked to the crimping lead to a braking of the flow detected in the experimental and numerical studies. From all haemodynamic factors, wall shear rate is the most frequently cited parameter affecting the pathobiology of arterial walls [4, 5]. The low shear stress observed in wall crimping can explain the deposit of particles and excessive cell development, which might affect prostheses. Thrombosis, the formation of clots in sanguine vessels from blood constituents, is induced by the wall alteration linked to the slowing of the sanguine current. The zones near crimping could facilitate the adherence of platelets to the wall, releasing the coagulation in the prosthesis. In this area, multiplication of endothelial cells can be explained by the low shear stresses in crimping zones. This mechanical factor can also be responsible for the haemolysis phenomenon characterized by red cell destruction under high shear rates. Several researchers, e.g., Siegel el al. [6], Blustein et al. [7], Siouffi [8], Stergiopulosel al [9] have used laser doppler anemometry, ultrasonic anemometry, or magnetic resonance imaging to measure arterial flow velocity. They attempted to study the impact of particular shapes of artery walls, like stenosis or aneurysm, on flow properties. They agree about the implication of those shapes for decreased downstream shear stress and associate the deposit of particles causing thrombosis to low shear stress. The in-vitro study led by Moore and Ku [10] on unsteady flow in a blown glass abdominal aorta model observed by magnetic resonance imaging shows that at the end of the cardiac pulsation, although the debit remains positive, low negative velocities are recorded in zones close to the wall. They have established a correlation between low shear stress measured in the anterior wall of the aorta and the progression of atherosclerosis and hyperplasia. The numerical analysis of steady and pulsatile blood flows in a vascular prosthesis have been studied. The design of textile artificial vessels requires knowledge of prosthesis flow properties, especially near the wall. These data are of great interest to manufacturers of prostheses who model the architecture of the implant as a function of local mechanical causes of physiological and physic-pathological processes. Quantitative and qualitative studies of flow fields could provide solutions for some pathology linked to haemodynamic factors in prostheses. The low wall shear stress observed in the crimping area can explain some problems that could affect prosthesis, such as particle deposit and cell wall development.

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Further work will add additional realism to blood flow-simulation. The next factor to be considered is wall motion under arterial pressure. A specific computer code presents a module solving Napier-Stokes equations for deformable mesh, which can be used for simulations in moving wall flow fields.

3. WOVEN BIFURCATED PROSTHESIS Three-dimensional fabrics have recently entered the medical field. Their specific area of application is in the weaving of vascular prosthesis. Vascular prostheses are surgically implantable materials. They are used to replace the defective blood vessels in patients so as to improve blood circulation. Conventional types of prosthesis were made from air corps parachute cloth, vignon sailcloth and other types of clothing materials. Materials such as nylon, teflon, orlon, stainless steel, glass and dacron polyester fiber have been found to be highly suitable for the manufacture of prosthesis. These materials were found to be significantly stable with regard to resistance towards degradation, and were not adversely affected by other factors [11]. Dacron polyester, which has bio-compatibility and high tensile strength, is being used over a period of time as suture thread or artificial ligaments [12–14].

3.1. Comparison of Woven and Knitted Grafts Vascular grafts are manufactured on a very small scale as woven and knitted grafts, and also as Velour and Gore Tex. Knitted grafts may be of warp or weft knitted types [15]. Velour is a fabric made from textured yarns, wherein the filaments are exposed on either or both sides of the velour grafts. The woven grafts have been used earlier. Gore Tex grafts are made of polytetrafluoroethylene and molded as one single piece. Woven grafts have a good bursting strength and resistance to fatigue. They can be woven compact enough to make them least permeable to water and blood. They are manufactured as seamless tubes on special tape looms with shuttles. Knitted grafts are comparatively more porous than woven grafts. In the case of grafts with weft-knitted structures, the mobility of yarn is higher in the course direction than in the wale direction. This is a drawback since it leads to increase in diameter with time. Such a problem ultimately leads to rupture of the graft. Hence, weft-knitted structures are not preferred in the manufacture of grafts. Conversely, warp-knitted fabrics are highly versatile since they can imitate woven- or weft-knitted fabrics with regard to mechanical performance. Also, they are dimensionally stable comparatively and show higher compliance in the course direction than in the wale direction. Woven grafts are manufactured on tape looms with shuttle, specially designed for vascular prosthesis. The grafts are made as tubes without seams. Single jersey grafts are manufactured on flat knitting machines with very fine gauge and specifically designed for producing grafts. Tubular warp-knitted structures are produced on warp knitting machines equipped with two needle bars.


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3.2. Manufacturing Technology A prototype of a manually operated loom has been developed, which is suitable for weaving of straight as well as bifurcated vascular prosthesis [15]. It is based upon the principle of 3D weaving. A separate warp yarn selection device is incorporated. The main trunk of the bifurcated prosthesis has been woven as a tubular structure using weft from the same pirn. The filling yarn is inserted in the top layer of the warp shed and then the bottom layer of the warp shed. The bifurcated branches are more difficult to make as they are individually woven. The warp sheet is split into two layers so as to weave a tubular structure. Both the layers of warp sheet are manually wound around a warp beam. After string up, the warp yarns are passed through the dents of the reed and then wound onto the cloth roll. The two branches of the bifurcated prosthesis are woven by using two weft pirns in succession. For weaving one branch of the prosthesis, the weft from a pirn is passed from the selvedge to the centre of the top layer of warp shed and then inserted from the centre of the bottom layer of warp shed to the same selvedge. The second branch is woven by repeating the operation with the second weft pirn. It is to be noted that the weft yarns do not cross the entire width of the warp shed. This requires special selection of heald frames. Hence, the warp sheets have been divided longitudinally into two equal sections. Each half of the warp sheet corresponding to one branch of the prosthesis has been selected with a special heald frame group. Eight heald frames have been used for weaving. Each of the heald frame can be placed in three different positions, namely, higher, middle and lower positions.

Figure 1. Flow chart indicating weaving of prosthesis main trunk.

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The middle position is used for weaving the branches. The two branches of the prosthesis have been woven simultaneously. The first filling yarn is inserted successively in the top layer and then the bottom layer warp sheds of the right branch and the second filling yarn is inserted in the top layer and bottom layer warp sheds of the left branch.

Figure 2. Flow chart indicating weaving cycle of prosthesis branches.


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During the first selection, the odd numbered warp threads are lifted, and during the second selection, the even numbered warp threads are lifted. The woven bifurcated prosthesis thus has the following technical particulars:      

Type of material – Texturised dacron polyester yarns (circular cross-section). Linear density – warp and weft – 16 tex (34 fibres per yarn cross-section). Number of yarns per warp sheet – 160 (for right branch).160 (for left branch). Reed particulars – 20 dents/cm. 4 ends/dent – 2 yarns for top warp sheet. 2 yarns for bottom warp sheet.

Dacron polyester yarn has been found suitable as it has sufficient resistance to be woven without ruptures. Mechanical treatments comprising of compaction and crimping and also thermal finishing treatments impart the desired tubular shape to the prosthesis. The weaving of the branches of the bifurcated prosthesis requires special heald frames so as to enable selection of the two sections of the warp sheets individually. The heald frames have been set in the intermediate position and the filling yarn has been inserted manually to the middle of the warp sheet so as to perform this special weaving. Such an arrangement is not found on existing looms weaving narrow width fabrics. The 3D weaving machine could also be utilized for the manufacture of thick ribbons consisting of two bonded fabrics and being used as artificial knee ligaments. The same material as used for the vascular prosthesis, namely, biocompatible polyester can be used. In this case, the heald frame selection requires some modification and also the yarn linear density and the density of reed have to be changed.

5. ANALYSIS OF MECHANICAL BEHAVIOR OF PROSTHESIS Graft implantation is a common surgical procedure in the management of patients having severe blood circulation difficulties. Textile technology has provided several solutions for vascular surgery and a large number of textile vascular prostheses have been implanted in patients to revascularize downstream from diseased or injured arteries. Since 1954, the date of the first transplant on man, textile implants have saved millions of people, but they are not yet perfect because of the complexity of arterial biology and textile mechanics. Biocompatibility has been achieved but the problems of compliance and resistance to the blood flow remain. In previous studies [16, 17], correlations between flow nature and pathologies in prostheses such as progression of atherosclerosis, thrombosis and hyperplasia, have been established. The first generation of cardiovascular textile prostheses made of hand-sewn woven structures demonstrated some difficulties after implantation because of lack of compressionnal resistance and a tendency to kink. Today, crimped textile implants made of polyester share the market with those molded in one single piece of PTFE. In comparison with the flat shape of molded grafts, the crimping of textile vascular prostheses showed several mechanical advantages. In fact, crimping was achieved by fixation of an “accordian” pleat deformation permitting the surgeon to control the longitudinal tension and improving the resistance to kinking. Furthermore, knitted and woven structures showed better aptitude for sutures than molded ones. For these reasons, textile implants are exclusively used in particular sites

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needing long grafts with satisfactory bending properties such as femoral bypass at the knee level. The mechanical behavior of vascular prostheses under steady and pulsatile flow has been investigated. First, a theoretical model of the deformation based on elasticity hypotheses has been established and a test system simulating blood flow conditions has been built. This test system was linked to an image-processing device permitting the measurement of prosthesis wall displacements. In the literature, the mechanical properties of biological arteries have been widely investigated. Most studies [18-20] consider that arterial tissue is a perfectly elastic material whereas studies concerning the mechanical behavior of textile vascular prostheses appear to be extremely rare. Under steady and pulsatile flow the prosthesis was bent and its axis remained in the same vertical x-y plane of prosthesis deformation under flow pressure. The image processing provided the coordinates of all points belonging to the graft boundaries and permitted the determination of vertical displacement of the mid-point of the prosthesis lower boundary. Vertical displacements in steady flow conditions, and the evolution of theoretical and experimental values at different pressure levels, corresponding to a flow variation between 0 and 60 mL s-1, have been tested. The experimental results showed that vertical deformation remained constant between p = 10 and p = 30 mm mercury and increased with pressure elsewhere. The theoretical model predicted linear behavior for the vertical displacement. The Dialine® II prosthesis tested showed complex displacements of the boundaries under pulsatile conditions. This deformation was essentially characterized by prosthesis bending associated with a low horizontal deformation evolution of textile graft bending during a cardiac pulse. The vertical displacement of the mid-point in the lower boundary of the prosthesis under pressure and vertical displacements in pulsatile flow conditions have been studied. These show a periodic deformation of the textile graft having the same frequency as the pressure wave. The highest vertical displacements were obtained during the pressureincreasing period (systole). This deformation shows a sudden and rapid drop at the beginning of the pressure-decreasing period (diastole). The pressure variation obtained with the pulsatile flow system and measured with the image processing device shows that the system correctly simulates the physiological flow. The pressure curves obtained have the same shape as physiological pressure curves measured for the human body and described by Westerhof et al. [19] and Womersly [20]. This flow system made it possible to see that the textile vascular prosthesis bends under flow pressure. This bending, which has never been observed with natural or molded grafts, is certainly due to the crimping of the textile prosthesis. The theoretical and experimental results show some divergences probably due to the elasticity hypotheses considered as the developed theoretical model was based on describing textile prosthesis bending under flow pressure on them. This elastic behavior was broadly suggested by natural blood-vessel deformation, cited in the literature [17, 20, 21]. Several studies concerning arterial mechanics showed that pressure inside natural grafts only induces augmentation of the diameter of the elastic natural artery. The complex behavior of the textile prosthesis seems to be linked to the viscoelastic character of the knitted fabric. An investigation of the instantaneous elasticity and relaxation module recommended by Hofer et al. [22] would lead to better results. The experimental results show the influence of the pulsed character of unsteady flow on the graft deformation. Indeed, in the case of steady flow, the vertical displacement evolves almost proportionally to the flow and pressure inside the prosthesis. In the case of pulsatile


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flow, the prosthesis bends in a periodic manner but not according to pressure evolution. During the cardiac pulse, the graft bends almost permanently. It returns to its linear position when pressure drops and bends again during that quarter of the cycle. Pulsatile flow evidently generates a complex mechanical behavior of the knitted graft in which linearity between pressure and deformation is not observed. This confirms the inadequacy of the elasticity hypotheses selected in the case of steady flow. The prosthesis behavior seems to be viscoelastic at higher stresses and elastic at low stresses because of the crimped shape of the graft walls.

6. WEAVING TECHNIQUE OF SMALL BLOOD VESSELS For success in vascular surgery involving small-diameter (< 6 mm) vessels, a graft must closely match the internal diameter of the host artery and have desired high elasticity, porosity and transverse compliance. Thus although arterial grafts have gained acceptance in larger-caliber (> 6 mm) applications, where the requirements are flexible, a vein from the body continues to be preferred for small-vessel repair. An attempt has been made to develop an understanding of the material and the construction factors that affect the values of a woven tube's diameter, pore size, elastic recovery and transverse compliance [23-25]. This information is largely absent in literature. By varying yarn size and fabric structure, seamless tubes (1.5–7 mm diameter) were constructed. These were heat set for circular shapes and characterized for size, geometry and radial elasticity. Property–structure correlation models have been presented. Grafts of desired size can be engineered and their properties predicted. A number of factors are to be considered in the design of the blood vessels. These are a) b) c) d) e)

Determination of the graft dimensions Determination of the optimum heat setting conditions for the grafts Determination of the pore size of the grafts Determination of the compliance in grafts Determination of the elastic recovery properties of grafts

The factors that affect the graft internal diameter are a) b) c) d) e)

Denting order Number of warps Yarn size Denting order x number of warps Yarn size x denting order

The factors that affect the pore size of the graft are a) Denting order b) Pick density c) Yarn size

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N. Gokarneshan, P. P. Gopalakrishnan, V. Rajendran et al. d) Number of warp yarns e) Yarn size x denting order

7. TEXTILE HEART VALVE PROSTHESIS 7.1. Manufacture and Performance Evaluation Following the first attempt by Hufnagel [26] in 1952 to replace a faulty human valve with a mechanical prosthesis, a large variety of artificial valves have been developed. There are currently two types of prosthesis that fit the surgeons’ needs. Mechanical prostheses with tilting disks (mono- or bileaflet) have shown good durability [27] but require long-term anticoagulant medication for the patient because of the high risk of thrombo-embolism. Biological valves (porcine valves or valves obtained from bovine pericardial tissue) respect the haemodynamics of humans with a central opening, carrying less thrombo-embolic risk, and in general do not require anticoagulation. Their durability (~10 years) is nevertheless limited [28] due to tissue degeneration and accelerated calcification, especially in young patients. The development of non-invasive surgical techniques [29, 30] (which are less traumatic for the patient) requires flexible material that is less fragile than biological tissue to prevent valve leaflets from rupturing when folded in a catheter. In this case, fabric seems to be particularly adaptable because of both its resistance and flexibility. A fabric prosthesis has been manufactured that is expected to respect haemodynamics, with a central opening, and that is associated with good fatigue resistance for long-term durability. At the same time, textile materials have very low bending stiffness due to the discontinuity of the fabric and yarn structure (essential for good fatigue resistance and thereby durability of the valve leaflets during the cyclic opening and closing phases), and good orthotropical traction stiffness (essential for bearing the diastolic membrane stress under the closing pressure). At the same time, the non-smooth surface of the material, when manufactured with controlled porosity, should allow limited tissue in growth, making the prosthesis completely biocompatible. The fabric material used is PET, which has been used extensively for vascular grafts and has been demonstrated to be well tolerated in the bloodstream. The prosthesis is manufactured using a forming process that will limit yarn deformation and optimize flow tightness through adapted forming geometry.

7.1a. Testing and Analysis To test the prototype in vitro, a sewing ring (also realized with fabric) is adapted to the formed valve. In the closed position, the three cusps come together to ensure proper floodtightness. In the open position, flexibility of the cusps allows flow to push them aside with low flow resistance. Free-edge curvature inverts easily during this process. Static Regurgitation As fabric has a more porous structure compared with biological material, leakage across the textile prototype in the closed position is higher than in the bio-prosthesis. Compared with a mechanical valve, the difference is not as relevant because the required functioning tolerance on the mechanical valve also partly induces leakage of the device. Changing the


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parameters of the fabric used (saturation index and yarn structure) could reduce porosity and consequently leakage. However, from a biological point of view, tissue in growth on the fabric scaffold can be expected once the valve is implanted in its biological environment. Porosity of the material should therefore naturally decrease.

Dynamic Regurgitation Dynamic regurgitation is higher for the fabric valve than for the reference valves used. However, the closing volume (14%), corresponding indirectly to the time the valve needs to close, is not far from that obtained with a biological valve (8%). It represents the largest part of the whole dynamic regurgitation and it should be easy to reduce this value by using a fabric with lower bending rigidity. The lower the material bending rigidity, the easier will be the valve cusps movement from the closed to the open position. Valve closing time will thereby be reduced. A plain weave fabric made up of microfilaments yarns and with a reduced saturation index would be the best adapted material concerning this aspect. It should be possible to reach at least the performances of the mechanical valve that do meet the physiological requirements. Pressure drop across the valve, when comparing the fabric prototype with a mechanical valve, did not show significant difference, although the fabric valve is characterized with a central opening geometry offering no flow resistance. This is due to the roughness of the cusp’s fabric surface which induces a pressure drop at the flow–material interface. In contrast, the smoothness of the biological tissue causes a reduced pressure drop with the biological prosthesis. However, the tissue in growth that will occur on the fabric scaffold, once implanted, should transform the initially rough surface into a smooth surface. Pressure drop values will therefore decrease.

7.2. Fabric Construction and Durability The rapid development and success of percutaneous vascular surgery over the last two decades [31], with the now common stent graft implantation, make this non-invasive technique attractive today even for heart valve replacement [32]. Research has been focused to study the long term fatigue behavior of woven polyester fabrics of different yarn and construction factors to find whether they are suitable for heart valve replacement. A heart valve undergoes a combination of flexural and tensile stress during operation. A fabric having lower flexural resistance can be expected to have a longer working life. Textiles are unique materials in that they have low weight, high tensile strength, and high flexibility. The latter is what makes them comfortable as apparel products. These properties in textiles are primarily due to bonding between the chains in fibers and no direct bonding between fibers in the yarn and between yarns in the fabric. Fibers in yarns and yarns in a fabric can slip when flexed. Among the fibers available, one that has been used most extensively in implants (arterial and stent grafts, for example) is polyester. It is biocompatible and resistant to degradation when in contact with body fluids [33, 34]. Polyester fabric has already been shown to be able to behave dynamically like a valve in vitro [35–37]. Tests were however only performed over a short period of time. When an assembly is bent, the resistance to bending will be governed by the combined bending rigidity of the individual elements and the frictional forces between the elements that resist

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slippage between them [38–39]. The role of friction or cohesion between the elements of an assembly is not well detailed in the literature [41, 42]. For textile heart valve development, in which extensive cyclic flexing must occur, inter-filament cohesion becomes a central issue. At each valve cycle, the valve leaflet’s material undergoes flexure and tension stress. The leaflet tension force, borne by the filaments, will generate radial yarn-to-yarn and filament-tofilament forces due to the cohesion of the fabric structure. At the contact zones, these radial forces will generate friction forces. During the flexure of the leaflet, these friction forces will consequently need to be overcome before the required flexing will occur. The energy associated with that movement will be dissipated at the contact zone where the phenomenon occurs. Cyclic flexing, therefore, leads to an increase in the energy that is dissipated, which may cause damage to the surfaces in contact after a period of time. Even if the overall (global) stiffness of fabrics is low, repeated cycling of textile heart valve prosthesis at heart pulse rate may still lead to filament damage or rupture. A detailed assessment of these effects will help to predict a material’s durability when used as a heart valve. In order to find which fabric construction factors will provide the suitable structure for the application, the effects of yarn and fabric construction on the long term cyclic bending of fabrics, have been investigated. Fabric strips of 5 mm width and of different yarn and fabric structures have been subjected to combined flexure and tensile fatigue generated by cyclically pulsating water flow. The test samples were taken out periodically from the dynamic tester and characterized for change in their bending stiffness. As flexing of the specimen involved only small strains which were well below a fiber’s elastic yield strain, the inherent elastic stiffness of specimen was assumed to remain constant. Any change in bending stiffness was then assumed to be a result of a change.

8. WEFT KNITS AS CARDIAC STENTS Weft knits are used as stents in arterial implant. Stents have been used in treating coronary arterial diseases. The stents could be implanted through a catheter to compress the plaque and open the artery lumen for efficient flow of blood after the implant. The stent needs to be flexible so as to enable it to be carried to the place in the artery where the injury is located [42]. The stent should keep the artery open by allowing flow of blood and it should also be elastic so that it may accompany contraction and expansion of the arteries as the heart beats. The radial expansion force is the resistance of the stent to collapsing during expansion [43]. This is a determining factor of the capacity of the stent to keep the adequate artery geometry for the blood to flow. The structural design and the type of material determine the radial elasticity and the flexibility of the stent. Another important property of the stent is its fluoroscopic visibility, which enables its exact detection on the harmed area of the artery. This is related to the material used to make the stent and to its dimensions. Stainless steel has a low fluoroscopic visibility, while tantalum has a good fluoroscopic visibility owing to its radio-opacity. If the stent is too small, its fluoroscopic visibility is also poor. Yet another aspect to be considered is that the stent should be able to be sterilized so as to avoid being contaminated by bacteria. A textile stent should necessarily have lengthwise flexibility, high radial expansion force, high elastic


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recovery after radial expansion, resistance to corrosion, good fluoroscopic visibility, and high biocompatibility. Invariably, biocompatibility becomes a necessary criterion for a stent for its effective use [44, 45]. The performance of a stent will depend on its interaction with the human cells and fluids. Recent developments have focused on developing a stent that minimizes the occurrence of restenosis (blocking of artery). The problem is common with metallic stents and could be improved by applying textile materials over the metallic stent or by the application of special substances over the metallic structure. Polyester is generally used in covering metallic stents. In other cases, the metallic stent is impregnated with anti blood clotting substances. Researchers have proved that occurrence of restenosis may be reduced by covering metallic stents with textile fibers, and this has paved way for the development of the 100% textile stent. Modern day stents are textile materials that could be designed with improved properties over the metallic ones. Both knitted and braided textile stents could be easily compressed, resulting in blocking of artery and thus lead to heart attack, or other problems such as stent migration etc. [46]. The flexibility of a stent is one of the most important characteristics, as without this property it may not be possible to reach the harmed part of the artery. However, to obtain the ideal flexibility of the stent, the radial compression force may be compromised. This latter property refers to the resistance to collapse when the stent expands and is the stents capability to maintain the lumen geometry. Another critical property of the stent is its biocompatibility which has to be very high to minimize the risk of thrombosis or a neo-intimate proliferative response. Recent studies have focused on development of 100%textile stents to replace commercially available metal and hybrid ones [47]. Polypropylene fiber has been found to be suitable owing to its economical cost as well as compatibility in physical properties. It is effective, readily available, versatile, and cheap. The use of monofilament will enable a greater stiffness and better results when the stent is subjected to compression, tensile, and bending forces as these will be directly borne by the yarn.

MECHANICAL PROPERTIES Studies on the radial compression tests for both knitted and braided fabrics have revealed that the best results have been obtained for the braided fabrics with a marginal increase for those heat-set at 140oC. It has been observed that as the fabric cover increases the resilience of the structures also increases [48] Studies on bending tests at 90oC for both knitted and braided samples have shown that the best results have been obtained for the braided fabrics with the effect of the heat-setting temperature producing small and unclear differences. It has been observed that resilience of the structures increases with the fabric cover. Studies on tensile tests for the knitted fabrics have shown that the structures produced with the thicker yarn have a greater stiffness. For the same yarn diameter, the shorter loop length resulted in the stiffer structure. The braided structures produced with the thicker yarn have a greater stiffness. For the same yarn diameter, the higher the braid angle the stiffer is the structure. The braided structures were considerably stiffer than the knitted structures and therefore performed better.

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Overall, the braided structures had better mechanical properties, that is, higher stiffness, than the knitted ones and this was due to their structure being made up of straight yarns rather than loops. The tightness of the construction increased the stiffness in all cases as more fiber per unit area is available to resist the loads. It has been observed that as the yarn diameter increased, the thickness of the fabrics (stent wall) also increased. This may explain the increase in the stiffness of the stents with yarn diameter due to an increase in the thickness of the stent wall.

CONCLUSION Polyester prosthesis used in vascular surgery has been crimped and analyzed for blood flow. The effect of crimping on the blood flow has been measured. Experimental studies have revealed that there are two zones of flow- one is the undisturbed central zone and the other is the disturbed zone at the vascular wall caused due to crimping. A weaving technique has been developed to manufacture bifurcated vascular prosthesis. Dacron polyester has been used owing to its biocompatibility. Studies on the mechanical behavior of crimped polyester prosthesis indicate that the behavior seems to be visco-elastic at higher stresses and elastic at low stresses because of the crimped shape of the graft walls. Yarn size and fabric structure have been varied to produce seamless tubes ranging between 1.5 – 7 mm in diameter. These were heat set for circular shapes and characterized for size, geometry and radial elasticity. Property–structure correlation models have been presented. Grafts of desired size can be engineered and their properties predicted. A fabric prosthesis has been manufactured that is expected to respect haemodynamics, with a central opening, and that is associated with good fatigue resistance for long-term durability.

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N. Gokarneshan, P. P. Gopalakrishnan, V. Rajendran et al. implantation of an aortic valve prosthesis for calcific aortic stenosis: First human description. Circulation, 106(24), 3006-3008. Hufnagel, C.A. (1951), Aortic plastic valvular prosthesis, Bull. Georgetown Univ. Med. Cent. 5, 128-130. International Organization for Standardization (2013), Cardiovascular implants Cardiac valve prostheses – Part 3: Heart valve substitutes implanted by trans-catheter techniques, ISO 5840-5843. Oxenham, H., Bloomfield, P.(2003), A twenty year comparison of mechanical heart valve with porcine bioprosthesis, Heart and education in heart, 89(7), 715-721. Sigwart, U., Puel, J., Mirkovitch, V., Joffre, F., Kappenberger, L.(1987), Intravascular stents to prevent occlusion and restenosis after trans-luminal angioplasty, N. Engl. J. Med. 316(12),701-706. Henry, M., Klonaris, C., Amor, M., Henry, I., Tzetanov, K.(2005), State of Art: Which stent for which lesion in peripheral interventions. Text. Heart Inst. J., 27(2), 119-126. Cribier, A., Eltchaninoff, H., Bash, A., Borenstein, N., Tron, C., Bauer, F., Derumeaux, G., Anselme, F., Laborde, F., Leon, M. B.(2002), Percutaneous trans-catheter implantation of an aortic valve prosthesis for calcific aortic stenosis: First human case description. Circulation, 106(24), 3006-3008. Van Damme, H., Deprez, M., Creemers, E., Limet, R. (2005), Intrinsic structural failure of polyester (Dacron) vascular grafts: A general review, Acta Chir. Belg.105(3), 249255. Von Recum, A., Jane, E.(1998), Handbook of biomaterials evaluation: Scientific, technical, and clinical testing of implant materials, 2nd Edition. CRC Press 1-915. Heim, F., Durand, B., Kretz, J. G., Chakfe, N.(2003), Method for producing an aortic or mitral heart valve prosthesis and resulting aortic or mitral heart valve, WO03/090645. Heim, F., Durand, B., Chakfe, N.(2008), Textile Heart Valve Prosthesis: Manufacturing process and prototype performances, Text. Res. J., 78(12), 1124-1131. Heim, F., Durand, B., Chakfe, N.(2006), Textile heart valve prosthesis: Influence of the fabric parameters on its hydrodynamic performances in vitro. Res. J. Textile Apparel, 58, 75-86. Backer, S. (1952), Mechanics of bent yarn, Text. Res. J. 22, 668-681. Grosberg, P.(1966), The mechanical properties of woven fabrics, Part II: The bending of woven fabric, Text. Res. J.36(3), 205-211. Platt, M. M., Klein, W. G., Hamburger, W. J.(1959), Mechanics and elastic performances of textile materials: Part XIV: Some aspects of bending rigidity of single yarns, Text. Res. J. 29 (8), 611-627. Skelton, J. (1974), Frictional effects in fibrous assemblies, Text. Res. J. 44, 716-722. Skelton, J., Schoppee, M.M. (1976), Frictional damping in multi-component assemblies, Text. Res. J. 46, 661-667. Owen, J. D., Livesey, R.G.(1964), Cloth stiffness and hysteresis in bending, J. Text. Inst., 55, 516-530. Palmaz, J. C. (1992), Cardiovasc. Interv. Radiol. 15(5), 279-284. Roubin, G. S, Pinkerton, C. A., Gianturco- Roubin, (1992), Stent: Development and investigation, Coronary Stents, 79-99.


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[44] Anand, S. C., Kennedy, J. F., Mirafbat, M., Rajendran, S. (Eds) (2005). Implantable devices- An overview, Medical textiles and biomaterials for health care, Cambridge, Woodhead,329-334. [45] De Arjuo, M., Fangueiro, R., Hong, H. (2001), Technical textiles: Materials of the new millennium, Braga Williams/DGI 329-336. [46] Irsale, S., Adanur, S.(2006), Design and characterization of polymeric stents, J. Ind. Text., 35(3), 189-199. [47] De Arjuo, M., Freitas, A., D. P., Zu, W. W., Fangueiro, R. M. E. (2010), Development of weft knitted and braided polypropylene stents for arterial implants, J. Text. Inst. 101(12),1027-1034. [48] Benson Dexter, H. (1998), Development of textile reinforced composites for air craft structures, 4thinternational symposium for textile composites, Japan, 5.



Chapter 19

EFFECT OF CLOTHING MATERIALS ON THERMOREGULATORY RESPONSES OF THE HUMAN BODY P. Kandha Vadivu* Department of Fashion Technology, PSG College of Technology, Coimbatore, India

ABSTRACT The human body continuously generates heat by its metabolic processes. The heat is lost from the surface of the body by convection, radiation, evaporation and perspiration. In a steady-state situation, the heat produced by the body is balanced by the heat lost to the environment by maintaining the body core temperature around a small range between 36 °C and 38 °C. Clothing is used outside the skin to extend the body’s range of thermoregulatory control and reduce the metabolic heat by thermo regulation. Clothing has a large part to play in the maintenance of heat balance, as it modifies the heat loss from the skin’s surface and at the same time has the secondary effect of altering the moisture loss from the skin. The properties of clothing materials critically influence the comfort and performance of the wearer in different weather conditions. Heat transfer through a textile assembly or a fabric system is a complex process, involving conduction, radiation and convection across the fabric system, consisting of fabric and air layers. This study discusses the thermoregulatory process of the human body, the thermal comfort properties of fabrics and the effect of clothing material on the thermoregulatory process of human body in different weather conditions.

1. INTRODUCTION Comfort may be defined as ‘a pleasant state of physiological, psychological and physical harmony between a human being and the environment. Physiological comfort is related to the *

Corresponding author: E-mail: [email protected].

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human body’s ability to maintain life, psychological comfort to the mind withstanding the effect of the external environment on the body [1]. Thermo physiological comfort is defined as the attainment of a comfortable thermal and wetness state; it involves transport of heat and moisture through a fabric. For getting thermo physiological comfort the clothing should have suitable thermal insulation properties as well as sufficient permeability to water vapour and / or sufficient level of ventilation [2]. Comfort involves thermal and non-thermal components and it is related to wear situations such as working, non-critical and critical conditions [3]. Comfort is related to complex interactions between the fabric, climatic, physiological and psychological variables. A person feels comfortable in a particular climatic condition if his energy production and energy exchange with environment are evenly balanced so that heating or cooling of the body is within tolerable limits. A core body temperature of approximately 37 °C is required by an individual for his well being. Hence, the body temperature is the most critical factor in deciding comfort. Heat is gained by the body from the sun or intermediate source of energy, by internal metabolism, by physical exercise or activity, or by involuntary contractions of skeletal muscles in shivering [4]. The heat transport to the environment is achieved through a dry flux (conduction, convection and radiation) and a latent flux produced by perspiration. The first flux depends on the insulation property of clothing while the second one depends on its moisture transport properties. The body vapour must have the opportunity to pass immediately from the skin to the outer surface of the clothing. Heat loss by conduction, convection or radiation, depends partly on the temperature gradient between the skin and the environment and this gradient is modified by varying the skin temperature. Excessive heat may be dissipated rapidly by vapourization of body water and the clothing system that hinders the free evaporation to any appreciable extent will thus be uncomfortable. On the other hand, undesirable heat loss can be prevented by increasing the thermal resistance of the barrier between the body and its environment and a fabric with low resistance will again result in discomfort to the wearer [4]. So it is clear that clothing is a key to body comfort and it should essentially help the wearer in his / her effort and not to give additional physical and heat stress.

2. MECHANISM OF THERMAL REGULATION OF HUMAN BODY The metabolic heat generated by a human body differs based on the physical activity. A base level of metabolism has been defined as the metabolism of a seated person resting quietly and for a man of typical height and surface area, the metabolic rate is about 100W. To normalize among people of different sizes, metabolism is typically expressed in per unit skin surface area. A specialized unit, the ‘met’ has been defined in terms of multiples of basal metabolism: one met is equal to 58.15 w/m². A sleeping person has the rate of 0.7 met, and reclining awake is 0.8 met. Office work (a mostly seated activity but one that involves occasionally moving about) is 1.2 met: Walking slowly (0.9 m/s or 2 mph) is 2 met, moderate walking (1.2 m/s or 2.7 mph) is 2.6 met, and fast walking is 3.8 met and jogging 8 to 12 met. In terms of energy, a sleeping person has the rate of 40.71 w/m², and reclining awake is 46.52 w/m², Office work is 69.78 w/m² [5].

Effect of Clothing Materials on Thermoregulatory Responses ...

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The body’s heat loss is through radiation, convection, conduction, evaporation and through respiration. In a neutral environment, where the body has no need to take thermo regulatory action to preserve its balance, evaporation provides about 12% of total heat loss and sensible heat loss provides 88%. In general, the heat transfer by conduction through the soles of the feet or to a chair is small, around 3%. In normal indoor environments with still air, the convective and radiation heat transfer are about equal. In the outdoors, wind strongly affects convective heat loss or gain and radiation can also cause large losses and gains. Sweating is important for heat regulation, and it is also a major source of water absolute loss. There are two types of water loss: insensible perspiration and sweating. Insensible perspiration loss from the skin cannot be eliminated. Daily loss is about 400 ml in an adult and the respective heat loss is 238 kcal. The heat loss can be quite significant because there is a loss of 0.58 kcal for every ml of water evaporated. The maximum rate of sweating is up to 5 ml/min or 2000 ml/hr in an acclimatized adult. This rate cannot be sustained, but losses up to 25% of total body water is possible under severe stress and could be fatal. There is always a constant amount of trans-epidermal loss of water vapour directly diffused through the skin resulting in heat loss by insensible evaporation. In addition the breathing cycle involves humidifying exhaled air producing another evaporative heat loss. The transversal moisture diffusion is about 100 to 150 ml per day per m² of skin surface representing a heat loss of 6% as great as the evaporation from a fully wetted surface. The respiratory portion of the body’s total heat loss is estimated to be 12% depending on the metabolic rate. Clothing is used outside the skin to extend the body’s range of thermoregulatory control and reduce the metabolic heat by thermo regulation. It reduces sensible heat transfer, while in most cases, it permits evaporated moisture to escape. Bed clothes are a form of clothing used for sleeping, because the metabolic rate during sleep is lower than the basal rate and the body‘s skin temperature tends to be higher during sleep, bed clothes typically have a higher insulation value than clothing.

3. MECHANISM OF HEAT TRANSFER To understand the thermal properties of the textile system, it is necessary to assess the contributions of the various heat-transfer mechanisms that may be operative. These mechanisms are conduction, convection and thermal radiation for dry heat transfer [6,7]

3.1. Conduction Fibers and air intermingle together in any textile yarns and fabrics hence the fabrics are neither homogeneous nor isotropic. However, with the preposition that the average heattransfer properties of fabrics are to be measured and calculated through the theoretical and practical work, it is reasonable to assume that a fabric is a homogeneous and isotropic material in heat transfer. In addition, since thickness of a fabric is substantially smaller than the fabric width and length in normal clothing situations, it is also feasible to consider the heat transfer through a fabric is a one-dimensional problem. Under such assumptions, the

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transient heat-transfer process through the insulating material is described as in Equation (3.1) [8].

T   2T  . t cp x 2 Where,

T t λ ρ c x

(3.1)

temperature (°K); time (s); conductivity (W m -1 K -1 ); mass density (kg m -1 ); specific heat (W S kg -1 K -1 ); and direction of heat transfer.

3.2. Convection As one of the basic heat-transfer mechanisms, convection involves the transport of energy by means of the motion of the heat-transfer medium, in this case the air surrounding the human body. When cold air moves past a warm body, it sweeps away warm air adjacent to the body and replaces it with cold air. It has been found that there is no convection inside clothing insulation even with a very low density [9]. In the finite element analysis, the convective heat transfer will be set as a boundary condition. The heat flux due to convection can be expressed as follows [10].

q  h(Tr  Tx )

(3.2)

heat flux (W m -2 ); h film coefficient (W m -2 K -1 ); TΓ out surface temperature of the fabric (°K); and T∞ temperature of the ambient atmosphere (°K).

Where, q

3.3. Radiation The heat loss carried out by radiation from a clad human body to the environment is a situation where the clad human body as the heat source is enveloped by the environment. In this case, the heat flux by radiation at the outer surface of the textile assembly is governed by the following equations (3.3) and (3.4) [6]. q    (Tr4  Tx4 ) 

Where, q

y  h( Tr  Tx )   ( Tr4  Tx4 ) n

heat flux (W m -2 );

(3.3) (3.4)

Effect of Clothing Materials on Thermoregulatory Responses ... σ ε h TΓ T∞ λ

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Stefan-Boltzmann constant which is 5.6703×10-8 W m-2 K-4 emissivity of the surface. film coefficient (W m -2 K -1 ); out surface temperature of the fabric (°K); and temperature of the ambient atmosphere (°K). conductivity (W m -1 K -1 ).

4. MEASUREMENT OF CONDUCTIVE, CONVECTIVE, RADIATIVE AND EVAPORATIVE HEAT TRANSFER OF HUMAN BODY In order to clarify the heat transfer area involved in convective heat exchange for the human body, which is required for calculating heat exchange between the human body and the environment, Yoshihito Kurazumia et al. (2004) [11] calculated the total body surface area of six healthy subjects and the non convective heat transfer area and floor and chair contact areas for the various body positions. The effective thermal convection area factor for nine common body positions such as standing, sitting in a chair, sitting in the seiza position, sitting cross-legged, sitting sideways, sitting with both knees erect, sitting with a leg out, and the lateral and supine positions are measured. The results showed that the effective thermal convection area factor for the naked whole body in the standing position was 0.942, when sitting in a chair 0.860, when sitting in a chair, excluding the chair contact area 0.918, in the seiza sitting position 0.818, in the cross-legged sitting position 0.843, in the sideways sitting position 0.855, in the both-knees-erect sitting position 0.887, in the leg-out sitting position 0.906, in the lateral position 0.877 and the supine position 0.844. For all body positions, the effective thermal convection area factor was greater than the effective thermal radiation area factor, but smaller than the total body surface area. Kurazumia et al. (2008) [12] scrutinized the convective and radiative heat transfer coefficients of the human body, while focusing on the convective heat transfer area of the human body. Thermal sensors, directly measuring the total heat flux and radiative heat flux, were employed. The mannequin was placed in seven postures. The regression equations for the convective heat transfer coefficients (hc [W/ (m2 K)]) for natural convection, driven by the difference between the mean skin temperatures corrected using the convective heat transfer area and the air temperature, are given below: Standing (exposed to atmosphere) Standing (floor contact) Chair Sitting (exposed to atmosphere) Chair Sitting (contact with seat, chair back and floor) Cross-Legged Sitting (floor contact) Legs-out Sitting (floor contact) Supine (floor contact)

hc = 1.007∆T 0:406 hc = 1.183∆T0:347 hc = 1.175∆T0:351 hc = 1.222∆T 0:299 hc = 1.271∆T 0:355 hc =1.002∆T 0:409 hc = 0:881∆T 0:368

where hc is the convective heat transfer coefficient [W/(m2 K)], and ∆T the difference between mean skin temperature corrected using convective heat transfer area and air temperature [K].

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Richard et al. (1997) [13] analyzed the convective and radiative heat transfer coefficients for individual human body segments and found that the radiative heat transfer coefficient measured for the whole-body was 4.5 W/(m2 K) for both the seated and standing cases, closely matching the generally accepted whole-body value of 4.7 W/(m2 K). Similarly, the whole-body natural convection coefficient for the manikin fell within the mid-range of previously published values at 3.4 and 3.3 W/(m2 K) when standing and seated respectively. In the forced convective regime, heat transfer coefficients were higher for hands, feet and peripheral limbs compared to the central torso region. The ASHRAE Handbook of Fundamentals (1993) has indicated a linearized radiative heat transfer coefficient hr=4.7 W/m2 per K which has been widely accepted as a reasonable whole-body estimate for general purposes [14]. Jones (1998) [15] addressed the need to include the radiation non-uniformity commonly found in indoor environments in body heat loss calculations. Extensive research has been carried out to evaluate the sweating rate. In 1998, Toshio Ohhashi et al. [16] reviewed the methods of human perspiration evaluation. In 1986, Kraning and his co-operator [17] reported a new forced-evaporation-type skin capsule for measuring local sweat gland activity in humans. Shamsuddiny and Togawa (1998) [18] reported a method of continuous monitoring of sweating in which deion solution was perfused at a constant flow rate through a chamber attached to the skin surface.

5. EFFECT OF CLOTHING ON THERMAL COMFORT Clothing has a large part to play in the maintenance of heat balance as it modifies the heat loss from the skin surface and at the same time has the secondary effect of altering the moisture loss from the skin. However, no one clothing system is suitable for all occasions. A clothing system which is suitable for one climate may not be suitable for another climate. Good thermal insulation properties are needed in clothing and textiles used in cold climates. The thermal insulation depends on a number of factors, viz, thickness and number of layers, drape, fiber density, flexibility of layers and adequacy of closures. The thermal insulation value of clothing when it is worn is not just dependent on the insulation value of each individual garment but on the whole outfit as the air gaps between the layers of clothing can add considerably to the total thermal insulation value. This assumes that the gaps are not so large that air movement can take place within them, leading to heat loss by convection. Because of this limitation the closeness of fit of a garment has a great influence on its insulation value as well as the fabric from which it is constructed. The resistance that a fabric offers to the movement of heat through it is of critical importance to its thermal comfort.

6. THERMAL COMFORT PROPERTIES OF FABRICS Thermal properties of textile materials especially thermal conductivity have always been the major concern when the comfort properties of clothing are concerned. The properties of clothing materials critically influence the comfort and performance of the wearer. Clothing is not just a passive cover for the skin. It interacts with and modifies the heat regulating function of the skin and its effects are modified by the environment. Thermal conductivity and thermal


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insulation or thermal resistances and thermal absorptivity are few measures of thermal comfort.

6.1. Thermal Conductivity The ability of a fabric to conduct heat through it is of critical importance to its thermal comfort. Thermal conductivity is a property of materials used to describe the thermal transfer behavior of the heat flow through a fabric due to a combination of conduction and radiation where the convection within a fabric is negligible. The conduction loss can be determined by the thickness of the fabric and its thermal conductivity. As defined by ASTM, thermal conductivity is the time rate of unidirectional heat transfer per unit distance, per unit difference of temperature of the planes. Another relevant concept is thermal conductance (C), also defined by ASTM as the time rate of heat flux through a unit area of a body induced by unit temperature difference between the body surfaces. Normally thermal conductivity can be expressed in equation 6.1

k

Q/ A  T / L

(6.1)

Where Q is the amount of heat passing through a cross-section A, causing a temperature difference ∆T, over a distance of ∆L. Q/A is therefore the heat flux which is causing the thermal gradient. The measurement of thermal conductivity, therefore, always involves the measurement of the heat flux and temperature difference. The difficulty of the measurement is always associated with the heat flux measurement. Guarded hot plate, as described in ISO 8302, is a widely used and versatile method for measuring the thermal conductivity of textiles. Another widely used simple method is directly using a heat flow meter as described in ASTM C 518.

6.2. Thermal Insulation Thermal insulation property of the fabric refers to the ability to resist the transmission of heat by all modes. It can also be defined as effectiveness of a fabric in maintaining the normal temperature of the body under equilibrium conditions. The most important thermal property in most of the apparels is the insulation against heat flow, which is measured by thermal resistance. It is defined as the ratio between temperature difference between the two faces and heat flux. The thermal resistance, R and thermal conductivity, K are related as follows, R = d /K

(6.2)

Where d is the thickness of the material. Since K is roughly constant for different fabrics, hence thermal resistance is approximately proportional to fabric thickness. Thermal insulation value is higher in case of silk fabric compared to cotton fabric. It is due to openness of knit

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structure of silk fabric. Silk fiber contains higher thermal insulation value as it has lower thermal conductivity (50 mw/m/k) than cotton (71 mw/m/k). In studying the thermal insulation properties of garments during wear, it is reported that thermal resistance to transfer of heat from the body to the surrounding air is the sum of three parameters: (i) the thermal resistance to transfer heat from the surface of the material, (ii) the thermal resistance of the clothing material and (iii) the thermal resistance of the air interlayer. It is obvious that heat transfer through a fabric is a complex phenomenon affected by many factors. The three major factors in normal fabrics appear to be thickness, enclosed still air and external air movement. Out of which, the entrapped air is the most significant factor in determining thermal insulation. There are "microlayers" (those between contacting surfaces of the materials) and "macrolayers" (between non-contacting surfaces) of air enclosed within an assembly and an increase of either of these can increase thermal insulation. However, the characteristics of fiber, yarns, fabrics and garment assemblies have also a major contribution towards thermal comfort. Most textile fibers are poor conductors of heat, but air conducts even less heat. If air is confined in small spaces, then convection is also minimized, and the air is ‘dead’. The higher the volume of dead air within a textile structure, the lower the thermal transmittance, therefore, the better the insulation value of the textile material [19].

7. FACTORS AFFECTING CLOTHING COMFORT Thermal wear comfort is mainly related to the sensations involving temperature and moisture. This factor responds mainly with the thermal receptors in the skin and relates to the transfer properties of clothing such as heat transfer, moisture transfer and air permeability. Clothing protects cold or heat to maintain body thermal comfort throughout the full range of human activity. Various types of tactile moisture and thermal interactions between the clothing material and the human skin determine the comfort level of a person at a given environmental condition while engaged in specific activity. The fabric type and its blend composition, the tactile and thermal insulation behavior of the fabric assembly and the moisture management capabilities of the clothing can affect the comfort [20]. A number of properties of fibers, yarns, fabrics and garments are significantly related to comfort and must be taken into account in producing suitable apparel items. However, suitable fabrics from the comfort point of view must be developed by textile technologists by proper selection of fiber content, yarn and fabric construction techniques and finishing treatments as they influence physiological comfort level through thermal retention or transmission, moisture vapour permeability, water resistance, static charge build-up, UV protection etc., Quality of fabrics for clothing depends to a great extent on aesthetic performance, comfort related properties and wear related properties [21]. Of the various properties affecting comfort, fiber type, fineness, cross – sectional shape, crimp, length and surface properties are extremely important. Fabric structure includes yarn linear densities, sett, weave, crimp levels and can influence such critical fabric properties as cover, thickness, bulk density, mechanical and surface behavior which have direct relation with fabric comfort. Finishes which affect the properties of the fabrics and appearance can


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also significantly change the performance of a fabric in clothing. Fabric properties, together with the garment design and size influences the various garment properties [21]. For getting thermo physiological comfort, the clothing should have suitable thermal conducting properties as well as sufficient permeability to water vapour and / or sufficient level of ventilation [2]. The textile structures can be developed to enhance the clothing comfort by focusing principally on the thermal and mechanical properties [4]. There is general agreement that the movement of heat and water vapour through clothing are probably the most important factors in clothing comfort, and Rees [22] describes the temperature regulation of the body in order to define the system in which comfort must be maintained. Hollies (1977) [23] stresses the importance of ‘contact comfort’ in dealing with a clothing system.

8. HEAT TRANSFER THROUGH TEXTILES In the case of clothing, the body temperature is nearly always higher than the temperature of the surrounding environment, so the normal direction of heat transfer is from the warm body to the outside environment. Of course, in particularly hot climates, the reverse is true. When the surrounding environment is colder than the body, resistance to heat transfer increases as the volume of dead air in the clothing increases, and more heat is kept near the body. As long as the air within a fabric or fabric assembly is so called ‘dead’ air, it provides good resistance to heat transfer. However, as the volume of air space increases, the likelihood of air movement, or convection, increases. When convection occurs, it is usually the dominant mode of heat transfer, overpowering any effects of reduced conduction of heat [19]. Heat transfer through a textile assembly or a fabric system is a complex process, involving conduction, radiation and convection. The combined heat transfer across the fabric system, consisting of fabric and air layers, is not simply the sum of what each mechanism would do in the absence of the others. The three heat transfer mechanisms work together to determine the characteristics of the overall heat transfer process. Heat transfer refers to the transfer of heat energy from one environment to another. Heat transfer occurs whenever a temperature difference (∆T) exists between the two environments; heat moves from the warmer surface or area to the cooler surface or area. Heat transfer will continue until the two areas attain same temperature (at equilibrium). The rate at which heat is transferred depends on ∆ T as well as any resistance imposed between the two environments. For people, this means that if the ambient temperature is lower than the body temperature (37° C), heat will flow from the body to the surrounding area. If the ambient temperature is higher than the body, heat will flow the other way and the body will become warmer. Clothing can provide resistance to heat transfer in either direction by serving as insulation between the two environments [19]. For clothing textiles, heat transfer is a complicated transient process. Generated from the body, heat transfers through the air gap between skin and fabric, then through the fabric system, to the outer surface of the fabric system. During this process, conduction, convection and radiation are all involved, may be to different extent, in determining the total heat loss.

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8.1. Effect of Fiber Properties on Heat Transfer Because various fibers differ little in thermal transmittance behavior, fiber physical structure more than chemical make-up affects the overall insulation capacity of a fabric and the thermal comfort of the user or wearer. Fibers have a high surface to volume ratio; thus there are many small spaces for dead air within a fibrous structure. In those spaces, there is little thermal transmittance because air is a very poor conductor of heat; and there is little radiation because although air is transparent to radiation, fibers are not [19]. Some fibers have physical characteristics that enhance this effect of air insulation. For example, wool is a good fiber for insulation because its natural crimp maintains a high volume of dead air. Likewise, manufactured fibers are often given a degree of crimp or surface irregularity that increases thermal resistance. In addition, hollow fibers that inherently entrap air are produced specifically for end-uses in cold weather apparel. Finally, fiber size is consideration in insulation effectiveness. Finer fabrics have more surface area, which results in more dead air space between fibers. An example is the effective use of micro-fibers in coats for use in cold climates [19].

8.2. Effect of Fabric Structure on Heat Transfer Fabric construction also influences thermal insulation. Knitted fabrics generally have a soft hand and higher heat-retaining properties compared with that of woven fabrics of a specific thickness or weight. Knits usually will entrap more air than woven fabrics, although the tightness of the weave or knit is a factor as well. In addition to the openness of the structure, other fabric characteristics are influential in thermal insulation. Pile or napped constructions are often good for cold weather because the yarns or fibers perpendicular to the surface provide numerous spaces for dead air. This effect is maximized when such fabrics are worn with the napped or pile surface next to the body, or when they are covered with another layer. Otherwise, the protruding fibers in the nap structure may conduct heat away from the body [19]. Fabric thickness is of primary importance and is usually considered to be the single more important variable in determining thermal insulation and hence thermal comfort. A thicker fabric provides more air space and, therefore, more resistance to heat transfer that a thin fabric. However, there is a limit for the thickness of the fabric. It must also be lightweight enough to be worn comfortably and, therefore, the ratio of thickness to weight is important [19].

8.3. Heat Transfer through Multilayered Structures Several textile properties affect the thermal resistance or insulation effectiveness of a fabric or a layered assembly of fabrics. An important consideration is the amount of air space contained within a textile structure. Air has low thermal transmittance and high thermal resistance. Most textile fibers are poor conductors of heat, but air conducts even less heat. If air is confined in small spaces, then convection is also minimized, and the air is ‘dead’. The


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higher the volume of dead air within a textile structure, the lower the thermal transmittance, therefore, the better the insulation value of the textile material [19]. Voinov and Karlina (1972) [24] suggested that in clothing assemblies that include air layers, the thermal resistance of the air layer varies in a complex manner with the clothing thickness; they used their results to postulate that better use of the insulating ability of air layers could be made by suitable clothing structure design. Weiner and Shah (1969) [25] however, made attempts to isolate the factors of thickness and weight, and found that for a fixed weight, thermal insulation increases with thickness, whereas the property decreases with increased weight if the thickness is maintained constant. Karlina, with various co-workers (1971) [26] distinguishes microlayers (those between contacting surfaces of the materials) and macrolayers (between non-contacting surfaces) of air enclosed within an assembly and then shows that an increase in either of these can increase thermal insulation. Fonseca (1970) [27] claims that the thermal characteristics of a clothing assembly are governed decisively by the properties of outer layer and that any interior layers merely occupy a part of the still-air layer; their presence therefore merely serves to prevent a decrease in the size of the still-air layer by collapse of the outer garments onto the body. Kawabata and Akagi (1977) [28] found a close correlation between the feeling of warmth on first touching a fabric and the maximum absorption rate of heat flow as measured physically. Markus Weder et al. [29] used Neutron radiography to study moisture transport in textiles for the first time. Clothing systems composed of layers with differing water transport properties were studied to demonstrate the feasibility of using the technique. The results were compared to the weights of the individual layers and the results of the three measurement approaches agree with respect to layer wise moisture distribution in the different textile combinations, and the radiography data provide a lateral visualization of the distributions.

9. CONTROL OF HEAT TRANSFER IN TEXTILES For effective use of textiles to enhance or control heat transfer, one must first identify the primary mode of heat transfer and then select textiles that will modify or enhance that particular mode. Textured, thick, bulky fabrics, and fabrics used in multiple layers reduce conduction. Tightly woven fabrics and designs that restrict air movement control heat transfer by convection. Finally, fabrics with smooth reflective surfaces influence heat transfer by radiation [19]. Peirce and Rees (1946) [30] pointed out that at the outer surface of the clothing exposed to the air; heat is lost by means of both convection and radiation. Farnworth (1983) [31]presented a theoretical treatment of heat transfer through a bed of fibers considering conduction and radiation and reported that no detectable convective heat transfer took place inside the fiber bed. In a more recent study, Mohammade et al.(2003) [32] presented a theoretical equation of the combined thermal conductive, convective, and radioactive heat flow through heterogeneous multi-layer fibrous materials. Dul’nev and Muratova (1968) [33] discussed heat transfer processes in fibrous materials and derived formulae from which effective thermal conductivity can be calculated from thermal, geometrical, and volumetric parameters of the components. Mitu and Potoran (1971) [34] used a formula derived by earlier workers for calculating the thermal resistance of

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clothing to determine a series of values of this property that represent acceptable comfort limits for the human body when engaged in lying, sitting, walking, running and other such activities. As long as the air within a fabric or fabric assembly is so called ‘dead’ air, it provides good resistance to heat transfer. However, as the volume of air space increases, the likelihood of air movement, or convection, increases. When convection occurs, it is usually the dominant mode of heat transfer, overpowering any effects of reduced conduction of heat [19]. Fibers have a high surface to volume ratio; thus there are many small spaces for dead air within a fibrous structure. In those spaces, there is little thermal transmittance because air is a very poor conductor of heat; and there is little radiation because although air is transparent to radiation, fibers are not [19]. Heat transfer through a textile assembly consisting of fabric and air layers can be calculated based on a theoretical model capable of dealing with conductive, convective and radioactive heat transfer. The size of the air gaps has a significant influence on the heat transfer. The balance heat flux drops by 40 per cent when the air gap increases from 2 to 10 mm. The influence of the air gap tends to become smaller as the air gap is further increased. The number of fabric layers in the textile assembly has a noted influence; more so when the ambient temperature is lower [35].

10. MEASUREMENT OF CLOTHING COMFORT USING THERMAL MANIKIN Since the first one segment copper thermal manikin in the world was made for the US army in the early 1940s, more than 100 different thermal manikins have been employed for research and product development worldwide. Holmer [36] reviewed thermal manikin development history and summarized the milestones. Interest in using thermal manikins in research and measurement standards is steadily growing and several international testing standards have been developed in the field of the thermal comfort evaluation. To date, thermal sweating manikins are widely used in large scale textiles and clothing research laboratories all over the world for analyzing the thermal interface of the human body and its environment. Normally, the thermal manikin is made from metal or fabric e.g., copper, plastic or water / windproof fabric with an independent controllable heating/sweating subsystem, data measurement and analyzing subsystems. With the development of computer and computation technologies, visual realization models have become more and more important and are now widely applied in the field of thermal comfort estimation. Li et al. [37] developed a computer based model for studies of heat moisture transfer in clothing systems. Buxton et al. in the UK are also developing a similar model that allows the use of human body data from whole body scanners and motion patterns derived from real recordings.


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11. MEASUREMENT OF CLOTHING COMFORT USING THERMAL / SWEATING PLATE The thermal/sweating plate has been used for years to determine the thermal and moisture resistance properties of fabrics. The applications and description of sweating hot plates can be found in Goldman [38] and Holmer et al. [39]. There are several types of skin model employed in clothing comfort research. Firstly, Kawabata [28] reported the application of hot plate technology for the measurement of fabric warm and cool feelings. The thermal lab is only used to evaluate the warm or cool feeling produced upon touching a fabric. Thermal conductivity is measured in the steady state. A damp paper was put on the hot plate to stimulate human skin. A representative sweating hot plate is described in the Farnworth’s paper [31]. This sweating hot plate is designed to maintain a constant surface temperature of 35ºC and consists of a circular shaped inner plate, a guard ring plate and a base plate. The sides of the inner plate are separated from the guard ring plate by a 1 mm air gap and the bottom of the inner plate is separated from the base plate by 50mm of foam insulation. The guard ring plate and the base plate prevent heat flow away from the inner plate in the lateral and downward directions, respectively. Electrical heaters, connected to DC power supplies, are used to maintain the inner plate at a constant temperature of 35oC, which is determined by a thermistor. All three plates are located inside a heated box to eliminate further heat flow away from the inner plate in any direction other than that upward from the plate surface. Typical structure and detailed description of a sweating hot plate can be found in ISO 119021993(E).

CONCLUSION The properties of clothing materials critically influence the comfort and performance of the wearer. Clothing is not just a passive cover for the skin, it interacts with and modifies the heat regulating function of the skin and its effects are modified by the environment. The combined effects of the properties of clothing materials and wind on the physiological parameters of human wearers are the critical factors to be considered in designing functional clothing and are going to be the niche area of research in future.

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[3] [4]

Slater, K. (1977). Comfort Properties of Textiles. Textile progress, 9, 1-91. Jeffries, R. (2005). Functional Aspects of High performance clothing. Book of Abstracts, Fashion the future, British Textile Technology Group, Shirley Publication, 126-128. Fourt, L. and Hollies, N.R.S. (1970). Clothing: Comfort and Function. Marcel Dekker Inc., New York, USA Bhat, P. & Bhonde, H. U. (2006). Comfortable clothing for Defence Personnel. Asian Text. J. 73-77.

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[18] [19] [20] [21] [22] [23]

[24] [25]

P. Kandha Vadivu Butera, F. M. (1998). Principles of thermal comfort. Renew. Sust. Ener. Rev., 2(1-2), 39-66. Gagge, A. O., Buston, A. C. & Bazett, H. C. (1941). A Practical system of units for the description of heat exchange of Man with his environment. Science, 94, 428-430. Rohsenow, W. M. & Hartnett, J. P. (1973). Handbook of Heat Transfer, McGRAQHALL Book, New York. Yang. S. M. & Tao., W. Q. (1999). Heat Transfer. Higher Education Press, Beijing. Peirce, F. T. & Rees, W. H. (1946). The transmission of heat through textile fabrics, Part II. J. Text. Inst., 37, 181-204. Incropera, F. P. & DeWitt, D. P. (2002). Fundamentals of Heat Transfer, 5th ed. Wiley, Somerset, NJ. Kurazumi, Y., Tsuchikawa, T., Matsubara, N. & Horikoshi, T. (2004). Convective heat transfer area of the human body. Eur. J. Appl. Physio., 93, 273-285. Kurazumia, Y., Tsuchikawab, T., Ishiia, J., Fukagawaas, K., Yamatoc, Y. & Matsubara, N. (2008). Radiative and convective heat transfer coefficients of the human body in natural convection. Building and Environment, 43, 2142-2153. Richard, J., Dear, D., Arens, E., Hui, Z. & Oguro, M. (1997). Convective and radiative heat transfer coefficients for individual human body segments. Int. J. Biometeorol., 40, 141-156. Fanger, P. O. (1977). Local Discomfort to the Human Body caused by Non-Uniform Thermal Environments. Ann. Occup. Hyg., 20(3), 285-291. Jones, B. W. (1998). Radiant heat transfer between the human body and its surroundings. ASHRAE Transactions, 104(2), 1340-1350. Ohhashi, T., Sakaguchi, M. & Tsuda, T. (1998). Human perspiration measurement. Physiological Measurement, 19, 44. Kraning K. K. & Gonzalez, R. R. (1991). Physiological consequences of intermittent exercise during compensable and uncompensable heat stress. J. Appl. Physiol., 71(6), 2138-2145. Shamsuddin A. K. M & Tatsuo, Togawa. (1998). Continuous monitoring of sweating by electrical conductivity measurement. Physiological Measurement, 19(3), 375. Collier, B. J. & Epps, H. H. (1999). Textile Testing and analysis. Prentice-Hall Inc., New Jersey, U.S.A. Kothari, V. K. (2006). Thermophysiological comfort characteristics and blended yarn woven fabrics. Indian J. of Fib.Text. Res., 31(1), 179-186. Kothari, V. K. (2004). Fabric comfort. Proc. of the seminar on comfort in textiles, IIT Delhi, New Delhi, India, Rees, W. H. (1972). Materials and Clothing in Health and Disease-The Biophysics of Clothing Material, Lewis Pub., London. Hollies, N. R. S. & Goldman, R. F. (1977). Clothing comfort: Interaction of thermal, Ventilation construction and Assessment Factors. Michigan, Ann Arbor Science publishers Inc. ann harbor, USA. Voinov, Y. F. & Karlina K. V. (1972). Assessment of the Thermal Resistance of clothing. DRIC translation, 2920. Weiner, L. I. &Shah, J. (1969). Insulating Characteristics of Battings. Text. Chem. Color., 1, 301-306.


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[26] Karlina, E. V. & Tretyakova, L. I. (1971). Investigation of the Effect of Macro-Layers of Air on the Thermal Insulation Properties of Clothing Assemblies. Teknolngiva, Legrol Drom., 2, 98-102. [27] Fonseca, C. F. &Breckenridge,J. R. (1965). Wind Penetration Through Fabric Systems, Text. Res. J., 35, 95-103. [28] Kawabata, S. & Akagi, Y. (1977). The Standardization and Analysis of Hand Evaluation. Text. Mach. Soc. Japan, 3, T13. [29] Weder, M., Brühwiler, P. A. & Herzig, U. (2004). Neutron Radiography Measurements of Moisture Distribution in Multilayer Clothing Systems. Text. Res. J., 749s(8),695700. [30] Peirce, F. T. & Rees, W. (1946). The transmission of heat through textile fabrics, Part II. J. Text. Inst., 37, 181-204. [31] Farnworth, B. (1983). Mechanisms of heat transfer through clothing insulation, Text. Res. J., 53, 717-725. [32] Mohammade, M. & Banks-Lee, P. (2003). Determining effective thermal conductivity of multilayered nonwoven fabric. Text. Res. J., 73, 802-808. [33] Dul’nev, G. N. & Muratova. (1968). Thermal Conductivity of Fibrous Systems, J. Eng. Phys. Thermo physics, 14(1), 15-18. [34] Mitu, S. & Potoran, I., (1971). Fundamentals of Textile Clothing Technology. Bul. Inst. polytech. Iasi, 17(1-4), 61. [35] Sun, Y., Chen, X., Cheng, Z. & Feng, X. (2010). Study of heat transfer through layers of textiles using finite element method. Int. J. Clothing Sci. Technol., 22(2/3), 161. [36] Holmer, I. (2004). Thermal manikin history and application. Eur. J. Appl. Physiol., 92(6), 614-618. [37] Li, Y. & Holcombe, B. V. (1998). Mathematical Simulation of Heat and Moisture Transfer in a Human-Clothing-Environment System. Text. Res. J.,68(6), 389-397. [38] Goldman, R. F. (1981). Evaluating the Effects of Clothing on the Wearer. Bioeng. Thermal Physiol. Comfort, 41-55. [39] Holmér, I. & Elnäs, S. (1981). Physiological evaluation of resistance to evaporative heat transfer by clothing. Ergonomics, 24, 63–74.



Chapter 20

DESIGNING OF JUTE–BASED THERMAL INSULATING MATERIALS AND THEIR PROPERTIES Sanjoy Debnath National Institute of Research on Jute and Allied Fibre Technology, Indian Council of Agricultural Research, Kolkata, West Bengal, India

ABSTRACT Among the different natural fibres, jute is less expensive, annually renewable and commercially available fibre compared to other fibre crops. Jute is mostly cultivated in India and Bangladesh. This fibre is being popularly used as packaging material, hessian and carpet backing for over a century. After introduction of man-made fibres in the1950s, the market of such traditional products made out of jute has been almost replaced by the synthetic fibres due to their low cost and high production speed. As far as thermal insulating material is concerned, wool-based material either from natural wool or artificial fibres like acrylic is thought about but seldom jute/jute-blended materials. However, in the present chapter, effort has been made on diversification of jute usage, specifically, as thermal insulating material. To upgrade its thermal insulation properties, the suitable modifications done to the fibre/yarn structures, have been discussed here. Also, the structural design of weaving using jute-based yarns and the design parameters involving in designing of suitable warm garments from jute-based materials have been discussed. The measurement of thermal insulating property and its factors affecting its insulating property have also been covered. Besides, important area like nonwoven fabrics mostly used as industrial material, its design towards development of jute-based thermal insulating material has also been focused in this chapter.

Keywords: Blending of fibres, Chemical treatment, Jute fibre, Polyester fibre, Polypropylene fibre, Thermal insulation, Warm fabrics



E-mail: [email protected]; [email protected].

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INTRODUCTION Among the different fibre crops, jute is one of the oldest cultivated fibre crops in India. India is the highest producer of jute in the world, and is mostly cultivated in the eastern part of the country. It is the cheapest fibre crop available commercially in bulk quantities so jute fibre is being technically used extensively over the centuries. For example it is used as, packaging material, carpet backing, hessian as industrial applications. It is also used for reinforcement of rural mud houses, thermal insulating material for domestic animals like cattle, pet dogs etc. As far as the properties of jute fibre are concerned, it has both desirable and undesirable ones. Basically, this fibre has mesh like structure which provides better coverage, good tensile strength, toughness and durability. Due to its less extension at break, it ensures dimensional stability. The natural colour of the fibre renders it an ethnic value, which ensure its use as a material for various handicrafts and artefacts. Unlike any other fibres, the drawbacks of jute fibre crop are high surface roughness and prickliness, low extension at break and coarseness which restricts its use in textile garment. Keeping this in view warm clothes has been designed and developed using jute-based fibres and yarns. Thermal insulation is one of the essential properties for any warm fabrics [1]. Judicious modifications of the fibre/yarn structure is one of the important aspect as far as its development as thermal insulating material is concerned. The thermal insulation related properties mainly depends on the availability of amount of air pores in the textile structure. Air trapped in fabric pores, makes the fabrics act as thermal insulating media [2].

CLASSIFICATION OF WARM CLOTHS Structurally, the warm fabrics can be classified into different categories viz., knitted, woven, nonwoven and composite (more than one structure of fabric or combination of structures). Also, as per the usage of the warm cloths, it can differentiated as wearable textile and non-wearable textiles. Under the wearable textile the applications may be shawl, jacket, blazer, muffler, sweater, pullover etc. on the other side the non-wearable textiles include blanket, carpet, floor coverings, curtains, industrial insulation etc.

DESIGNING OF WARM FABRICS The basic structures like woven and knitted, require yarn as prerequisite material for designing of warm fabrics. However, in-case of nonwoven structures, instead of yarn, it may be directly from fibre, where modifications in fibre or fabric stages are needed to achieve desire properties for warm fabrics [3]. In case of woven and knitted structures modifications during yarn forming or fabric manufacturing stages or modifications of both the stages are essential to develop jute based warm fabrics. Bulking of yarn is prerequisite for designing of warm fabrics either from weaving or knitted structures [4]. Following process describes about the bulking methods used to achieve considerable bulk in the yarn structure of woven or knitted fabric.

Designing of Jute–Based Thermal Insulating Materials and Their Properties

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WOOLLENISATION OF JUTE As wool fibre is sourced from animal, fibre has limitation of production and also costly compared to jute fibre. However, jute fibre does not have any crimp or scale as found in case of wool fibre. Because of presence of these scales/crimps in wool fibre, the fibres do not come close to each other in the fabric or yarn structure and as a result more void occurs in the structure. The static air gets trapped in the void and acts as thermal insulating medium and hence any material made out of wool seems to have higher thermal insulation. Woollenisation is basically an alkaline treatment [5] and it is also called as chemical texturizing process of jute. This process produces wool like crimp [6, 7, 8, 9] and thus increases available air space. Breaking elongation increases after this treatment due to formation of crimp/lateral expansion of the yarn. In this process, jute is treated with the NaOH solution and it is found that 18% NaOH solution gives optimum result for the Woolenization [10]. Alkaline treatment removes significant amount of the hemicellulose and small quantity of soluble lignin present in the jute structure and as a result fall in strength of the jute has been observed. Several attempts were also made to recover NaOH after this delignification process, from the spent liquor. Woollenisation process introduces several changes in properties of the jute fibre. Accordingly, yarn properties after woollenisation treatment also changes significantly compared to un-treated yarn [11]. After this process, the surface of the yarn becomes rough, and exaggerated further when bleached. Because of these reasons, fully woollenised jute yarn is not solely appropriate for preparation of warm garments like shawl/wrappers, sweaters etc. However to improve the surface feel and softness of the yarn, different chemical softeners such as Velan PF and Sopamine OC, has been used. Further, to increase the water repellence different silicone treatment is needed. The introduction of the silicone treatment gives a semipermanent water repellence property and it withstands laundering fairly well.

WOOLLENISED JUTE AND WOOL BLENDED YARN Woollenised jute can be well mixed with natural wool at 50:50 ratio [1]. We can produce coarse yarn in woollen/worsted systems. Other than the wool fibre, other natural or synthetic fibres such as cotton or polypropylene (PP) can be blended with woollenised jute to produce different unconventional high value products [5]. Bleaching of blended yarn produced from woollenised jute and wool can be done with 0.75 vol H2O2 solution for 2 hours at 80oC [5]. Twelve different shades were obtained by dyeing of woollenised jute blended yarn; both bleached and unbleached woollenised jutes were used and they were mixed with wool at the ratio of 35:65 [6, 12, 13].

WOOLLENISED JUTE AND POLYPROPYLENE BLENDED YARN In several studies, different fibers were blended with the woollenised jute. One the fibres that is often mixed with woollenised jute is Polypropylene (PP). The blend ratio of 80:20 (Jute: PP) is used to produce yarn and it is found that incorporation of PP to the blend gives a higher bulk with stretch. It also facilitates the preferential migration to the surface of the yarn.

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Woollenised jute and PP blended yarn have higher bulk in comparison to the yarn which is produced from Indian Chokla wool. However, this wool yarn shows higher breaking elongation and uniformity of diameter. The Tenacity of textured Jute:PP blended yarn is higher than the wool yarn (Indian Chokla Wool), though at the time of woollenisation the tenacity of the jute component drops significantly [1]. It is also found that wet/dry tenacity ratio is higher in jute: PP blended textured yarns than the wool yarn [14, 15, 16].

WOOLLENISED JUTE-POLYESTER, JUTE-HOLLOW POLYESTER AND JUTE-ACRYLIC BLENDED KNITTING YARN Rotor spun short staple jute-polyester blended yarns were texturized and compared with conventional apron draft jute spun texturized yarn by Ghosh and Samanta, 1997 [17]. It was found that 70:30 of jute and polyester blended rotor spun yarn showed the optimum result. Sinha and Basu, 2001 [18] used jute-shrinkable acrylic fibre to develop bulked knitted yarn. They used a simple technique to develop bulk in the raw jute-acrylic blended yarn. The bulk in the raw yarn can be developed by boiling the yarn in water for 15-30 min or steaming treatment. Study was also conducted on effect of sodium hydroxide on jute-acrylic blended yarn spun in DREF spinning system [19]. They studied the effect of treatment time, concentration and blend proportion on yarn bulk, strength, extension and packing of juteacrylic blended DREF spun yarns. Jute and hollow polyester fibre (80:20) blended fine yarn (130 tex) has been developed [20]. These yarns was further plied and made into 2-ply and 3-ply yarns. Woollenisation treatment was done for 2-ply and 3-ply blended yarns. Further, bleaching and dyeing was also conducted. The yarn shrinkage and weight loss properties have been studied at every stage and compared with the untreated yarn. Also, other physical properties viz., tenacity, breaking strain, diameter, coefficient of friction, specific work of rupture, bulk density have been studied and compared with the similar woollen and acrylic commercial yarns. This study (Debnath et al. 2007a) established that jute-hollow polyester blended yarn has higher bulk over similar commercial yarns due to low yarn packing [20]. The 3-ply jutehollow polyester blended bulked yarn has better bulk, regularity (cv %), extensibility, pliability and work of rupture than those of 2-ply yarn. The tenacity of 3-ply blended bulked yarn deteriorates after 18% (w/w) NaOH chemical treatment while breaking extension remarkably increases (Figure 1). However the percentage coefficient of variation of both tenacity and breaking extension decreases after bleaching and dyeing. This yarn shows almost similar tenacity with lower extension compared to wool yarn (Figure 2). The lowest specific work of rupture is observed in the 3-ply blended bulked yarn. This 3-ply blended bulked yarn also shows lower coefficient of friction than wool yarn (Table 2). The specific flexural rigidity of jute-hollow polyester blended yarns are lower than woollen yarn but comparatively higher than acrylic yarns.


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Table 1. Yarn shrinkage and weight loss behaviour of 80:20 jute-polyester (hollow) blended bulked yarn [20] Chemical Processes Bleaching Dyeing

2-Ply blended yarn Shrinkage (%) Weight loss (%) 10 15.37 10 18.01

3-Ply blended yarn Shrinkage (%) Weight loss (%) 12.5 14.27 12.5 16.74

Table 2. Comparison of 80:20 jute-Polyester (hollow) bulk yarn with acrylic and wool commercial yarns [20] Properties 3-ply acrylic Linear density (tex) Diameter (mm) Packing factor Packing factor C.V.% Bulk density (g/cm3) Tenacity (cN/tex) Tenacity C.V.% Breaking strain (%) Breaking strain C.V.% Specific work of rupture (mJ/tex-m) Coefficient of friction of yarn () Specific flexural rigidity (mN-mm2/tex2 X 10-4)

Commercial yarns 4-ply acrylic

4-ply wool

3-Ply dyed jute-hollow polyester yarn

170 1.19 0.128 15.46 0.153 7.44 7.01 37.35 9.83

290 1.71 0.106 11.56 0.126 9.10 6.55 45.42 11.57

300 1.35 0.161 11.61 0.210 4.00 10.12 18.01 16.73

370 1.85 0.094 16.14 0.138 3.84 9.09 8.6 7.83

16.85

14.00

4.47

1.27

0.81

0.80

0.90

0.84

9.57

5.20

23.20

11.98

Figure 1. Stress strain behaviour of jute-hollow polyester blended yarns [20].

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Figure 2. Comparison of stress strain behaviour of jute-hollow polyester blended yarn with acrylic and wool yarns [20].

BLANKET AND CARPET PRODUCTS FROM WOOLLENISED JUTE AND POLYPROPYLENE BLENDED YARN Different products have been developed out of woollenised jute and polypropylene fibre blends, some of them are listed below: CAPLON Blanket – Main advantages of this blanket over wool blanket is higher Strength, moth resistance, and good thermal insulation properties. Carpet – Different kinds of carpets that can be produced from the woollenised jute: PP blended yarns are Chenile, hand knitted, tufted and woven carpets. Chenile carpets – These kind of carpets can be produced by doubling the woollenised pile yarn and varying the length of pile. Main advantage of this kind of carpet is that, pile yarns do not easily come out from the carpet body. Hand knitted carpets – This kind of carpets shows a similar tuft withdrawal force and recovery from compression properties to wool carpets and its properties are superior than carpets which are produced from the polypropylene. Tufted carpets – Tufted carpets have also been developed from woollenised-Jute/PP blended yarn. They showed better performance because of high strength and uniformity of the yarns. Woven carpets – Woven carpets are also known as Wilton and Tapestry carpets. Main advantages of this kind of carpets are fly generation and fibre shredding are almost absent at the time of production. The yarn breakage during production are also less. It gives a better stretch property which enhance the formation of proper piles with less tension, and this piles show better results to the seat and grip than jute pile yarns [16, 20].


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Blanket from Woollenised Jute and Hollow Polyester Blended Fibre Traditionally, one of the application of wool is well known to all of us for use in making blanket. However, due to limited production of this natural fibre, nowadays synthetic fibres like acrylic, polyester etc. are also being used in the area of blanket making. It is found that, jute is still the most cheapest textile fibre available in some part of the world. Hence the product made out of this cheap fibre will reduce the cost of production. The jute and hollow polyester (PET) fibre were blended homogeneously in the ratio of 80:20 in first drawing machine of jute spinning system [4]. The final blended yarns were spun in jute slip draft spinning machine to achieve the yarn linear density of 276 tex (8 lbs/spy). These yarns are directly used in warp direction during weaving. Further, these same yarns were plied into two ply and twisted to obtained linear density of 552 tex (16 lbs/spy). This 2 ply is use as weft yarn during weaving of blanket. Both these warp and weft yarns were chemically texturized separately using standard procedure [10] and further dyed in dark shade (Figure 3). The yarns were finished as per standard method to obtain melange effect. Jute-hollow polyester (80:20) blended yarns were used to weave into fabric (2/2 twill) with 276 tex (8 lbs/spy) single yarn in weft direction (18-20 picks/inch). In warp direction, 276 tex (8 lbs/spy) 2-ply yarn (9-10 ends/inch) was used [22]. Normally, it is recommended that a reed width of more than 78“ is essential for weaving of blanket fabric, considering the loom stage shrinkage. It has been found from the literature that 80:20 jute-PET blended blanket and 100% woollen blanket are having thermal insulation values (TIV) of 0.78 tog and 0.86 tog respectively [23]. Performance and cost wise jutehollow polyester (80:20) blended raised blanket and 90:10 raised blanket is lower (Rs.295/-) compared to commercial woollen (Rs.450/-) and acrylic (Rs.825/-) blankets [23].

Figure 3. Blanket from chemically texturized jute-hollow polyester blended yarns.

SPINNING OF JUTE-BASED BLENDED FINE YARN FOR WARM CLOTHS In case of apparels, wherein person has to wear it or wrap it around the body it is essential to have the fabrics as light as possible. The final weight of the fabric for the aforesaid purpose has to be reduced, so very fine yarn of 122 tex has been developed using jute spinning system. The polyester (hollow) fibre of 6 denier, 110 mm is used to develop the

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yarn for the warm cloth weaving. Jute-hollow fibre blended yarn has higher bulk density compared to other blended yarns [24, 25]. The conventional jute spinning system is used to produce blended yarn. The blended yarn of jute and polyester (hollow) fibre was successfully spun from drawing stage of blending processes. The raw jute of TD-3 was used for development of overall blended samples. The conventional jute batching oil was used before piling for 48 hours. The blended yarn samples were produced both with 70:30 and 80:20 jute:polyester fibres [26]. These samples produced from spinning was of 122 tex with 6 t.p.i. (twist per inch), ‘Z’ twist. All these blended yarn samples were spun suitably in apron draft spinning system over slip draft spinning system.

WEAVING OF SHAWL FABRIC FROM VERY FINE YARN AND CHARACTERISATION The jute-blended yarn was used as weft yarn and commercial cotton yarn of 5.9 tex (100s Ne) as warp yarn for development of the shawl fabric. Handloom weaving machine [27] with jacquard attachment (at least 100 hooks) and handloom preparatory machinery were used to weave these fabrics. Plain and twill (3/1) are the two basic designs used to weave the fabrics. For body and border of the shawl separate jacquard weaves were used. Ornamentation was done with introduction of extra weft yarns [28] (commercial polyester-viscose of 14.7 tex or 40s Ne two ply) at the jacquard design areas on the fabric. Few samples were also developed using localised dyeing in the warp yarn, giving a Kotkee look (tie-dye) to the fabric. Attempt was also made to develop fabric with combination of plain and twill weave (Figure 4). The developed shawl fabrics were characterised and compared with the commercial (khadi) cotton and acrylic shawls. The fabric weight, fabric thickness, fabric cover factor, thermal insulation value (tog) and flexural rigidity are the various properties that have been studied using standard testing methods [29]. The thermal insulation value was studied using the instrument developed by NIRJAFT [30, 31] where the test is non-destructive in nature.

Figure 4. Shawl from jute-polyester blended and cotton yarns.


507

The fabric weight increases with the increase in pick density for both the plain and twill weaves [2]. The fabric weight is between 147 and 160 g/m2 for commercial fabrics under consideration. However, the fabric weight of the developed fabric ranges between 169 and 263 g/m2. Both the thickness and thermal resistance values of the developed jute blended fabric samples are closer to that of cotton/acrylic commercial shawl fabrics. The cloth cover factor was also higher compared to commercial shawl fabrics (cotton/acrylic). The flexural rigidity in warp direction of the developed fabrics is comparatively lower than the cotton/acrylic fabrics due to use of very fine cotton yarn in warp direction (5.9 tex). Jute has higher rigidity due to its coarseness, so when it is used in the weft direction of the jute blended fabric, a tremendous increase in flexural rigidity in weft direction is observed in the developed fabrics. It also increases with the increase in pick density of the fabric. Few fabrics were developed where slit film were used alternately in weft direction along with jute-polyester blended yarn. The fabric weight is between 147 and 160 g/m2 for commercial fabrics under consideration. However, the fabric weight of the developed lightweight shawl fabrics ranges between 136 and 162 g/m2. The thickness values of the developed shawls are closer to cotton shawls but lower than acrylic shawls. Cover factor values of the developed shawls are between 17 and 20 (which, is between the cover factor values of commercial acrylic and cotton shawls). The thermal resistance values of the developed jute blended fabric samples are 19% higher compared to acrylic and 66% higher compared to cotton commercial shawl fabrics [32]. These developed shawl fabrics are moreor-less equally porous compared to commercial shawls under consideration as per as the sectional air permeability is concerned. The tenacity and breaking extension behaviour of the developed jute blended shawls and compared with the commercial cotton and acrylic shawls both in warp and weft directions. The tenacity values of the jute-blended shawls are closer to that of cotton shawls and lower than acrylic shawls in warp direction. However, in weft direction, tenacity is little higher than cotton and closer to acrylic shawls. Breaking extension values of the developed shawls are much lesser than acrylic or cotton shawls both in warp and weft directions of the fabric samples [31]. The effect of washing (after five-repeated detergent washing) on tensile and air permeability property of jute-polyester and cotton blended shawls and compared with their original values (before washing). This study reveals though there is little drop in tenacity after wash in warp direction (cotton yarns) but no change have been found in weft direction (jutepolyester blended yarns). Little improvement in extension have been observed in weft direction. There is a fall in flexural rigidity values in warp direction and an increase in trend was found in weft direction after washing treatment. A significant drop in sectional air permeability was observed after washing of the developed shawl samples [31].

Jacket from Jute-Based Yarn and Evaluation Jackets have been developed using handloom to weave winter fabric. Three different types of jute-polyester and cotton blended jacket fabrics have been developed. Handloom jacquard has been used to introduce design in the fabric during weaving. The jute-blended yarn and commercial cotton yarn were used alternately as weft and commercial cotton yarn of 5.9 tex (100s Ne) was used as warp for development of the jacket fabric of 136 g/m2. For

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other two fabrics, in warp direction, cotton yarns were dyed in dark blue shade. In weft direction alternate use of cotton and jute-blended yarn improves the fabric appearance and other physical properties (Figure 5).

Figure 5. Jacket from jute-based jacket fabric.

The fabric weight and thermal insulation values were measured for the developed fabrics and compared with the commercial (khadi) cotton and acrylic jacket fabrics. The developed jacket fabric shows 30 % and 62 % higher thermal insulation value compared to commercial acrylic and cotton jacket fabrics respectively. This developed fabric is also 8 % and 17 % lighter in weight compared to commercial acrylic and cotton jacket fabrics respectively. The fabric thickness of the developed jute based fabric is 47% and 19% lower compared to commercial acrylic and cotton jacket fabrics respectively [32]. Alternate use of jute-polyester and cotton yarn in weft direction has been used to improve the aesthetic and physical properties of developed fabrics. Other four different types of jackets have been tailored using these developed jacket fabrics. Other than zip, buttons and sewing yarn, all these developed jackets comprise of three basic materials: a) jacket fabric; b) lamination material and c) lining material. In one case the lining material for developed jacket used as acrylic fabric and rest of the cases polyester lining material have been used. Out of all these jackets, one reversible jacket has been developed using developed jacket fabric. Weight, thermal insulation and thickness properties of the developed jute-blended jackets have been evaluated and compared with commercial jacket (Oswal make). It is found that overall the thermal insulation of the developed jackets are higher than commercial jackets (Anonymous, 2008). The thermal insulation of jackets can be lower or higher depending on the constructional design of the jacket fabric and lining material of the jacket. The weight of the jackets depend on the design of the jacket fabric and jacket type. Thickness values of all developed jackets except those of reversible ones, are lower than commercial jacket (Oswal


509

make). Apart from these no dimensional changes of jackets have been observed after one cold water detergent wash.

Thermal Insulation Behaviour of Jute-Based Nonwoven Fabrics Different types of parallel laid and random laid needle punched and adhesive bonded nonwoven fabrics were prepared using blending of different fibre materials (polypropylene, acrylic, jute, woollenised jute, jute caddis, cotton, wool, ramie, pineapple leaf fibres etc.). Two types of blending methods were used such as sandwich and homogeneous. Sandwich blending of polypropylene or acrylic with woollenised jute shows better thermal insulation compare to homogeneous blended materials as found by Debnath et al., 1987 [3]. They also found that nonwoven prepared out of woollenised jute-wool (2:1), woollenised jute-acrylic (2:1) and woollenised jute-pineapple leaf fibre (2:1) have better thermal insulation property. Air permeability and thermal conductivity of jute needle-punched nonwoven fabrics have been studied by Sengupta et al., 1985 [33] and found that jute needle punched nonwoven has poor in heat transmission. Further, Box and Behnken factorial design [34] was used to design and development of needle-punched nonwoven fabrics made from jute and polypropylene blends to study the effect of fabric weight, needling density and blend proportion on thickness, thermal resistance, specific thermal resistance, air permeability and sectional air permeability. Polypropylene fibre of 0.44 tex fineness, 80 mm length and jute fibres of Tossa-4 grade were used to develop the jute-polypropylene blended needle-punched nonwoven [35]. Some of the important properties of these jute and polypropylene fibres are presented in the Table 3. Table 3. Properties of jute and polypropylene fibres [35] Property Fibre fineness, tex Density, g/cm3 Moisture regain at 65% RH, % Tensile strength, cN/tex Breaking elongation, %

Jute 2.08 1.45 12.5 30.1 1.55

Polypropylene 0.44 0.92 0.05 34.5 54.13

PREPARATION OF JUTE-POLYPROPYLENE BLENDED THERMAL INSULATION NONWOVEN FABRICS The jute reeds were opened in a roller and clearer card, which produces almost mesh-free stapled fibre. The woollenised jute and polypropylene fibres were hand opened separately and then blended using three different blend proportions (Table 4). The proportion of woollenised jute fibres taken is 2% higher than the blends showcased in Table 4 considering droppings of jute component [35] in the card and subsequent processes to maintain target blend in the output material. The blended materials were thoroughly opened by passing them through one carding passage.

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Table 4. Actual and coded values for three independent variables and the experimental design [35] Levels of variables Fabric code

X1 level

Coded

Actual

Coded

Actual

Coded

Actual

1

–1

250

–1

150

0

60 : 40

2

–1

250

1

350

0

60 : 40

3

1

450

–1

150

0

60 : 40

4

1

450

1

350

0

60 : 40

5

–1

250

0

250

–1

40 : 60

6

–1

250

0

250

1

80 : 20

7

1

450

0

250

–1

40 : 60

8

1

450

0

250

1

80 : 20

9

0

350

–1

150

–1

40 : 60

10

0

350

–1

150

1

80 : 20

11

0

350

1

350

–1

40 : 60

12

0

350

1

350

1

80 : 20

13

0

350

0

250

0

60 : 40

14

0

350

0

250

0

60 : 40

15

0

350

0

250

0

60 : 40

X2 level

X3 level

X1 – Fabric weight, g/m2; X2 – Needling density, punches/cm2; and X3 – Blend ratio (polypropylene: woollenised jute).

The blended fibres were then fed to the lattice of the roller and clearer card at a uniform and predetermined rate so that a web of 50 g/m2 can be achieved. The fibrous web coming out from the card was fed to feed lattice of cross-lapper, and cross-laid webs were produced with cross-lapping angle of 20. The web was then fed to the needling zone. The required needling density was obtained by adjusting the throughput speed [36]. As per the fabric weight (g/m2) requirement, certain number of webs were taken and passed through the needling zone of the machine for a number of times, depending upon the punch density required. A punch density of 50 punches/cm2 was applied on each passage of the webs reversing the face of the web alternatively [36]. The fabric samples were produced as per the coded and actual levels of three variables (Table 4). The depth of needle penetration was kept constant at 11 mm. For all webs, 15  18  36  R/SP, 3½  ¼  9 needles were used.

Evaluation of Thermal Insulation and Resistance The thermal insulation and resistance can be tested by using appropriate thermal insulation and resistance tester. The conventional Marsh method and guarded two plate


511

method are more popular methods of measuring thermal insulation behaviour of textile fabrics. The thermal resistance (TRs) of jute-polypropylene blended needle-punched nonwoven fabrics was measured using guarded two-plate thermal resistance instrument [30]. This instrument [30,31,35] (Figure 6) is based on a microprocessor and provides automatic results of thermal resistance value. The area of the test specimen used is 706.85 cm2 (diameter 30 cm). The test is non-destructive and process of preparation of sample is free from human error. TRs of each fabric sample was measured randomly at five different places under a pressure of 0.3352 kPa. Average of five readings was considered and the coefficient of variation of readings was  2%. Specific thermal resistance (STRs) value was used to compare the thermal resistance of different fabric samples. STRs values of all the samples were determined using the following equation [35, 31]: STRs 

TRs T0

(1)

where STRs is the specific thermal resistance in K m/W; TRs, the thermal resistance value of fabric in K m2/W; and T0, the mean thickness in meter at 1.55 kPa pressure of the fabric sample.

Figure 6. NIRJAFT thermal resistance instrument.

EFFECT OF FABRIC WEIGHT, NEEDLING DENSITY AND BLEND PROPORTION OF JUTE-POLYPROPYLENE BLENDED NEEDLE-PUNCHED NONWOVEN ON THERMAL RESISTANCE It is found that the thermal resistance increases with the increase in fabric weight [35]. This can be supported by the existence of significant (p < 0.05000) positive correlation (r =

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Sanjoy Debnath

0.82) between fabric weight and thermal resistance, as observed from the correlation matrix (Table 3). With the increase in fabric weight, thermal resistance increases more prominently at lower needling density (150 punches/cm2), but its effect is negligible at higher needling density (350 punches/cm2). However, at 40% and 60% jute content levels, the effect of fabric weight on thermal resistance is almost similar at all needling densities between 150 punches/cm2 and 350 punches/cm2. The highest thermal resistance of 8.5  10–2 K m2/W has been obtained at 430 g/m2 fabric weight and 150 punches/cm2 needling density for 40% jute content level [34]. With the increase in fabric weight, the number of fibres per unit area of the fabric increases. This causes increases in fabric thickness and also amount of pores in the fabric structure, causing increase in thermal resistance. However, with the increase in needling density, thermal resistance decreases because the fabric structure tends towards higher degree of consolidation and hence reduces amount of pores in the structure. This can also be supported by significant (p < 0.05000) negative correlation which exists between needling density and thermal resistance (r = – 0.67), as observed from the correlation matrix (Table 5). Thermal resistance = 4.0520833 – 0.0114167X1 – 0.0007917X2 + 0.0558333X3 0.0000079X12 – 0.0000104X22 – 0.0021979X32 + 0.0000250X1X2 – 0.0002125X1X3 – 0.0001X2X3 (R=0.9002; F9,5=15.04) ...

(2)

Table 5. Correlation matrix of variables Variables

FW

N

J%

T

TRs

STRs

AP

SAP

FW N J% T TRs

1.00 0.00 – 0.00 0.05 0.51

– 1.00 0.00 – 0.49 * – 0.67

– 0.00 0.00 1.00 – 0.39 – 0.26

0.50 – 0.49 – 0.39 1.00 0.82*

0.51 – 0.67* – 0.26 0.82* 1.00

0.28 – 0.61* – 0.02 0.29 0.78*

– 0.93* – 0.11 – 0.19 – 0.36 – 0.37

– 0.75* – 0.33 – 0.43 0.08 – 0.02

* 1.00 – 0.22 – 0.11 – 0.02 0.29 0.78* – 0.61 * * AP – 0.93 – 0.11 – 0.19 – 0.36 – 0.37 – 0.22 1.00 0.89 * * SAP – 0.75 – 0.33 – 0.43 0.08 – 0.02 – 0.11 0.89 1.00 FW – Fabric weight, g/m2; N – Needling density, punches/cm2; J% – Jute proportion, T0 – Fabric thickness, cm; TRs – Thermal resistance  10–2, K m2/W; STRs – Specific thermal resistance, K m/W; AP – Air permeability, cm3/cm2/s; SAP – Sectional air permeability, cm3/s/cm. * Correlations are significant at p < 0.05000.

STRs

0.28

EFFECT OF FABRIC WEIGHT, NEEDLING DENSITY AND BLEND PROPORTION OF JUTE-POLYPROPYLENE BLENDED NEEDLE-PUNCHED NONWOVEN ON SPECIFIC THERMAL RESISTANCE This study show the effect of fabric weight and needling density on specific thermal resistance at the jute content levels of 20%, 40% and 60% respectively (Figure 7). It is found that the specific thermal resistance decreases with the increase in needling density, irrespective of the blend composition in jute-polypropylene blend [35]. Also, a significant (p


513

< 0.05000) negative correlation (r = – 0.61) has been found between needling density and specific thermal resistance, as observed from the correlation matrix (Table 5). This is due to the formation of consolidated structure with the increase in needling density. The number of fibres per unit area increases with the increase in fabric weight. This generates more air pockets per unit thickness of the fabric apart from better entanglement, resulting in increase of specific thermal resistance. The specific thermal resistance value initially increases up to 375 g/m2 fabric weight and thereafter it decreases, with the increase in fabric weight at 40% jute content and higher needling density (350 punches/cm2) levels [35] as observed form Figure 7a. The similar phenomenon has also been observed at higher jute content level (60%) but the decrease in trend of specific thermal resistance occurs at lower fabric weight (325 g/m2) as obtained from Figure 7b.

Figure 7. Effect of fabric weight and needling density on specific thermal resistance at (a) 20% jute, (b) 40% jute and (c) 60% jute content levels [26].

Jute can easily form consolidated structure due to its poor resilience compared to polypropylene fibre. Hence, at higher needling density and jute content levels, the fabric consolidation initially improves and beyond certain fabric weight (325 g/m2) the bulkiness increases. With the increase in fabric weight, more number of fibres will be available to the

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needle barb during needling. Beyond certain level (325 g/m2) of fabric weight, the increasing amount of fibres at the same needling density and needle barb is insufficient to form better entanglement, resulting in poor consolidation. Hence, at higher jute content level (60%), the fabric consolidation occurs at lower level of fabric weight (325 g/m2) as found from Figure 7c, compared to that at 40% jute content level [35, 36]. However, highest specific thermal resistance of 20.6 K m/W is observed at 150 punches/cm2 needling density and 400-450 g/m2 fabric weight for 40% jute content in jute-polypropylene blended needle-punched nonwoven (Figure 7a, 7b and 7c). Specific thermal resistance= – 2.3122917 + 0.0612292X1 – 0.0160917X2 + 0.5955833X3 – 0.0000490X12 + 0.0000452X22 –0.0056073X32 – 0.0000365X1X2  0.0002725X1X3 – 0.0002163X2X3 (R=0.9327; F9,5=7.69) ...

(3)

MEASUREMENT OF THERMAL INSULATION VALUE AND COMPARATIVE STUDY OF DIFFERENT JUTE BASED MATERIALS Paul and Mukhopadhyay, 1977 used a simple method to measure the thermal insulation value of different textile materials based on jute and cotton fibres [37]. The methods which are commonly used for measurement of thermal insulation value are the disc method, the constant temperature method and cooling method. Out of these three methods, cooling method is the simplest compared to other two methods. In this method of measurement of thermal insulation, a hot body is wrapped with the fabric and its rate of cooling is measured. The outer side of the fabric is exposed to air. In this experiment, the time taken by a hot body covered with the fabric sample (tc) and without the sample (tu) to cool through a particular temperature range under identical atmospheric conditions. To measure the thermal insulation with this method, a brass cylinder (45 cm length, 5 cm external diameter and 2 mm thickness) closed at one end with a cork was filled with distilled water heated to about 50C. The mouth of the cylinder was closed with a cork through which a thermometer was inserted. To simulate the actual condition, a wire mesh has been wrapped on the surface of the cylinder to obtain a clearance of 2 mm between fabric sample and brass cylinder. A rectangular specimen of the fabric was used to cover the entire outer surface of the brass tube. The length-wise edges of the specimen were made to touch each other closely avoiding overlapping and kept in position by using cello-tape over the joint running parallel to the length of the cylinder. The experiment was started when the temperature of the water was exactly 48C. A stop watch was used to find the time taken for the temperature fall at every 1C. A cooling curve was drawn from these data and the time taken to cool from 48C to 38C was found. The thermal insulation value (TIV) was calculated by Marsh method is as follows [37, 38]:



TIV = 1 



tc    100 tu 

(4)


515

where, (tc) is time taken by the covered body to cool through a certain temperature range and (tu) is time taken by the uncovered body to cool through the same temperature range. They found that thermal insulation value is related to the thickness of the fabric, the basis weight(fabric weight) and the number of layers of the fabric [37]. The intra fabric air aspces and inter space between fabric and body are also important. The thermal insulation value of the fabric is greater when a non-conducting mesh (polythene) is present between the cylinder and fabric instead of conducting metal mesh in the same position. Increase in any of these factors increases the thermal insulation value significantly. There has been marginal effect on thermal insulation value with varying fabric nature.

CONCLUSION It is concluded that the thermal insulation of the warm fabric increases significantly after chemical treatment. The blending with synthetic fibres like acrylic, polypropylene, polyester improves the thermal insulation apart from appearance. With the change in structural design of the garment/jacket, the thermal insulation varies widely. Overall, knitting yarn, warm fabric, warm garments, blankets etc. can be developed from jute-based materials effectively. These materials are comparable with commercially available similar material out of synthetic/wool. It has been established that the thermal insulation value is directly proportional to the thickness of the fabric, the fabric weight and the number of layers of the fabric present irrespective to the woven/nonwoven and raw material used to develop the fabric. The air spaces within the fabric and between the body and fabric are also influence the thermal insulation of the fabric. The thermal insulation value of the fabric is greater when a nonconducting mesh (polythene) is present between the cylinder and fabric, instead of conducting metal mesh in the same position. With regards to the nonwoven material, it has been observed that thermal resistance and thickness increase but air permeability and sectional air permeability decrease significantly with the increase in fabric weight at all levels of jute contents. The influence of fabric weight on thickness is more prominent at 40% and 60% jute content levels than at 20% jute content level. Both thermal resistance and specific thermal resistance decrease with the increase in needling density as supported by significant (p < 0.05000) negative correlations r = – 0.67 and r = – 0.61 respectively. The highest values of thermal resistance and specific thermal resistance of 8.5  10–2 K m2/W and 20.6 K m/W respectively are found at 150 punches/cm2 needling density and 430 g/m2 fabric weight for 40% jute content level. Cluster analysis reveals that the thickness and thermal resistance form a cluster and specific thermal resistance being sub-cluster depends on them. Thickness, thermal resistance and specific thermal resistance as dependent variables together form a cluster influenced by jute percentage as an independent variable. Sectional air permeability among the dependent variables are highly influenced by fabric weight (Euclidean distance ~ 560) which is a different cluster identity. This study is useful to develop thermal insulating material for industrial applications from jute-polypropylene blended needle-punched nonwoven.

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REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

[15]

[16]

[17] [18] [19]

Singh, U. S., Bhattacharya, G.K., Bagchi, N.N., Debnath, S. (2004). Comparative Study of Woollen Blanket and Jute-Wool Blanket. Textile Trends 47, 9, 27-28. Anonymous. (2008a). Annual report 2007-2008, National Institute of Research on Jute & Applied Fibre Technology, ICAR, 12, Regent Park, Kolkata, India, pp. 33. Debnath, C.R., Bhowmick, B.B., Ghosh, S.K., Das, P.K. (1987). Thermal insulation behaviour of some nonwovens. Textile Trends 30, 5, 45-49. Anonymous. (2006). Annual report 2005-2006, National Institute of Research on Jute & Applied Fibre Technology, ICAR, 12, Regent Park, Kolkata, India, 69-70. Anonymous. (1981). Annual report, Jute Technological Research Laboratories, ICAR, 12, Regent Park, Kolkata, India. Chakravarty, A.C. (1962). Crimp produce in jute fibre by treatment with solution of sodium hydroxide. Textile Research Journal 32, 6, 525-526. Chakravarty, A.C. (1963). Woolenization of jute: some physical aspect, Jute Bulletin 26(1), 16-17. Ganguly, P.K., Sao, K.P., Ambally, C. (1985b). Crimp in alkaline treated jute, Effect of treatment time. Textile Research Journal 55(4), 253-254. Sao, K.P., Jain, A.K.(1995). Mercerization and crimp formation in jute. Indian Journal of Fibre and Textile Research 20(4), 185-191. Saha, P.K., Chatterjee, K.K., Sarkar, P.B. (1961). Woollenised Jute as Wool Substitute. Indian Central Jute Committee Monogram. Ganguly, P. K., Sao, K.P. (1985a). Effect of treatment time on swelling of jute. Textile Research Journal 55(6), 376-377. Sao, K.P., Jain, A.K., Anantha Krishanan, S.R. (1983). A comparative study of the Woollenised jute fibres of several strains. Textile Trends 26, 7, 47-49. Sao, K. P., Jain, A. K. (1984). On Crimp measurement in alkali treated jute. Journal of Textile Association (India) 46, 155-159. Gupta, N.P., Bhattacharyya, G.K. (1984). Performance of yarns and blankets from chemically treated jute-polypropylene blends. Indian Journal of Textile Research 9(4), 160-163. Gupta, N.P., Mazumdar, A., Bhattacharyya, G.K., Sur, D., Roy, D. (1982). Chemically texturizing jute and jute-polypropylene bleached yarns. Textile Research Journal 52(11), 694-702. Sinha, A.K., Mathew, M.D., Roy, D. (1988). Properties of jute polypropylene blended yarns texturised by sodium hydroxide solution. Indian Journal of Textile Research 13(1), 26-30. Ghosh, P., Samanta, A.K. (1997). Chemical Texturing or bulking of rotor-spun jute/polyester fibre blended yarns. Journal of Textile Institute 88( 3), 209-231. Sinha, A.K., Basu G. (2001). Studies on Physical Property of jute-acrylic bulked yarn. Indian Journal of Fibre and Textile Research 26, 268-272. Chaudhury, A., Basu, G. (1998). Studies on the properties of DREF spun acrylic yarn. Indian Journal of Fibre and Textile Research 23(3), 8-12.


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[20] Debnath, S., Sengupta, S., Singh, U.S. (2007a). Properties of Jute and Hollow-polyester Blended Bulked Yarn. Journal of The Institution of Engineers (India): Textile Engineering 87(2), 11-15. [21] Sinha, A.K., Gupta, N.P. (1986). Performance of texturized jute blended carpet. Indian journal of Textile Research 11(1), 35–37. [22] Debnath, S., Bhattacharya, G.K., Singh, U.S. (2009). A blanket from jute-hollow polyester blended bulk yarn and method of preparing the same. Indian Patent Application No. 1102/KOL/2009, August 28. [23] Anonymous. (2008b). Annual report 2007-2008, National Institute of Research on Jute & Applied Fibre Technology, ICAR, 12, Regent Park, Kolkata, India, pp. 76-83. [24] Singh, U.S., Debnath, S., Naskar, R.B., Bhattacharya, G.K. (2006). Studies on Properties of Jute-Viscose Blended Yarn. Textile Trends 49(2), 45-46. [25] Debnath, S., Sengupta, S., Singh, U.S. (2007b). Comparative Study on the Physical Properties of Jute, Jute-viscose and Jute-polyester (hollow) Blended Yarns. Journal of The Institution of Engineers (India): Textile Engineering 88(1), 5-9. [26] Debnath, S., Sengupta, S. (2009). Effect of linear density, twist and blend proportion on some physical properties of jute and hollow polyester blended yarn. Indian Journal of Fibre & Textile Research 34(1), 11-19. [27] Sengupta, S., Debnath, S., Bhattacharyya, G.K. (2008). Development of handloom for jute based diversified fabrics modifying traditional cotton handloom. Indian Journal of Traditional Knowledge 7(1), 204-207. [28] Sengupta, S., Debnath, S., (2010). A new approach for jute industry to produce fancy blended yarn for upholstery. Journal of Scientific & Industrial Research 69(12), 961965. [29] Sengupta, S., Debnath, S. (2012). Studies on Jute-based ternary blended yarn. Indian Journal of Fibre & Textile Research, 37 3, 217-223. [30] Roy, G., Naskar, M., Ghosh, S.N. (2009). Development of Digital Thermal Insulation Value Tester for Jute Products. Indian Journal of Fibre and Textile Research 34(1), 3640. [31] Debnath, S., Madhusoothanan, M. (2010). Thermal insulation, compression and air permeability of polyester needle-punched nonwoven. Indian Journal of Fibre & Textile Research 35(1), 38-44. [32] Debnath, S., Sengupta, S., Singh, U.S. (2008). A method for producing jute-hollow polyester blended yarn, union fabric of said yarn and method of preparing said union fabric and shawl from the said yarn. Indian Patent Application No. 1187/KOL/2008, July 09. [33] Sengupta, A.K., Sinha, A. K., Debnath, C.R. (1985). Needle-punched non-woven jute floor coverings: Part III – Air permeability and thermal conductivity. Indian Journal of Fibre & Textile Research 10(4), 147-151. [34] Box, G.E.P., Behnken, D.W. (1960). Some New three level designs for the study of quantitative variables. Technometric, 2, 455-475. [35] Debnath, S., Madhusoothanan, M. (2011). Thermal resistance and air permeability of jute-polypropylene blended needle-punched nonwoven. Indian Journal of Fibre & Textile Research, 36(2), 122-131.

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[36] Debnath, S., Madhusoothanan, M. (2012). Compression creep behaviour of jutepolypropylene blended needle-punched nonwoven. Textile Research Journal, 82(20), 2097-2108. [37] Paul, N.G., Mukhopadhyay, M. (1977). Thermal insulation values of jute fabrics and its blends with other fibres, Indian Journal of Textile Research 2(3), 88-91. [38] Marsh, M.C. (1931). The thermal insulation properties of fabrics. Journal of Textile Institute 22(4), T245-273.



Chapter 21

EFFECTS OF RING FLANGE TYPE, TRAVELER WEIGHT AND COATING ON COTTON YARN PROPERTIES Muhammet Uzun1,2, and Ismail Usta2 1

Institute for Materials Research and Innovation, University of Bolton, Deane Road, UK 2 Department of Textile Engineering, Faculty of Technology, Marmara University, Goztepe, Istanbul, Turkey

ABSTRACT Ring spinning is the most important and effective staple yarn production process. A ring spinning machine consists of a variety of parts of which rings and travellers are the dominant elements. This experimental study has highlighted that the ring flanges and the ring travellers have an effect on the properties of 100% cotton yarn. The interaction between the yarn quality and the spinning elements has been analysed. Ne 40/1 cotton yarns were produced by using both flange 1 and flange 2 rings, half round (dr) and flat (f) profile of ring travellers with four different traveller masses and five different traveller coatings. 80 copses of yarn were produced by using different process combinations. The yarn properties were tested in terms of yarn count, yarn twist, irregularity, yarn hairiness, strength, elongation, spinning tension and balloon angle. As a result, yarn twist and count decreased with increasing spinning tension. Spinning tension in Flange 1 was greater than spinning tension in Flange 2. Increasing the spinning tension improved the following yarn properties; yarn hairiness and yarn twist. The properties of the yarns produced with Flange 2 show better properties than the yarns produced with Flange 1. Increase in ring traveller weight also improved the yarn properties.

Keywords: Cotton yarn, Ring spinning, Flange, Traveller, Hairiness, Yarn irregularity



Email: [email protected] and [email protected].

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Muhammet Uzun and Ismail Usta

INTRODUCTION The main advantages of spinning technology are high productivity, improved yarn characteristics and special twist-imparting mechanism. In recent years, new yarn spinning systems have been designed such as open-end rotor, friction, Sirospun®, Vortex and compact spinning. Despite the emergence of new spinning technologies, conventional ring spinning still remains the most used. This process accounts for 80% of the total staple yarn production due to its superior yarn properties and wide range of yarn productions. The ring spinning and traveller system are illustrated in Figure 1 [1-5]. The spinning tension is one of the critical ring spinning parameters which depends entirely on the ring and the traveller. Some studies aimed to determine the perfect balanced spinning geometry yet there is still room for improvement to produce yarns with optimum characteristics. During the production of yarn with ring spinning, the machine parameters must be taken into consideration. These are traveller weight, traveller and ring geometry, traveller and ring coating, ring position and traveller drive angle to the ring. An ideal combination for production would be: higher traveller speed (which means higher productivity), lower working temperature between ring flange and traveller, extended ring and traveller usage time, better yarn quality (which means less hairiness), reduction of end breaks which has negative effect on productivity, and also avoidance of yarn tension peaks [6-11]. The main conclusion from the previous ring traveller studies show that yarn hairiness can be reduced by using optimum traveller weights. It has also been observed that yarn hairiness strongly depends on mean fibre position, with an inward shifting of the packing density leading to low yarn hairiness [5]. The intervals of helix profiles decreased as the twist increased, the yarn twist value can affect the mean fibre position and hairiness [12,13]. The main aim of this work is to utilise the ring flanges and travellers for the yarn quality in terms of hairiness, twist, breaking strength and irregularity. For this purpose, 80 different combinations were employed to produce yarns. The yarn characteristics were determined by using standard test methods. The tests aimed to establish the impact of the machine parts on the quality of cotton yarns. The results were conducted in an attempt to analyse the optimum production parameters.

Figure 1. Ring and traveller system.

521

Effects of Ring Flange Type …

MATERIALS AND METHODS Materials The cotton fibre specifications are shown in Table 1. The cotton roving was provided by Marmaris Iplik Co., Kahramanmaras, Turkey. The roving count was 655tex (Ne0.91) and irregularity values of 4.8 CV%. Table 1. Cotton fibre specifications

Cotton fibre

Linear Density (dtex) 1.7

Mean length (mm) 28.1

Tenacity (cN/tex) 17.5

Breaking elongation (%) 4.9

The ring flanges and travellers were obtained from Temak Textile Machinery Accessories Industry and Trade Co., Istanbul, Turkey. The ring flange 1 is 3.2mm wide and flange 2 is 4.1mm wide. C type traveller with half round (dr) and flat (f) profiles with five different coating types of blacknic (oxidized), bluenic (oxidized), micronic (nickel plated), silvernic (silver plated) and superpolish (special polished) and four different traveller weights of 35mg, 40mg, 45mg and 50mg were used in this study.

Methods Yarn Production The yarns were produced using a conventional laboratory-type ring spinning machine, SUESSEN-Ringspinntester, the machine specifications are given in Table 2. The 15tex (Ne40) yarns were produced with αtex40 (αe 4.2) twist level and spindle speed 10000rpm. The yarn production was carried out in a conditioned laboratory at 65 % RH and 200C atmosphere. Table 2. Ring machine component specifications Specifications Size in mm Machine size 650×1960×1000 Drafting rollers 28 Front drafting zone 45 Main drafting zone 42 F1-Flange 1 and F2- Flange 2.

Specifications Spindle length Tube length Ring diameter Flange widths

Size in mm 210 260 50 (F1) 3.2 and (F2) 4.1

The Yarn Physical Properties The produced yarn samples were tested individually and analysed to provide a comprehensive understanding of their yarn count, yarn twist, irregularity, yarn hairiness, strength, elongation, spinning tension and balloon angle. Whole yarn production and tests were carried out under standard atmosphere condition (200C±2 and 65%±2 RH) [14].

522

Muhammet Uzun and Ismail Usta a) Yarn counts: The yarn counts were determined in accordance with TS 244 EN ISO 2060: 1999. The yarn samples were prepared in 100m lengths for each yarn types and their masses were weighed by using OHAUS balance and the results were calculated in Ne. b) Yarn twist: The twists were assessed in accordance with TS 247 EN ISO 2061: 1999, by using James H. Heal twist counter equipment. c) Yarn tensile properties: The breaking strength (cN) and elongation (%) properties of yarns were determined using Instron 4411 with test parameters of 500 mm gauge length, 10 cN pre-tension, 5 kg load cell with a test speed of 500mm/min [15,16]. d) Yarn irregularity: The irregularity of yarns were characterised by using Uster Tester I equipment, in accordance with DIN 53817 [17]. The yarn properties obtained were irregularity CV%, thin places (-50%), thick places (+50%) and neps (+200%) for one km of yarn. e) Yarn spinning tension: The aim of this test is to study the influence of the traveller weight on yarn properties. The tension of yarn spinning was determined between the end of the drafting system and yarn guide during the production process. The measurement was performed by using Schmidt ZF2 [18,19]. f) Yarn hairiness: The yarn hairiness was determined by using Shirley Yarn Hairiness Tester. This equipment can detect over 3mm hairs in the yarn surface over a chosen period (5 to 40 seconds). g) Balloon angle: The yarn ballooning angles were photographed during the yarn production by using a Kodak digital camera. From these pictures the angle values were calculated manually [19].

RESULTS AND DISCUSSION The Yarn Physical Properties a) Yarn Counts The yarn counts in Ne are given in Figure 2. It can be observed that the counts are affected by the weight of travellers. The yarns thinned when the traveller’s weights were 50 mg, for all the coatings. The differences were less than Ne 0.5. It has been found that the yarns which were produced by flange 1 were slightly thinner than those produced using flange 2. In general, the yarn counts ranged from Ne 38.46 to Ne 41.12. b) Yarn Twist The number of twists per meter is affected by yarn production tension. The yarn twist number produced with flange 1 was slightly higher than flange 2, but the differences were insignificant (Figure 3). In this study, the highest twist number was found to be 1034.8 T/m, which was produced by using flange 2 and 50 mg traveller weight. The effect of profile of the travellers on yarn twist was analysed and it was observed that the flange 2 yarns with dr profile traveller had more twists than flange 1 with dr and f profile travellers, and also flange 2 with f profile traveller.

523


Yarn Count, Ne

F1-50 F1-45 F1-40 F1-35 F2-50 F2-45 F2-40 F2-35

Traveller profile and coating type Figure 2. Yarn counts (dr: Half round, f: Flat, F1: Flange 1, F2: Flange 2). F1-50 F1-45 F1-40 F1-35

Twist, T/m

F2-50 F2-45 F2-40 F2-35

Traveller profile and coating type Figure 3. Yarn twists (dr: Half round, f: Flat, F1: Flange 1, F2: Flange 2).

The lowest twist number was for the f type profile. The weight level of the travellers had a significant effect on the yarn twist for flange 1. When the yarns were produced with heavier travellers, the twist values increased. The traveller coating’s effect on the yarn twist were not statistically significant.

c) Yarn Breaking Strength and Elongation The yarn breaking strength is directly dependent on the number of twists per meter in the yarn. The strength will increase with increasing twist value. The flange 2 yarn breaking strengths’ were higher than flange 1’s breaking strength. Significant differences were observed (50 cN) (Figure 4). The highest breaking strength value was demonstrated by flange 2 with 50 mg traveller mass. The traveller profile cross-section also affects the strength and f profile had higher breaking strength than dr profile. The yarn which was produced by a superpolish coating and f profile had superior breaking strength compared to other flangecoating-profile combinations. In general, increased traveller weights increases the yarn strength.

524


Figure 4. Yarn breaking strength (dr: Half round, f: Flat, F1: Flange 1, F2: Flange 2).

Due to the difference in twist, elongation values of flange 2 were found to be higher than flange 1. The elongations of the yarns were affected by the coating and weight in a variable way. There was no constant interaction between the coatings and traveller weights. The breaking elongation ranged from 3.5% to 5.5% (Figure 5). The traveller profiles did not have a decisive influence on the breaking elongation of yarns. However, flange 2 dr profile did have the highest elongation value which is about 5.5%.

d) Yarn Irregularity In general, CV% values of the flange 2 had lower yarn unevenness than flange 1. Flange 1’s unevenness was CV% 11 and flange 2’s unevenness was CV% 8. The coatings were found to be significantly important in terms of yarn unevenness (Figure 6). Blacnic and micronic coatings had less unevenness compared to bluenic, silvernic and superpolish. Only superpolish had less unevenness with flange 2 and f profile. Increased traveller weights decreased the yarn unevenness. The minimum unevenness values were observed for flange 2 ring and dr profile traveller with black and micronic coatings.

Elongation, %

F150 F145 F140 F135

Traveller profile and coating type Figure 5. Yarn elongation (dr: Half round, f: Flat, F1: Flange 1, F2: Flange 2).

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Irregularity, CV%

F150 F145 F140 F135

Traveller profile and coating type Figure 6. Yarn irregularity (dr: Half round, f: Flat, F1: Flange 1, F2: Flange 2).

The yarn neps decreased with increase in traveller mass. The number of neps in the yarn varies between flanges. Another important finding of this assay was the effect of traveller profile. f type traveller had significantly higher number of neps than dr type traveller. There are no significant differences between the traveller coatings.

e) Yarn Spinning Tension Yarn spinning tension is one of the important spinning parameters which can directly affect the quality of yarn. Previous studies on the interaction between the traveller weights and the spinning tension has confirmed that when the mass of traveller increase, the spinning tension also increases [6, 18, and 19]. The results from this study confirm the hypothesis (Figure 7). The traveller with 50 mg weights had the highest spinning tension for all the coating types. Flange 2 had slightly higher spinning tension compared to flange 1 in some coatings. The spinning tension differences between coatings are not significantly important.

Spinning tension, cN

F150 F145 F140 F135 F250

Traveller profile and coating type Figure 7. Spinning tension (dr: Half round, f: Flat, F1: Flange 1, F2: Flange 2).

f) Yarn Hairiness In the case of yarn hairiness, the hairiness decreased when the traveller weights were increased. It is observed that the yarns which were produced by using flange 2 had lower hairiness value than those produced using flange 1. dr profile traveller caused less hairiness when used with flange 1. The f profile traveller was effective when used in conjunction with

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flange 2. The coating types did not affect the yarn hairiness significantly. The hairiness ranged from 30 to 70 H/m (Figure 8).

Hairiness, H/m

F150 F145 F140 F135 F250

Traveller profile and coating type

Balloo angle, degree

Figure 8. Yarn hairiness (dr: Half round, f: Flat, F1: Flange 1, F2: Flange 2).

F150 F145 F140 F135

Traveller profile and coating type

Figure 9. Balloon angle (dr: Half round, f: Flat, F1: Flange 1, F2: Flange 2).

g) Balloon Angle It was found from the statistical analyses that the balloon angle decreased with increased traveller weight. Figure 9 shows the relationship between the traveller weight and the spinning balloon angles. In this study, the angle of the spinning balloon decreases when the travellers with an increase in weight was due to the increase in tension values. In general, most types of coatings produced with flange 1 had higher balloon angle than flange 2.

Statistical Analysis Variance analysis has been applied to check whether the results obtained are important statistically. The tests of significance were made at 95% and 99% confidence limits. Yarn properties were investigated by two-way variance analysis depending on the traveller weight and coating type. All the analysis results are given in Table 3.

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Effects of Ring Flange Type … Table 3. Variance analysis of yarn properties with different traveller weight and coating

Properties Yarn count

Variation Sources Traveller weight Traveller coating

Flange 1 Traveller profile dr f α0.05 α0.01 α0.05 α0.01 ns ns ns ns ns ns ns ns

Traveller weight ns Traveller coating ns Yarn Traveller weight ns strength Traveller coating s Traveller weight s Elongation Traveller coating s Traveller weight s Irregularity Traveller coating s Spinning Traveller weight s tension Traveller coating s Traveller weight ns Hairiness Traveller coating s Balloon Traveller weight s angle Traveller coating s s – significant, and ns – not significant. Yarn Twist

ns ns ns s s s ns ns s s ns s s s

ns ns ns ns ns ns ns ns s s ns ns s s

ns ns ns ns ns ns ns ns s s ns ns s s

Flange 2 Traveller profile dr f α0.05 α0.01 α0.05 α0.01 ns ns ns ns ns ns s s ns ns ns ns ns ns ns s s s s s ns s

ns ns ns ns ns ns ns s s s s s ns ns

s ns ns s s ns ns s s s ns ns s ns

s ns ns ns ns ns ns s s s ns ns s ns

When Table 3 is examined, it can be clearly seen that traveller weight and coating have an important effect on spinning tension in both significance levels. Balloon angle effect from traveller weight and coating is important in flange 1 in both significance levels. Traveller weight has not important effect on yarn count and yarn strength. Also traveller coating has not important effect on yarn twist. Except flange 2 with f profile, traveller coating has not important effect on yarn count. Except flange 2 with f profile, traveller weight has not important effect on yarn twist. Traveller coating has an important effect in flange 1 with dr profile. Yarn elongation effect from traveller weight and coating is important in flange 1 with dr profile. Traveller coating has an important effect on yarn irregularity in flange 2 with dr and f profiles. Yarn hairiness effect from traveller coating is important in dr profile with both flange 1 and flange 2.

CONCLUSION In order to define the relationship between the physical properties of the yarn and the production process, it is considered that the usage of flange 2 has some advantages over flange 1. In this study demonstrated that the traveller weight and yarn spinning tension are important production parameters. From the results and discussion of this study it can be concluded that the yarns produced with flange 1 are slightly finer than flange 2, yet for most of the yarn this was not found to be of a significant level. It was significant only for f profile travellers. Except flange 2 with f profile, the traveller coatings did not have any important effect on the yarn counts.

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The observed twist values of flange 1 and flange 2 were very similar. The highest twist number(T/m) was found in the yarn that was manufactured by using flange 2 with a traveller weight of 50 mg. Traveller profile had a variable effect on the yarn twist. Flange 2 with dr profile traveller had higher twists in general. When the traveller weight was increased, the twist value also increases. In general, flange 2’s breaking strengths were more than flange 1’s breaking strength, and the differences were of a significant level (50 cN). The highest breaking value was demonstrated by flange 2 ring and 50 mg travellers. The yarn which was produced using the superpolish coated f profile traveller had superior breaking strength compared to the other combinations. Yarn elongation was affected by the coating and weight in a variety of ways. The traveller profiles did not have a decisive influence on the yarn elongation behaviour. For most of the combinations, flange 2 had much lower yarn irregularity than flange 1. Flange 1’s irregularity was 11 CV% and flange 2’s irregularity was 8 CV%. The coatings had a considerable effect on the yarn irregularity. The yarn spinning tension of this study was found to be similar to the previous studies. When the traveller weight increased, the spinning tension increases. Flange 2 had slightly higher spinning tension compared to flange 1. The coatings have important affect in the spinning tension. The yarn hairiness decreased with increased traveller weight and yarns produced using flange 2 had less hairiness than those produced using flange 1. The balloon angle changed with traveller weight changes, higher the traveller weight lower the lower angle.

ACKNOWLEDGMENTS The authors are thankful to Marmaris Iplik Co., Kahramanmaras, Turkey and Temak Textile Machinery Accessories Industry and Trade Co., Istanbul, Turkey for their support during this research.

REFERENCES [1] [2] [3] [4] [5]

Johnson, T.F.N. (1996). World fiber demand 1890-2050 by main fiber type. Man Made Fiber Year Book (CFI), 31-37. Mourad, K., Ethridge. D. (2004). A Qualitative Approach to Estimating Cotton Spinnability Limits. Textile Research Journal, 74(7), 611-616. Krifa, M., Ethridge, M.D. (2006). Compact Spinning Effect on Cotton Yarn Quality: Interactions with Fiber Characteristics. Textile Research Journal, 76(5), 388-399. Demir, A., Torun, A. (2003). Tekstilde Üretim Yöntemleri. İ.T.Ü., 75-92. Huh, Y., Kim, Y.R., Oxenham W., (2002). Analyzing Structural and Physical Properties of Ring, Rotor, and Friction Spun Yarns. Textile Research Journal, 72(2), 156-163.

Effects of Ring Flange Type … [6] [7]

[8]

[9] [10] [11] [12] [13] [14] [15]

[16] [17] [18] [19]

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Usta, İ., Canoglu, S. (2002). Influence of Ring Traveller Weight and Coating on Hairiness of Acrylic Yarns. Fibres & Textiles in Eastern Europe, 39, 20-24. Barella, A., Manich, A.M. (1988). The Influence of the Spinning Process Yarn Lineer Density and Fibre Properties on the Hairiness of Ring Spun and Rotor Spun Cotton Yarns. The Journal of the Textile Institute, 79/2, 189-197. Viswanathan, G., Munshi, V.G., Ukidve, A.V., Chandran K. (1989). A Critical Evaluation of the Relationship Between Fiber Quality Parameters and Hairiness of Cotton Yarns. Textile Research Journal, 59/11, 707-710. Subramanian, V., Mohamed, A.P. (1991). A Study of Double-rove Yarn Hairiness in the Short-staple-spinning Sector. The Journal of the Textile Institute, 82/3, 333-339. Sonntag, E. (1995). Analysis of the Forces Generated During the Clipping of Travellers onto Rings. Textile Research Journal, 65, 178-184. http://www.textiletechnology.co.cc/spinning/Rings-and-Travellers-4.htm Morton, W.E. (1956). The Arrangement of Fibres in Single Yarns. Textile Research Journal, 26, 325-331. Hearle, W.S., Gupta, B.S. (1965). Migration of Fibres in Yarns. Part III: A Study of Migration in a Staple Fibre Rayon Yarn. Textile Research Journal, 35, 788-795. ASTM (D-1776-90), “Standard Practice for Conditioning Textiles for Testing. American Society for Testing and Materials, West Conshohocken, PA, 483-446. Uzun, M., Patel, I. (2010). Mechanical properties of ultrasonic washed organic and traditional cotton yarns. Journal of Achievements in Materials and Manufacturing Engineering, 43/2, 608-612. TS EN ISO 2062: 2010. DIN 53817-1, (1981). “Testing of Textiles; Determination of Unevenness of Slivers and Yarns” Deutsches Institut Für Normung. Demir, A., (1990). İplik Gerginliğinin Önem ve Ölçümü, Bölüm 3: İplik Ölçümlerinin Uygulamaları. Tekstil & Teknik, 94-99. Usta, I. (2008). Effect of Balloon Angle on the Hairiness and other Yarn Properties of Polyester Ring Spun Yarn. Fibres&Textiles in Eastenr Europe, 70, 40-47.



Chapter 22

OPTICAL FIBER EXAMINATION BY CONFOCAL LASER SCANNING MICROSCOPY Andrea Ehrmann Niederrhein University of Applied Sciences, Faculty of Textile and Clothing Technology, Moenchengladbach, Germany

ABSTRACT Confocal laser scanning microscopy (CLSM) is a microscopy technique which can be used to obtain high-resolution optical pictures. By acquiring images from a series of depth layers using a focused laser beam, a computer program can be used to reconstruct a three-dimensional picture of a sample surface. This technique is on the one hand similar to a scanning electron microscope (SEM); on the other hand, a CLSM needs no introduction of samples into a vacuum chamber. The lateral resolution of a CLSM of about 150 nm is most often sufficient to examine textile fibers, e.g., to distinguish between different natural and man-made fibers as well as between different natural fibers. This chapter will give an introduction into the technique of confocal laser scanning microscopy and depict optical differences between several textile fibers, enabling a nondestructive examination of natural and chemical fibers.

INTRODUCTION The resolution of optical microscopes is limited by the wavelengths of the visible light spectrum, resulting in maximal resolutions of around 1 micron (i.e., 0.001 mm). Scanning electron microscopes (SEM) can have resolutions in the order of 1 nm (0.001 micron); however, they mostly require some sample preparation, such as sputtering a thin conductive film on the surface, and samples are normally introduced into a vacuum chamber for measurement. 

Corresponding author: Andrea Ehrmann. Niederrhein University of Applied Sciences, Faculty of Textile and Clothing Technology, Webschulstr. 31, 41065 Moenchengladbach, Germany. E-mail: andrea-ehrmann@gmx. de.

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For non-invasive examination of samples which require a higher resolution than possible in optical microscopes, but should be measured without pretreatment (especially valid for biological samples), a confocal laser scanning microscope can be the ideal solution. The method of confocal laser scanning microscopy (CLSM) was patented by Marvin Minsky, who needed to make real-time microscopic pictures of living systems, in 1961 [1]. It tries to overcome the resolution limits of wide-field optical microscopy and additionally enables “seeing” through semi-transparent sample parts into defined depths. After the first confocal microscope built by Egger and Petran in the late 1960s, the development of CLSMs was supported by advances in laser and computer technology, until in the late 1980s the first commercial instruments became available [2]. The principle setup of confocal laser scanning microscopes is depicted in Figure 1. A coherent laser beam is emitted through a pinhole and a lens onto a sample surface. The reflected beams can only pass the second pinhole if both pinholes are in conjugate planes, i.e., confocal. This leads to elimination of out-of-focus signals (dotted line in Figure 1) as well as of stray light. Refocusing of the microscope’s objective results in a new plane of the sample under examination being confocal with the pinhole planes and thus becoming visible in the photo-detector. In contrast, a sample examined by optical wide-field microscopy is evenly lit in all focal planes, leading to a large unfocused background in the camera or photo-detector of a digital microscope or in the user’s eye for an analog microscope, respectively. While a usual optical microscope’s lateral resolution can be calculated due to the Rayleigh criterion as ropt = 0.6  / NA (with the light wavelength  and the numerical aperture of the objective lens NA), experimental investigations of CLSMs show that this value is reduced to rCLSM = 0.4  / NA in confocal microscopes. With ultraviolet laser light (e.g., 408 nm wavelength [3]) and numerical apertures next to 1 (e.g., 0.95 for the highest-resolution objectives [3]), resolutions of 170 nm are possible.

After [1], modified. Figure 1. Principal sketch of a confocal microscope.

Optical Fiber Examination by Confocal Laser Scanning Microscopy

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While the confocal technique can significantly enhance the optical resolution by deleting undesirable light from other focal planes, the elimination of large parts of the light by the pinhole also results in longer measurement times. For each experiment, resolution and exposure time have to be balanced according to the demands of the respective analysis. Scanning the sample happens via the scan head which rasterizes the scans and collects the signals from the sample in a CCD camera or a photomultiplier. The scan head contains inputs from the laser sources by a fiber optic coupler, normally followed by a beam expander leading to the laser beam filling the complete objective rear aperture, dichromatic mirrors, a scanning system for x- and y-direction, variable pinhole apertures to generate the confocal image, and a light detector [2]. Beam scanning can happen via two different techniques: Most CLSMs use single-beam scanning, working with a pair of computer-controlled galvanometer mirrors which let the laser beam scan the sample in a raster pattern. However, if faster scanning rates are desired for real-time videos of living systems, a spinning Nipkow disk with an array of pinholes and micro-lenses can be used instead. In these multiple-beam systems, arc-discharge lamps can replace the laser to reduce possible damage of the sample. Such microscopes can capture complete images with an array detector, such as a CCD camera. The aperture in front of the detector can contain pinholes of different diameters in a rotating disk, allowing for adjustment of the focal plane thickness by the pinhole size. The illumination spot on the sample, which is in the order of magnitude of 0.1 to 1 micron, is defined by the numerical aperture of the objective [2]. Some CLSMs use a white light source additional to a short-wavelength (ultraviolet) laser. While the laser light creates a high-resolution grayscale picture, as described above, the white light produces a colored picture with lower resolution, showing the real colors of the observed object. Superposing both pictures results in a high-resolution colored picture [3]. Other CLSMs allow for fluorescence pictures of biological samples. For this purpose, multi-wavelength laser systems for ultraviolet, visible, and near-infrared spectral regions, enhanced interference filters and sensitive low-noise wide-band detectors are of special interest [2]. The software packages belonging to a commercial CLSM are normally able to generate three-dimensional views of the sample under investigation, including the possibility of measuring the depth of sample features or depicting the surface roughness by false color representation.

EXPERIMENTAL Several natural and chemical fibers used in the textile industry have been examined by CLSM, giving rise to differences in the surface structure, allowing for differentiation between natural and chemical fibers, on the one hand, but also between different kinds of wool etc. Sometimes, the results of chemical or physical treatment are also visible, which is shown here exemplarily by a chemical treatment of hemp and a laser-treated polyester fiber. All microscopic images in this chapter have been taken with the microscope VK-9700 by Keyence.

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Figure 2. Overview on VK-9700 by Keyence (left panel); objectives with 20 x, 50 x, and 100 x magnification (right panel).

Figure 2 (left panel) gives an overview on the CLSM system used for the microscopic pictures in this chapter. The display on the left side shows the results of the measurements performed with the laser head and the objective system on the right side. The objectives (Figure 2, right panel) can be rotated to change the magnification and can be completely exchanged. Figure 3 shows the software front panel which is used to setup the CLSM. Firstly, the software is switched to “Camera” to search the height area in which parts of the picture are sharp. This area defines the measurement range, set by the values for the upper and lower position of the motor stages. An auto gain allows for taking photographs which are neither too dark nor too bright. The Z pitch defines the steps for the movement of the laser head relative to the sample. The duration of taking one photograph can vary between a few seconds (for rather flat samples, high Z pitch and low resolution) and ten or twenty minutes for rough samples, low Z pitch and high resolution. A special feature of the VK-9700 by Keyence is the possibility to superpose the laser intensity with a color picture with lower resolution, which adds real colors to the sharp laser intensity picture. Most images in this chapter have been taken using an objective with 50 x magnification, corresponding to a nominal magnification (on a 15’’ display) of 1000 x. That means each microscopic picture (besides Figure 4) in this chapter shows an area of 202 m x 270 m. These values can be extended to a magnification of 15 x / 3000 x by changing the objective. Additionally, an optical zoom can add up to 6 x magnification, resulting in a maximum nominal magnification of 18,000 x. Opposite to a digital zoom, this optical zoom does not decrease the resolution, but can really add more information. Since the optical zoom is not connected with a change of the lenses, it can be very helpful, especially for investigations of fibers which may be touched during a rotation of the objective system. For comparison, Figure 4 depicts microscopic images of wool fibers with nominal magnifications of 1000 x (left panel) and 3000 x (right panel). The typical scales on the fibers are clearly visible in both pictures.


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Figure 3. The software used to control the CLSM allows for several adjustments, dependent on the respective sample to be examined.

Figure 4. Wool fibers, microscopic images with nominal magnifications of 1000 x (left panel) and 3000 x (right panel).

Since the working distance for the objective with highest magnification is only ~ 0.2 mm, fiber examinations can be performed more easily with a lower resolution. As Figure 4 shows, it is often sufficient to work with a nominal magnification of 1000 x; otherwise, the optical zoom can be used to enlarge the magnification.

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Figure 5. Report with line measurement of the height of the wool scales.

Nevertheless, higher resolutions can be very helpful for more exact measurements, e.g., of the height of the scales on wool fibers. In Figure 5, a line measurement of this scale height is depicted, performed on the microscopic image shown in Figure 4 (right panel). The precision of measurements in lateral direction (i.e., in the sample plane) is defined by the resolution of the microscopic image, while for measurements in z-direction (i.e., perpendicular to the sample plane) the Z pitch also influences the possible measurement precision. Depending on the desired accuracy in distance measurements, it might be supportive to enhance the magnification and / or the Z pitch, the latter resulting in more images taken in different heights and correspondingly longer measurement times. After this short introduction into the technique of CLSM, the next sub-chapters will give an overview of different natural and man-made fibers and possibilities of differentiation between them.

ANIMAL FIBERS Animal fibers, e.g., wool, silk, cashmere wool, mohair, angora, but also not commercially used hair of dog, cat, wild pig etc. or feathers, consist mostly of proteins. In mass production, sheep wool and silk are used most often, but alpaca or mohair are also quite common.


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Figure 6. Undercoat (short hair lying underneath the longer outer hair) of dog (left panel) and guard hair (hair on top) of wild pig (right panel). The magnification is identical for both pictures.

Differences in the fiber structure and surface (length, thickness, crimp, scale) define the properties of the yarns and textiles produced from these fibers. Thus, microscopic pictures can be a tool to distinguish between different animal fibers – not only between, e.g., silk and wool, but also between different sorts of sheep wool. In Figure 6, undercoat of a dog and guard hair of a wild pig are shown. Compared with the wool fibers in Figure 4 (left panel), both sorts of hair have a larger diameter. The scale structure of the dog undercoat differs significantly from sheep wool, the latter having larger, higher and more clearly defined scales. The wild pig guard hair, however, shows a significantly larger diameter, with several well-defined scales positioned side by side on the surface, opposite to sheep wool which mostly shows one or two scales on one circumference. Apparently, distinguishing between different animals is possible with CLSM, if a reference database is available. But can confocal microscopy also help in differentiating between, e.g., the wool of different sheep? One of the properties which can often be used to distinguish between different fibers is the fiber diameter. In Figure 7, microscopic images of the wool of a mountain sheep and a Texel sheep are shown, both photographs taken with the same magnification. The difference in the diameters of both sorts of wool is obvious. Additionally, the forms and dimensions of the scales can support differentiation between both types of wool. While the mountain sheep wool has irregular scales, partly forming “spikes” and having similar heights and widths (left panel), the Texel sheep wool shows more rounded scales which are mostly less high than wide (right panel). Moreover, the Texel sheep wool shows several dot-like “hills”, additional to the scale structure (right panel), which is significantly less pronounced in the picture of the mountain sheep wool. Such sub-structures, however, must be treated carefully, since they might arise from contaminations with other materials – since the CLSM is not element-sensitive, only the color of such features can give a hint about their nature. The final decision whether small structures are a basic part of a certain sort of fiber, or if some impurities become visible in the CLSM pictures, is often up to the experimentalist’s experience. A simpler, but also more common question deals with fiber blends. Especially for financial reasons, fiber blends may be declared incorrectly. Figure 8 shows microscopic pictures of a fabric which has been declared to consist of 100 % finest wool.

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Figure 7. Wool of mountain sheep (left panel) and Texel sheep (right panel), microscopic images both taken at a nominal magnification of 1000 x.

Figure 8. Fine wool fibers (left panel) and unexpected addition of synthetic fibers (right panel).

While parts of the fabric do indeed consist of wool (left panel), additional synthetic fibers can be found in the textile (right panel), which can clearly be identified by their flat surfaces without any scale structures. In this way, microscopic images can even help to identify possible imitations of fabrics made of valuable fibers, such as cashmere or pashmina, a mixture of cashmere and silk [4].

PLANT FIBERS Plant fibers can be bast fibers extracted from field crops, which are typically harvested after one season of growing, opposite to trees which can be harvested continuously. Thus, plant fibers often have to be stored for long times before they can be used in pulp mills. Among the bast fibers, hemp, flax / linen, jute, nettles, ramie etc. can be found. Cotton, bamboo, sisal and other fibers, however, are produced from leaf, fruit, and other fibers of plants besides the stem-skin bast fibers. Plant fibers are based on cellulose which is often bound by lignin, a material which can be found in the cell walls between cellulose, hemicelluloses, and pectin. Some synthetic fibers are also based on cellulose fibers, such as Lyocell, rayon or bamboo.


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All bast fibers have a similar appearance, different from the typical scale structures of animal fibers. Hemp fibers (Figure 9, left panel) are connected by pectin to form fiber bundles. The single fibers become visible here due to biological and chemical treatment which dissolves the pectin bonds. The transverse thickenings can be attributed to mechanical load during growth or during digestion [5, 6]. Mechanical digestion separates the fibers from the wooden parts. Flax fibers (Figure 9, right panel) have been used for clothing production for tens of thousands years until in the nineteenth century cotton became more popular. The fiber is quite straight and smooth, soft and flexible, although less elastic than cotton. The chemical procedure of retting the flax and the mechanical breaking, scotching, and heckling processes separate the fibers from the inner wooden part of the stem and remove the straw from the fibers. Figure 9 (right panel) shows a single fiber (smooth, shiny fiber in the middle of the picture) between fiber bundles. The optical appearance of both types of bast fibers, as can be seen in Figure 9, is thus strongly dependent on the physical and chemical treatment prior to taking the CLSM pictures. While the fibers can clearly be identified as types of bast fibers, optical differentiation between them can be difficult, depending on the amount of digestion. Complete fiber bundles, still containing the original amount of pectin and straw, can be hard to identify, as visible in Figure 9, comparing the pectin-surrounded fiber bundles in both images. If the single fibers are visible, then the irregularly formed hemp fibers can, e.g., be distinguished from the polygonal flax fibers. Cotton fibers, consisting nearly completely of cellulose, grow in a capsule around the seeds of cotton plants. Nowadays cotton is the most often used natural fiber for clothing. Opposite to bast fibers (Figure 9), cotton fibers have a characteristic flatoval cross-section form which allows for differentiation from the triangular cross-section of silk as well as from the smooth, even synthetic fibers.

CELLULOSE FIBERS Synthetic fibers are normally produced by extrusion of the respective materials through spinnerets into the air where the thread is formed. They can be subdivided into cellulose fibers, polymer fibers, mineral, metallic and other fibers.

Figure 9. Microscopic images of hemp fibers (left panel) and flax fibers (right panel).

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Figure 10. CLSM image of cotton fibers.

Figure 11. Lyocell (left panel) and alginate (right panel) fibers as examples for regenerated cellulose fibers.

Manufactured cellulose fibers are extruded from a pulp of regenerated or pure cellulose. Rayon (viscose), including modal and Lyocell fibers, are quite common. Other man-made fibers from cellulose are, e.g., bamboo fibers or alginate, produced from seaweed. Lyocell fibers (Figure 11, left panel) are, opposite to other viscose fibers, normally quite smooth, with a roughly round cross-cut. The longitudinal grooves which are typical for viscose fibers are not visible in Lyocell [7, 8]. The smooth, even alginate fibers (Figure 11, right panel) are often used as wound dressing, since they swell during gelatinization due to the moisture in the wound, thus completely filling even very deep wounds with nearly inaccessible areas. Due to the spinning process from a pulp, synthetic cellulose fibers can normally not be distinguished, although some cross-sections and surface structures can be typical for certain materials.

POLYMER FIBERS Opposite to synthetic cellulose fibers, polymer fibers are produced from synthetic chemical materials.


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Amongst them, materials like polyester, polyamide, polyolefin fibers or acrylic fibers can be found as well as aromatic polyamides (aramids) or polyethylene with partly extremely long chains, resulting in ultra-high-molecular-weight polyethylene (UHMWPE) fibers with very special physical properties, such as very low elasticity and friction combined with very high abrasion resistance. Polyester (PES) (Figure 12) belongs to the polycondensation fibers which are based on monomers reacting step-wise to dimers, trimers, and longer and longer oligomers, losing small molecules as by-products. Polyester fibers normally have a round cross-section and a flat, smooth surface; however, the structure can be influenced by the form of the spinneret and chemical treatments. Other polyconcensation fibers are polyamides or polyurethanes. Aliphatic polyamide 6 (PA 6) fibers are depicted in Figure 13 (left panel), aromatic polyamide (aramide) fibers are shown in Figure 13 (right panel). Both look very similar to each other and to the PES fibers in Figure 12. Chain-growth polymerization fibers, e.g., polypropylene, polyethylene, or polyvinyl chloride, are based on unsaturated monomer molecules adding on the active position of a growing polymer chain without producing by-products with low molecular weight.

Figure 12. Microscopic image of polyester fibers.

Figure 13. CLSM pictures of polyamide 6 (left panel) and aramide fibers (right panel).

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Figure 14. Polyacrylonitrile (PAN) fibers (left panel) and UHMWPE fiber “Dyneema” produced by DSM, Netherlands (right panel).

PAN (polyacrylonitrile) fibers (Figure 14, left panel) as well as the UHMWPE fiber Dyneema (Figure 14, right panel) show structured surfaces, the PAN fibers additionally a not round cross-section. However, these properties depend on the form of the spinnerets and thus cannot be used for a differentiation between different types of fibers [8]. Nevertheless, the fibril structure visible in the Dyneema fibers is a typical feature due to the special spinning process. The loose fibril in Figure 14 (right panel) is the result of an improper rewinding process.

METALLIC FIBERS Pure metal fibers are mostly round, since they are drawn step-wise through smaller and smaller spinnerets. Figure 15 shows stainless steel filaments from a pure stainless steel yarn. Opposite to optical examinations by eye, the typical metallic brilliance is not visible here, due to the auto gain function of the microscope which avoids too bright picture parts. On the surface, fine longitudinal marks are visible, less pronounced than in the Dyneema fiber (Figure 14, right panel), but also continuous, unlike the structure of the PAN fiber depicted in Figure 14 (left panel). Although the surface structure of the metal filaments seems to be unique, compared with the other figures in this chapter, care must be taken due to the possible influences of the spinnerets and physical / chemical treatments of metal and other fibers.

PHYSICAL AND CHEMICAL TREATMENTS OF FIBERS Opposite to pure metal fibers, partly metalized fibers can be recognized easily in CLSM images. Figure 16 (left panel) shows fibers of a Shieldex yarn, consisting of pure PES and silver coated fibers, the fine silver layer being partly destroyed by several washing cycles. Here, the rougher surface structure, compared to pure polyester, and the metallic glittering on the coated fibers clearly indicate a metallic coating on parts of the fibers. Another way of physical treatment of PES fibers is exposition to a pulsed excimer laser. The results are shown in Figure 16 (right panel).


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The lateral ripples are produced by the sudden heating and cooling due to the intense laser pulses. In the middle of the image, several tipped-over ripples can be identified, additional to a part of one fiber which has apparently been shaded from the laser light, thus still presenting a flat surface without ripples. For the detection of such structures, a CLSM is ideally suited, while a simple optical microscope can only give a rough idea of these laserproduced surface structures without more detailed information. In some cases, the influence of chemical treatment of fibers is also visible in CLSM. Figure 17 show hemp fibers treated by hammer mill, without (left panel) and with (right panel) chemical after-treatment, i.e., digestion of the fibers by chemical retting in, e.g., sulfuric acid. Comparing both pictures, the vanishing of the pectin in the fiber bundle apparently leads to dissolving of the fibers which become singularly visible. It should be mentioned, however, that other chemical treatments, nano-coatings, etc., are normally not visible in a confocal laser scanning microscope, since the resolution is not sufficient to identify nano-scale features.

Figure 15. Stainless steel filaments, recorded by CLSM.

Figure 16. Shieldex yarn, produced by Statex, Bremen, Germany (left panel) and laser treated PES fibers (right panel).

544

Andrea Ehrmann

Figure 17. Hemp fibers treated by hammer mill only (left panel) and additionally treated chemically (right panel).

Figure 18. Wool fibers with insufficient measurement range (left panel) and Lyocell fibers with only one part of the possible measurement range (right panel).

CHANCES AND PROBLEMS While especially natural fibers and physical treatments of fibers can often be identified by CLSM, the technique possibilities are nevertheless limited. Especially the basic principle of confocal laser scanning microscopy, i.e., scanning only in well-defined distances to the objective, may be problematic. Figure 18 depicts an image of wool fibers (left panel) for which an insufficient measurement range has been chosen, leading to black areas inside the fibers where the surface was not positioned between upper and lower limit of the measurement range. While such a problem is evident and can thus be corrected in a new picture with extended limits, it is also possible to completely miss some fibers. Comparing Figure 18 (right panel) with Figure 11 (left panel), both pictures clearly show the same area of the same yarn; however, in Figure 18 (right panel), some fibers are missing due to a wrong limit in the measurement range. The shading effects, caused by higher fibers which are missed in this way can nevertheless influence the appearance of the depicted fibers which might cause additional interpretation problems.


545

CONCLUSION Similar to an SEM, a CLSM is not able to distinguish between all sorts of synthetic fibers which often look identical, independent of their chemical composition. However, confocal laser scanning microscopy is a powerful tool for optical examination of fibers, combining some of the advantages of optical light microscopy and scanning electron microscopy. For most fibers, the resolution of a CLSM is sufficient to analyze the surface structures which can be used to identify the type of fiber.

REFERENCES [1] [2]

[3] [4]

[5] [6] [7]

[8]

Minsky, M. (1961). Microscopy Apparatus. US Pat. 3,013,467. Claxton, N. S., Fellers, T. J., Davidson, M. W. (2013). Laser scanning confocal microscopy. Olympus website. 1-37. Available at: http://www.olympusfluoview.com/ theory/LSCMIntro.pdf. Instruction book of VK9700K, Keyence. Tillmanns, A., Korger, M., Weber, M. O. (2012). Konfokale LaserscanningMikroskopie – Zerstörungsfreie Faseruntersuchung. forward textile technologies 4, 4647. Thygesen, L. G., Hoffmeyer, P. (2005). Image analysis for the quantification of dislocations in hemp fibres. Ind. Crop Prod. 21, 173-184. Wang, H. M., Wang, X. (2005). Surface morphologies and internal fine structures of bast fibers. Fiber Polym. 6(1), 6-12. Abu-Rous, M., Ingolic, E., Schuster, K. C. (2006). Visualisation of the nano-structure of Tencel® (Lyocell) and other cellulosics as an approach to explaining functional and wellness properties in textiles. Lenzinger Berichte 85, 31-37. Kleinhansl, E., Mavely, J. (1986). Denkendorfer Fasertafel 1986; Textilpraxis Int., Leinfelden-Echterdingen, GE.

INDEX # 20th century, 84, 201, 268, 319 21st century, 16

A A(H1N1), 384 abatement, 311 abrasion, 23, 25, 41, 42, 43, 44, 48, 218, 343, 345, 375, 383, 386, 389, 541 abrasion resistance, 218, 375, 541 abrasion test, 383, 386 absorption spectra, 104, 177, 181, 183, 184, 185, 194, 200 absorption spectroscopy, 177, 321 abstraction, 176 access, 5, 195, 314, 356, 372 accessibility, 5, 129, 130, 140, 141, 148, 149, 268, 401, 411, 413, 419 accordion, 466 accounting, 113 acetic acid, 99, 123, 136, 137, 138, 140, 155, 179, 406 acetic acid content, 138, 140 acetone, 139, 140, 148, 149, 151, 179, 238 acetonitrile, 208 acetyl content, 138, 139, 140 acetylation, 136, 137, 139, 140, 141, 155, 404 acidic, 116, 177, 178, 179, 375, 412, 419 acidic functional groups, 412, 419 acidity, 217 acrylate, 155, 365 acrylic fibers, 165, 541 acrylic resin, 242, 321, 345 acrylics, 98, 100, 157, 159 acrylonitrile, 154, 217 activated carbon, 397, 430, 436, 444, 445

activation energy, 112 active site, 295, 420, 422 active smart textiles, 240 active thermal insulation effect, 242 active transport, 199 active type, 190 actuation, 244 actuators, 188, 189, 239, 241, 245, 250, 448 AD, 264, 266, 270, 276, 337 adaptation(s), 67, 68, 69, 82, 188, 400, 449 additives, 79, 82, 102, 109, 116, 208, 210, 220, 365 adhesion, 87, 101, 196, 249, 250, 256, 277, 283, 306, 313, 343, 362, 363 adhesion properties, 101, 196, 256 adhesives, 124, 344, 352 adjustment, 457, 533 adsorption, 115, 155, 280, 307, 351, 400, 412, 415, 419, 420, 421, 422, 436, 437, 438, 440, 441, 443, 444, 445 adsorption isotherms, 420 adsorption properties, 155, 400, 440 advancement(s), 188, 274, 415 adverse conditions, 320 adverse environmental effects, 294 aesthetic, 1, 21, 22, 24, 192, 244, 339, 490, 508 aesthetic finishing process, 21 aesthetic satisfaction, 192 aesthetics, 3, 191 AFM, 305, 306 Ag-agglomeration process, 301 agar, 296, 300 Ag-clusters, 277, 279, 282, 286, 306 Ag-disinfection performance, 289 age, 8, 9, 13, 322 aged textiles, 316, 336 aggregation, 113, 184, 292 Ag-hospital textiles, 289 Ag-nanoparticulate films, 278 Ag-nitrides, 278

548

Index

Ag-polyester fibers, 285 agriculture, 362 Ag-sputtered films, 277 Ag-textile surfaces, 278 air permeability, 384, 490, 507, 509, 512, 515, 517 air pollutants, 100 air temperature, 487 Akaike information criterion, 420, 421 alcohols, 98, 217, 328 aldehyde functionalities, 406 aldehydes, 370, 431 algae, 289 alginate, 350, 351, 383, 384, 385, 389, 395, 540 alginate chains, 384 alginate fibers, 540 algorithm, 61, 65 alkali-clearing property, 165 alkaline treatment, 324, 404, 407, 408, 412, 440, 501 alkyl methacrylates, 122 allergenic effect, 400, 403 allergic responses, 370 alters, 249 amine(s), 77, 154, 159, 165, 168, 173, 361, 372, 375 amine group, 361 amino, 23, 34, 43, 55, 78, 158, 164, 165, 166, 169, 170, 171, 172, 177, 179, 184, 185, 205, 236, 238, 373, 374, 375 amino acid(s), 23, 34, 43 amino groups, 158, 373, 374, 375 aminoazobenzene derivatives, 159 aminosilicone softener, 374, 375 ammonia, 99, 280 ammonium, 165, 167, 182, 218, 374 amorphous regions, 326, 329, 333, 401, 410, 413 amylase, 23 amylopectin, 23 anaerobic conditions, 271 anatase, 314 anatomy, 17 aneurysm, 467, 478 angioplasty, 480 angora, 536 anhydroglucose units, 405 aniline, 165, 172, 173, 176, 235, 236 ANOVA, 384, 387, 388, 391, 395 ANOVA analysis, 388 Anthraquinone, 159, 160 Anthraquinone derivatives, 159 Anthraquinone disperse dyes, 160 anthraquinone dyes, 159 anti-back staining agent, 28 antibacterial activity, 278, 301, 313, 314, 365 antibacterial surfaces, 278, 288

anticoagulant, 474 anticoagulation, 474 anti-counterfeit, vii, 81, 103, 118, 210 antimicrobial agents, 310, 365, 384 antimicrobial nanoparticulate films, 289 antimicrobial properties, 362, 403 antique, 2, 8 aorta, 467, 479 aortic stenosis, 479, 480 aortic valve, 480 apparel, 3, 8, 19, 20, 21, 22, 23, 24, 25, 26, 31, 34, 35, 36, 37, 38, 39, 40, 41, 42, 44, 46, 47, 48, 49, 136, 191, 211, 227, 243, 246, 367, 368, 390, 475, 490, 492 apparel industry(ies), 20, 21, 22, 23, 367 apparel manufacturers, 21, 22 apparel products, 475 apron draft spinning system, 506 aptitude, 471 aqueous solutions, 34, 177, 412, 413, 441, 443, 444 arabinofuranose units, 402 arc-discharge lamps, 533 archaeological excavations, 83 archaeological sites, 316 archaeological textiles, 274, 275, 276, 317, 336 archaeologists, 259, 260, 269, 270, 271, 272, 273, 274 archaeology, 269, 274, 276, 339 aromatic diazo compound, 163 aromatic polyamide, 541 aromatic rings, 207, 214 arteries, 471, 476 artery, 465, 467, 472, 473, 476, 477, 478, 479 artificial fibres, 278, 499 artificial textile prosthesis, 466 aryl azo pyridone dyes, 162, 185 aseptic, 400 aseptic properties, 400 Asia, 441, 442, 461 assessment, 31, 79, 181, 182, 227, 338, 476 atherosclerosis, 467, 471 atmosphere, 12, 278, 286, 290, 292, 301, 303, 306, 430, 432, 486, 487, 521 atmospheric pressure, 280, 441 atomic absorption spectroscopy, 321 atomic force, 305, 306 atoms, 108, 262, 263, 279, 283, 285, 286, 289, 297, 310, 375, 377, 432 ATP, 206 attachment, 77, 239, 254, 265, 506 attenuated total reflection FTIR spectroscopy, 321, 324 attractiveness, 5, 6

Index attribution, 324 Austria, 264 authentication, 107, 117, 195, 209, 210 authenticity, 4, 9, 10, 11, 13 automation, 85 avoidance, 520 awareness, 5, 10, 12, 20, 22, 270, 271 azo colorants, 157, 159, 162, 163, 179 azo compounds, 157, 159, 166 azo coupling, 163 azo dyes, vii, 157, 159, 163, 164, 165, 167, 170, 175, 176, 177, 179, 180, 181, 182, 183, 184, 185 azo groups, 159, 179, 197 azo pigments, 167 azobenzene, 105, 159, 197, 208 azobenzothiazoles, 162 azo-hydrazone equilibrium, 158 Azo-hydrazone tautomerism, 157, 179 azopyrazolone, 162 azopyridones, 162 azothiophenes, 162 azulenes, 197, 203

B backlash, 3 bacteria, 23, 165, 263, 277, 278, 279, 280, 283, 285, 289, 290, 291, 295, 296, 300, 305, 306, 310, 311, 313, 384, 395, 418, 460, 476 bacteria inactivation, 277, 297 bacteria respiratory enzyme, 278 bacterial cell wall membrane, 297 bacterial colonies, 296 bactericide surfaces, 290, 292 balloon angle, 519, 521, 526, 528 bamboo fibers, 540 ban, 400 band gap, 223 Bangladesh, viii, ix, xii, 19, 20, 26, 48, 49, 123, 124, 136, 153, 154, 499 baroque, 316 barriers, 22, 116, 314 base, 11, 13, 56, 61, 124, 129, 158, 168, 179, 185, 190, 212, 216, 227, 234, 241, 242, 251, 264, 363, 365, 369, 372, 406, 411, 425, 449, 461, 462, 484, 495, 499 basic dyes, 103, 165 bast fibers, 400, 441, 538, 539, 545 bath exhaustion, 343, 345 bathochromic effect, 176 baths, 76, 349 batteries, 210, 240, 252, 447, 448, 449, 450, 453, 454, 455, 460

549

beams, 166, 532 BED, 352 bedding, 243, 246 behaviors, 450, 455 Beijing, 496 Belgium, 121 bending, 19, 25, 31, 36, 51, 240, 247, 250, 253, 254, 328, 386, 390, 472, 474, 475, 477, 480 bending length, 19, 31, 36, 51, 386, 390 bending rigidity, 25, 475, 480 beneficial effect, 278 benefits, 5, 6, 16, 242, 253, 371 benzene, 176, 179, 235, 406, 419 benzene ring cleavage, 406, 419 benzodifurane, 159 beverages, 352 bias, 275 Bifurcated prosthesis, 466 bifurcated vascular prosthesis, 465, 469, 478, 479 bing, 351 biochemistry, 188 biocidal action, 263 biocidal properties, 263, 264 biocidal surfaces, 278, 384 biocompatibility, 278, 292, 299, 362, 465, 466, 471, 477, 478 biodegradability, 362, 403 biodegradable enzymes, 23 biodeterioration, 317, 320, 321, 337 biofinishing cotton, 47 biological samples, 532, 533 biological systems, 194 biomass, 399, 418, 430, 436, 441, 445 biomaterials, 54, 189, 480, 481 biomedical applications, 89, 90, 205, 292, 312, 351, 384 biomimetic systems, 219 biomimetics, 240 biomonitoring, 227 bioprocessing, 240 biosorbents, 399, 401, 418 biosorption capacities, 419 biostatic properties, 373, 381 biostoning denim, 47 biosynthesis, 50 biotechnology, 188, 240, 350, 455 biotic, 337 bisphenol, 217 blankets, 505, 515, 516 bleach wash, 20, 21 bleach washing process, 21 bleaching, 125, 353, 384, 406, 414, 502 bleeding, 59, 92

550 blends, 54, 164, 226, 249, 351, 442, 504, 509, 516, 518, 537 blood, 448, 465, 467, 468, 471, 472, 473, 476, 477, 478, 479 blood circulation, 468, 471 blood clot, 477 blood clotting substances, 477 blood constituents, 467 blood flow, 465, 467, 468, 471, 478 blood vessels, 465, 466, 468, 473, 479 bloodstream, 474 bluenic, 521, 524 body core temperature, 483 body fluid, 475 body temperature, 210, 211, 244, 384, 484, 491 Boltzmann constant, 487 bonding, 177, 230, 280, 329, 358, 404, 418, 475 bonds, 35, 268, 280, 289, 306, 317, 322, 323, 328, 329, 331, 332, 362, 368, 402, 430, 432, 539 bone(s), 246, 264 boric acid, 147, 217, 381 bounds, 414 boutique-style shops, 12 braided edge, 271 braided structure, 477, 478 braids, 136 brain, 241 branching, 401 brand image, 12, 13 brand name, 6, 9 brand protection, vii, 81, 107, 117, 118, 194, 209, 210 brass, 248, 514 breakdown, 159, 268, 317 breaking elongation, 56, 330, 334, 502, 524 breaking extension, 387, 388, 502, 507 breaking force, 30, 33, 51, 56 breaking strengths, 523, 528 breaking stress, 330, 334 breathing, 370, 455, 485 brilliant yellows, 161 Britain, 4 brittleness, 249, 333 brushing action, 24 bulk coloration, 171 bundle cross-section, 409 burial environment, 262, 264, 273, 274 buried contemporary materials, 318 burn, 310, 311 businesses, 7, 14, 55, 83 butadiene, 246 buttons, 11, 508 buyer(s), 20, 25

Index by-products, 445, 541

C Ca2+, 314 cables, 448, 455 CAD, 90 cadmium, 428, 429, 436, 444, 445 calamitic molecules, 215 calcification, 474 calcium, 94, 259, 321, 442 caliber, 473 calibration, 286 calorimetry, 361 camera, 55, 195, 522, 532, 533 candidates, 107, 224 cane sugar, 154 capillary, 408, 413, 414, 415, 416, 417, 419, 443 capsule, 488, 539 carbon, 152, 163, 201, 233, 234, 241, 248, 249, 262, 264, 294, 313, 377, 397, 399, 401, 404, 405, 407, 430, 432, 434, 436, 438, 440, 444, 445 carbon atoms, 377, 432 carbon dioxide, 263, 431 carbon materials, 399, 401, 430, 432, 434, 436, 438, 445 carbon monoxide, 431 carbon nanotubes, 233, 234, 249, 445 carbon precursor chemical structure, 432 carbon skeleton of the cellulose backbone, 405 carbonaceous materials, 430, 436 carbon-carbon bond cleavage, 405 carbon–carbon linkages, 404, 407 carbonization, 399, 400, 430, 432, 433, 434, 436, 439, 440 carbonized hemp fibers, 400, 432, 433, 434, 437, 438, 439, 440, 441 carbonyl groups, 329, 358, 418 carboxyl, 280, 294, 384, 405, 411 carboxylic acid(s), 356, 357, 358, 360, 362, 365, 373, 375, 379, 381, 382, 402, 405 carboxylic groups, 371, 405, 434 carboxymethyl cellulose, 123, 124, 125, 153, 154, 155 carboxymethylation, 124, 125, 129, 130 carcinogenic amines, 159 cardiac care, viii, 465 cardiac pulse, 472, 473 cardiovascular surgeries, 465 cardiovascular textile prostheses, 471 carsolchromic, 246 case study(ies), 265, 266, 271, 272, 310 cashmere, 536, 538

Index cashmere wool, 536 catalysis, 192, 231, 263, 313 catalyst, 27, 177, 263, 302, 357, 358, 362, 363, 364, 372, 375, 377, 378, 381 catalytic activity, 301 catalytic domain, 23 catalytic properties, 445 catheter, 474, 476, 479, 480 cation, 405 cationic agent printed cotton, 54 cattle, 500 CBD, 23 C-C, 150, 294, 406 cell development, 467 cell killing, 279, 311 cell phones, 250 cell surface, 361 cell wall components, 412 cellulase, 19, 20, 21, 23, 24, 25, 27, 33, 34, 35, 36, 37, 38, 39, 40, 41, 43, 44, 46, 47, 48, 49, 50, 51, 52, 340 cellulase enzyme, 19, 20, 21, 23, 27, 33, 36, 46, 47, 48, 49, 50 cellulose acetate, 123, 124, 136, 141, 153, 155, 157, 158, 159, 160 cellulose chains, 43, 323, 326, 329, 355, 367, 368, 369, 371, 372, 373, 375, 401 cellulose crystallinity, 323, 324 cellulose derivatives, vii cellulose fibers, 355, 404, 442, 443, 445, 538, 539, 540 cellulose fibre, 211, 323, 397 cellulose I, 340, 404, 434, 442 cellulose II, 404, 434 cellulose macromolecules, 324, 330 cellulose microfibrils, 401, 403, 408 cellulose molecules, 360, 375, 403, 404 cellulose nitrate, 123, 124, 145, 152, 153, 155, 156 cellulose-binding domain, 23 cellulosic, 23, 24, 49, 51, 123, 124, 125, 136, 145, 153, 170, 263, 264, 266, 267, 273, 276, 318, 319, 321, 322, 326, 331, 336, 337, 340, 341, 355, 356, 360, 361, 363, 367, 371, 372, 377, 380, 381, 397, 401, 405, 430, 441 cellulosic derivatives, 123, 124 cellulosic textiles, 337, 367, 372 cellulosic wastes, 123, 153 cellumonas fimi, 23 cell-wall membrane, 300 Central Europe, 265 ceramic, 82, 93, 95, 245, 261 cesium, 199 CFI, 528

551

chain branching, 401 chain scission, 317 challenges, 11, 20, 55, 91, 92, 104, 276 changed appearance, 317 charge density, 418 charge transfer sites, 296 charity shops, 4 charm, 3 chemical characteristics, 76, 124, 133, 405, 416 chemical damage, 317 chemical fibers, viii, 400, 531, 533 chemical interaction, 99 chemical modification, 400, 407, 411, 432, 436, 440, 441, 443 chemical phenylpropane units, 402 chemical processing steps, 19 chemical properties, 104, 195, 340, 378 chemical reactions, 92, 377 chemical softeners, 501 chemical stability, 344 chemical structures, 335, 377 chemical texturizing process of jute, 501 chemical treatments, 31, 404, 405, 406, 411, 541, 542, 543 chemicals, vii, 20, 21, 22, 23, 25, 26, 28, 47, 48, 54, 55, 76, 78, 362, 365, 369, 371, 377, 384, 400, 441, 448, 461 CHF, 437 Chicago, 15, 17, 451 children, 188, 211, 460 China, 56 chiral molecules, 210 chirality, 207 chitin, 361 chitosan, 55, 78, 350, 351, 362, 365, 378, 443 Chitosan, 350, 361, 365 chlorine, 20, 24, 356, 406 chlorine bleach, 20, 24 chloroform, 179 cholesteric liquid crystal, 210 cholesterol, 210 Christianity, 320 chromatic adaptation-transformed values, 69 chromatography, 321, 438, 446 chromic materials, 193, 239, 240, 246, 247, 252 chromium, 167, 182 chromophore, 196, 215, 216 chromophoric azo group, 157, 159 circulation, 93, 468, 471 cities, 7, 264, 275 civilization, 83 clarity, 210 classes, vii, 86, 91, 92, 105, 107, 115, 158, 218, 438

552

Index

classification, 15, 85, 86, 158, 192, 193, 211, 220 cleaning, 21, 288, 310, 311, 312, 384, 406, 448 cleavage, 106, 107, 184, 405, 406, 419, 430, 432 climate(s), 244, 453, 488, 491, 492 clinical performance, 466 clinical trials, 250 Clostridium difficile, 384, 396 clothing materials, 400, 468, 483, 488, 495 clothing structure design, 493 clusters, 7, 277, 278, 279, 280, 282, 285, 306 CMC, 69, 79, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 139, 144, 145, 147, 153, 154, 374, 375 CO2, 430, 431, 433, 434, 435, 436 coal, 400, 430 coatings, 122, 136, 154, 188, 220, 232, 248, 249, 256, 283, 289, 295, 313, 314, 519, 522, 524, 525, 526, 527, 528, 543 cobalt, 221, 234 coding, 87, 89, 90 coefficient of capillary diffusion, 416 coefficient of friction, 502 coefficient of variation, 409, 414, 502, 511 coffee, 444 collaboration, viii, 188, 259, 260, 269, 271, 272, 273, 274, 455 collagen, 466 colleges, vii collisions, 280 colloidal suspension, 280 colonisation, 317 colonization, 279, 338 color constancy, 67, 68 color difference equations, 56 color fastness determinations, 286 color fields, 63 color filters, 157, 163, 179, 180, 182 color gamut, 55, 59, 62, 63, 64, 66, 67 color inconstancy index, 53, 54, 56, 67, 68, 69, 70, 76, 79 color management, vii, 53, 54, 55, 58, 59, 61, 65, 66, 79 color management application, vii, 53 color patches, 59, 60, 63, 65, 67 color patterns, 53, 55, 65, 74 color photography, 157, 159 color prints, 53, 54 color profiles, 53, 55, 56, 58, 61, 63, 65, 76 color stabilization, 58 color tone, 54 color transformations, 66 colorimetric matching, 65 colorimetrically transforms in-gamut colors, 67

colour change, 82, 99, 103, 104, 106, 108, 109, 113, 115, 117, 121, 190, 192, 193, 194, 195, 196, 197, 198, 199, 203, 209, 210, 211, 212, 213, 214, 216, 217, 218, 219, 220, 221, 222, 224, 229 Colour Index, 158, 159 combined effect, 495 comfortable garments, 367 comfortness, 36 commercial, 23, 49, 89, 90, 103, 106, 122, 159, 177, 188, 195, 245, 250, 289, 343, 345, 346, 400, 439, 440, 452, 502, 503, 505, 506, 507, 508, 532, 533 commercial colorants, 159 commercial fabrics, 507 communication, 6, 12, 13, 14, 84, 201, 229, 239, 250, 251, 252, 253, 260, 274, 447, 448, 449, 455 communication technologies, 252 community(ies), 12, 337, 338 compact spinning, 520 compaction, 471 comparative analysis, 311 compatibility, 98, 468, 477 compensation, 65 competition, 2, 5, 11, 84, 453, 462 competitive advantage, 5, 10, 17, 190 competitive conditions, 419 competitors, 5, 6 complex interactions, 484 complexity, 2, 71, 402, 419, 466, 471 compliance, 466, 468, 471, 473 composite materials, 145, 188, 399 composites, 189, 226, 240, 248, 249, 256, 303, 402, 441, 442, 481 composition, 19, 27, 91, 92, 97, 99, 100, 102, 145, 155, 181, 210, 222, 286, 295, 322, 325, 344, 345, 350, 382, 399, 401, 403, 404, 407, 409, 410, 411, 412, 414, 415, 416, 419, 440, 441, 490, 512, 545 compounds, 55, 78, 105, 107, 157, 158, 159, 161, 163, 166, 170, 171, 176, 183, 200, 205, 208, 211, 213, 214, 215, 216, 221, 230, 247, 249, 355, 361, 369, 370, 371, 372, 406, 430, 444 compressibility, 25 compression, 466, 477, 504, 517 compression resistance, 466 computation, 250, 494 computer, 55, 84, 188, 452, 467, 468, 478, 494, 531, 532, 533 computer program, 531 computer technology, 532 computer-aided design, 478 computer-controlled galvanometer mirrors, 533 computing, 188, 227 condensation, 167, 212 conditioning, 30, 33, 51, 255

Index conductance, 489 conducting polymer composites, 256 conduction, 222, 223, 278, 282, 305, 483, 484, 485, 489, 491, 493, 494 conductive fibers, 239, 248, 249, 253, 447 conductive materials, 239, 240, 248, 254, 449 conductive smart textiles, 250 conductive textiles, 248, 249, 250, 257 conductive threads, 253, 254 conductivity, 92, 94, 98, 195, 219, 222, 233, 248, 249, 250, 254, 357, 383, 384, 386, 390, 391, 392, 394, 486, 487, 488, 489, 490, 493, 495, 496, 497, 509, 517 conductor(s), 211, 219, 247, 249, 254, 490, 492, 494 conference, 51, 255, 364, 447, 448, 453 confidence limits, 526 confocal laser scanning microscopy, 531, 532, 544, 545 confocal magnetron-sputtering systems, 292 conformity, 3 Congo, 236 Congress, 119, 364 conjugate planes, 532 conjugated double bond, 430 conjugated electrochromic polymers, 224 conjugation, 106, 193, 202, 212, 214, 215 consciousness, 190 conservation, 145, 259, 260, 268, 269, 270, 271, 272, 273, 274, 276, 316, 320, 325, 336, 338, 341 conservation process, 270 conserving, 260, 275, 276, 316 consolidation, 268, 273, 512, 513 constant ink composition, 100 constituent materials, 270 constituents, 2, 321, 402, 467 Constitution, 119 construction, 118, 242, 245, 270, 386, 455, 465, 473, 475, 476, 478, 490, 492, 496 consumers, 3, 4, 8, 9, 10, 11, 12, 13, 14, 21, 22, 25, 191 consumption, 2, 3, 14, 449, 450 contact time, 302, 309, 418, 419 contactless printing, 166 containers, 12, 266 contaminate historical textiles, 336 contamination, 289, 290, 315, 337, 339, 384, 396 contemporary costumes, 271 continuous inkjet printing technique, 85, 87, 94 continuous washing cycles, 349 controversial, 400 convection, 127, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 496 conventional dyes, 82

553

conventional pad–mangle systems, 242 conventional ring spinning, 520 conventional textile materials, 384 convergence, 188, 239 COOH, 177, 411, 412 cooking, 352 cooling, 216, 241, 242, 244, 245, 289, 484, 514, 543 cooling process, 242 cooperation, 91 coordination, 211, 234 copolymer(s), 143, 150, 153, 235, 246, 255, 350, 365, 378 copolymerisation, 220 copolymerization, 154, 155 copper, 208, 231, 232, 248, 249, 259, 262, 263, 264, 266, 267, 268, 273, 276, 313, 383, 384, 385, 387, 388, 389, 390, 391, 393, 394, 395, 396, 444, 445, 494 copper alginate, 384, 389 copper sulphate, 383, 385, 395 copper volumes, 390 correlation(s), 71, 74, 176, 303, 409, 420, 437, 438, 467, 471, 473, 478, 479, 493, 512, 515 correlation coefficient, 420 correlation matrix, 512, 513 corrosion, 92, 94, 98, 99, 249, 262, 263, 264, 274, 275, 477 cortex, 332 cosmetic(s), 124, 157, 159, 195, 210, 344, 377, 455 cost, 76, 89, 101, 118, 123, 124, 136, 159, 221, 344, 356, 373, 399, 401, 430, 436, 440, 443, 477, 499, 505 cost effectiveness, 159 cotton and acrylic jacket fabrics, 508 cotton commercial shawl fabrics, 507 cotton fabrics, 24, 49, 50, 51, 54, 63, 129, 134, 136, 312, 347, 348, 352, 353, 356, 361, 362, 363, 364, 365, 367, 368, 370, 377, 378, 379, 380, 381 cotton fiber, 24, 55, 136, 144, 153, 154, 313, 346, 348, 349, 362, 365, 377, 539, 540 cotton linters, 124, 154 cotton textiles, 268, 282, 367, 370, 371, 375 cotton twill fabric, 21 cotton/acrylic commercial shawl fabrics, 507 cough, 370 country of origin, 6 coupling reaction, 163, 170, 179 covalent bond, 358 covalent chemical bond, 76 covering, 90, 322, 368, 387, 477 CPU, 252 crabs, 361 cracks, 44, 326, 413

554

Index

creatinine, 155 creativity, 3 creep, 518 crimped textile implants, 471 critical fabric properties, 490 critical ring spinning, 520 crop, 444, 500 crop residue, 444 crops, 438, 499, 500, 538 cross-contamination, 384, 396 crosslinking, 333, 355, 356, 357, 358, 360, 361, 362, 363, 364, 365, 367, 369, 370, 371, 372, 373, 374, 375, 377, 378, 379, 380, 381, 382 crown, 197, 199, 208, 230, 231 crystal structure, 434, 442 crystalline, 24, 155, 215, 232, 263, 268, 279, 323, 324, 329, 357, 368, 384, 401, 404, 412, 414, 442 crystalline structure, 279, 357, 384, 404 crystalline supermolecular structure, 401 crystallinity, 112, 268, 323, 324, 325, 328, 329, 330, 334, 336, 340, 408, 412, 414 crystallinity index, 324, 340, 414 crystallization, 241 crystallographic Ag-clusters, 285 crystals, 24, 193, 210, 215, 233, 247, 279, 285, 289, 449 Cuba, 351 cultivation, 268 cultural heritage, 316, 317, 337 cultural property, 260 culture, x, 2, 4, 8, 259, 260, 270, 272, 274, 295, 300, 351 cure, 85, 91, 100, 364, 372 curing process, 77, 102, 356, 379 currency, 20 current limit, 226 customer service, 6, 11, 14 customers, 8, 9, 10, 11, 12, 13, 14, 20, 22 cuticle, 332 CV, 521, 522, 524, 528 CVD, 289, 313 cyanamide, 362 cyanide, 205 cycles, 115, 196, 204, 230, 250, 289, 297, 305, 346, 348, 349, 363, 542 cycling, 22, 292, 476 cyclodextrins, 231, 377, 382 cyclohexanone, 179 cysteine, 333 cysteine residues, 333 cytotoxicity, 278, 292, 303, 305 Czech Republic, 386, 387, 397

D dacron, 468, 471 damping, 245, 437, 480 damping coefficient, 437 danger, 251, 336 darker-grey metallic Ag-color, 292 data analysis, 7 data communication, 84 data processing, 251 data set, 387, 391 data transfer, 252, 253 database, 537 DC-magnetron sputtering, 277, 283, 286, 312 decay, 112, 315, 337, 341 decolouration, 112, 113, 114 decomposition, 92, 116, 176, 200, 268, 300, 305, 317, 340, 361, 365, 430, 431, 432, 434, 435, 445 decomposition temperature, 176 decontamination, 337 deconvolution, 290 decoration(s), 84, 90, 100, 210, 316, 447 decorative-protective applications, 455, 460 decoupling, 128 defects, 289 defence, 191, 397 deficiency, 249 deflate, 348 deformation, 89, 253, 329, 334, 368, 390, 466, 471, 472, 474 degradation, 24, 37, 43, 44, 116, 155, 177, 184, 196, 263, 264, 313, 317, 319, 320, 331, 337, 338, 339, 340, 341, 357, 372, 377, 405, 406, 407, 468, 475 degradation process, 320 degree of fiber swelling, 412 degree of lattice transformation, 404 degree of polymerisation, 329 degree of substitution, 123, 124, 126, 129, 136, 138, 139, 147, 148, 153 degree of swelling, 404, 412 Degussa, 177 dehydration, 211, 430 delignification process, 501 denim, vii, 8, 11, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51, 397 denim apparel, 19, 20, 21, 22, 23, 24, 25, 26, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 46, 47, 48 denim designs, 22, 23, 25 denim ready-made apparels, vii, 19, 20, 25, 47 denim trousers, 19, 28, 29 Denmark, 274

Index dependent variable, 515 depolymerisation, 323, 326, 328, 329, 330, 333, 334, 336, 430 depolymerization, 404, 430 deposition, 82, 94, 136, 145, 153, 249, 253, 254, 279, 283, 286, 288, 289, 290, 292, 297, 298, 302, 311, 314, 345, 353, 428, 478 deposition rate, 286, 297, 298 deposits, 279, 286 depth, 31, 32, 90, 190, 389, 510, 531, 533 derivatives, vii, 23, 49, 123, 124, 136, 155, 159, 161, 164, 165, 168, 177, 181, 182, 183, 184, 185, 200, 202, 204, 205, 207, 208, 210, 216, 220, 230, 232, 234, 365, 372, 378, 381, 382, 402, 406, 432, 442 design, vii, 9, 20, 21, 22, 49, 50, 81, 82, 83, 92, 107, 117, 118, 119, 191, 194, 209, 210, 226, 227, 228, 239, 242, 247, 250, 251, 305, 381, 450, 455, 461, 462, 465, 467, 473, 476, 491, 493, 499, 506, 507, 508, 509, 510, 515 design and fashion apparel, 20 designers, 3, 4, 9, 15, 20, 21, 22, 25, 55, 78, 191 designing of warm fabrics, 500 desizing, 23, 28 desizing agent, 28 desorption, 377, 430, 434, 435, 436, 445 desorption of water, 430 destruction, 264, 271, 305, 397, 467 detectable, 104, 493 detection, 297, 455, 462, 476, 543 detection system, 462 detergent, 21, 28, 507, 509 detergents, 55, 63 detrimental effects, 262 developed countries, 344 developed fabrics, 507, 508 developed jacket fabric, 508 deviation, 421, 439 diabetic wound dressing, 289 diarylethenes, 107, 111, 115, 194, 197, 199, 201, 208 diastole, 472 diastolic membrane stress, 474 diazo compounds, 163 diazo printing, 157, 159 diazonium salts, 163, 164, 170, 177, 179 diazotization, 163, 170, 171 diazotized aromatic amines, 168 dichromatic mirrors, 533 dielectric constant, 105, 195 differential scanning, 361 differential scanning calorimetry, 361 diffraction, 155, 193, 285

555

diffusion, 158, 184, 221, 282, 295, 306, 386, 416, 417, 421, 422, 423, 425, 426, 427, 428, 437, 444, 485 digestion, 539, 543 digital cameras, 250 digital dyeing, 82, 103 digital microscope, 532 digital printing, vii, 53, 54, 55, 61, 77, 79, 84, 100, 120, 250 digital technologies, 118 digital textile printing, 53, 54, 55, 58, 66, 78, 85 diketone keto esters, 167 dimensional stability, 20, 49, 54, 355, 500 dimensions, 8, 233, 263, 272, 285, 376, 386, 404, 450, 460, 473, 476, 537 dimethyl sulfoxide, 128, 139, 147, 155 dimethylformamide, 176, 178, 184 diodes, 189, 449, 453 diphenyldiazene, 159 dipoles, 306 direct mail, 90 dirndl skirts, 10 disabled patients, 188 disazo pyridone compound, 171 disazo reactive dyes, 183 discomfort, 252, 484 discontinuity, 474 discriminant analysis, 341 diseases, 460, 476 disinfectant, 279, 384 disinfectant reactivity, 279 disinfected properly, 384 disinfection, 278, 279, 288, 289, 303, 311, 314 disorientation of the fibrils, 409, 412, 417 disoriented fibrillar network, 409 disperse dyes, 84, 103, 116, 121, 122, 157, 158, 159, 160, 161, 162, 163, 164, 165, 179, 181, 182, 184, 229 dispersing metallic particles, 248 dispersion, 91, 94, 99, 158, 181 displacement, 89, 254, 472 dissociation, 5, 185, 195 distillation, 139 distilled water, 31, 123, 126, 128, 137, 146, 385, 514 distribution, 4, 5, 16, 52, 70, 112, 113, 155, 295, 345, 419, 420, 493 diverse core materials, 344 diversification, viii, 499 diversification of jute, viii, 499 diversity, 315, 336 DMF, 176 DNA, 54, 77, 234, 278, 305 DNA damage, 278, 305

556

Index

doctors, 447, 460 dogs, 500 DOI, 381 domestic animals, 500 domestic washing, 348, 349 donors, 217 doping, 222, 224, 296 doppler, 466, 467 dosing, 85 double bonds, 430 downstream shear stress, 467 draft, 53, 56, 58, 59, 502, 505, 506 draught, 453 drawing, 416, 451, 505, 506 dressings, 384 drop-on-demand inkjet printing technique, 86 DRS, 296, 303 drug carriers, 350 drug delivery, 192, 199, 209, 350 drug release, 188, 199, 205 drugs, 157, 159, 344 drying, 29, 30, 87, 90, 98, 100, 128, 343, 345, 346, 350, 351, 403 DSM, 352 durability, 21, 39, 54, 121, 191, 221, 250, 343, 344, 345, 346, 349, 353, 362, 363, 365, 370, 371, 465, 474, 476, 478, 500 durable fragrances, vii, 344 durable press, 355, 356, 362, 363, 364, 367, 368, 372, 377, 378, 379, 380 durable press finishing, 356, 362, 363, 367, 372, 377, 378, 379, 380 dye manufacturing companies, 158 dyeing, 34, 49, 51, 82, 84, 103, 122, 158, 160, 164, 165, 166, 170, 172, 174, 176, 179, 181, 182, 183, 184, 192, 195, 196, 200, 204, 218, 220, 242, 381, 384, 396, 414, 501, 502, 506 dyeing characteristics, 158, 183

E Eastern Europe, 10, 256, 353, 397, 529 easy care finishing, 367, 377 easy-ironing clothes, 368 eco-fashion, 25 ecology, 450, 461 economic downturn, 4 economical cost, 477 economics, 162 eczema, 370 editors, 122, 154, 228, 229 education, 480 educational background, 269

egg, 396 Egypt, 83, 268, 337 Egyptian mummies, 338 elaboration, 252 elasticity, 95, 192, 245, 401, 403, 472, 473, 476, 478, 541 elasticity hypotheses, 472, 473 election, 469 electric charge, 410 electric current, 220 electric field, 87, 94, 244, 280 electrical conductivity, 248, 496 electrical properties, 249, 250, 256, 403 electricity, 82, 84, 119, 246, 401, 403, 447, 448, 449, 453 electrochemical reaction, 263 electrochromic dye, 103 electrochromic materials, 219, 220, 221, 224, 234 electrochromic switches, 187, 190, 194, 208 electrochromic textile production, 219, 224 electrodes, 201, 219, 227 electrolyte, 98, 220, 221, 235 electromagnetic, 192, 194, 280, 448, 460 electromagnetic influences, 448 electron diffraction, 155 electron microscopy, 44, 45, 285, 299, 303, 304, 316, 321, 322, 326, 327, 332, 341, 343, 345, 346, 545 electron-accepting group, 177, 179 electron-donating substituents, 177, 179, 229 electronic and photonic textiles, 190 electronic devices, 251, 254, 344 electronic materials, 54 electronic smart textile, 239, 252, 254 electronic structure, 195, 203 electronics, vii, viii, 54, 90, 96, 188, 189, 226, 227, 230, 240, 247, 249, 250, 256, 447, 448, 450, 452, 453, 455, 461 electrophotographic (, 55 electrospinning, 220 electrostatic properties, 400 elementary fibers, 408 elongation, 25, 30, 51, 56, 89, 132, 142, 150, 330, 334, 409, 501, 502, 509, 519, 521, 522, 524, 527, 528 e-marketing, 12 embedding microencapsulated phase change materials, 455 embolism, 474 emergency, 64, 188 emerging markets, 10 emission, 193, 194, 195, 243, 295 empirical studies, 6 employees, 11

Index employment, 273 emulsions, 351 encapsulate, 264 encapsulated nanoparticles, 344 encapsulation, 189, 344, 351 encouragement, viii endangered, 320, 325 endorsements, 5 endothelial cells, 467 endothelium, 479 energy, 82, 92, 100, 112, 122, 158, 162, 190, 193, 198, 202, 214, 222, 223, 224, 230, 239, 241, 245, 251, 279, 280, 285, 301, 306, 308, 309, 383, 384, 385, 387, 388, 390, 392, 394, 395, 396, 444, 448, 449, 452, 453, 476, 484, 486, 491 energy constraint, 239 energy density, 241 energy supply, 251 energy transfer, 122, 193, 230, 241 enforcement, 250 engineering, 54, 77, 90, 188, 191, 210, 227, 239, 240, 245 England, 28, 29, 120, 124, 136, 145, 255, 276 entangled fibers, 399, 401, 418 entangled hemp fibers, 399, 401 entanglements, 245 entrapment, 98, 418 entrepreneurs, 7, 16 environmental change, 189, 245 environmental conditions, 103, 115, 117, 189, 190, 209, 271, 273, 278, 315, 320, 321 environmental effects, 294 environmental factors, 263 environmental impact, 441, 443 environmental influences, 368 environmental issues, 9 environmental pollution, 124 environmental protection, 240 environmental stimuli, 190, 192, 193, 214 environmental warning system, 117, 209 environmentally friendly clothes, 399 environments, vii, 83, 87, 109, 196, 240, 244, 260, 264, 268, 274, 321, 336, 449, 485, 488, 491 enzymatic action, 23 enzymatic degradation, 24, 377 enzymatic hydrolysis, 24, 41, 401 enzymatic process, 20, 24 enzyme(s), 19, 20, 21, 22, 23, 24, 26, 27, 28, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 117, 180, 192, 209, 278, 317, 338, 341, 403, 441 enzyme wash, 19, 20, 21, 22, 23, 26, 27, 28, 33, 34, 35, 37, 38, 39, 40, 41, 42, 44, 47, 48

557

enzyme washing process, 21, 22, 23 epidemic, 396 epidermis, 352 equilibrium, 158, 177, 178, 179, 212, 280, 414, 415, 416, 420, 421, 422, 423, 424, 426, 427, 436, 489, 491 equilibrium adsorption process, 422 equilibrium ion concentration, 423, 424, 426, 427 equipment, 24, 80, 100, 252, 522 ergonomics, 191 Escherichia coli, 384 estate sales, 4 ester, 30, 132, 134, 143, 150, 153, 163, 171, 173, 236, 356, 357, 358, 362, 363, 364, 365, 372, 379, 380 ester bonds, 362 etching, 254 e-textile applications, 462 e-textile fabric, 254 ethanol, 97, 98, 123, 124, 125, 129, 138, 145, 168, 178 etherification, 125, 129, 130, 131, 132, 154 ethers, 197, 217, 231, 434 ethical awareness, 10 ethical issues, 13 ethics, 276 ethyl alcohol, 124 ethylcellulose, 362, 365 ethylene, 164, 214, 246, 255, 350 ethylene glycol, 350 ethylene oxide, 255 EU, 226 Europe, 3, 10, 84, 180, 256, 265, 316, 353, 397, 529 evaporation, 92, 100, 295, 430, 483, 484, 485, 488 evaporative heat loss, 387, 395, 485 evenness, 401, 403 everyday life, 124, 136, 145, 260, 449 evidence, 7, 134, 143, 150, 260, 263, 270, 271, 272, 275, 283, 294 evolution, 2, 33, 42, 77, 260, 436, 472, 473 examinations, 535, 542 excavated textiles, 259, 260, 270, 271, 273, 274 excavation project, 270, 271 excavations, 83, 265, 271 excitation, 107, 116, 222, 224 execution, 66 exercise, 479, 484, 496 exertion, 244 expensive organic materials, 450 experimental condition, 426 experimental design, 510 expertise, 5, 9, 10, 12, 14, 113

558

Index

exposure, 74, 75, 76, 99, 104, 112, 113, 114, 115, 194, 196, 197, 205, 206, 218, 250, 322, 337, 340, 533 extension at break, 500 external compression, 466 external environment, 190, 484 external influences, 323 external surface adsorption, 422 extinction, 157, 159, 162, 280 extraction, 128, 247, 400, 438, 440, 441, 446 extrusion, 211, 218, 220, 241, 352, 539

F fabric antibacterial kinetics, 280 fabric based circuits, 253 fabric construction factors, 476 fabric cover factor, 506 fabric deformation, 466 fabric dimensional properties, 385 fabric prosthesis, 465, 474, 478 fabric scaffold, 475 fabric thickness, 386, 391, 392, 489, 506, 508, 512 fabric weight, 19, 31, 34, 35, 36, 37, 39, 41, 345, 506, 507, 508, 509, 510, 511, 512, 513, 515 fabrication, 54, 77, 253 Fabrication, 119, 462 family members, 11 fashion, vii, x, xiii, xiv, xv, 1, 2, 3, 4, 7, 8, 9, 10, 12, 13, 15, 16, 18, 20, 21, 22, 23, 25, 49, 50, 63, 81, 85, 107, 117, 118, 119, 136, 187, 192, 209, 225, 234, 240, 247, 250, 367, 449, 450, 455, 457, 460, 465 fashion aspects, 367 fashion consumer, 1, 2, 7 fashion effects, 21 fashion industry, 2, 3, 4, 63 fashion trends, 3, 4, 8, 10, 20, 23, 450, 460 fastness properties, 104, 157, 163, 165, 168, 175 fat, 418 fatigue resistance, 106, 196, 200, 253, 465, 474, 478 fatty acids, 217 feelings, 495 fiber bundles, 409, 414, 415, 539 fiber content, 490 fiber crystalline phase, 414 fiber diameter, 406, 409, 414, 537 fiber movement, 449 fiber optic coupler, 533 fibre compositions, 319 fibre identification, 266 fibre position, 520

fibrillation, 331, 405, 406, 408, 411, 413, 417, 419, 432 fibrils, 24, 35, 44, 47, 332, 336, 402, 406, 408, 409, 412, 417 field crops, 538 filament, 249, 476 film thickness, 286 films, 101, 112, 123, 127, 128, 132, 136, 139, 145, 150, 155, 221, 224, 233, 234, 235, 253, 254, 277, 278, 283, 285, 286, 288, 289, 290, 292, 294, 297, 298, 301, 305, 306, 313, 314, 452 filters, 157, 163, 179, 180, 182, 195, 533 filtration, 94, 127 financial, 17, 180, 310, 537 financial support, 310 fineness, 24, 56, 401, 403, 407, 409, 490, 509 finishing, 19, 20, 21, 25, 48, 49, 58, 90, 344, 352, 353, 356, 361, 362, 363, 365, 367, 369, 371, 372, 373, 377, 378, 379, 380, 381, 382, 384, 386, 394, 462, 471, 490 finishing material, 386 finite element method, 467, 497 Finland, 256 fire fighting, 250 fire-retardant fabrics, 384 first aid, 240, 273 first generation, 240, 466, 471 fish, 351 fish oil, 351 fishing, 246 fitness, 250 fixation, 55, 78, 100, 377, 381, 466, 471 flame, 240, 356, 360, 361, 363, 364, 365 flame protection, 240 flammability, 243, 361, 373 flavor, 344 flavour, 351, 352, 353 flax, 266, 268, 320, 321, 322, 323, 324, 325, 337, 400, 410, 441, 443, 538, 539 flax fiber, 443, 539 flex, 460 flexibility, 19, 31, 55, 84, 191, 216, 240, 243, 248, 249, 253, 402, 409, 410, 474, 475, 476, 477, 488 flexible circuit boards, 253 flexible display techniques, 188 flexural rigidity, 51, 383, 384, 386, 390, 396, 502, 503, 506, 507 floating clothing, 448 floods, 453 flora, 339 flow field, 467, 468 flow properties, 94, 467 flowers, 218

559

Index fluctuations, 241 fluid, 83, 85, 87, 90, 93, 94, 95, 96, 97, 98, 99, 118, 195, 414, 467, 478, 479 fluorescence, 19, 32, 33, 46, 47, 192, 202, 204, 205, 301, 533 fluorescence microscope, 19, 32, 33, 46 fluorescent brighteners, 64, 161 fluorescent lights, 67 fluorescent sensor, 204 fluorotriazine groups, 172 focal plane thickness, 533 food, 18, 54, 90, 124, 210, 344, 351, 362, 450, 455, 460 food decorating, 54 food products, 124 foods, 157, 159, 351 footwear, 104, 242, 243 force, 30, 33, 51, 56, 88, 96, 193, 305, 306, 308, 460, 476, 477, 504 forced-evaporation-type skin capsule, 488 formal suit, 8 formaldehyde, 345, 356, 362, 363, 364, 365, 369, 370, 371, 378, 379, 380 formaldehyde-based chemicals, 369 formaldehyde-free easy care agents, 370 formation, 82, 87, 88, 94, 98, 132, 141, 153, 155, 195, 213, 222, 239, 245, 254, 263, 276, 278, 279, 280, 285, 289, 290, 308, 333, 356, 357, 358, 361, 362, 368, 371, 372, 380, 404, 406, 408, 419, 432, 467, 472, 501, 504, 513, 516 formula, 32, 127, 395, 493 Fourier transform infrared spectroscopy, 316, 340 fragmentary painted clay-covered basketry, 270 fragments, 261, 264, 265, 272, 275 fragrance microcapsule, 344, 345 France, 10, 51, 479 free radicals, 233, 357, 375 free volume, 112, 113 free world, 450 freedom, 108, 390 freezing, 102, 244, 272, 351 friction, 25, 35, 245, 283, 346, 476, 502, 503, 520, 541 frictional washing, 347 fruits, 446 FTIR, 123, 128, 132, 133, 134, 139, 142, 143, 145, 147, 150, 151, 153, 274, 321, 322, 323, 324, 326, 328, 329, 330, 332, 333, 334, 337, 339, 340, 341, 357, 358, 363, 364, 380, 397 FTIR spectroscopy, 321, 323, 324, 326, 339, 341, 380 fulgides, 107, 194, 197, 199, 201, 202, 230 fulgimides, 107, 197, 202

functional dyes, 81, 82, 103, 104, 118 functional inkjet ink, 98, 103 functionalized smart textiles, 239 fundamental weave, 385 funding, 153 fungal colonisation, 317 fungal contaminations, 316 fungal growth, 92, 283, 316, 320, 321, 322, 323, 330 fungal infection(s), 320, 321, 322, 324, 325, 336 fungal proteolytic activities, 333 fungal species, 315, 317, 325, 326, 331, 332, 333, 334, 336 fungal spores, 320 fungi, 23, 50, 289, 315, 316, 317, 318, 320, 321, 323, 326, 329, 330, 331, 332, 334, 336, 338, 340, 341 fungus, 326, 340 furan, 202 furnishings, vii, 316 fusion, 191, 242, 276 fusion technology, 191

G galactoglucomannans, 402 Galaxy, 451 garage sales, 4 garment industries, 20, 124 gasification, 435 gasification process, 435 gel, 91, 122, 128, 132, 139, 142, 147, 150, 235, 277, 278, 362, 375, 384 gel content, 132, 139, 142, 147, 150 gelation, 350 genus, 320 geometry, 58, 116, 208, 211, 297, 473, 474, 475, 476, 477, 478, 520 Georgia, 319 Germany, ix, xi, xiv, 28, 99, 124, 227, 228, 255, 256, 257, 295, 310, 313, 346, 367, 387, 453, 531, 543 germination, 317 gland, 488 glass transition, 245 glass transition temperature, 245 glass transition temperature polymers, 245 glasses, 195, 232 global awareness, 22 global brands, 2 Global Positioning System, 241 glucose, 20, 23, 199, 328, 329, 377 glucoside, 401 glue, 242 glycerol, 98, 441 glycol, 98, 350

560

Index

glycoside, 322, 323, 328, 329 glycosidic bonds, 402 glycosidic linkages, 401 GPS, 241, 250 grades, 123, 124, 153 graduate students, viii graft implantation, 475 graft polymerization, 139, 147 grafting, 124, 127, 132, 134, 141, 143, 149, 150, 362, 382 grafting efficiency, 127, 141, 149 grafts radial resistance, 466 grain size, 306 graphite, 432 grass, 85 gravimetric analysis, 360, 361 gravity, 92, 414, 416 gravure printing, 242 Great Britain, 4 Greece, v, x, xii, xiv, 259, 260, 261, 262, 265, 266, 268, 269, 273, 274, 276 green chemistry, 22 growing polymer chain, 541 growth, 2, 18, 84, 92, 99, 264, 272, 278, 281, 283, 285, 295, 296, 316, 317, 320, 321, 322, 323, 326, 330, 331, 336, 361, 400, 402, 415, 440, 474, 475, 539, 541 guidance, 270, 272 guidelines, 320

H haemodynamics, 467, 474, 478 haemolysis phenomenon, 467 hair, 339, 341, 536, 537 hairiness, viii, 519, 520, 521, 522, 525, 526, 527, 528 hallucinogenic properties, 400 halochromic, 218 halogenation, 184 hand sewn woven structures, 466 handloom preparatory machinery, 506 hardwoods, 402 harmony, 483 harvesting, 103, 452 hazardous substances, 448 hazards, 101, 370 HCC, 323, 329 headache, 370 healing, 310 health, 92, 101, 187, 188, 190, 199, 225, 227, 240, 250, 252, 253, 278, 279, 356, 448, 449, 481 health care, 187, 199, 225, 250, 252, 278, 448, 481 health information, 240

health status, 240, 252 heart attack, 477 heart rate, 240, 455 heart valve application, 466 heart valve replacement, 465, 475 heat loss, 246, 384, 387, 395, 483, 484, 485, 486, 488, 491 heat release, 242 heat resistance, 158, 163, 171, 180, 289 heat resistance surfaces, 289 heat transfer, 158, 393, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 496, 497 heat transfer coefficients, 487, 488, 496 heat transfer printing, 158 heating rate, 432 heat-retaining properties, 492 heat-setting temperature, 477 heat-storage capacity, 242 heat-transfer mechanisms, 485, 486 heavier travellers, 523 heavy metal biosorbents, 399, 401 heavy metal ions biosorption, 399, 440 heavy metal ions solution, 418 heavy metals, 400, 420, 422, 430, 436, 437, 440, 443 height, 324, 414, 415, 416, 484, 534, 536 helix profiles, 520 hemicellulose(s), 321, 323, 329, 399, 401, 402, 403, 404, 405, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 430, 432, 441, 442, 443, 501, 538 hemp fiber chemical composition, 399, 417, 440 hemp fiber surface, 411, 413, 417, 419 heterocyclic components, 159, 162, 184 heterogeneity, 56, 112 heterogenous chemical composition, 399, 401 hexane, 176, 197 high energy disperse dyes, 158 high fat, 200 high performance fabrics and garments, 241 high performance photo-responsive surfaces, 88 high strength, 34, 40, 43, 48, 504 high value-added products, 384 high-density imperfections, 289 higher molar mass dyes, 158 high-pressure liquid chromatography, 321 high-resolution optical pictures, 531 high-tech dresses, 450 high-technology applications, 81, 103, 118 historical and archaeological textile objects, 318 historical overview, 85 historical textiles, 317, 318, 320, 321, 322, 325, 335, 336, 337, 339

561

Index history, 9, 10, 13, 83, 210, 233, 270, 272, 315, 321, 322, 335, 462, 494, 497 homeland security, 250 homogeneity, 113, 419 Hong Kong, 28 hormones, 344 host, 192, 199, 271, 473 hot-melt inks, 157, 173, 179, 183 House, 255, 312 HPLC analysis, 266 hub, 187 hue, 59, 65 human, viii, 21, 67, 71, 191, 209, 226, 243, 251, 260, 278, 279, 292, 310, 316, 339, 356, 368, 377, 387, 472, 474, 477, 479, 480, 483, 484, 486, 487, 488, 490, 494, 495, 496, 511 human activity, 490 human body, viii, 191, 243, 368, 472, 483, 484, 486, 487, 488, 494, 496 human health, 356 human perspiration, 488 human skin, 209, 377, 387, 490, 495 human visual system, 71 Humicola insolens, 23 humid wound-pads, 279 humidity, 54, 74, 104, 112, 118, 219, 244, 250, 283, 285, 315, 317, 320, 324, 326, 336, 377, 384, 403, 410, 411 humidity sensor, 54 Hunter, 182, 442 hunting, 12 hybrid, 77, 113, 118, 122, 234, 255, 452, 455, 461, 477 hybrid film/fiber, 452 hydazone tautomers, 179 hydrazone, 157, 177, 178, 179, 185 hydrocarbons, 217 hydrochromic, 247 hydro-extractor, 28 hydrogels, 205, 206, 219, 351 hydrogen, 22, 124, 125, 136, 163, 169, 170, 172, 176, 177, 178, 212, 218, 230, 232, 306, 323, 329, 358, 368, 375, 401, 404, 414, 418 hydrogen abstraction, 176 hydrogen bonds, 306, 323, 368 hydrogen peroxide, 22, 124, 125, 136 hydrogen peroxides, 22 hydrolysis, 24, 33, 34, 35, 38, 39, 41, 43, 44, 48, 51, 123, 139, 140, 263, 317, 323, 329, 338, 375, 401 hydrolytic degradation, 319, 340 hydrophilic gel, 384 hydrophilicity, 311 hydrophobic fibers, 157, 158, 164, 165, 181

hydrophobic lignin network, 403 hydrophobic synthetic fibers, 164 hydrophobicity, 95, 307, 308 hydroxide, 123, 124, 125, 126, 400, 404, 406, 410, 417, 434, 436, 440, 445, 502, 516 hydroxyl, 129, 130, 134, 141, 148, 152, 158, 172, 179, 355, 356, 357, 358, 362, 368, 371, 372, 373, 375, 377, 401, 402, 404, 405, 406, 430 hydroxyl groups, 130, 134, 141, 149, 152, 355, 358, 362, 368, 371, 372, 373, 377, 401, 405, 406, 430 hygiene, 396 hygroscopicity, 400 hyperplasia, 467, 471, 479 hyphae, 317, 318, 322, 329 hyphal penetration, 317 hypochlorite bleaches, 22 hypothermia, 244 hypothesis, 525 hypsochromic shifts, 176 hysteresis, 480

I ICC, 54, 55, 58, 59, 61, 63, 64 ideal, 109, 240, 241, 397, 477, 520, 532 identification, 147, 189, 211, 266, 268, 283, 341, 457 identity, 5, 316, 515 illumination, 56, 65, 67, 69, 75, 76, 533 image analysis, 462 image generation software, 90 image makers, 3 imagination, 457 imitation, 5 immersion, 31, 33, 52, 128, 147 immobilization, 145, 442 implantable materials, 468 implants, 188, 279, 313, 465, 466, 471, 475, 480, 481 impregnation, 263, 283, 343, 345, 346 improvements, vii, 101, 103, 250 impurities, 99, 136, 289, 401, 403, 406, 537 in vitro, 350, 474, 475, 480 in vivo, 279 incandescent light, 67, 69 incidence, 285, 313 income, 1 incompatibility, 98 increased competition, 2 incubation, 316, 326, 327, 328, 329, 331, 333, 334, 336 incubation period, 316 incubation time, 329, 334, 336 independent variable, 510, 515

562

Index

India, x, xiii, xiv, xv, 28, 124, 136, 145, 268, 396, 465, 483, 496, 499, 500, 516, 517 indigo dye, 23, 25, 27, 35, 49 individuality, 2 individuals, 10 inducible enzyme, 23 induction, 50, 246 inductively coupled plasma mass spectrometry, 321 industrial environments, 87 industrial wastes, 430 industries, 20, 22, 23, 24, 47, 54, 83, 123, 124, 136, 153, 455 industry, vii, 1, 2, 3, 4, 20, 21, 22, 23, 24, 47, 49, 50, 55, 63, 65, 81, 82, 84, 102, 120, 124, 136, 145, 154, 188, 190, 210, 246, 343, 344, 352, 353, 356, 361, 367, 399, 401, 440, 455, 517, 533 infants, 250, 455 infection, 320, 324, 325, 331, 336, 460 information technology, 188, 240 infrared spectroscopy, 316, 340, 341, 379 ingredients, 94, 99 inhibition, 121, 281, 338, 367 inhibitor, 97, 99 inhomogeneity, 71, 74, 76 inhumation burials, 259, 261, 265, 266, 268, 273 initial state, 109 injury, 240, 476 ink droplet, 82, 88, 89, 92, 95, 98 ink formulations, 92, 95, 97, 98, 99, 106, 108, 109, 112, 116 inkjet disposing fluids, 97 inkjet inks, 64, 81, 84, 86, 88, 91, 92, 94, 98, 99, 100, 101, 102, 103, 104, 105, 109, 111, 115, 117, 118, 121 inkjet inks formulations humectants, 98 inkjet nozzles, 94 inkjet printed image, 81, 103, 118 Inkjet printed photo-responsive textiles, 197, 229 inkjet printed substrates, 82, 104, 111, 113, 115, 116, 117 inkjet printing, 54, 55, 61, 64, 71, 76, 77, 78, 81, 82, 84, 85, 86, 87, 88, 90, 91, 94, 95, 98, 100, 101, 103, 104, 105, 108, 111, 115, 118, 119, 120, 166, 192, 195, 220 inkjet printing technology, 54, 82, 86, 95, 103, 104, 120 inoculation, 316, 326, 330, 331, 334 insect repellents, 344 insertion, 190, 247, 457 inspections, 316 institutions, 316, 317, 320, 321, 322, 324, 335, 336, 337 Instron, 386, 522

insulating material, 486, 499, 500, 515 insulation, 242, 243, 246, 251, 254, 386, 397, 484, 485, 486, 488, 489, 490, 491, 492, 493, 495, 497, 499, 500, 501, 504, 505, 506, 508, 509, 510, 514, 515, 516, 517, 518 insulin, 443 integration, 90, 100, 104, 118, 188, 190, 210, 226, 228, 234, 248, 350, 447, 448, 455 intelligent coating/membranes, 240 intense laser pulses, 543 interactive textiles, 249, 449 interface, 247, 251, 253, 283, 424, 475, 494 interfacial capillary forces, 414 interfacial charge transfer, 278, 297, 301, 305, 306, 308, 309, 314 interfacial charge transfer mechanism, 297 interference, 193, 533 interfibrillar regions, 412 interfibrillar spaces, 427 inter-filament cohesion, 476 interlacing, 247, 455 intermolecular interactions, 113, 334 international competition, 453 interventive action, 271 intramolecular bonding, 329 intraparticle diffusion model, 421 intrinsic ink characteristics, 92 intrinsic viscosity, 126, 127, 130, 131 invertebrates, 264, 275 investment, 4, 289 inward diffusion, 295 iodine, 351, 413, 414 iodine sorption, 413, 414 iodine sorption values, 413 ion exchange mechanism, 384 ion transport, 422, 427, 437, 438 ion-exchange, 443 ion-fiber interactions, 427 ionic crosslinking, 374, 377, 381 ionization, 283, 404, 410, 418 ionochromic dye, 103 IPO, 440 IR spectra, 177 IR spectroscopy, 341, 380 Iran, ix, 239 iridium, 220, 221 iron, 262, 264, 267, 268, 273, 313, 351 irradiation, 103, 105, 106, 107, 108, 109, 110, 111, 114, 115, 117, 167, 180, 194, 196, 197, 199, 200, 206, 207, 278, 280, 288, 289, 292, 293, 294, 295, 300, 301, 305, 306, 309, 313, 317, 337, 357, 364, 376, 381 IR-spectra, 128

563

Index Islam, viii, 154 isomerization, 105, 208 isomers, 112, 113, 194 isotherms, 420 isotope, 185 issues, 7, 9, 10, 13, 81, 90, 98, 101, 104, 195, 225, 239, 251, 260, 288 Italy, 256

J jacket fabric, 507, 508 jacquard weaves, 506 Japan, 32, 44, 46, 49, 56, 121, 127, 128, 129, 226, 228, 280, 311, 481, 497 jettable inks, 81, 118 Jordan, 270, 276 jute fibre, 500, 501, 509, 516 jute spinning system, 505 jute-acrylic blended yarn, 502 jute-based materials, viii, 499, 515 jute-blended yarn, 506, 507 jute-hollow polyester blended yarns, 502, 503, 505 jute-polyester blended yarns, 502, 507 jute-polypropylene blended needle-punched nonwoven fabrics, 511 jute-shrinkable acrylic fibre, 502 juxtaposition of vintage, 3

K K+, 221, 296, 297, 300, 314 KBr, 128, 132 keratin, 333, 341 keratin oxidation, 333 ketones, 217 kidney, 346, 348, 349 kill, 165 kinetic model, 112, 420, 421, 444 kinetic parameters, 421 kinetics, 24, 112, 113, 114, 176, 184, 263, 277, 278, 279, 280, 283, 284, 287, 290, 292, 295, 297, 301, 303, 305, 306, 341, 415, 444, 479 knees, 487 knitted fabrics, 397, 468, 477 knitted rag, 124, 125, 126, 128, 129, 130, 132, 133, 136, 137, 138, 139, 141, 143, 145, 146, 148, 149, 150, 153 knitted structure, 468, 477, 500 knitting machines, 254, 468 knitting yarn, 515 KOH, 404, 435, 436, 444, 445

Korea, 257 Kubelka-Munk function, 108

L lactose, 50 lamella, 408, 409, 413, 417, 419 laminar, 82, 444 lamination, 101, 242, 508 Langmuir and Freundlich adsorption isotherms, 420 laptop, 452 laser and computer technology, 532 laser beam, 166, 531, 532, 533 laser-produced surface structures, 543 lasers, 193 laser-treated polyester fiber, 533 lattice transformation, 404 law enforcement, 250 leaching, 278, 289, 294 leadership, 5 leakage, 297, 300, 361, 474 Leather, 11, 119, 121, 122, 229 LED, 64, 101, 118, 447, 448, 450, 451, 453, 454, 455, 457, 459, 460 LED light, microcontroller, 448 leisure, 226, 247 lending, 248 lens, 246, 532 leuco dyes, 210 leuco-derivative, 204, 205 leveling properties, 158 liberation, 407, 408, 411 ligand, 211 light conditions, 56, 109, 457 light- induced colour changes, 194 Light irradiation photo-activates, 300 light transmission, 115 light-emitting diodes, 189 light-emitting polymers, 189 lightfastness, 53, 54, 56, 76, 78, 184, 217, 218 lightweight optical fibers, 253 lightweight shawl fabrics, 507 lignin, 399, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 430, 432, 440, 441, 442, 443, 501, 538 lignocellulosic fibers, 404, 405 lignolytic white rot fungi, 326 limestone, 264 linear cellulose chains, 401 linen, 51, 54, 58, 315, 339, 443, 538 lipids, 24 liposomes, 351 liquid chromatography, 321, 438, 446

564

Index

liquid chromatography–tandem mass spectrometry technique, 438 liquid crystals, 193, 210, 215, 233, 247 liquid phase, 127, 244 liquid-crystal display panels, 157, 182 liquids, 414, 415, 441 Listeria monocytogenes, 384, 396 lithium, 98 lithography, 233 livestock, 250 living organism, 23, 418 longevity, 21 long-term preservation, 270, 272 long-term storage, 317 low temperatures, 202, 320 lower breaking strain, 330 lubricants, 414 luggage, 457 lumen, 476, 477 luminescence, 230, 322 Luo, 79, 80, 226, 255 luxury vintage gowns, 3 lying, 494, 537

M machinery, 84, 506 macromolecular chains, 113, 430 macromolecular systems, 212, 214 macromolecule orientation, 329 macromolecules, 214, 317, 324, 330, 333, 334 magazines, 9 magnesium, 94 magnetic field, 244, 245 magnetic resonance, 156, 467 magnetic resonance imaging, 467 magnetic shape memory alloys, 245 magnitude, 67, 277, 421, 426, 533 majority, 8, 12, 25, 102, 105, 158, 247, 252, 259, 265, 266, 273, 308 man, 158, 211, 397, 400, 471, 484, 499, 531, 536, 540 management, vii, 4, 6, 16, 18, 53, 54, 55, 58, 59, 61, 65, 66, 78, 79, 93, 191, 227, 246, 455, 471, 490 manganese, 221 manipulation, 193, 210 man-made fibres, 499 manufacturing, 22, 28, 89, 90, 93, 118, 124, 136, 158, 159, 241, 397, 457, 466, 500 manufacturing companies, 158 mapping, 210 market position, 6, 17 market segment, 227

market share, 101 marketing, 4, 5, 6, 12, 15, 17, 397 marketing literature, 4, 6 marketing strategies, 17 marketing strategy, 6 marketplace, 6 masking, 268 mass, 3, 4, 9, 32, 51, 56, 82, 158, 286, 296, 297, 300, 305, 321, 390, 422, 423, 430, 438, 446, 455, 486, 523, 525, 536 mass loss, 430 mass spectrometry, 286, 296, 297, 300, 305, 321, 438, 446 material surface, 255, 434 matrix, 107, 112, 113, 115, 116, 117, 193, 194, 242, 247, 249, 306, 350, 401, 402, 408, 443, 512, 513 matrixes, 122 matter, 190, 263, 368, 372 maxi dresses, 10, 11 maximum sorption, 418, 419 meat, 351 mechanical abrasion, 23, 25, 41 mechanical properties, 19, 29, 30, 36, 51, 248, 249, 315, 322, 329, 334, 336, 372, 386, 403, 442, 466, 472, 478, 480, 491 mechanical resistance, 240 mechanical responsive materials, 240 media, 2, 3, 4, 12, 13, 55, 63, 65, 66, 67, 92, 112, 113, 177, 190, 200, 220, 230, 292, 405, 462, 500 medical, vii, 85, 188, 210, 240, 244, 245, 247, 250, 257, 278, 344, 395, 449, 455, 460, 465, 468, 479 medical and health care applications, 278 medical textiles, vii, 85, 188, 244, 247, 449, 465, 479 medication, 474 medicinal applications, 447 medicine, 227, 240, 255, 344, 362 Mediterranean, 276 MEG, 16 MEK, 98 melamine-formaldehyde, 369 melt, 102, 157, 165, 173, 179, 183, 220 melting, 210, 216, 241, 357 melts, 241 membranes, 240, 300, 370 memory, 188, 189, 206, 210, 226, 239, 240, 244, 245, 246, 255, 432 MEMS, 77, 84, 88, 103, 118, 189, 449 mercerization, 404, 442 merchandise, 6, 10, 12, 13, 14, 15 merchandise strategy, 6 merchandising, 4, 7 mercury, 263, 280, 472 mesh-free stapled fibre, 509

Index messages, 252 metabolic processes, 483 metabolism, 484 metabolites, 317 metal corrosion products, 262, 263, 264, 275 metal fibers, 248, 542 metal ion(s), 199, 208, 218, 221, 230, 231, 262, 263, 389, 399, 412, 418, 419, 420, 422, 423, 424, 425, 426, 427, 428, 429, 436, 437, 438, 440, 441, 443, 445, 446 metal nanoparticles, 279, 285 metal oxides, 220, 221, 248, 249 metal salts, 94, 248, 249 metallic brilliance, 542 metallic glittering, 542 metals, 189, 193, 211, 219, 221, 223, 248, 249, 250, 262, 263, 264, 267, 273, 289, 400, 418, 420, 422, 430, 436, 437, 440, 443 meter, 31, 56, 489, 511, 522, 523 methacrylates, 122 methanol, 123, 127, 145, 146 methicillin-resistant, 384, 396 methodology, 76, 184 methyl methacrylate, 123, 124, 127 micro encapsulation, 189 microbial attack, 283, 317 microbial communities, 337 microbial community, 338 microbial degradation, 320, 339 microcapsules, 195, 216, 241, 242, 243, 255, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 353, 362, 365, 455, 462 microcapsules stability, 343, 348, 349 microclimate, 243, 244 micro-disposal technique, 83, 85, 87, 90 micro-electromechanical machines, 240 micro-electronic mechanical systems, 189 microelectronics, 240 microemulsion, 77 micro-engineering industries, 54 microfibril, 401 micro-lens, 533 microorganism(s), 50, 317, 339, 377, 384 micro-organisms inhibitors, 263 microporous structure, 436 microscope, 19, 32, 33, 44, 46, 57, 58, 266, 323, 358, 531, 532, 533, 542, 543 microscopic images, 533, 534, 535, 537, 538 microscopy, viii, 44, 45, 46, 47, 284, 285, 299, 303, 304, 305, 306, 308, 310, 316, 321, 322, 326, 327, 332, 339, 341, 343, 345, 346, 531, 532, 537, 544, 545 Microsoft, 7, 462

565

Microsoft Word, 7 microspheres, 350 microstructure, 277, 286, 303, 305, 306, 307, 351, 401 microtome, 282 microwave irradiation, 167, 180 middle class, 3 middle lamella, 408, 409, 413, 417, 419 migration, 120, 158, 171, 263, 477, 501 migration resistance, 171 military, 194, 240, 244 military applications of smart textiles, 240 mineralised fibres, 263 mineralization, 177, 274 mini dresses, 11 Ministry of Education, 153, 180 mixing, 248 MMA, 123, 124, 127, 128, 131, 132, 133, 134, 139, 141, 142, 143, 149, 150, 151, 152 mobile phone, 190, 241, 450, 460 mobile phone technology, 241 mobile telecommunication, 239 modelling, 121, 274 models, 10, 78, 80, 101, 112, 113, 311, 420, 421, 450, 473, 478, 494 modifications, 216, 254, 499, 500 modified hemp fibers, 399, 405, 407, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 440 modules, 190, 251 modulus, 330, 334 mohair, 536 moisture, 123, 132, 139, 142, 147, 150, 154, 191, 242, 246, 250, 265, 283, 367, 368, 397, 410, 414, 415, 483, 484, 485, 488, 490, 493, 494, 495, 540 moisture content, 123, 132, 139, 142, 147, 150, 410, 415 moisture sorption, 154, 415 molar extinction coefficient, 157, 162 moldings, 136 mole, 172, 280 molecular chains, 262, 368 molecular motors, 201, 206, 207, 229 molecular orientation, 214, 418 molecular sensors, 230 molecular stoichiometry, 430 molecular structure, 107, 134, 143, 153, 193, 203, 211, 248, 360, 364 molecular weight, 98, 123, 124, 126, 127, 130, 131, 139, 141, 147, 149, 153, 245, 372, 379, 402, 405, 541 molecules, 34, 54, 107, 108, 109, 112, 113, 115, 116, 158, 164, 176, 193, 199, 203, 206, 210, 211, 212,

566

Index

213, 215, 220, 290, 333, 360, 367, 372, 375, 377, 402, 403, 404, 410, 413, 414, 435, 541 momentum, 82 monoazo, 158, 159, 163, 164, 165, 175, 176, 181, 184 monoazo pyridone dyes, 163, 164, 175, 176 monoclinic crystalline lattice, 404 monolayer, 286 monomer molecules, 541 monomers, 102, 154, 155, 248, 384, 541 monosaccharide, 401, 432 morphological changes, 326, 331, 336 morphology, 129, 268, 316, 326, 358, 400, 402, 406, 408, 409, 432, 436, 437, 440 motivation, 13, 25 mountain climbers, 240 mountain sheep wool, 537 mucous membrane(s), 370 multi-colour printing, 101 multidimensional, 409 multi-functional switches, 203, 207 multifunctional textiles, 240 multimillion pound industry, 1 multiples, 484 multiplication, 467 multi-wavelength laser systems, 533 murals, 101 muscles, 484 museum collections, 337 museums, vii, 259, 260, 315, 316, 317, 320, 321, 322, 324, 335, 337 music, 8, 12 mycelium, 319, 322 mycology, 316

N Na+, 221, 297, 300, 314 Na–cellulose I lattice, 404 NaCl, 127, 131, 237, 295 nano-coatings, 543 nanoimprint, 233 nanomaterials, 240 nanometer, 357, 375 nanoparticle(s), 235, 249, 278, 279, 285, 286, 289, 303, 305, 309, 310, 311, 312, 313, 344, 356, 362, 375, 376 nanotechnologies, 239 nanotechnology, 188, 240, 279, 312, 375 naphthalimide, 159, 161 naphthopyrans, 105, 122, 194, 197, 201 native cellulose, 155, 402, 430, 442 natural blood-vessel deformation, 472

natural colour, 115, 500 natural crystalline structure, 404 natural fibers, 158, 400, 404, 531, 544 natural textiles fibers, 278 needling density, 509, 510, 512, 513, 515 negative casts, 263, 264 negativity, 307 neighbourhood feel, 12 nematic liquid crystals, 210 Netherlands, 542 nettles, 538 neurobiology, 233 neutral, 23, 27, 32, 34, 35, 36, 37, 38, 39, 40, 43, 48, 99, 178, 179, 234, 313, 485 neutral cellulose, 34, 36 new spinning technologies, 520 Newtonian fluids, 94 next generation, 118 NH2, 167 nickel, 220, 248, 263, 521 NIR, 296, 341 nitrates, 156 nitration, 145, 146, 148, 149, 152 nitrides, 278, 307 nitrodiphenylamine, 159 nitrogen, 105, 147, 148, 202, 214, 217, 306, 314, 361, 365, 370, 375, 432 nitrogen content, 147, 148 N-methylol compounds, 369, 370 NMR, 123, 128, 134, 139, 143, 147, 151, 152, 155, 177, 185, 340, 341 no dimension, 509 nominal magnification, 534, 535, 538 noncellulosic components, 400, 403, 405 nonconductive threads, 253, 254 non-destructive examination, viii, 531 non-heat resistant surfaces, 279 non-invasive examination, 532 non-ionic compounds, 158 non-linear least-squares regression, 426 non-linear optics, 296 non-porous media, 92 non-radiative transition, 107 non-wearable textile, 500 North America, 259, 339 nostalgia, 9, 13 nouveau vintage, 3 novel technique, 384 nozzle density, 88 nozzle spray technique, 242 nuclear magnetic resonance, 156 nucleus, 159 numerical analysis, 467

567

Index numerical aperture, 532, 533 nutrient, 283, 295 nutrition, 317 nylon, 81, 112, 113, 115, 117, 118, 121, 157, 158, 162, 163, 164, 174, 204, 229, 246, 468

O objective rear aperture, 533 obstacles, 455 obstruction, 428 occlusion, 480 odor intensity, 349 odor measurements, 344 OFS, 256 OH, 125, 130, 141, 143, 148, 149, 157, 167, 168, 177, 285, 294, 301, 323, 329, 362, 402, 404, 406 OH-groups, 404 oil, 102, 338, 351, 352, 353, 400, 414, 415, 417, 441, 506 old clothes, 4 older customers, 9 oligomers, 102, 231, 361, 541 opacity, 476 open-end rotor, 520 openness, 490, 492 operations, 196 opportunities, 2, 10 optic sensors, 227 optical brightener, 53, 55, 63, 65 optical brightening agents, 55 optical density, 113 optical differences, viii, 531 optical examinations, 542 optical fiber, 239, 240, 247, 253, 257, 462 optical fibers, 239, 247, 253 optical light microscopy, 545 optical microscopes, 531, 532 optical microscopy, 321, 532 optical properties, 220, 247, 314 optical wide-field microscopy, 532 optimal performance, 48 optimization, 177, 297, 399, 429, 438, 440 ores, 500 organ(s), 77, 211, 241 organic chemicals, 400 organic chemicals resources, 400 organic compounds, 100, 317 organic fibres, 262, 263 organic matter, 263 organic polymers, 113, 317, 449 organic solvents, 167 organism, 23, 263

original garment, 9 originality, 2, 9 orthotropical traction stiffness, 474 Ostwald viscometer, 126 outdoor clothing, 246, 251 out-of-focus signals, 532 ownership, 3 ox, 430 oxidation, 105, 195, 196, 208, 220, 221, 248, 256, 279, 283, 285, 290, 292, 294, 297, 303, 317, 329, 333, 351, 353, 405, 406, 408, 409, 419, 434, 442 oxidative agents, 405 oxidative reaction, 341 oxidative stress, 341 oxidizing agents, 405 oxygen, 214, 261, 262, 264, 266, 273, 277, 279, 280, 290, 306, 310, 312, 314, 317, 400, 433, 434, 436, 440, 445

P padding, 343, 345 pagers, 250 pain, 449 paints, 157, 159, 211 palladium, 346 PAN, 442, 542 paper, 53, 55, 56, 58, 65, 66, 67, 69, 71, 74, 76, 80, 82, 83, 85, 101, 119, 124, 128, 154, 157, 159, 166, 256, 260, 317, 318, 337, 340, 341, 355, 448, 461, 495 paper sludge, 124, 154 parallel, 44, 301, 401, 509, 514 parentage, 5 participants, 7, 8, 9, 10, 11, 12 passive smart textiles, 240 passive thermal insulation effect, 242 pathogenic bacteria, 278, 289 pathogenic biofilms, 278 pathogens, 310, 311, 313 pathological effects, 467 pathology, 467 patients wear clothing, 449 PCA, 357, 363 PCBs, 77 PCM, 239, 241, 242, 243, 244, 255, 449 PCT, 119 peace, 450, 460 peat, 418 pectin, 399, 401, 403, 405, 418, 441, 538, 539, 543 pectin-surrounded fiber bundles, 539 pedal, 8 pendant side groups, 401

568

Index

pentose sugars, 401 peptide, 332 percolation, 249 permeability, 36, 190, 297, 361, 383, 384, 387, 395, 396, 397, 484, 490, 491, 507, 509, 512, 515, 517 permit, 123, 409, 414, 449 peroxide, 124, 125, 136, 314, 345, 406 personal communication, 260 personal contact, 5 personality, 6, 12, 13, 14 perspiration, 168, 176, 218, 251, 368, 483, 484, 485, 488, 496 perspiration resistance, 218 PES, 56, 312, 397, 541, 542, 543 pesticide(s), 352, 400, 430, 438, 439, 440, 441, 444, 445, 446 pesticide analysis, 400, 438, 440 PET, 246, 466, 474, 505 pH, 19, 27, 90, 92, 93, 94, 97, 99, 103, 158, 164, 178, 185, 192, 193, 194, 203, 210, 215, 216, 218, 219, 230, 235, 236, 237, 238, 244, 300, 301, 313, 360, 372, 380, 405, 411, 418, 455, 462 pharmaceutical(s), 54, 124, 350, 351, 362, 377, 455 phase change materials, 189, 239, 240, 241, 242, 243, 244, 344, 352, 455, 462 phase transitions, 195, 211 phase-transfer catalysis, 231 phenol, 217, 218, 402 phenolic compounds, 216, 444 phosphate, 372 phosphorescence, 193 phosphorus, 145, 361, 365, 372, 380 photocatalysis, 305, 311, 314 photocatalysts, 312, 314 photocatalytic efficiency, 288 photochromic azulene, 203, 204, 205 photochromic colorants, 109 photochromic disperse dye, 204 photochromic dyes, 81, 99, 103, 104, 105, 108, 111, 113, 115, 116, 117, 118, 121, 122, 194, 195, 228, 229 photochromic fluorescent fabrics, 203 Photochromic napthopyrans, 106 photochromic reaction, 105, 106, 107, 195, 208 photochromic smart textiles, 209 photochromic spirooxazine, 109, 111, 114, 116, 196 photochromic textiles, 112, 196, 202, 219 photodegradation, 176, 177, 184 photo-detector, 532 photoelectron spectroscopy, 291 photo-excited organic molecules, 107 photofading kinetics, 176 photographs, 32, 332, 408, 433, 534, 537

photo-induced charge transfer, 297 photoisomerization reactions, 107 photoluminescence, 189 photomultiplier, 533 photonic fibers, 240 photonics, vii, 226, 227, 240, 249 photons, 109, 194 photo-responsive, vii, 81, 82, 88, 104, 108, 109, 110, 111, 113, 116, 117, 118, 195, 197, 199, 200, 204, 205, 206, 209, 229 photo-responsive fluorescence, 204, 205 photo-responsive inkjet printed textiles, 82 photostability, 107, 176, 184, 196 photoswitching, 108, 202 photovoltaic cells, 447, 448, 449, 452, 453, 454, 460 photovoltaic fibers, 449, 452 photovoltaic-piezoelectric device, 452, 461 physical activity, 484 physical and mechanical properties, 29, 30 physical characteristics, 71, 123, 190, 492 physical environment, 215 physical exercise, 484 physical features, 384 physical properties, 132, 142, 150, 193, 194, 200, 242, 249, 364, 383, 389, 407, 440, 477, 502, 508, 517, 527, 541 physical structure, 368, 492 physical treatments, 544 physicochemical properties, 92, 116 physics, 239, 240, 497 Physiological, 386, 483, 496, 497 physiological comfort, 397, 484, 490, 491 physiological measurement sensors, 251 physiological pressure curves, 472 physiological properties, 383, 384, 401 Pie chart, 261, 262, 265, 266, 269 piezo crystals, 449 piezochromic, 246 piezoelectric drop-on demand ceramic print heads, 95 piezoelectric element, 89 piezoelectric inkjet print head, 83, 88 piezoelectric materials, 240 piezoelectric resistance, 189 pigmentation, 317 pigmented binder-less inkjet inks, 84 pigments, 82, 91, 102, 103, 163, 167, 182, 193, 195, 210, 216 pinhole size, 533 pitch, 90, 210, 534, 536 plain fabric, 343, 345, 349 plain weave, 56, 286, 385, 475 plain woven woollen fabric’s resistance, 389

Index plants, 10, 218, 264, 418, 538, 539 plaque, 476 plasma chamber, 290 plasma deposition, 286 plasma particle deposition, 286 plastic shielded wires, 253 plastics, 63, 101, 157, 159, 167, 171, 313 platelets, 467 platform, 8 playing, 84, 248 plethora of guides, 2 point defects, 289 Poiseuille flow, 467 polar, 178, 213, 277, 279, 307 polar groups, 277, 279 polar solvents, 178, 213 polarity, 105, 112, 113, 158, 177, 306, 402, 414 police, 240 pollutants, 100, 430 pollution, 123, 124, 153 pollution problems, 153 poly(ethylene terephthalate), 164 polyacetylene, 248 polyacrylonitrile, 164, 165, 542 polyacrylonitrile fast yellow shades, 165 polyacrylonitrile fiber, 164 polyamide(s), 64, 121, 157, 159, 165, 170, 172, 176, 182, 229, 278, 541 polyamide fiber, 165, 170, 182 polyaniline, 220, 223, 234, 235, 248, 250 polycarbonate, 101, 247 polycarboxylic acid, 355, 356, 357, 361, 362, 363, 364, 365, 371, 372, 373, 375, 379, 380, 381 polyconcensation fibers, 541 polycondensation, 541 polyester fibre, 502, 506, 516 polyester vascular prosthesis, 465, 479 polyesters, 157, 159, 179 polyethylene, 98, 246, 278, 286, 289, 541 polyethylene-terephthalate, 286 polyglucuronic acids, 405 polyhydric alcohol, 98, 405 polymer chain(s), 33, 245, 248, 541 polymer composites, 226, 248, 256 polymer fibers, 539, 540 polymer films, 233, 278, 289 polymer matrix, 112, 113, 194 polymer media, 112 polymer melts, 241 polymer photovoltaic solar cells, 453, 454 polymer solutions, 241 polymer structure, 389 polymer-chain scission, 317

569

polymerization, 127, 139, 147, 154, 364, 375, 379, 401, 432, 462, 541 polymethylmethacrylate, 247 polymorphic transformation, 434 polymorphism, 155 polyolefin fibers, 541 polyolefins, 157, 159 polypeptide, 333 polypeptide chains, 333 polypropylene, 98, 101, 278, 481, 501, 504, 509, 510, 511, 512, 513, 515, 516, 517, 518, 541 polypropylene fibre, 504, 509, 513 polypyrrole, 220, 223, 233, 248, 250, 256 polysaccharide(s), 23, 24, 136, 155, 377, 396, 401, 402, 418, 442 polystyrene, 220, 246, 248 polythene, 272, 515 polythiophene, 220, 223, 234, 248 polyurethane, 77, 242, 245, 250, 255, 278 polyurethane foam, 242 polyurethane foam matrix, 242 polyurethanes, 344, 541 polyvinyl chloride, 541 population, 7, 400 porosity, 81, 115, 118, 190, 263, 307, 415, 437, 473, 474, 475 porous fiber matrices, 399, 422, 429, 440 porous media, 92 porous membrane, 387 positioning statement, 6 positive correlation, 511 potassium, 98, 124, 400, 405, 406, 434, 440, 445 potassium bromide, 124, 405 potassium permanganate, 406 poverty, 3 precipitation, 92, 125, 263, 418 pregnancy, 188 preparation, 11, 53, 55, 64, 66, 88, 125, 126, 138, 146, 148, 154, 155, 163, 164, 171, 181, 182, 183, 199, 219, 248, 278, 279, 283, 305, 313, 430, 438, 444, 445, 501, 511, 531 preservation, vii, 259, 261, 262, 263, 264, 265, 266, 267, 268, 270, 271, 272, 273, 274, 275, 276, 315, 317 prestige, 6 prevention, 240, 336 preventive conservation, 273 primary fibrils, 403 primary structural network, 403 primary wall, 24, 35, 402 principles, 4, 50, 71, 76, 83, 415

570

Index

print head, 71, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 99, 100, 103, 104, 108, 118, 120, 121 print head nozzle, 94, 95, 96 print head technologies, 88, 93, 97 print media, 92 print mottle, 71, 80 print simulation, 53, 54, 55, 65, 67, 76 printed circuit boards, 54, 253, 254, 448, 450, 455 printed dress, 452 printed-textile, 82 printer color profiles, 53, 65 print-head clogging, 100 printing colors, 53, 55 printing electronic materials, 54 printing industry, 81, 84, 120 printing inks, 157, 159, 163, 167, 179, 195, 232, 250 printing technology, 54, 81, 82, 86, 88, 90, 95, 103, 104, 118, 120 procurement, 11 producers, 22 product design, 49, 210 product performance, 5 production technology, 400 professionals, 3, 260, 269, 270, 272, 273, 274 profilometer, 286 prognosis, 16 programming, 448, 450, 457, 461 project, viii, 49, 90, 153, 180, 270, 271, 274, 338, 396 propagation, 89 propane, 406 proposition, 6 proprietors, 12, 13, 14 prostheses, 466, 467, 468, 471, 474, 480 prosthesis, 465, 466, 467, 468, 469, 470, 471, 472, 474, 475, 476, 478, 479, 480 prosthesis flow properties, 467 prosthesis to kinking, 466 prosthesis wall displacements, 472 protection, vii, 81, 107, 117, 118, 194, 209, 210, 240, 320, 337, 395, 400, 403, 440, 447, 448, 449, 490 protective clothing, 243, 246, 250, 397, 447 protective coating, 133 proteinaceous fibres, 266, 267, 268, 273, 317, 318, 323, 336 proteinaceous material, 264, 316, 322, 325 proteins, 24, 145, 268, 321, 332, 341, 536 proton-accepting solvents, 178 proton-donating solvents, 179 protons, 279 prototype(s), 256, 452, 455, 469, 474, 475, 480 pseudomorph, 263

pseudo-vintage, 10 psychological variables, 484 PTFE, 471 PTT, 164, 165 public safety, 250 pulp, 125, 154, 538, 540 pulsatile flow conditions, 472, 478 pulse plasma power magnetron sputtering, 277 pulsed direct magnetron sputtering, 277 pumice stone, 19, 20, 21, 24, 25, 27, 41, 42, 43, 44, 47, 48 pumice stone-enzyme, 19, 41, 42, 47 purification, 136, 145, 400, 401, 430, 440 purity, 92, 153 PVC, 100 pyridinium group, 165 pyrolysis, 360, 430, 432, 444, 445 pyrolysis of celluloses, 430

Q quality control, 53 quantification, 545 quantum size nanoparticles, 309 quaternary ammonium, 165, 182 quaternary ammonium salt, 165, 182 Queensland, 341 questionnaire, 259, 260 quinoline derivatives, 159 quinones, 434

R radial distance, 426 radiation, 64, 65, 119, 194, 203, 205, 229, 256, 280, 375, 403, 448, 460, 483, 484, 485, 486, 487, 488, 489, 491, 492, 493, 494 radicals, 233, 279, 285, 290, 301, 357, 375 radio, 189, 280, 476 radiography, 493 radius, 415, 416, 423, 424, 427 Raman spectra, 185, 322, 323, 327, 328, 329 Raman spectroscopy, 185, 316, 321, 322, 326, 329, 332, 339, 340, 341, 357 ramie, 51, 442, 509, 538 rate of change, 425, 427 raw materials, 155, 321, 400 rayon, 51, 157, 159, 538 reactant, 356 reactants, 377, 380 reaction mechanism, 105, 106, 107, 111 reaction time, 107, 167, 294

571

Index reactions, 27, 92, 105, 107, 109, 170, 183, 200, 230, 279, 301, 357, 358, 375, 377, 405, 419, 430 reactive azo dyes, 170, 182, 183 reactive group(s), 375, 377 reactive oxygen, 278, 312 reactive polymers, 344 reactivity, 116, 132, 142, 150, 279, 289, 360, 364, 404, 405, 407, 436 reagents, 356, 362, 378 realism, 468 reality, 188, 226, 256, 311, 312 receptors, 117, 209, 490 recognition, 2, 192, 231 recombination, 301, 306, 309 recovery, 139, 244, 245, 255, 270, 283, 351, 356, 360, 367, 372, 375, 377, 381, 386, 393, 473, 477, 504 recycling, 4, 9, 10, 13, 124, 293, 297, 399, 401, 430 recycling plants, 10 red cell destruction, 467 red shift, 303 reflectance spectra, 296, 303, 304 refractive index, 105, 194, 195 refractive indices, 194 regenerated cellulose, 540 regeneration, 166 regression, 420, 426, 487 regression analysis, 420 regression equation, 487 rehabilitation, 188, 240, 252 reinforcement, 441, 500 relative humidity, 74, 315, 317, 320, 326, 410, 411 relaxation, 111, 112, 472 relaxation model, 112 relaxation process, 111 reliability, 5, 6, 54, 93, 98, 221, 250 remote sensing, 187, 225 renaissance, 400 repair, 473 reparation, 444 repeating unit, 401 repellent, 363, 365 repression, 50 reproduction, 55, 63, 71, 84 repulsion, 206 reputation, 5 requirements, 5, 54, 61, 88, 90, 91, 92, 93, 97, 100, 104, 109, 118, 191, 196, 227, 228, 239, 243, 251, 252, 253, 292, 473, 475 researchers, 23, 24, 55, 124, 191, 260, 272, 324, 363, 372, 384, 455, 467 residuals, 421, 426 residues, 34, 43, 154, 182, 307, 333, 361, 402, 444

resilience, 477, 513 resins, 321, 344, 367, 369, 378 resolution, 87, 297, 531, 532, 533, 534, 535, 536, 543, 545 resources, 6, 16, 120, 400 respiration, 240, 455, 485 response, 6, 111, 115, 184, 192, 200, 210, 219, 220, 221, 231, 244, 246, 250, 341, 350, 360, 368, 477 response time, 200, 221 restenosis, 477, 480 restoration, 337, 338 restrictions, 272 retail, 2, 3, 4, 6, 7, 13, 15, 16, 17, 18, 79, 250 retail guru, 4 retail marketing literature, 6 retail premises, 7 retailing planning context, 6 retro subculture, 3 RF-plasma pretreatment, 280 RH, 30, 31, 261, 509, 521 Rhizopus, 319 rice husk, 445 rights, 10 ring flanges, viii, 519, 520, 521 ring spinning, viii, 519, 520, 521 ring spinning machine, 519, 521 ring travellers, 519 rings, 198, 207, 208, 214, 323, 328, 329, 399, 401, 404, 436, 519 risk(s), 100, 101, 252, 316, 317, 384, 395, 474, 477 risk factors, 317 room temperature, 158, 197, 198, 208, 211, 213, 214, 222, 244, 285, 320, 386, 404 root, 306 roughness, 306, 404, 408, 413, 417, 419, 475, 500, 533 routes, 279 Royal Society, 50, 119, 228, 232, 339 rubber, 31, 157, 159, 242, 245 rubbing fastness, 165 Russia, 10 ruthenium, 221

S saccharin, 217 safety, 5, 92, 145, 187, 191, 192, 227, 250, 447, 448, 449, 453, 457, 460 salts, 94, 163, 164, 167, 170, 177, 179, 241, 248, 249, 259, 261, 263, 264, 267, 268, 273, 279, 321, 372 sample surface, 300, 306, 531, 532 SAP, 512

572

Index

satisfactory whiteness, 372 saturation, 296, 475 saturation index, 475 scaling, 478 scaling law, 478 scanning calorimetry, 361 scanning electron microscopy, 316, 321, 322, 326, 327, 341, 346, 545 scanning electronic microscope, 32 scarcity, 11 scattering, 108, 303, 341 scent, 346 school, 13, 278, 289 science, vii, 260, 269, 270, 288, 316, 336, 362, 377, 397 scope, 74, 82, 84, 190, 193, 260 screen-printing, 242 seafood, 361 second hand clothing stores, 10 second hand stock, 11 Second World, 84, 400 secondary cell, 24, 403 secondary hydroxyl groups, 130, 141, 149 secretion, 317, 319, 331 security, vii, 5, 81, 103, 107, 117, 118, 187, 194, 195, 209, 225, 250, 253, 448 sedimentation, 96 selectivity, 52, 312, 419 self-expression, 1 self-indicating alert systems, 81, 118 SEM micrographs, 346, 347, 348 semiconductor(s), 211, 222, 277, 278, 279, 289, 308, 309, 311, 314, 453 semiconductor TiO2, 279 sensation(s), 393, 490 senses, 241 sensing, 118, 187, 190, 192, 194, 209, 225, 227, 240, 244, 247, 252, 460 sensing applications, 247 sensitivity, 176, 271, 290 sensors, vii, 188, 189, 208, 226, 227, 230, 239, 240, 245, 247, 250, 251, 252, 257, 447, 448, 449, 450, 455, 460, 461, 462, 487 Serbia, ix, x, xii, xiii, 162, 163, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 319, 399 serine, 338 services, 17, 252, 253, 259, 260, 271 severe stress, 485 shade, 31, 34, 35, 36, 37, 39, 40, 41, 42, 43, 65, 164, 505, 508 shape, 107, 127, 188, 189, 190, 194, 206, 208, 226, 239, 240, 244, 245, 246, 247, 253, 255, 262, 265, 296, 346, 348, 349, 450, 471, 472, 473, 478, 490

shape memory alloys and polymers, 189, 244 shape memory materials, 226, 239 shape memory polymers, 206, 240, 245, 246 shape-memory, 245 shawl fabric, 506, 507 shear, 25, 51, 86, 93, 94, 95, 253, 467, 478 shear rates, 467, 478 shear rigidity, 25 sheep, 536, 537, 538 sheep wool, 536, 537 short-chain polysaccharides, 23 showing, 104, 182, 200, 261, 262, 265, 266, 269, 283, 291, 296, 299, 313, 314, 322, 327, 332, 533 side chain, 402 signals, 84, 134, 152, 240, 294, 448, 455, 532, 533 significance level, 527 signs, 64, 101, 227, 250, 252, 256, 329, 457, 462 silane, 404 silica, 127, 155, 362 silicon, 449 silicone treatment, 501 silicones, 375 silk, 54, 55, 78, 81, 112, 113, 115, 117, 118, 157, 158, 159, 168, 266, 268, 315, 317, 321, 325, 337, 339, 375, 400, 490, 536, 537, 538, 539 silk screen printed polyester, 168 silver, 165, 182, 246, 249, 262, 264, 267, 268, 273, 278, 280, 283, 286, 289, 294, 310, 311, 312, 313, 314, 384, 389, 397, 521, 542 silver biocidal surfaces, 278 silver treated wound dressings, 384 silvernic, 521, 524 simulation, 53, 54, 55, 56, 65, 66, 67, 71, 76, 115, 444, 467, 468, 479 simulations, 65, 467, 468, 478 Singapore, 381 SiO2, 27, 288, 362 SIP, 90 sisal, 538 skeletal muscle, 484 skeleton, 405 skin, vii, 209, 244, 250, 251, 264, 344, 370, 377, 387, 393, 460, 483, 484, 485, 487, 488, 490, 491, 495, 538 skin softeners, vii, 344 skin temperatures, 487 slip draft spinning system, 506 slow fashion, 3 sludge, 124, 154 small business sector, 4 small businesses, 55 small diameter blood vessels, 465, 466 small-scale retailers, 12

Index smart clothing, viii, 191, 192, 226, 251, 252, 253, 447, 448, 452 smart clothing design, 191 smart clothing system, 191, 192 smart materials, 189, 190, 227 smart medical textiles, 188 smart or intelligent textiles, 188 smart products, 384 smart structures, 247, 255 smart textile, vii, 187, 188, 189, 190, 191, 192, 194, 195, 196, 197, 199, 200, 201, 203, 204, 206, 207, 209, 211, 218, 219, 225, 226, 227, 239, 240, 242, 243, 244, 246, 248, 250, 251, 252, 254, 255, 344, 449, 450, 461, 462 smart wound-care materials, 188 smoothness, 475 social judgment, 3 social order, 15 societal acceptance, 1 sodium, 123, 124, 125, 126, 145, 147, 154, 155, 167, 172, 237, 241, 356, 361, 363, 364, 365, 372, 373, 375, 380, 383, 384, 385, 395, 404, 405, 406, 407, 408, 410, 417, 419, 502, 516 sodium alginate, 383, 384, 385, 395 sodium carbonate, 124, 372 sodium chlorite, 406, 407, 408, 410, 419 sodium chlorite modification, 406 sodium hydroxide, 123, 124, 125, 126, 404, 406, 410, 417, 502, 516 sodium hypochlorite, 405 Sodium periodate oxidation, 406 sodium salts, 372 softener, 374, 375 softness, 19, 36, 40, 49, 242, 501 software, 58, 59, 61, 65, 76, 79, 90, 290, 457, 533, 534, 535 softwoods, 402 solar cells, 189, 226, 449, 453, 454, 462 solar simulator, 294, 295, 297 soldier and weapons camouflage, 247 sol-gel, 277, 278, 375 sol-gel films, 277 sol-gel processes, 375 solid matrix, 107 solid phase, 244, 438 solid state, 109, 158, 232 solidification, 102 solubility, 92, 94, 98, 124, 129, 136, 140, 148, 157, 158, 159, 195, 279, 289, 418 solvatechromic, 246 solvation, 176, 427, 428 solvatochromism, 213 solvent molecules, 211

573

solvents, 87, 97, 98, 99, 100, 102, 121, 157, 167, 176, 177, 178, 179, 184, 185, 213, 216, 217, 229, 401, 402 sorption, 154, 399, 400, 403, 405, 406, 408, 413, 414, 415, 418, 419, 420, 423, 424, 428, 429, 436, 437, 440, 442, 443, 444 sorption process, 418, 419, 436, 437 sorption properties, 400, 403, 405, 406, 408, 415, 418, 440 SP, 510 Spain, x, xi, xii, xiii, 343, 345, 346, 353, 355 specialists, 271, 346 species, 112, 194, 195, 197, 208, 218, 230, 241, 278, 279, 280, 289, 290, 292, 294, 306, 312, 313, 315, 317, 318, 319, 320, 321, 325, 326, 328, 329, 331, 332, 333, 334, 336, 411, 427, 445 specific computer code, 467, 468 specific flexural rigidity, 502 specific gravity, 92 specific heat, 394, 486 specific properties, 400 specific structure, 399, 401 specific surface, 399, 402, 411, 432, 434, 435, 436, 440 specific surface area, 399, 411, 432, 434, 435, 436, 440 specific surface morphology, 402 specific thermal resistance, 509, 511, 512, 513, 514, 515 specific work of rupture, 502 specifications, 7, 20, 26, 367, 521 spectroscopy, 134, 155, 177, 185, 224, 290, 296, 312, 313, 316, 321, 322, 323, 324, 326, 329, 332, 339, 340, 341, 357, 364, 365, 379, 380 spherical shape, 346, 348, 349 spin, 289 spindle, 521 spindle speed, 521 spinnerets, 539, 542 spinning balloon angles, 526 spinning off primary fibrils, 403 spinning tension, 519, 520, 521, 522, 525, 527, 528 spirooxazines, 105, 107, 110, 115, 194, 197, 201, 213 spiropyrans, 105, 107, 194, 197, 201, 213, 216 sports clothing, 455 sports garments, 243, 247 sportsmen, 240 sportswear, 246, 457 Spring, 17 sputtering, 249, 277, 278, 283, 285, 286, 288, 289, 290, 292, 295, 296, 297, 301, 302, 303, 305, 306, 307, 312, 531

574

Index

Sri Lanka, 27 stability, 20, 27, 49, 54, 74, 92, 94, 104, 105, 107, 160, 166, 182, 198, 200, 208, 221, 243, 248, 249, 256, 288, 312, 343, 344, 345, 348, 349, 351, 355, 466, 500 stabilization, 58, 146, 198, 436 stable states, 192 stainless steel filaments, 542 stainless steel yarn, 542 standard deviation, 421, 439 standard Martindale abrasion test method, 386 standard plastic optical fiber, 247 standard relative humidity, 410 standard test method, 383, 520 standard washing procedure, 28 Staphylococcus, 279, 313, 384, 396 Staphylococcus aureus, 279, 313, 384, 396 staple yarn production process, viii, 519 starch, 23, 36, 351, 377 static electricity charges, 401, 403 statistical analysis, 55, 259, 261, 296, 394 statistical significance, 296, 384 steady and pulsatile regimes, 467 steel, 95, 248, 254, 396, 468, 476, 542, 543 stenosis, 467, 478, 479, 480 stent, 465, 475, 476, 477, 478, 480 stereoisomeric forms, 214 stereomicroscope, 57 steric obstruction for sorption, 428 sterile, 295, 319 stiffness tester, 31, 386 stigma, 3 stimuli-responsive materials, 190, 226 stimuli-responsive smart textiles, 187, 225 stimulus, 103, 116, 190, 193, 194, 200, 208, 218, 220, 226, 244, 246 STM, 30 stock, 10, 11 stoichiometry, 430 Stokes-Einsteind diffusion coefficient, 423 stone wash, 20, 21, 24, 41, 51 stone-wash effect, 25 storage, 92, 103, 104, 182, 194, 195, 210, 220, 239, 241, 242, 260, 269, 271, 272, 274, 315, 317, 320, 322, 335, 336, 337, 370, 449 storage and exhibition rooms of museums, 320 storage conditions, 320, 322, 335 store image, 12, 13 store interior, 12, 14 strategic management, 18 strategic position, 6 street style, 4

stress, 6, 241, 244, 245, 329, 330, 334, 341, 357, 409, 466, 467, 474, 475, 476, 484, 485, 496, 504 stress-strain curves, 330, 329, 330, 331, 334 stretching, 132, 134, 143, 150, 330 STRs, 511, 512 structural changes, 112, 321, 322, 323, 326, 330, 336, 339, 417 structural characteristics, 317 structural design of weaving, 499 structural formation, 213 structuring, 402 style, 2, 3, 4, 8, 9, 10, 11, 12, 13, 14, 243 stylists, 3, 9 styrene, 98 sublimation fastness, 158, 165, 176 sublimation ink, 84 sublimation transfer printing techniques, 84 substitutes, 466, 480 substitution, 106, 123, 124, 126, 129, 130, 131, 136, 138, 139, 140, 141, 147, 148, 149, 153, 341, 400 substitution reaction, 129, 131, 141, 148, 149 succession, 469 succinic acid, 319, 326, 331, 357, 360, 361, 364, 371, 375, 376, 381 sugar beet, 154 sugar industry, 154 sulfadiazine-Ag salt, 279 sulfate, 167, 169, 170 sulfuric acid, 136, 145, 543 Sun, 365, 396, 443, 446, 497 super-hydrophilic, 279 supermolecular structure, 316, 321, 322, 332, 401, 442 superpolish, 521, 523, 524, 528 supply chain, 4, 90 surface area, 279, 295, 400, 411, 412, 430, 432, 433, 434, 435, 436, 440, 484, 487, 492 surface characteristics, 20, 432 surface deformation, 390 surface energy, 92, 279, 306, 308 surface functional groups, 412, 432, 436 surface layer, 249, 326 surface modification, 382 surface plasmon resonance, 303 surface pore structure, 408 surface properties, 324, 415, 440, 490 surface reactions, 279 surface structure, 67, 384, 533, 540, 542, 543, 545 surface tension, 92, 94, 99, 416 surfactants, 99, 350 surgical technique, 474 surplus, 243 surrogates, 5

Index survival, 260, 268, 281, 282, 293, 396 sustainability, 13, 20, 22, 25, 49, 50, 118 sustainable denim, 20, 21, 22, 23, 25, 26 sustainable development, 353 suture, 468, 479 sweat, 377, 455, 488 Sweden, 83, 244 swelling, 92, 125, 404, 409, 412, 413, 415, 417, 423, 516 swelling and shrinkage of ultimate cells, 412, 417 swelling process, 423 Switzerland, x, xi, xiv, 51, 128, 136, 277 synergistic effect, 208 synthesis, v, vii, 107, 123, 124, 129, 136, 139, 140, 145, 146, 148, 157, 163, 167, 168, 170, 171, 173, 175, 179, 180, 181, 182, 183, 185, 191, 215, 216, 231, 234, 352 synthetic antibiotics, 278, 289 synthetic chemical materials, 540 synthetic fiber, 157, 163, 164, 184, 288, 400, 410, 538, 539, 545 synthetic fibers, 157, 163, 164, 184, 288, 400, 410, 538, 539, 545 synthetic organic colorants, 157, 159 synthetic textiles, 165, 317

T tailor-made eco-smart clothes, 450 tantalum, 476 tapestries, 316 target, 5, 6, 189, 283, 286, 292, 298, 438, 509 taste-makers, 3 tear resistance, 253 technical applications, 465 technical textiles, vii, 85, 189, 243, 344, 399 techniques, vii, 6, 20, 81, 82, 84, 85, 90, 92, 93, 94, 95, 103, 108, 116, 117, 118, 119, 124, 188, 189, 192, 195, 196, 199, 204, 209, 216, 220, 278, 326, 338, 340, 344, 351, 355, 356, 462, 474, 480, 490, 533 technological advancement, 274 technological advances, vii, 465 technology(ies), 5, 21, 49, 54, 55, 77, 78, 80, 81, 82, 83, 84, 85, 86, 87, 88, 90, 92, 95, 100, 101, 103, 104, 118, 120, 188, 189, 190, 191, 227, 228, 234, 240, 241, 250, 252, 253, 260, 272, 275, 344, 350, 351, 377, 400, 447, 449, 450, 452, 455, 460, 461, 466, 471, 495, 520, 532, 545 teflon, 468 telecommunications, 240 TEM, 282, 285, 303 temperature-programmed desorption, 434, 445

575

TEMPO oxidation process, 405 temporarily prevent active fungal growth, 320 tenacity, 242, 403, 409, 410, 502, 507 tensile properties, 329, 330, 334, 336, 383, 384, 387, 388, 389, 409, 442, 522 tensile strength, 19, 20, 25, 30, 33, 34, 36, 37, 39, 41, 42, 128, 132, 139, 142, 147, 150, 321, 326, 357, 360, 371, 372, 373, 381, 383, 387, 388, 389, 396, 409, 468, 475, 500 tension, 92, 93, 94, 99, 416, 466, 471, 476, 504, 519, 520, 521, 522, 525, 526, 527, 528 TEOS, 375, 381 territory, 191 test prints, 65 testing, 5, 6, 7, 51, 53, 56, 74, 76, 154, 305, 313, 326, 351, 386, 397, 480, 494, 506 tetrachloroethylene, 164 tetraethoxysilane, 375 textile artificial vessels, 467 textile conservator, 271, 272, 273 textile fabrics, 51, 78, 101, 219, 240, 281, 386, 393, 397, 496, 497, 511 textile fibers, viii, 50, 248, 345, 449, 455, 477, 490, 492, 531 textile finishing process, 384, 394 textile fragments, 264, 275 textile heart valve, 466, 476 textile heart valve prosthesis, 476 textile historians, 259, 269, 273 textile implants, 471 textile industry, vii, 20, 23, 24, 47, 49, 50, 55, 63, 124, 136, 343, 344, 353, 356, 399, 401, 440, 533 textile materials, vii, 225, 239, 257, 312, 316, 322, 339, 362, 367, 377, 378, 384, 400, 440, 443, 465, 474, 477, 480, 488, 514 textile polymer surface, 280 textile preservation, 262, 273 textile printing, 53, 54, 55, 58, 66, 77, 78, 81, 83, 84, 85, 89, 90, 100, 120 textile prostheses, 466, 467, 471 textile reinforced synthetic material, 241 textile researchers, 260, 272 textile scaffolds, 241 textile sciences, 316 textile sensors, 188, 226, 250 textile substrates, vii, 53, 56, 59, 61, 76, 99, 108, 112, 114, 115, 117, 248, 249, 253, 345, 453 textile surface structure, 384 textile synthetic substrates, 56 textile vascular prosthesis, 472, 478 textile-based drug release systems, 188 textiles excavated, 260, 261, 262, 265, 266, 269, 272, 273

576

Index

texture, 80, 115, 247, 317, 351 TGA, 360, 361 theatre, 9 therapy, 118, 189, 209, 252, 310, 460 thermal (bubble) inkjet printers, 54 thermal absorbtivity, 383, 384, 386, 391, 393, 394, 396 thermal absorbtivity values, 383, 394, 396 thermal analysis, 360, 361, 380 thermal comfort, viii, 383, 384, 395, 397, 483, 488, 489, 490, 492, 494, 496 thermal comfort properties, viii, 383, 384, 395, 483 thermal conductivity, 384, 386, 391, 392, 394, 488, 489, 490, 493, 497, 509, 517 thermal decolouration, 112, 114 thermal decomposition, 361, 365, 430, 431, 432, 445 thermal degradation, 116, 155 thermal diffusion, 386 thermal energy, 190, 241 thermal feeling, 387 thermal history, 210 thermal inkjet print heads, 86 thermal insulating applications, viii thermal insulating material, 499, 500, 515 thermal insulation, 242, 246, 397, 484, 488, 489, 490, 492, 493, 499, 500, 501, 504, 505, 506, 508, 509, 510, 514, 515, 518 thermal insulation properties, 397, 484, 488, 490, 499, 504, 518 thermal management system, 93 thermal properties, 384, 391, 485 thermal resistance, 383, 384, 386, 391, 392, 396, 484, 489, 490, 492, 493, 507, 509, 511, 512, 513, 514, 515 thermal stability, 105, 198, 208 thermal storage materials, 241 thermal transmittance, 490, 492, 494 thermal treatment, 404, 444 thermal-transfer recording, 165, 181 thermo physiological properties, 383, 384 thermochromic dye, 210 thermochromic materials, 189, 211, 214, 247 thermochromic molecular switches, 211 thermochromic pigments, 210, 216 thermodynamics, 184, 444 thermofixation, 158 thermo-regulating effect, 242, 243 thermoregulatory process of human body, viii, 483 thickness, 56, 242, 243, 286, 287, 288, 295, 306, 323, 384, 386, 391, 392, 427, 455, 478, 485, 488, 489, 490, 492, 493, 506, 507, 508, 509, 511, 512, 513, 514, 515, 533, 537 thin films, 101, 155, 224, 283, 292, 314

thinning, 94 thrombo-embolism, 474 thrombosis, 467, 471, 477 time periods, 2, 279 time use, 450 TiN-Ag nanoparticulate films, 292 tinctorial strength, 159, 171 TIR, 323 tissue, 77, 90, 128, 188, 240, 466, 472, 474, 475 tissue degeneration, 474 tissue engineering, 77, 90, 188, 240 titanate, 89 titania, 313 titanium, 220, 248, 311, 357, 364, 375, 376, 381 titanium dioxide (TiO2) nanoparticles, 375 TLC analysis, 266 tobacco, 377 tobacco smoke, 377 toluene, 128 tones, 62 torus, 377 toxic metals, 219 toxicity, 263, 289, 352, 362 toys, 195, 210, 245 trade, 7, 10, 12 traditional vintage retailers, 2 training, 101 transcripts, 7 transformation(s), 66, 73, 104, 105, 116, 194, 201, 213, 289, 313, 404, 430, 434 transition metal, 193, 211, 220, 221 transition temperature, 244, 245 translation, 87, 496 transmission, 84, 108, 115, 195, 240, 251, 297, 323, 341, 449, 479, 489, 490, 496, 497, 509 transparency, 248 transplant, 471 transport, 90, 199, 249, 260, 271, 353, 395, 399, 415, 422, 423, 427, 428, 429, 437, 438, 440, 446, 484, 486, 493 transport phenomena within the fibers, 429 transportation, 85, 447 transverse thickenings, 539 traveller coating, 519, 523, 525, 527 traveller coating’s effect, 523 traveller drive angle, 520 traveller profile cross-section, 523 traveller profiles, 524, 528 traveller weight, 519, 520, 521, 522, 523, 524, 525, 526, 527, 528 treatment methods, 384 triangular cross-section, 539 tricarboxylic acid, 379

577

Index Trichoderma ressei, 23 trickle down, 4 trisazo pyridone colorants, 173 trypsin, 442 tungsten, 64, 220, 221 Turkey, xi, xiii, 27, 383, 519, 521, 528 twill fabric, 21 twist, viii, 329, 384, 506, 517, 519, 520, 521, 522, 523, 524, 527, 528

U United Kingdom (UK), xi, xiii, xiv, 1, 3, 10, 14, 15, 18, 30, 50, 81, 84, 119, 121, 153, 187, 190, 229, 255, 259, 286, 289, 290, 292, 339, 383, 385, 386, 494, 519 ultra-high local temperature, 88 ultra-high-molecular-weight polyethylene, 541 ultra-microtome, 282 ultrasonic anemometry, 467 ultrasonic application, 385, 393, 394 ultrasonic bath, 385 ultrasonic energy, 383, 384, 387, 388, 390, 392, 394, 395, 396 ultrasonic energy application, 383, 385, 387, 390, 396 ultrasound, 396 underclothes, 251 unethical practices, 2, 3 unevenness, 524 uniform, 72, 92, 99, 112, 113, 249, 254, 279, 280, 283, 289, 305, 306, 314, 510 unique features, 124, 197 uniqueness, 1, 3, 4, 9, 13 universities, vii, 247 unpleasant mouldy odour, 317 unsaturated monomer molecules, 541 upholstery, 85, 517 urea, 54, 237, 356, 369, 370 urea-formaldehyde, 369 uronic acid monomers, 384 United States (USA), 56, 58, 59, 72, 74, 83, 99, 119, 120, 121, 190, 227, 228, 229, 235, 255, 257, 275, 345, 346, 378, 386, 495, 496 7, 364, 375, 376, 381, 400, 403, 447, 460, 490 UV absorption spectra, 184 UV irradiation, 103, 105, 106, 107, 108, 109, 110, 111, 114, 115, 117, 196, 197, 206, 317, 357, 364, 376, 381 UV light, 82, 100, 101, 102, 103, 104, 105, 107, 108, 109, 110, 111, 113, 115, 116, 117, 194, 196, 197, 200, 201, 203, 205, 206, 207, 244, 357, 460 UV protection properties, 400

UV radiation, 64, 65, 375, 403 UV-curable inkjet inks, 100, 101 UV-vis reflectance, 303

V vacancies, 296 vacuum, 88, 125, 128, 280, 281, 286, 289, 531 valence, 222, 223, 375 Valencia, 351 validation, 16, 26 valuation, 80, 480, 488, 494, 497 valve, 89, 465, 466, 474, 475, 479, 480 van der Waals forces, 306 vanadium, 220 vapor, 36, 155, 245, 290, 308, 401 variables, 154, 345, 424, 484, 510, 512, 515, 517 variance analysis, 526 variations, 66, 71, 79, 108, 157, 159, 221, 222, 242, 388, 409 varieties, 47, 199 varnishes, 157, 159, 167 vascular prostheses, 466, 471 vascular surgery, 466, 471, 473, 475, 478 vascular wall, 467, 478 VDF, 452 vegetables, 218 vehicles, 64, 352 vein, 473 velocity, 87, 88, 90, 92, 93, 96, 466, 467, 479 ventilation, 336, 484, 491 versatility, 84, 216 vessels, 266, 465, 466, 467, 468, 473, 479 vibration, 134, 330 videos, 533 vintage, vii, 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14 vintage clothing, 1, 2, 3, 4, 8, 10 vintage concept, 12, 13 vintage connoisseur, 3 vintage consumer, 3, 4, 8 vintage definitions, 2 vintage era, 10 vintage fashion, vii, 1, 2, 3, 4, 7, 8, 9, 12, 13 vintage fashion clothing, vii, 1 vintage fashion community, 12 vintage fashion consumer, 1, 2, 7 vintage fashion retailers, 1, 2, 7, 13 vintage retail store, 7 vintage retailing literature, 7 vintage trend, 2, 4, 8, 10 vinyl monomers, 154 viscoelastic character, 472

578

Index

viscose, 51, 112, 113, 115, 117, 157, 159, 340, 410, 506, 517, 540 viscose rayon, 51, 157, 159 viscosity, 54, 90, 92, 93, 95, 98, 126, 127, 130, 131, 139, 141, 149, 195, 385, 414, 416, 467 viscosity control agent, 98 visible light spectrum, 531 vision, 191, 227, 455 visual impression, 67 visual system, 71 visualization, 195, 493 vitamin A, 351 vitamins, 210, 344 volatile organic compounds, 100, 317 volatile solvent, 87, 100 volatility, 98 volume electric resistance, 410, 411

W walking, 449, 450, 484, 494 wall crimping, 467 war, 84 wardrobe designers, 9 warehouse, 8 warm body, 486, 491 warm cloth weaving, 506 warm fabrics, 500 warm garments, 499, 501, 515 warning systems, 104, 240 warp directions, 386, 387 warp-knitted fabrics, 468 wash fastness, 104, 115, 165, 176, 182, 396 washing effects, vii, 20, 21, 23, 24, 33, 41, 48, 345 washing industries, 20, 24, 47 washing process, 21, 22, 23, 24, 35, 48, 55, 348, 349 washing techniques, 20 washing/finishing treatment, 20 Washington, 50, 79, 120, 314, 336, 339, 340 waste, 22, 100, 101, 153, 338, 399, 401, 418, 430, 436, 440, 441, 443, 444, 445, 450, 455 waste disposal, 399, 401, 430 waste management, 455 wastewater, 440, 443 watches, 11 water absorption, 19, 25, 31, 33, 35, 36, 38, 39, 40, 42, 43, 48, 52, 132, 139, 142, 147, 150 water holding capacity, 413 water purification, 399, 401, 430 water repellence property, 501 water retention value, 412, 413 water sorption, 414 water vapor, 36, 245, 308

water vapour permeability, 383, 384, 395, 396 waterproof elements, 457 waterproof fabrics, 384 wavelengths, 64, 107, 116, 192, 194, 200, 210, 295, 531 WAXS, 340, 442 wealth, 190 weapons, 247, 252 wear, 10, 11, 14, 20, 21, 22, 211, 239, 242, 243, 255, 367, 386, 389, 449, 484, 490, 505 wear performance, 21, 22 wearable computers, 226, 227, 240 wearable electronics, 188, 249, 250, 447, 448, 450, 455 wearable textiles, 188, 500 wearing apparel, 136 weather conditions, viii, 74, 246, 251, 252, 253, 447, 483 weaving technique, 466, 478 web, 120, 510 websites, 7, 12 wedding dress, 8 weft directions, 30, 34, 35, 37, 38, 39, 40, 41, 42, 386, 507 weft-knitted structures, 468 weight changes, 528 weight loss, 30, 31, 34, 35, 37, 39, 40, 41, 42, 43, 48, 407, 430, 502, 503 welfare, 270, 272 wellness, 545 wet-spinning process, 241 wettability, 51, 192, 415, 416, 417 wettability relationships, 416 wetting, 92, 94, 95, 99, 249, 393, 414, 415, 417 white light source, 533 White Paper, 461 wide band-gap semiconductors, 278, 314 wide-field optical microscopy, 532 windows, 244 wires, 189, 200, 240, 248, 253, 447, 452, 462 Wisconsin, 340 withdrawal, 504 wood, 101, 124, 154, 155, 166, 264, 317, 326, 338, 339, 340, 341, 430, 441 wood residue, 124, 154 wool fabric, 325, 382, 383, 384, 385, 387, 389, 390, 391, 395 wool fibre, 266, 331, 332, 334, 336, 340, 383, 501 wool proteins, 268 wool-based material, 499 woollen blanket, 505 woollenisation, 501, 502 woollenised jute, 501, 504, 509, 510

579

Index woollenised jute yarn, 501 workers, 101, 244, 289, 316, 360, 409, 449, 493 workflow, 53 working conditions, 239 workload, 251 worldwide, 262, 400, 494 wound dressing, 289, 384, 540 wound infection, 310 woven and knitted grafts, 468 woven bifurcated prosthesis, 471 woven carpets, 504 woven fabrics, 136, 386, 390, 392, 393, 394, 480, 492, 493, 496 woven polyester fabrics, 465, 475 wrinkle resistant cotton, 367 wrinkle resistant textiles, 371 wrinkle-resistant effect, 371 wrinkling, 240, 355, 367, 368

X xerophilic species, 318 xerotolerant fungi, 320 XML, 180 X-ray photoelectron spectroscopy (XPS), 280, 282, 283, 290, 291, 292, 294, 313, 353 X-ray diffraction (XRD), 285

Y yarn breaking strength, 523 yarn characteristics, 520 yarn count, 519, 521, 522, 527 yarn elongation, 528 yarn hairiness, 519, 520, 521, 522, 525, 528 yarn irregularity, 527, 528 yarn production tension, 522 yarn properties, 329, 384, 501, 519, 520, 522, 527 yarn spinning, 242, 520, 522, 527, 528 yarn spinning systems, 520 yarn spinning tension, 527, 528 yarn structure, 474, 475, 499, 500, 501 yarn twist, 519, 520, 521, 522, 523, 527, 528 yarn twist number, 522 yarn twist value, 520 yield, 109, 127, 129, 130, 131, 132, 140, 141, 148, 149, 150, 168, 172, 208, 272, 361, 400, 430, 476 young people, 3 young professionals, 3

Z zeitgeist, 8 zero-test length, 409 zinc, 420, 421, 422, 428, 429, 436, 444, 445 ZnO, 211

Textiles- History, Properties and Performance and Application 2014

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