Packaging Technology.pdf

PACKAGING TECHNOLOGY

�� This note on “Food Packaging Technology” is based on the syllabus of B. Tech. (Food) 4th year. I have tried my best to collect and put together information as precise as possible and there may be some mistakes as well. This note is for educational purpose and there is no restriction in its use and distribution. All the views and comments about this note are most welcomed and are requested to address at [email protected] or [email protected]

Sandesh Paudel Central Campus of Technology Hattisar, Dharan

Co n t e n t s INTRODUCTION TO PACK PACKAGING AGING ................................................................ ................................ ......................................................... ................................ ................................ ......................... 1 PRINCIPLES OF PACKAG PACKAGING ING ................................................................ 6 ................................ ............................................................... ................................ ............................... 6 PACKAGING MATERIALS ................................ ................................................................ ................................................................ ................................ ................................... ................................ ... 10 METAL METAL PACKAGING ................................................................ ................................ ................................................................ ................................ ............................................ ................................ ............ 12 PLASTICS PACKAGING................................ ................................................................ ................................................................ ................................ ....................................... ................................ ....... 28 GLASS PACKAGING................................................................ ................................ ................................................................ ................................ ........................................... ................................ ........... 64 PAPER AND PAPERBOARD PACKAGING................................................................ 74 ................................ ......................................... ................................ ......... 74 WOOD AND SHIPPING CO CONTA NTAINERS NTAINERS ................................................................ ................................ ............................................... ................................ ...............87 ...............87 SPECIAL PACKAGING TE TECHNIQUES CHNIQUES ................................................................ 92 ................................ ................................................ ................................ ................ 92 PACKAGING NEEDS OF F FOODS OODS ................................................................ ................................ ....................................................... ................................ ....................... 100 100 SHELF LIFE OF PACKAG PACKAGED ED FOODS ................................ ................................................................ ................................................ ................................ ................106 106 EVALUATION OF PACKAGING ................................ .................................. PACKAGING MATERIALS ................................................................ ................................ ................................ .. 112 SPECIFICATIONS AND QUALITY CONTROL ................................................................ Q UALITY CONTROL ................................ .................................. ................................ .. 129 SAFETY AND LEGISLATIVE PACKAGING ING .............................................. LEGISLATIVE ASPECTS OF PACKAG ................................ ..............134 .............. 134 ECONOMICS OF PACKAGI PACKAGING NG ................................................................ 136 ................................ ........................................................... ................................ ...........................136 THE MARKETING ROLE O OF F PACKAGING ................................................................ ................................ ....................................... ................................ ....... 138

�� Introduction Packaging is an important part of all food processing operation. The food industry is a major user of packaging. Packaging is a means of ensuring safe delivery of product, in sound condition to the final user at the minimum overall cost (in terms of protective role). In terms of business, packaging is defined as a techno economic function for optimizing the cost of delivering goods to maximize sells and profit. Packaging has been defined in a number of ways, some of which are: - The art, science and technology of preparing goods for transport and sale. - The art of and the operations involved in the preparation of articles or commodities for carriage, storage and delivering to the consumer. - Packaging is a technical operation in the preparation of a package that must protect what it sells and sell what it protects by making the product look attractive and encourage the consumer to buy it. Packaging is as defined above the overall concept, a “coordinated system of preparation of goods for shipment, distribution, storage, protection and marketing at optimum cost, compatible with the requirement of the product.” The word packaging is also used to describe the materials used, i.e. the glass, plastic or paper packaging material. Development of Packaging Over the years several developments have taken in packaging technology. These have included composition, form, presentation, properties, and the packaging machines themselves. Composition of packaging materials relates to hazard/safety in its use. Form includes size and shape of the package. Presentational aspects deal with the appeal, and it encourages sale. Properties include a range of features of packaging material and the package itself. This includes ease of handling, reusability, biodegradability, edibility, strength, preservative properties, and so forth. These have all been made possible by developments in food science and technology, packaging materials and machine technology. Packaging machines have also been developed, mainly with respect to speed, automation, cleaning and sterilization. The manual packaging that were the forerunners have been replaced with semi-manual and fully automatic machines in newer industries. Automation has led to use of robots and robotics thereby increasing the production rate, minimizing the manpower requirement and enhanced safety and quality. Some of the packaging techniques developed in the recent years are aseptic packaging, modified atmosphere packaging and active packaging .

The driving force behind these developments can be summarized as: 1. Social factors: convenience, quality, safety 2. Legislation 3. Economy 4. Competition 5. As a support to newer methods of non-thermal food preservation, e.g., pressure preservation, pulsed electric field processing 6. Better protection against faulty practice

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Compiled by: Sandesh Paudel

A reliable way to better packaging consists of:

Selection of suitable packaging materials This is a very delicate job in that it warrants considerable knowledge about both the properties of both packaging material and food. Some of the points to be considered in the selection of a packaging material are: a. Pre-requisite knowledge about the products b. Knowledge about the packaging material c. Product-package compatibility d. Chemical nature (chemical composition and reaction nature) e. Physical aspects (powder, crystal, solid, liquid, hygroscopic, hydrosensitive) f. Physical properties (strength, barrier to water vapor, oxygen, light, CO 2, etc) g. Behavior in aqueous and fat medium h. Availability and economy of packaging material. Needs to produce successful packaging - Facts about the products - Facts about the hazards - Facts about the market - Facts about the packaging materials, forms, machinery and labour cost. Facts about the product - How can the product be damaged or deteriorated? - Nature of the product and raw materials (how they deteriorate). - Interaction with packaging material. - Size and shape. - Weight and density. - Its weakness – breakable, scratchable, bendable, volatile, etc - Effect of moisture and temperature change, pH and oxygen. - Effect of light, which may cause fading or oxidation. Facts about the hazards - Types of transport – air, ship, road, train, etc. - The degree of control over the transport (private or public transport). - The form of transport: passenger train, freight train, etc. - The mechanical condition of the transport. - Duration of transport and storage. 2


Facts about the market - Consumer need. - Competition with other products. - Environmental pollution. - Reuse/recycle. - Price. Facts about the packaging materials - Barrier properties - GTR (gas transmission rate) & WVTR (water vapour tr ansmission rate). - Mechanical properties. - Optical properties. - Availability and economy. - Machineability. - Seal properties (heat sealable) and so on. Functions of packaging There are various functions of packaging. However, good packaging serves two main purposes . They are essentially technical and presentational. Technical changes in packaging aim to extend the shelf-life of the product and to preserve its quality by better protecting the food from all the hazards it will meet in storage, distribution and use. Presentational aspects of packaging do not actually do anything to make the food keep longer or in better condition. Such packaging increases sales by creating a brand image that the buyer instantly recognizes. It also aims to appeal to the customer in terms of shape, size, color, convenience, etc. The ultimate aim of good packaging is increased sales against any competition and thus improved income for the producer. Packaging can be divided into two main classes: primary and secondary. Primary packaging refers to the retail pack, the one that encloses the product, as sold in the retail outlet. Secondary packaging refers to the transit or outer packaging, sometimes called the shipping container, used to protect the primary packages in their journey from the factory to the retailer. Primary, secondary and tertiary functions are divided into the following sub-functions:  Primary functions: Protective function, Storage function & Loading & transport function  Secondary functions: Sales function, Promotional function, Service function and Guarantee function  Tertiary functions: Additional function

Packaging is a means of providing the correct environmental conditions for food during the length of time it is stored and/or distributed to the consumer. A good package has to perform the following functions: 1. Protection Protection applies to both primary and secondary packaging. The protective function of packaging essentially involves protecting the contents from the environment and vice versa. The product must be protected from the influences that will cause its quality to deteriorate. These include micro-organisms, oxygen, moisture, dust, light, odours, insects, rodents, etc. The secondary package protects the primary package from theft, dust, climate, breakage or damage in transit due to compression, vibration, drops, etc. A suitable packaging must keep the product clean and provide a barrier against dirt and other contaminants. It should prevent losses. Its design should provide protection and convenience in 3


handling, during transport, distribution and marketing. In particular, the size, shape and weight of the packages must be considered. 2. Preservation It refers to the prevention or inhibition of chemical changes, biochemical changes and microbiological spoilage Preservation is a function of primar y packages such as cans in which the product can be sterilized. The package provides an environment inside which the product is preserved and recontamination is prevented. 3. Containment It implies to both primary and secondary function. Primary pack contains a finite amount of product in a portion size that is convenient for the consumers’ requirement, such as 100 gm, 500 gm or 1000 gm. Secondary pack contains an appropriate quantity of primary packs to be delivered to the retailer, for sale as individual packs to the ultimate consumer, such as ten, dozen, and so on. 4. Information It also implies to both primary and secondary function. It must provide identification and instruction so that the food is used correctly and have sales appeal. The primary package must provide information about weight, ingredients, date of manufacture and expiry, etc. The main information is the name of the product and the brand. This identifies the pack and makes it distinct from other similar products. Other details such as how to cook, store and serving suggestions may also be provided. Examples are the nutritional details on yoghurt pots or dosage information on medicines. The secondary package provides information about the methods of handling, address to which the product is to be sent and so on. The handling instructions give details of how high it should be stacked to prevent damage due to excessive weight on the lower packages. It also informs if the contents are breakable and the storage conditions to be maintained, such as dry, chilled or frozen, etc. 5. Marketability It refers to the use of packaging as a marketing tool. It is an important primary function to make the product look attractive and to make it stand out from its competitors. Packaging also enables or promotes sales process and makes it more efficient. Sales promotion such as money off or free extra contents can be advertised on the pack. 6. Convenience Packaging makes the product easier to handle, use, open, dispense, store, etc. A convenient primary pack can encourage sales by making life easier for the users. A pack that is easy to open, is reclosable, and comes in convenient unit size and stores well, offers many advantages to the consumer. 7. Efficiency It refers mainly to the package in the manufacturing process. If the production is possible on a high speed filling/sealing machine, it improves the output efficiency. The package needs to suit the mechanized line by being consistent in quality. Otherwise, it may give problems such as faulty seals, breakages, etc. 8. Economy It applies to both primary and secondary packs. The package cost must be low; otherwise the product may be too expensive. Insufficient packaging causes damage to the product, leading to losses in sales and reputation. The cost of transport, storage and the economics of recycling are important. 4


9. Disposability It is important for both primary and secondary packaging. Where possible, the package should be returnable, recyclable or be easy and safe to discard. 10. Loading and transportation function Convenient goods handling entails designing transport packaging in such a manner that it may be held, lifted, moved, set down and stowed easily, efficiently and safely. Packaging thus has a crucial impact on the efficiency of transport, handling and storage of goods. Packaging should therefore be designed to be easily handled and to permit space-saving storage and stowage. The shape and strength of packages should be such that they may not only be stowed side by side leaving virtually no voids but may also be stowed safely one above the other. Where handling is to be an entirely or partially manual, package must be easy to pick up and must be of a suitably low mass. Heavy goods must be accommodated in packages which are well suited to mechanical handling. Such items of cargo must be fork liftable and be provided with convenient load-bearing lifting points for the lifting gear, with the points being specially marked where necessary (handling marks). 11. Storage function The packaging materials and packaging containers required for producing packages must be stored in many different locations both before packaging of the goods and once the package contents have been used. Packaging must thus also fulfill a storage function. 12. Guarantee function By supplying an undamaged and unblemished package, the manufacturer guarantees that the details on the packaging correspond to the contents. The packaging is therefore the basis for branded goods, consumer protection and product liability. There are legislative requirements which demand that goods be clearly marked with details indicating their nature, composition, weight, quantity, and storage life. 13. Additional function The additional function in particular relates to the extent to which the packaging materials or packaging containers may be reused once the package contents have been used. The most significant example is the recycling of paper, paperboard and cardboard packaging as waste paper.

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�� Packaging Hazards Product goes through various steps from production to sale and reuse of package. A number of packaging hazards are involved in the chain of distribution. The hazards depend on the mode of transportation, method of handling and storage.

a. Hazards arising from mode of transport The modes of transport include bullock cart, road-trucks, rail goods trains, sea ship, and air cargo. Hazard is inevitable in all of these modes. Bullock cart The stacking and drop height is about 5ft. Bumping occurs due to rough road. Directional placing of packages may not be possible because of the constructional constraint of the cart. Road trucks Road has the advantage of being cheap, and can take the goods directly from the producer to the retailer. However, the quantity that can be carried in one vehicle is limited. It is also affected by weather. It is used for short and long distance as well as door to door service. The package dimension should suit the body dimension for maximum use of space. It is costlier that by rail. Maximum stacking and drop height are 7ft and 5ft respectively. Puncturing of package by protruding bolts is possible. Bumping in the rough road may cause damage to the contents. Rail goods trains Rail is excellent for moving large quantities in bulk. However, it is not direct and the extra loading and unloading operations introduce extra hazards. Also, pilferage is possible. It has no problem for inter-state transport. There is no interruption of journey even in rainy season. Stacking height = 8ft. vibration in railway joint. Shunting shock is possible. In summer, the steel wagons get heated. Sea ship Sea or river travel is also slow and not direct to the end user, requiring extra handling. Stacking height = 10-15ft. High humidity may be a problem. Swaying can occur due to waves. Salt spray on decks and docks can harm the package. Air cargo Freight charge is very high. There is limitation in size and weight of package, and sometimes even the product type. Air travel is too expensive for all but the lightest or luxury items. The journey time is less and there is better handling but cooling facility is not available. Hazards include highfrequency vibration, low pressure and temperature when fl ying at high altitude. b. Hazards arising from handling Handling can be done manually or by mechanical means. Hazards are involved in both the methods. Manual handling In India and Nepal, single man handling is common and a man handles about 35-40kg. The drop height is about 6ft when carried on head and 3-4 ft when carried on shoulder. The packages are rolled on the floor when heavy and this damages the package. Mechanical handling Mechanical handling includes conveyors, fork, lift, etc., for handling palletized or unified loads. 6


c. Hazards arising from storage The product and the package undergoes compressive/static load during storage. During transportation, the package experiences dynamic load. The stacking height for an y package should not be greater than 20 ft. Types of hazards Packaging materials, packaged products and the packages themselves have to weather several hazards during storage and transportation. The major and most common hazards encountered during transportation and storage are as follows:

A. Physical hazards Physical hazards are mainly the mechanical hazards encountered in storage, during loading and unloading and in transit from the factory to the retailer and consumer. Physical hazards include: 1. Puncturing, piercing, tearing by hooks, nails, bolts 2. Crushing by rope 3. Drop hazard due to drop impact which occurs during loading/unloading and transportation 4. Drop impact results in breakage, distortion, leakage, bursting 5. Uneven lifting due to slinging 6. Vibration and bouncing (bumping) can occur during road transport, vibration and shock during rail transport, vibration during air transport due to high frequency vibration of engine. Vibration produces shock impact, shunting causing shunting shock. Vibration shock causes abrasion of goods, leading to wearing, distortion, breakage, leakage, fracture, loosening of fastening or strap. B. Chemical hazards It includes light and ultraviolet radiation that can affect the shelf life of the product. Other chemical hazards are enzymatic reactions such as browning, oxidation and the risk of odours or volatiles transferring into or from the product. It also includes the corrosion or migration of the constituents from the packaging into the product and vice-versa. C. Climatic hazards This type of hazard can be of several types, the more important of which are: 1. High/low temperature, high/low RH, high/low pressure 2. Chemical pollutants like sulfate, chlorides, acids, etc of the environment 3. Direct exposure to sun 4. Rain or drain water Climatic hazards arise due to the effect which humidity, rain, condensation, dust, changes in temperature and pressure, have on the product. These include physio-biochemical changes such as loss of crispness, mold growth, formation of hydrates, cracking or hardening of the product, rusting, etc. Low pressure can affect the seal integrity of the pack. D. Biological hazards It is caused by insects, rodents, birds and microorganisms during transportation and stor age. They cause decay, spoilage, material loss, contamination and spillage. Biological hazards can be divided into macro and micro sections. The macro includes birds, rodents, insects such as moths and beetles, flies, ants, termites, etc. Insects may account for up to 20% of the losses of some products. Some insects are capable of boring their way through packaging. A smooth, thick material is best, avoiding creases and folds in the style of pack in which insects could hide. For the protection 7


against rodents, the best way is to keep the storage areas in good condition, allowing them nowhere to nest and survive, setting bait to poison them, etc. The microbiological hazards are aerobic and anaerobic bacteria, yeasts, molds and fungi. Molds make the substrate acidic and break down paper products. The acidity can lead to problems with corrosion. These can be prevented by proper packaging by maintaining a vacuum or modified atmosphere, preventing the entry of micro-organisms, keeping the product dry, or allowing moisture to escape from moist products that would otherwise become moldy, etc. The product can be sterilized in the pack as in canning, or be irradiated or aseptically packed, etc. E. Static hazards Static hazards occur from compression of goods due to stacking loads and are influenced by factors such as: - Stacking pattern - Duration - Condition of floor such as evenness - Nature of goods F. Miscellaneous In addition to mechanical hazards in handling and transportation, the climatic and biological hazards to which packaged goods may be subjected during their life cycle should also be considered. Other possible hazards are: 1. Exposure to foreign odours; some corrosive chemical odours may cause stress cracking 2. Contamination by other products stored alongside which may have leaked, thereby affecting the external appearance 3. Hazards of pilferage 4. Fire 5. Floods, particularly evident in low lying areas during heavy rainfalls These hazards have been the basis for the development of transport packaging. Knowing the hazards, suitable packaging can be developed to protect the product. It is necessary to know all the facts about the product (discussed earlier) to develop suitable packaging. Interaction between the product and the packaging material includes considering toxicity, corrosion of metal packaging, migration of the constituents into the food, migration of solvents through the material, etc. The environmental conditions that it will encounter depend on the location of both the producer and the market. The climatic factors such as temperature and RH affect the choice of a suitable material. Dust or pollutants in the atmosphere, radiation, etc all cause deterioration. Storage factors such as the condition of the store and what products are stored nearby can affect the packaging requirements. Distribution Hazards Distribution hazards occur during loading & unloading, transit and in storage. These hazards can be assessed by observing handling procedures, by sending a trial shipment through the normal distribution system and inspecting its condition on arrival, or by simulating expected conditions in the laboratory, subjecting the package to impacts, drops, vibration, etc.

Loading and unloading hazards These are mainly drops and impacts. The important factor is the height from which the product has dropped or been impacted, the surface onto which it has dropped, and the edge which it lands (base, side or corner), etc. The weight of the unit is also important. If it is too light, it will be easy 8


to throw and thus increases the risk of such hazards. If it is too heavy, it requires two or more people to move and thus reducing the risk of such hazards. But the damage is higher in heavy goods, if occurred. Special handling equipments such as cranes may also cause damage to the pack by piercing or tearing with the hook. An ideal unit weight is 10-25 kg. Transit or movement hazards It depends upon the mode of transportation. For road transportation, it depends upon the condition of the road and the vehicle. A vehicle having more suspension system prevents the package from the more severe impacts. Speed also plays an important role. Higher speed on rough surface causes more damage. Other hazards in road transportation include crushing by ropes used for tying, side impacts with heavy breaking and drop during loading and unloading. For rail transportation, there are hazards such as vibrations, shunting and snatching due to the sudden start/stop of the loose coupled wagons. Sea transportation can give rise to crushing due to the practice of stacking the load very high in the hold. There is also the hazard of low frequency vibration and if the sea is rough, stresses may included by pitching and rolling. Air transportation has the risk of high frequency vibration, pressure and temperature drops. Shock is a stress induced by sudden deceleration, i.e. if the vehicle stops abruptly. This can cause internal stress distorting the product. The resistance to shock is known as the fragility of the product and it can be expressed in terms of fragility factor (ff). This is defined as the maximum stress that can be tolerated under specific conditions. The measurement unit is ‘g’, the acceleration due to gravity. For e.g. a package having ff of 50 can withstand an impact force of magnitude up to 50 times its own weight. Vibration can give rise to failure due to resonance and fatigue, can cause loosening of closures and fastenings, print abrasion, scuffing and have a destabilizing effect in stacked packs. It is a major problem with sensitive electronic equipments. Cushioning material (soft protective pad) can be used to dampen the frequency of vibration. Storage hazards It depends on the height of the stack and the stocking pattern used. Crushing will occur if too much weight is applied from packs above in a stack. If all boxes are stacked in the same orientation, it leads to a concentration of the load on the corners. This can be overcome by arranging them so that alternate layers in the stack are in opposite directions. This gives a better distribution of load, which reduces the compressive force and therefore the risk of crushing is reduced. Also, the stack is more stable. The compressive strength of a box depends on its cross sectional area over which the load is distributed. If a given box has theoretical compression strength of 300 kg and is to contain 5 kg of product, then it could in theory have 60 boxes placed on top of it before it would fail. However, in practice, a safety factor is applied to allow for damage to the boxes, a loss in strength due to an increase in moisture content/relative humidity, or shifting of the load as the vehicle goes around a corner, etc. Higher safety factor is needed in tropical countries where the boxes will lose strength due to their increase in moisture content. During storage the product may also incur climatic hazards and biological hazards such as bacteria, fungi, mice, rats, etc.

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�� Introduction There are many different types of packaging materials in use today. Originating from natural materials such as skins, leaves, and bark, tremendous progress has been made in the development of diversified packaging materials and packaging equipment. Packaging materials are commonly grouped into rigid and flexible structures. Plastic film, foil, paper, and textiles are flexible materials; whereas wood, glass, metals, and hard plastics are examples of rigid materials. Each material has advantages, disadvantages and limitations. The main packaging materials in use today are:  Metals  Plastics  Glass  Paper/board/wood Traditional packaging materials In general these materials are used to hold foods but they offer little in the way of barrier properties needed for a long shelf life. The exception is glazed pottery, which although heavy, has excellent properties.

Leaves Banana or plantain leaves are the most common and widespread leaves used for wrapping foods, such as certain kinds of cheese and confectionery (guava cheese). Cornhusk is used to wrap corn paste or block brown sugar, and cooked foods of all sorts are wrapped into leaves. 'Pan' leaves are used for wrapping spices; they are an excellent solution for products that are quickly consumed, as they are cheap and readily available. Bamboo and rattan These are widely used materials for basket making. Bamboo pots, cut out of the bamboo stem are also found. Coconut palm Green coconut palm and papyrus leaves are frequently woven into bags or baskets, which are used for carrying meat and vegetables in many parts of the world. Palyra palm leaves are used to weave boxes in which items such as cooked foods are transported. Vegetable fibres These natural raw materials are converted into fibres to produce the yarn, string or cord for packaging materials. Such materials, although categorized by the nature of the constituent fibre, have certain common characteristics. They are very flexible, to some extent resistant to tearing and permeable to water and water vapour. Their lightweight is an advantage in handling and transport. The rough surface makes stacking easier in comparison to man-made fibre sacks, which slide due to their smooth surface. Another difference with man-made fibres is that the natural raw materials are bio-degradable when left in their pure state. However, they rot when moist limiting the number of times that they can be re-used. Earthenware Earthenware is used worldwide for storage of liquids and solid foods such as curd, yoghurt, beer, dried food, honey, etc. Corks, wooden lids, leaves, wax, plastic sheets, or combinations of these 10


are used to seal the pots. If well sealed, it is a gas, moisture and lightproof container. Unglazed earthenware is porous and is very suitable for products that need cooling e.g. curd. Glazed pots are better for storing liquids e.g. oils, wine, as they are moisture proof and airtight, if properly sealed. All are lightproof and if clean, restrict the entry and growth of micro-organisms, insects and rodents. One should ensure that the glazing of the earthenware does not contain lead. Most traditionally glazed pots do have lead glazings which, although they are not really harmful for serving coffee or soup, should not be used for acid drinks and other products which are to be stored for a long time. Treated skins Leather has been used for many centuries as a non-breakable container or bottle. Water and wine are frequently stored and transported in leather containers (camel, pig and kid goat hides). Manioc flour and solidified sugar are also packed in leather cases and pouches. Properties of an ideal packaging material In general, an ideal packaging material must have the following properties: 1. Good barrier properties – low GTR and WVTR and Controlled transmission of required or unwanted gases 2. Protection from loss of flavor and odor 3. Good mechanical properties (i.e., strength in compression, wear, and puncture characteristics) 4. Resistance of migration or leaching from package 5. Have a functional size and shape 6. Give optimum efficiency 7. Easy machine handling and suitable friction coefficient 8. Low cost and availability 9. Compatible with products 10. Easy for cleaning, safe and easily disposable, recycle and r eusable 11. Heat sealability 12. Closure characteristics, such as opening, sealing and resealing, pouring 13. Convenience 14. Chemically inert and zero toxicity 15. High product visibility 16. Strong marketing appeal 17. Stable performance over a large temperature range 18. Ability to include proper labeling 19. Should meet legislation

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�� Introduction Metal is used in a number of forms in packaging, as cans, foil, tubes, drums and closures, etc. Steel, tin, and aluminum are used mainly for canned foods and beverages. The most commonly used metals for packaging are tin-coated steel and aluminum cans.

Metal packages for food products must perform the following basic functions if the contents are to be delivered to the ultimate consumer in a safe and wholesome manner:  preserve and protect the product  resist chemical actions of product  withstand the handling and processing conditions  withstand the external environment conditions  have the correct dimensions and the ability to be practically interchangeable with similar products from other supply sources (when necessary)  have the required shelf display properties at the point of sale  give easy opening and simple/safe product removal  be constructed from recyclable raw materials In addition, these functions must continue to be performed satisfactorily until well after the end of the stated shelf life period. Most filled food and drink containers for ambient shelf storage are subjected to some form of heat process to prolong the shelf life of the product. For food cans, this will normally provide a shelf life of up to 2–3 years or more. The heat process cycles used to achieve this are particularly severe and the containers must be specifically designed to withstand these conditions of temperature and pressure cycles in a steam/water atmosphere. Advantages Metal containers have a number of advantages over other types of container, including the following: 1. Complete barrier in terms of GTR and WVTR – provide total protection of the contents 2. 100% UV/light protection 3. Strong as compared to plastic, paper, glass and wood 4. Highly durable 5. Reusable and recyclable – economic 6. Good machineability – can be produced and filled in high speed machine automatically 7. Light in weight as compared to glass 8. Providing a cheap matter of preserving food – canning 9. Heat processable/resistance 10. Printable and embossable 11. Convenient for ambient storage and presentation – better protection against insects 12. They are tamperproof 13. Creates hermetically sealed/aseptic environment. 14. As regard to their opacity, it is an advantage for light-sensitive products. Disadvantages 1. The high cost of metal and the high manufacturing costs make cans expensive as compared to plastic and paper but not glass

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2. Not completely inert – Tendency to interact with contents and environment (internal and external corrosion). Takes part in chemical reactions thus leading to corrosion, rusting, leakage, etc. 3. Chance of migration of tin and lacquer material into food 4. Heavier than other materials, except glass, and therefore have higher transport costs 5. Completely opaque – contents can’t be seen without opening Commonly 4 types of metals are used for food packaging purpose: - Steel - Aluminium - Tin plate - Chromium plate – ECCS (electrolytically chromium coated steel plate) Lead and copper are also used but in soldering or welding of 3 piece can. Tin and aluminium are most widely used metals for the manufacturing of cans. Canning The most common use of metals for packaging is in tin and aluminum cans. The metal provides a highly effective barrier between the food product and the environment. Thus, the critical concepts of canning are to ensure that the product in the can is biologically stable and that the seal provided by the metal is complete. Food stability for non-powders is usually achieved by thermal processing. A. Tin Can This is also called open top sanitary can . It has a base of mild steel plate coated with tin (0.040.1%). Steel is easily corroded so is usually in the form of tinplate which consists of mild steel (low carbon content in the order of 0.1-0.5%) coated on both sides with a layer of tin. The tin coating protects the steel from rusting and corroding by forming a tin/iron alloy at the interface to prevent the attack on the steel base. The typical structure is shown in the fi gure below:

Fig: Structure of tin plate The base steel plate is also known as black plate which has low carbon content. Passivation treatment: This stabilizes the surface of tin coating by controlling the growth of natural oxide. The uncontrolled oxide growth can cause yellow discoloration of the plate surface and effects lacquering and printing process, i.e. it makes the surface more stable and resistant to atmosphere. An electrolytic treatment in a sodium dichromate electrolyte is widely used method. It results in the formation of thin (<1 m) film consisting of chromium and chromium oxides and tin oxide. Surface oiling: It is designed mainly to lubricate the plate to improve the slip characteristics and reduce surface scratching and adhesion properties when a plate is subsequently fabricated into container. The amount of oil used is 5-10 g. The oils used are dioctyl sebacate (DOS), acetyltributyl citrate (ATBC). The level of oil application must be controlled because excessive oil coating causes decoating of lacquer and disturbs in printing. 13


Advantage of tin coating The combination of steel and tin produces a material that has: - Good strength and barrier properties - Excellent fabrication quality such as ductility and drawability - Good solder and weld ability - Non-toxic in nature - Lubricity - Lacquer ability - Provide corrosion resistant surface of bright appearance – most important factor - They tend to be used for higher-value products, as the painted tin can look very effective. Types of steel for producing tin plate Tin cans can be classified on various bases, e.g., i) based on corrosion resistance, ii) based on grades of base plate, iii) based on size, and iv) New system based on ISO diameter.

a. Classification based on corrosion resistance Type MR: This is the most widely used grade used for moderately and mildly corrosive products, such as peas, apricots, meat, peaches and grapefruit. Residual elements are not limited except phosphorus which is kept at a low level. Typical composition contains 0.2% copper, 0.02% phosphorus and 0.5% sulphur. Type L: This is used for highly corrosive foods, i.e. those that are highly acidic such as apple juice, berries and pickles. In this type the amounts of phosphorus, silicon, copper, nickel, chromium and molybdenum are limited to as low as practicable, typically 0.06% copper, 0.015% phosphorus and 0.05% sulphur. Type LT: It is the same as type L, but it has been tested to confirm that it is corrosion resistant. Type MC/N: This has been rephosphorised for extra strength and stiffness. It is suitable for mildly corrosive or non-corrosive products such as peas, meat, fish, dried soups, milk, etc. it is used for making high-strength tin plate i.e. for can ends for carbonated beverages where the internal pressure is high. Type D/M: For making D & I (drawn and ironing) can. NOTE: Low copper cans are used for acid foods. The copper content of tin plate varies from 0.02 to 0.6%. The phosphorus content varies from 0.01 to 0.1%. The strength of can is proportional to phosphorus content in the base plate. b. Classification based on strength and ductility Tinplate is graded according to its strength and ductility in a grading system that refers to each grade as a temper (T) numbered from 1-6. T1 represents the most ductile but least strong grade; therefore it is easy to mold. T6 is nitrogenised steel, very stiff and suitable for ends subjected to high pressure. Each grade has a t ypical use, such as: T1 – T3: used for deep draw components, e.g. two piece cans T3 – T4: general purpose grades used for can bodies/ends T5 – T6: stronger grades used for heavy duty can bodies and ends. c. Classification based on size Based on size, American system of nomenclature is used, e.g., A1 Tall, A2½, etc. Each of these nomenclatures has a meaning. 11 4 161 ' '×4 16 ''

For example, A2½ can refers to diameter × height of

. 14


d. New system based on ISO diameter ISO diameter system is related to American system of nomenclature. The A2½ equivalent in this system is 401×411. The derivation of the relation is outlined below:

American system nomenclature A 2 12

=

ISO diameter system

01 4 16

×

11 4 16

401

×

411

Manufacturing principle of can base plate An outline of the manufacture of can base plate is shown in the figure that follows Hot steel ingots Cold rolling Steel strip of thickness ≈ 1.8mm Pickling (hot, dilute H2SO4 bath) Steel strip of 0.15-0.5mm Annealing and temper rolling (to give required hardness and surface finish) Coating on both sides (hot dipping or electrolytic process)

The steel plate is made by hot rolling cast steel ingots or continuous steel strip down to a thickness of 2 mm. It is then treated in a bath of sulphuric acid to remove the surface layer of iron oxide. Cold rolling follows, reducing the thickness further to 0.15-0.5 mm. It is heat treated to remove the manufacturing stresses and to improve ductility in a process known as annealing. This can be a continuous or batch type process. Continuous annealing takes the metal to a temperature o between 600-650 C for 1-1.5 minutes. The batch process holds a batch of metal at between 600o 650 C for 7-10 hours in a nitrogen/hydrogen atmosphere to prevent oxidation. A light rolling follows to achieve the required mechanical properties and surface finish. Inspection and degreasing follows before the tin is applied. Tin coating can be carried out by two methods: a. Hot dipping method Traditionally the tin coating was achieved by hot dipping the steel in a batch of tin. Hot dipping produces thick coating (a minimum of 22 gram per square meter; gsm), i.e. 11 gm tin per square meter on each plate, which tends to be expensive. It also produces uneven coating and differential coating can’t be achieved as well. b. Electroplating/electrotinning process

15


Nowadays, electroplating method is used to achieve more controlled and uniform coat weights, which can be adapted to the product requirements. The tin anode and the steel cathode are immersed in an electrolyte of acidic stannous (tin) sulphate. The tin dissolves and is deposited on the steel cathode. Electrolytic coating can give as low as 5.6 gsm, i.e. 2.8 gm tin per square meter of plate. It can also give differential coating such as D100/50. However, the resulting tin plate has a dull finish. A shiny appearance can be produced by a process known as flow brightening, which produces brightening by heating in hot oil bath or by electrical induction process. This not only gives bright appearance but also enhances resistance to corrosion. Finally it is treated with chromic acid, dichromate, perchromate or phosphate solution to stabilize the finish. Alternatively, oil such as dioctyl sebacate can be applied to the tinplate to act as a lubricant, minimizing the scratching of the plate. The tin coating may be the same weight on both the sides of the plate or it may be different by using a differential coating process. This allows for savings as only the required amount of tin, which is expensive, will be applied. The can is more vulnerable to the attack from the pack contents than from the atmosphere, so a thicker tin coating can be applied internally. Typical coating weights vary from 1.4-11.2 gsm on either side of the steel base. The code letter “E” refers to equal coat weight on both the sides whereas “D” refers to different coat weights. As tin is very expensive, efforts have been made to reduce the quantity required as in the electroplating method. Double cold reducing (DCR) involves giving the metal a second rolling process to reduce its thickness by 25-50%, while increasing the stiffness. This is used to achieve the same strength through thinner and therefore cheaper metals. Another alternative is the use of cans without tins. Principles of can manufacture (round can) Example: open top sanitary can strip of base plate cut to required size edges are notched and locked side seam is formed reforming in mandrel (body reformer) side seam

can ends are notched or plunged and flanges made gasket of rubber composition

flange

lid body blank one end is seamed with lid in double seamer

The side seam after reforming the can body is welded before fl anging. The rubber gasket in the lid helps seal the joints between lid and edges of body blank. Tin cans are made of sheet steel coated with 0.5 mm tin. The coating is applied by tinning, which 2 2 is electrolytic deposition of the tin at about 10 g/m , and hot dip, which uses about 30 g/m . The steel is rolled and ribbed (for added strength) and either sealed with solder (usually 95% lead, 5% 16


tin), or, more commonly, welded. The resulting tube ends are flanged, and the lids at both ends are attached by a double seam without solder. Since steel corrodes rapidly in the presence of acidic substances, the tin acts as a barrier. Some cans are lacquered internally for high-acid products (pH 3) or for products that change color in the presence of tin. Foods that contain sulfur produce a blackening of the tin. The steel can provide almost perfect barrier protection and, because of its structural strength and ability to handle pressure, can be retorted (cooked under pressure) after sealing. Tin coating or lacquering is an important part of can manufacture. The lacquer is a resin, such as an acrylic (which resists high temperatures), oleoresinous, alkyd,epoxy, phenolic, polybutadiene, or vinyl resin. More than 200 different protective coatings are now in use. The lacquering must be complete. Small gaps in the coating can lead to the iron being exposed. The interior coating has to withstand sterilization temperatures and action of acids, as well as sulfide staining. As iron corrodes it produces hydrogen gas, which can blow the can. The development of lacquers has meant that tin-free cans are possible. Another disadvantage of steel is the high-energy requirement during manufacture. Cans without tin

a. Tin free steel (TFS) TFS, also referred to as electrolytic chromium/chrome oxide coated steel (ECCS), is made from mild steel coated electrically with chromium (chromic acid). It is usually lacquered for better performance. Tin-free cans are cheaper. Such cans are used for dehydrated foods, beer, carbonated beverages, meat and fish.

It consists of: - Chromium coating – 0.07-0.15 gsm - Oxide layer – 0.03-0.06 gsm Advantages over tin plating 1. Cheaper than tin coated plates 2. Produce surface more acceptable for protective lacquer coating or printing ink o 3. Due to high melting point (232 C), tin layer show use of higher lacquer stoving temperature. Shorter stoving time can be used for TFS. Disadvantages 1. Low resistance to lacquer, so require high degree of lacquer protection 2. Can’t be sealed with traditional lead or tin solder; requires bonding by welding or use of organic solvent

b. Tinless steel (black plate) It is mild steel sheet dipped in phosphate solution and then lacquered. Phosphate treatment facilitates lacquering and is called bonderizing. The material is used in cans for beer and other carbonated beverages, biscuits, etc. c. Aluminized steel It is made by coating aluminum by hot dipping or vapor-coating on steel plate. 17


B. Aluminium Can Aluminum is used increasingly for canning due to its lightness, low cost, corrosion resistance, availability, and recyclability. It is third lighter in weight than tinplate but is not as strong, but is more ductile. It is easier to form in a variety of shapes and is ideal for easy open features. Aluminium for light metal packaging is used in a relatively pure form, with manganese and magnesium added to improve the strength properties. This material cannot be welded by canmaking systems and can only be used for seamless (two-piece) containers. The internal surfaces of aluminium containers are always coated with an organic lacquer because of the products normally packed. Advantages 1. Light weight 2. Good appearance 3. Good dead folding properties 4. Excellent barrier to moisture and gases 5. Good weight : strength ratio 6. Impermeable to light, odour and micro-organisms 7. Extensively corrosion-free (due to oxide film formation on surface) – no need of lacquer 8. Does not discolor the product 9. Resistant to sulfur-containing products (meat, fish, etc.) 10. Easy to open 11. Non-toxic and does not give metallic taste 12. High recycling 13. High quality surface for printing and decorating 14. Compatible with wide range of sealing resin and closure for different closure system 15. Aluminium foil can be laminated with paper or plastic to increase the barrier properties of paper and plastic Disadvantages 1. Not highly resistant to corrosion by acid fruit, hence extra protection through lacquering or anodization is necessary 2. Less strength, thus denting is possible 3. Retort pressure can cause permanent distortion if precautions, like use of overriding pressure, are not taken 4. Incompatible with use in microwave oven 5. Some chemical reactions are carried out with mild acid and alkali 6. Aluminum foil is difficult to use on modern fast packaging equipment because of creases, tearing, and marking effects. 7. Aluminum foil of fine gauge may have minute pinhole defects due to the tolerances of the rollers, crystal size, and lubricants used, which allow transmission of air and water.

Aluminum alloy Aluminum plate containing 1% manganese increases strength and corrosion resistance. This can has the strength equal to aluminum can with 20% higher thickness. Aluminium alloy is used because of the following reasons:  It has high strength as compared to pure aluminium  It improves formability characteristics  It influences corrosion characteristics 18


Wide range of aluminium alloy is used. The choice of use depends on the container design and fabrication design.  Cu – reduce the corrosion resistance  Mn – slightly increase the corrosion resistance  Mg – good corrosion resistance  Zn – corrosion resistance reduced in acidic media, but increased in alkaline media  Si – decrease the corrosion resistance  Fe – high iron content increase the bursting strength but reduce the corrosion resistance  Titanium – slightly influence the corrosion resistance Aluminium is generally used in the form of alloys as pure aluminium is too soft. The alloys contain varying amounts of manganese, iron, and copper giving different grades that have a number code to distinguish them. The first number in the four digit code identifies the main component in the alloy. Some major grades used in packaging include: Al 1100 contains at least 99% aluminium with small amounts of copper, iron and sil icon. Al 2000 series contains additional copper. Al 3000 series contains additional manganese which makes it stiff and corrosion resistant. Grade Al 3003 contains 1.25% manganese and is commonly used for packaging. Al 4000 series contains additional silicon. Al 5000 series contains additional magnesium; 5082 and 5182 are generally used for cans. Anodized aluminum cans Anodization and lacquering of aluminum cans improve corrosion resistance. Anodized can is used for packing sardine in oil, shrimps, crab, fish cake, mussels, green peas, beans, mushroom, condensed milk, meat, etc. Anodized and lacquered can is used in sardines in tomato sauce, spinach, asparagus, meat, etc. Making of Aluminium cans

1. Built-up can It is similar to 3-piece can. The plate is cut and sides are locked, cemented or welded. It is available in different shapes (oval, round, rectangular). It is ideal as presentation pack and is used for cakes, biscuits, tea, sweets, etc. The container is reclosable and reused in household for dry products like milk powder, coffee, cocoa, liquid and semi-liquid foods (cream, syrup). 2. Shallow formed type This type of can is made by blowing of body blank with stroke of press. Such cans have maximum height equal to half the diameter of container. They are round or rectangular in shape. They are used for fish, vegetables, and meat products. The interior is lacquered. 3. Deep drawn Deep drawn can differs from shallow formed can in height-diameter ration. The maximum height is 1.2 times the diameter of the container. The maximum practical diameter is 815mm. They are suitable for condensed milk, flavored cream, non-acid vegetables, meat, soup, etc. 4. Impact-extruded Maximum height is 3 times the diameter. The manufacturing process of aluminium can is similar to the steel plate production process; slabs are hot rolled to a thickness of about 10 mm. This sheet is then coiled and cooled before cold rolling in a mill down to thickness of 0.3-0.5 mm for can making purpose. The rolling stresses the o material and so it must be annealed at temperature of about 400 C. It is then further rolled to give it the ductility required for can manufacture. 19


At gauges less than 0.2 m, it is known as foil. This is produced by a high speed cold reduction process. In this form, it can be used on its own as in chocolate wrappers or in gauges as low as 812 m in a laminate with plastics and paper where it provides an excellent barrier to the passage of gases, water vapour and volatiles. Commercially pure aluminium can be used in these cases as maximum ductility is required. Metallization Metallization is a process whereby a very thin layer (0.02-0.05

m)

of aluminium is applied as a

coating to plastics such as PET, PS and cellophane. Small pinholes will be present through which light can be seen. This process gives an attractive metallic finish and improved barrier properties but not as good as foil. Vapour of aluminium is coated on the plastic under vacuum. Vacuum ensures that the aluminium reaches the material. Styles of metal packages The main metal can is the three piece can, but growing in popularity is the two piece can. Other styles are called “general line” cans. The term “general line” is used for containers that are not hermetically sealed for heat processing. These include the slip lid tin, lever lid can, pourer can, collapsible tubes as well as bulk containers.

a. Three Piece can Three-piece welded food cans are only constructed from steel, as aluminium is not suitable for welding by this particular process. It consists of a body and two ends, one being fitted before filling and one afterwards. 2 The metal sheets that have been pre-lacquered are cut into sheets approximately 1m . The cut sheets are then coated, and printed if necessary, to protect and decorate the surfaces. Areas where the weld will be made on the can body are left without coating or print to ensure the weld is always sound. The coatings and inks are normally dried by passing the sheets through a thermally heated oven where the temperature is in the range 150–205°C. Alternatively, for some non-food contact uses, UV-sensitive materials may be applied. These are cured instantaneously by passing the wet coating/ink under a UV lamp. The sheets are next slit into small individual blanks, one for each can body. Each blank is rolled into a cylinder with the two longitudinal edges overlapping by approximately 0.4mm. The two edges are welded by squeezing them together whilst passing an alternating electric current across the two thicknesses of metal. This heats up and softens the metal sufficiently for a sound joint to be made. If the can is internally coated with lacquer it is generally necessary to apply a repair side stripe lacquer coat to the inside of the weld to ensure coating continuity over the whole can.

. 20


The ends of the body are flanged outwards to receive the end piece. Sometimes to increase the compression strength of the can, it is corrugated or ribbed or beaded. This increases its area resisting the load and therefore its strength. The ends are punched out of a sheet of metal in staggered rows to reduce metal wastage. A lining compound which is a resilient material such as a synthetic rubber dispersed in water or a suitable solvent is injected into the periphery of the end piece. The solvent is evaporated in the curing stage. This fills any small gaps where the body fits into the end, ensuring seal integrity. The end is applied via a double seam. Where the side seem meets the end seam, they are merely overlapped and soldered due to the notches. This is known as the lap section of the seam. Soldering is becoming less popular as it requires a bare area of metal at the side seam, which prevents printing all around with a design. Alternate side seaming method involves using a thermoplastic polyamide adhesive to cement the seam or to use welding. Electrical welding by the soudronic machine uses continuous copper electrodes and an alternating current. Welded seams are stronger than soldered ones and have a neater side seam, especially at the intersection with the end seam. The side seam is unlacquered to facilitate welding and a stripe of lacquer is applied to the finished can. b. Two Piece can This consists of a body and a lid. It has the advantage of having no side or base seam and only one double seam, thereby reducing the risk of leakage and corrosion. The body is formed by impact extrusion of a thick piece of metal, generally aluminium as it is easier to form but low temper tinplate is also used. There are two methods of producing two piece cans, viz. DRD (draw and redraw) and DWI (draw and wall iron), depending on the end use of can.  DRD Process

This produces cans whose wall and base thickness are not much changed from original cup but diameter is successively reduced to achieve the required height. As the diameter is reduced, the can becomes taller and narrower. The area of the blank is the same as the area of the completed container. Pre-lacquered plates can be used in this process.

A slug of metal is impacted with a die to form a cup of the required diameter. During the drawing process, the metal is reformed from flat metal into a three-dimensional can without changing the metal thickness at any point. After this single draw, the can may be already at its finished dimension. However, by passing this cup through a similar process with different tooling, it may be re-drawn into a can of smaller diameter and greater height to make a draw–redraw can (DRD). It is drawn through dies of successively narrower diameters until it has been reduced to the required dimensions. This process may be repeated once more to achieve the maximum height 21


can. At each of these steps, the can base and wall thickness remain effectively unchanged from that of the original flat metal. Following this body-forming operation, necking, flanging and beading operations follow according to the end use and height-to-diameter ratio of the can (as for three-piece welded cans). The top is then trimmed and flanged. The base is profiled for added strength.  DWI Process rd

This produces cans that have very thin walls, about 1/3 of the original thickness, e.g. reduced from 0.3 mm to 0.1-0.14 mm. This becomes too weak for retort applications but is suited to carbonated beverages as the internal pressure ( ̴ 50 psi) provides the strength. Sometimes beads are formed in the body to give added strength. As in the DRD process, a disc of metal is impacted to form a redrawn cup of the required diameter. This cup is supported internally by a punch as it is forced through a series of annular dies. Each die is slightly smaller than the preceding one, thus elongating the wall by a stretching or ironing action. During ironing the wall thickness is reduced and the height correspondingly increased, while the base dimensions remain constant. The bottom is pushed in for added strength and the top is trimmed and flanged.

The appearance of the can is good (streamlined). It has printing and processing advantage. The exterior can be printed after forming and the interior can be sprayed to apply the lacquer before curing. There is no risk of lead contamination (because sealing of side seam is not needed). Two piece cans have a maximum height : diameter ratio of 1 : 1.5 as in the typical sardine can, or 2 : 1 for the beverage container. This is due to the distortion resulting from the forming process. Therefore, the depth is limited to avoid excessive distortion, which can lead to failure. The capital cost for equipment to make the two piece can is high. This method uses less material in the manufacturing of can as compared to the three piece can. For all two-piece cans pinhole and crack detection on finished cans is carried out in a light-testing machine. This measures the amount of light passing across the can wall using high levels of external illumination. One advantage of two-piece cans is that there is only one can end instead of two, i.e. one major critical control hazard point is eliminated. It also offers other advantages such as: - Uniform printing and lacquering - No simming problem on the top - No need of repeated lacquering - More pressure resistance, used for carbonated beverages 22


c. General line cans I.

Lever lid cans: It is usually a round, built-up tin, the ring component being secured to the body and having an orifice into which the inverted, hat-shaped lid is pressed. These are frequently used for powders such as milk, custard, coco, etc. Their main advantage is that they are resealable and are easier to open than three piece cans. It consists of 4 pieces; a body, an end, a drawn seamless ring double seamed to the top of the body, into which a shallow disk shaped seamless lid is pushed.

II. Slip lid cans: The body is normally seamless, and closed by a separate lid which fits over the mouth of the body. It is used for confectionary such as biscuits and toffees, especially for gift market. These can be round or square, with an interlocked side seam and a double seamed base. The lid is solid drawn and fits by friction. It is not airtight and to protect, the product is sealed to the base with a layer of sellotape until it is opened by the consumer. These tins tend to be highly decorated by printing and embossing. III. Oblong pourer tin: These are used for 5 liter containers of oil, etc. These tins are made from soldered or welded oblong bodies with end oblong panels that have rounded corners for ease of double seaming. The handle or pouring neck may be welded onto the top of the container. IV. Collapsible tubes: These are available in either metal or plastic, and are used for paste type products. It is basically a cylindrical container with a shoulder and nozzle at one end formed by impact extrusion of heat treated lubricated slugs of metal, generally aluminium. The process of extrusion leaves the metal stressed in a condition known as work hardened. Unless this is not removed, the tube will not collapse, so it must be annealed at a temperature of 500o 650 C. This also sterilizes the container. A closure is fitted to the nozzle after a screw has been cut into it by a lathe. The interior can be lacquered if required and the exterior can be enameled and printed, then dried. Metal collapsible tubes are better to collapse than plastic ones but as they are rolled up, the printed design disappears or becomes more difficult to read. Plastic tubes are made by blow moulding process and are heat sealed instead of being crimped. V. Bulk containers: Drums of high capacity (5-200 L) are used for the bulk storage of liquids. These are very strong cylindrical containers. The body is formed with a welded side seam; the ends are fitted by double seaming. Beads and hoops are pressed out of the body to increase its strength. Interaction of can and product 1. Fruit containing anthocyanins (blue grapes, cherry, plum) react with tin ions. The pigment is reduced to bleached color. 2. Sulfur containing foods (meat, fish, etc.) react with tin to form stannous sulfide (give purple color). This is referred to as purple colored sulfur staining. Sulfur and ferrous iron of base tin plate react to form ferrous sulfide, resulting in a black spot. 3. Oxalate-rich foods like asparagus, spinach, etc., are high detinners and lead to product discoloration. Lacquered can must be used. 4. Tomato product processed under typical condition and packaged in three piece can with a plain tin plate body and enamel ends over a storage period of 24 month at ambient storage temperature. The following degradative reactions occur: - Colour changes - Flavour changes - Compositional changes 23


The concentration of tin ion increases rapidly during the first 3 months from approximately 20-160 ppm reaching 280 ppm after 24 months. Iron also dissolves, increasing slowly from 8 ppm initially to 10 pp, after 18 months and 14 ppm after 24 months. The flavour score declines due to the increased quantity of dissolved tin and iron. Enamel can is required to increase the shelf life from 24 to 30 months. Also, the color value show a decrease due to an increase in brown pigment but remain acceptable. One of the most important recent developments in 3 piece can has been the introduction of aluminium pigment lacquer to improve the internal appearance of the can and give a greater protection against internal corrosion and staining reaction. Metal closures The use of metal is popular for closures due to its strength and impermeability. A closure must form a good seal with the container. This can be achieved by pressing a resilient material against the sealing surface using an even pressure. The resilient material may be a thick piece of cork or pulpboard sheet, faced with a layer of plastic known as the liner which prevents it contaminating the product. Due to its resilience, when the sealing pressure is applied, the material is compressed and then relaxes forming a tight seal. The sealing surface must be seamless, smooth and free from defects. The headspace must be sufficient to allow the expansion of the product as the temperature increases. In the case of carbonated beverages, the closure must tolerate the internal pressure, which is in the range of 350-1000 kN/sq.m. The force acting in the lid is this pressure multiplied by area. If the area increases, the thickness of the metal closure must also increase to accommodate the additional force. Hence, the narrow necked bottle is popular for carbonated beverages and it is easy to pour from it. Styles of closures

1. Crown cap This is a tinplate closure with a fluted edge, widely used for retail size carbonated beverages. It has a plastic flowed in liner. It is applied by a crimping machine at high speeds. 2. Roll on cap This is a metal screw cap, used for carbonated beverages in high volumes that need to be reclosed. The cap is generally aluminium due to its ductility. It consists of a plain, cylindrical lid, placed over the bottle neck threads by a wheel capper, so that it exactly follows the contours of the thread, giving a good seal. The resilient liner guarantees a gas tight fit. There can be a perforated band along the base of the cap that has to be broken before the cap can be unscrewed. 3. Twist off caps These have lugs, generally 2, 4 or 6, indented into the curled end of the lid skirt to give a screw closure finish. There is a non continuous thread in the neck of the container. The lugs are positioned under the corresponding threads of the container and when the cap is tightened the lugs pull the cap tightly onto it. This style is used for vacuum packed products such as jam. 4. Press twist caps This has a sealing compound injected into the curl which moulds to the contours of the screw finish on a glass jar, giving a tailor-made seal with screw off facility. This style is also used for vacuum packs. 5. Heat seal closures These are based on foil or plastic laminates (which are gaining popularity). 24


Developments in seam making 1. Locked side seam: Edges are locked, molten and solder applied 2. Cemented side seam: Lap joint is bonded by thermoplastic cement (nylon). Heating and rapid cooling bond the joints 3. Welded side seam: Side seams are bonded by welding under application of heat. No cement is used. Corrosion Internal corrosion is the main concern but external corrosion due to the environment is also important. Tinplate is more vulnerable to both types of corrosion whereas aluminium is not affected by atmospheric corrosion. Corrosion is an electrochemical reaction due to the occurrence of areas at different electropotentials, i.e. an anode and a cathode, between which a current will flow due to the transfer of electrons. In anodic polarization the metallic anode, the tin, dissolves exposing the base metal to the product, which will then attack it, weakening it or giving rise to pinholes. If the tin coating has not completely covered the steel base, the tin will act as cathode and the exposed iron in the steel will act as anode, leading to localized corrosion at those areas. This reaction involves hydrogen gas which causes the can to bulge, but is not due to microbial spoilage. Therefore the important factor is the metal which will act as anode. If the tin is attacked, it will dissolve giving rise to off flavours and discoloration of the product, but this is preferable to steel being attacked and perforated. If the oxygen concentration is low, the tin will act as anode and protect the steel. Thus, it is desirable to pack foods under vacuum. The use of lacquers to prevent corrosion is also common. The major factors that affect the internal corrosion are the pH of the product and the presence of certain additives such as emulsifiers, colorants, preservatives, etc. Trace elements such as copper picked up during processing can accelerate the rate. Other factors affecting the rate are plate quality, lacquer integrity and the storage temperature as the rate is faster at higher temperature. If the metal is stressed, it accelerates the rate of corrosion. The hydrogen gas that accumulates at the cathode can reduce the rate by creating a current flowing in the opposite direction, reducing the overall current; the effect known as polarisation.

Atmospheric corrosion affects the exterior of the metal and the resulting rust can be unattractive to the consumer. The principal factors are the RH, chemical composition of the environment as corrosion is catalysed by the presence of SO 2 or nitrogen oxide or by chlorine in the presence of sea water. Resistance is provided by the tin coating and secondary packaging such as shrinkwrap. The processing and handling of can is also important to minimize corrosion. Lubricants can be used to prevent scratch to the cans during handling. Steam used in the retort should not be alkaline and the cooling water should not contain too many salts. When the cans are removed from the retort, they should not be too cool; they should have enough residual heat to enable the surface o water to evaporate off. Typical exit temperature should be in the range of 37-48 C. During distribution, the cans must be protected from rain and condensation. If packed in cardboard boxes or trays, they should have a maximum salt content of 0.05% chloride as NaCl and 0.15% sulphate as sodium sulphate. Lacquer and lacquering Lacquer is called enamel in the US. These are applied to the surface of the metal to prevent corrosion by protecting product internally and externally to prevent oxygen and moisture reaching the metal. Lacquers are basically resins, which may be either natural or synthetic. Synthetic resins 25


are generally used; either water or solvent based, such as oleoresins, epoxides, acrylics, vinyls or formaldehyde. These are usually colourless or gold tinted. White pigments are sometimes used. There are two types of lacquer, viz. acid resistant lacquer and sulphur resistant lacquer. Acid resistant lacquer is ordinary gold coloured enamel, and the cans treated with it are called Renamel cans or AR cans, used for packing of acid fruits with soluble colouring matter, such as raspberry, strawberry, red plum and coloured grapes. Sulphur resistant lacquer is also golden coloured and the cans coated with it are called C-enamel cans or SR cans, used for non-acid products (corn, peas, beans, etc) containing protein rich in sulphur amino acids, which on heat processing release hydrogen sulphide gas. The gas reacts with iron i n the tinplate producing black ferrous sulfide (sulfur staining). For such products, a lacquer containing zinc oxide or carbonate is used to coat the internal can walls. Highly acidic foods should not be packed in SR cans. Functions of lacquer The function of lacquer is to protect the product, not the container. It does this by: - Preventing the metal dissolving in the product, which would produce changes in flavour or chemical reactions - Preventing discoloration of the product, and discoloration of the can interior - Preventing chemical reactions that could lead to corrosion, the evolution of hydrogen gas, or the pinholing of the container.

A lacquer can have a beneficial effect on shelf life. The choice of lacquer depends on the product composition, processing condition and the storage conditions. It is applied to the metal in the sheet form & must be able to withstand the mechanical stresses of the can manufacturing process. It must be easy to apply and to cure. All residual solvents which may taint the food must be driven off in the curing process. To ensure adequate protection, a stripe of lacquer is often applied to the side seam after can fabrication to cover up any cracks that may have occurred in the seaming process. The other desirable properties of lacquer are:  It must be non-toxic and free from odours and flavours  It should not injure the wholesomeness of the contents and should be of attractive appearance  It must be compatible with the product  It should resist stoving temperature 2 Lacquer weight is specified in milligrams per 25 cm . Typical lacquer weight for beer would be 4 2 mg/25 cm . Beer enamel consists of a double vinyl coating to prevent a tinny taste and an appearance of cloudiness in the product. Types of lacquer

1. Natural resins These include oleoresin lacquers. They are composed of natural resin, drying oils, dryer and solvent, etc. Acid resistant (AR) cans are used for fruits containing anthocyanins. - Low cost, general purpose, golden colour coating - Used for beer and fruits and vegetables drinks 2. Synthetic lacquers Synthetic lacquers include the following lacquers: a. Phenolic lacquer They are made of synthetic resin and solvent and are prepared by alkaline condensation of phenol and formaldehyde. - Resistance to acid and sulfide compounds - Used for canning meat, fish, soup, and fruits and vegetables 26


b. Vinyl lacquer They are made by copolymerization of vinyl chloride and vinyl acetate. These are used for beer and soft drinks, which are not processed at high temperatures. - Used as clear external coating - Have good adhesion and flexibility - Resistant to acid and alkali but do not withstand high temperatures. c. Epoxy lacquer They are made from eiphlorohydrin and bisphenol. They have fair resistance to sulfide staining. d. Epoxyphenolic lacquer - Resistant to acid - Good heat resistance and flexibility - Widely used for canning of meat, fish, fruits and vegetables - Suitable for canning of acid food, condensed milk, etc. - Also coated with zinc oxide or metallic aluminium powder to prevent sulphide staining with meat, fish and vegetables. e. Butadiene lacquer - High heat resistance - Prevent discoloration - Used for beer and soft drinks f.

Acrylic lacquer - White in colour - Used both internally and externally for fruit products - More expensive - Can cause flavour problem in some products

g. Epoxy amino lacquer - Good adhesion, heat and abrasion resistance - Expensive - Flexibility and no off flavours - Used for beer, soft drink, dairy product, fish and meat h. Alkyl lacquer - Low cost - Used externally as a varnish over ink - Not used internally due to off flavour problem. Summary Metal containers are the most frequently used package for canning foods. While they are produced in various shapes and forma, the conventional round represents 90% of the total metal cans. The metal or tin cans have the following desirable qualities:  They are sufficiently robust to enable them high rate of automatic production (up to 1000 cans/min)  Their high thermal conductivity aids the heat penetration during thermal processing  They can withstand a wide range of temperature and pressure changes  Once cans are hermetically sealed, they are impermeable to dust, gases, liquids and microorganisms, and are opaque to light and ionizing radiation, and  The used containers are recyclable. 27


�� Introduction Plastics form a very large, comprehensive family with a wide range of properties that can meet almost every requirement of the packaging industry. Plastics, being synthetic, can be tailormade to meet specific requirement or achieve a combination of properties. Plastics are used as both flexible films, such as pouches, bags, laminates, etc and as rigid containers, such as bottles, trays, etc. The plastic materials are the same but the thickness is different. Most plastic materials are derived from the distillation of oil into long chained hydrocarbons. These are broken down by cracking into short chained hydrocarbons such as ethane/ethylene, propane, etc. known as monomers. Polymerisation of these monomers converts into long chain polymers, i.e. polyethylene, polypropylene, etc. copolymers are formed when two monomers are combined into a single polymer chain in unequal proportion. It three monomers are combined, it is known as terapolymer. The advantage of copolymerization is that it creates a new material with modified properties which were not available from the either of the monomer. The following table shows some of the plastics manufactured from petroleum.

The British Standards Institution has defined plastics as “a wide group of solid composite materials which are largely organic, usually based on synthetic resins or upon modified polymers of natural origin and possessing appreciable mechanical strength. At a suitable stage in their manufacture most plastics can be cast, moulded or polymerized directly to shape.” Plastics can be divided into two main subgroups: thermoplastics and thermosets. Thermoplastics are those materials which can be heated and cooled repeatedly without appreciable loss of mechanical and physical properties. There is no cross linking and adjacent molecules are free to flow. For e.g. HDPE, LDPE, PVC, PVDC, EVOH, Nylon, Polyester, etc. On the other hand, thermosets when heated for the first time will change their shape permanently. If heat is reapplied, they will begin to decompose due to the cross linking of adjacent molecules. For e.g. Phenol formaldehyde, Urea, etc. 28


Advantages of Plastics 1. Light weight, less bulky and cheap with respect to metal and glass 2. Versatile – easy to mould into a wide range and style packages by different processes 3. Flexible with properties which can be tailored to suit the product requirements 4. Recyclable – economic 5. Good appearance and available in a variety of colours 6. Printable and heat sealable 7. Pilfer-proof, tamper proof, break resistant, corrosion resistant and leak proof 8. Quieter in use than metal or glass – noiseless unlike metals and glass 9. Excellent barriers properties to moisture, odour, oxygen and other gases so that they can maintain the desired shelf life for various products 10. Resistant to most chemicals, non-toxic in nature and absolutely safe to use even in direct contact with food products, medicines, etc 11. Safe in use as they do not break easily and the broken pieces are not harmful as those of glass and metal 12. Do not promote bacterial growth and can be sterilized by all conventional methods and hence provide wide applications in food, medical and chemical packaging 13. Single serve packs for food items such as ketchups, condiments, etc and small unit packs such as sachets can be made available at low costs 14. Do not pose any major disposal problems or environmental hazards, since almost all of plastics can be recycled for reuse. Disadvantages of Plastics 1. Flammable – as they are derived from petrochemicals 2. Permeable to the passage of gases, vapours, volatiles and some solvents to varying degrees 3. Can be degraded by UV light 4. Non-biodegradable 5. Some chemicals do attack particular plastics 6. Some plastics may absorb some food constituents, such as oils and fats 7. Abrasion resistance is not always adequate 8. Some plastics are not inert – PVC monomer may transfer to food which is carcinogenic

Gases such as oxygen, carbon dioxide and nitrogen together with water vapour and organic solvents permeate through plastics. The rate of permeation depends on:  type of plastic  thickness and surface area  method of processing  concentration or partial pressure of the permeate molecule  storage temperature Selection Criteria Plastics have different properties and to select the best material f or a required pack, it is necessary to consider: a. The requirements of the product b. The requirements of the market c. The requirements of the packing machine

The product can deteriorate in many ways. Dry products such as biscuits, crisps and soup will be damaged by moisture; therefore they require a moisture barrier, i.e. the use of material having low 29


WVTR. A good seal is also essential to ensure that the moisture remains outside the pack. Moist foods such as cakes must be prevented from drying out, without there being too much moisture retained in the pack that would lead to mold growth. Breathing foods such as vegetables and fruits continue to respire, producing carbon dioxide, which must be allowed to escape from the pack or all the oxygen will be consumed and anaerobic micro-organisms will grow. If there is too much oxygen inside the pack, the product will dry out, so an impervious film with ventilation holes is needed. Oxygen sensitive foods, such as high fat content food, must be protected from oxidative rancidity. As the rate is accelerated by light, it is necessary to use and opaque material. Liquids need a leakproof pack, resistant to chemical attack or penetration by the product. Some products need to be stored at low temperature or frozen whereas other products are heated or cooked in the pack. So, they must be packed in a material that will perform satisfactorily at the required temperature. Market requirements include the ease of handling and protection from the storage and distribution hazards. Display requirements such as visibility and stackability must be considered. The pack must be convenient such as easy to open features, reclosability, convenient unit/portion sizes, etc. The size of the pack and its surface area affects its permeability to gases and water vapour. It also affects the rigidity and strength. Bigger packs require thicker materials, strong enough to hold the weight of the product. If the plastic is to be printed, it must be abrasion resistant or scuff proof. This can be achieved by reverse printing, i.e. printing on the inner surface that will not be exposed to the abrasion. Economy is also a relevant factor. Packaging may make product unaffordable, or uncompetitive with similar products. Machine factors are very relevant to the selection of plastic materials as t hey are usually used with high speed machines. The properties important are elasticity, dead fold properties, tear strength, slip, friction, and melt strength. The material chosen must be suitable for the equipment on which it will be used. It must cut properly, seal well and run smoothly or else there will be stoppages and wastage, or the risk of product failing in the shops due to faulty packaging. Use of plastics in food packaging Plastics are used as containers, container components and flexible packaging. In usage, by weight, they are the second most widely used type of packaging and first in terms of value. Examples are as follows:  rigid plastic containers such as bottles, jars, pots, tubs and trays  flexible plastic films in the form of bags, sachets, pouches and heat-sealable flexible lidding materials  plastics combined with paperboard in liquid packaging cartons  expanded or foamed plastic for uses where some form of insulation, rigidity and the ability to withstand compression is required  plastic lids and caps and the wadding used in such closures  diaphragms on plastic and glass jars to provide product protection and tamper evidence  plastic bands to provide external tamper evidence  pouring and dispensing devices  to collate and group individual packs in multipacks, e.g. Hi-cone rings for cans of beer, trays for jars of sugar preserves etc  plastic films used in cling, stretch and shrink wrapping  films used as labels for bottles and jars, as flat glued labels or heat shrinkable sleeves  components of coatings, adhesives and inks 30


Types of plastics used in food packaging The following are the types of plastics used in food-packaging 1. Polyethylene (PE) 2. Polypropylene (PP) 3. Ethylene vinyl acetate (EVA) 4. Ethylene vinyl alcohol (EVAL/EVOH) 5. Polyvinyl chloride (PVC) 6. Polyvinylidene chloride (PVdC) 7. Ionomers 8. Polystyrene (PS) 9. Polyesters (PET, PEN, PC) (Note: PET is referred to as PETE in some markets) 10. Polyamides (PA) – Nylon 11. Polycarbonate (PC) 12. Styrene butadiene (SB) 13. Polymethyl pentene (TPX) 14. High nitrile polymers (HNP) 15. Cellulose-based materials 16. Polyvinyl acetate (PVA). Thermoplastics in Packaging

Polyethylene/Polyethene (PE) Polyethylene (PE), commonly called polythene, is structurally the simplest plastic and is made in one of two ways. Ethylene is polymerised at high temperature and pressure, in the presence of a little oxygen & the polymer converted into a film by extrusion. Alternatively, lower temperatures and pressures may be used to produce the polymer if certain alkyl metals are used as catalysts.

Types and density  Ultra low density polyethylene (ULDPE): 0.880-0.890  Linear low density polyethylene (LLDPE): 0.912  Low density polyethylene (LDPE): 0.910-0.939  High density polyethylene (HDPE): 0.940-0.965 Generally, PE is referred to as LDPE and HDPE. LDPE is formed at high pressures (1000–3000 atm). This results in long branched chains, weakly linked to each other by van der Waals forces (but strong overall force due to length). The branching is random, and so LDPE is an atactic polymer. Thus, neighboring chains can slip past each other, allowing the material to bend easily (flexible). As a result, the printability of LDPE is poor. However, many plastics with poor printability can be made printable by corona treatment, in which an ionic discharge is used to sensitize one side of the plastic. HDPE is produced at low temperatures and pressures of about 10 atm. This gives rise to an ordered molecular structure, which is called an isotactic polymer. The Ziegler process is used, employing a catalyst. HDPE is stiffer, harder, less flexible, and waxy. Higher temperatures are required to produce thermoplasticity (melting point, 134°C). HDPE is used for making containers, 31


e.g., crates, bottles, bags, tubs, plastic knives and forks, etc. It can be steam sterilized, whereas LDPE cannot. HDPE bottles are opaque and can be used to contain detergent and milk. HDPE resists fats and oils better than LDPE. However, it does not seal easily. They are waterproof and chemically resistant and are used instead of paper sacks. LLDPE is produced at lower pressure in a gas phase polymerisation. It is stiffer, due to its more linear structure and has better stress crack resistance than LDPE. It also has a higher surface gloss. It is stronger and as a film has a better puncture resistance and tear strength. It has a higher o softening point (118 C) and has better performance at both high and low temperature than LDPE. The film is available in low (LDPE), medium (MDPE) and high (HDPE) density grades. The lower density grades are most widely used in food packaging. The main functional properties of LDPE are its glossiness, strength, low permeability to water vapour and it forms a very strong heat seal. It is not a good barrier to gases, oils or volatiles. It is used on its own in the form of pouches, bags and sacks. It is also used for coating papers, boards and plain regenerated cellulose and as a component in laminates. It is used for wrapping fruits and vegetables because of high GTR and low WVTR, and also for frozen foods because it toughens at low temperature. It is less expensive than most films and is therefore widely used. HDPE has a higher tensile strength and stiffness than LDPE. It is used to prepare bottles, plates, etc because it is less vulnerable to stress cracking. Its permeability to gases is lower and it can withstand higher temperatures. It is used for foods which are heated in the package, so called ‘boil in the bag’ items. LLDPE, because of its better elongation and tensile strength is used to make heavy duty sacks. It is used for stretch wrapping as its elongation is up to 600%, but it is not good for shrink wrapping. Polyethylenes are widely accepted for the packaging of food products as well as chemical owing to their inert character, compatibility and safety in contact with most products as well as resistance to almost all commercially used chemicals, except oxidizing acids, such as conc. nitric or sulphuric acid, free halogens such as chlorine, and certain ketones. They are easy to process, economically priced and are used on their own or in combination with other polymers to meet the most exacting demands. They are very resistant to water and water vapour; the higher the density, the greater the resistance, i.e. the lower the value of WVTR, but the GTR is high. They are used in the form of single-layer or multilayer films, laminates, blow-moulded containers, sintered containers, tubes, moulded and extruded laminates, etc. Polypropylene (PP) This monomer has the formula CH 2CH–CH3. PP is the lowest density polymer (0.90 gm/cc) and extremely versatile because of its excellent processability, mechanical and physical properties and high heat distortion resistance.

Its structure is the same as the polyethylenes but one hydrogen molecule is replaced by a methyl (CH3) group. If all the methyl groups are arranged on one side of the polymer, it is known as isotactic material. If they are randomly arranged, it prevents the chains coming very close together and the result is a sticky material known as atactic. Catalysts are used in the polymerisation to encourage the formation of isotactic polypropylene. 32


PP is often used in oriented or biaxially oriented form, i.e. OPP and BOPP. Non oriented PP is also known as cast PP. Orientation is a process by which the material is stretched to improve its characteristics. By stretching, the molecules are straightened out giving a more rigid structure and stronger material. This improves the barrier properties, low temperature performance, impact strength and flex crack resistances. OPP has better mechanical properties than cast PP, particularly at low temperature, and is used in thinner gauges. It is a good barrier to water vapour but not gases. It is often coated with PP or PVdC/PVC copolymer to improve its barrier properties and to make it heat-sealable. It is normally heat-shrinkable. It is used in coated or laminated form to package a wide range of food products, including biscuits, cheese, meat and coffee. It is stable at relatively high temperature and is used for in-package heat processing. A white opaque form of OPP, known as pearlised film, is also available. Copolymers of PP and PE are also available. Their functional properties tend to be in a range between PP and HDPE. Properties  Properties similar to LLDPE and HDPE, but harder, stiffer, tougher and glossier than both  Stronger than PE, so can be used in thinner gauges  Chemically inert and resistant to most commonly found chemicals, both organic and inorganic, except chlorinated hydrocarbons; CCl 4, CHCl3, and strong oxidizing agents  PP is a clear glossy film with a high strength and has less waxy feel  Excellent grease resistance, puncture as well as flex crack resistance  Good resistance to fatigue if repeatedly flexed  Higher melting point than PE, so easily stand steam sterilization  Low density (0.89-0.905 gm/cc) than PE, so higher yield  Better barrier properties between LDPE & HDPE, and can be increased by orientation process  Excellent moisture and average gas-barrier properties, and not affected by changes in humidity  High clarity and gloss because of high crystallinity o  Heat resistance, softening point >150 C and suitable for hot filling applications  It can be printed on and is ideal for reverse or surface printing  Low heat sealable but cast PP has excellent heat sealability  Low impact strength at low temperature but can be improved by copolymerization with ethylene to butylenes Applications  PP is used for injection-molded containers and blister packs, laminations, carton overwraps, snack food bags, and confectionery bags  OPP is suitable for use in frozen storage  Cast PP is used for bags, candy twist-wraps, vegetable and fruit packing. It can be injection moulded into crates, hinged lids or thin wall rigid container. Due to its resilience, it is used as a linear, coating the inside of the bottle caps  BOPP and OPP are coated to make them heat sealable and are used in biscuits, bread and confectionary packaging. It can also be cold seal coated, which can be used for chocolate bar pack and is easy to peel. Elongation of up to 600% makes it suitable for stretch-wrapping. It has good resistance to creep under load so is suitable for use in crates and boxes.

Ethylene vinyl acetate (EVA) EVA is a copolymer of ethylene with vinyl acetate and is widely used. The properties of the blend depend on the proportion of the vinyl acetate component. Generally, as the VA component increases, sealing temperature decreases and impact strength, low temperature flexibility, stress 33


resistance and clarity increase. At a 4% level, it improves heat sealability, at 8% it increases toughness and elasticity, along with improved heat sealability, and at higher levels, the resultant film has good stretch wrapping properties. 25-28% acts like a flexible polyvinylchloride with the advantage of not containing plasticizers that could migrate into the food. A rubber like quality is achieved by adding 28-50% vinyl acetate and this is used to make bottle cap liners. EVA with PVdC is a tough high-barrier film which is used in vacuum packing large meat cuts and with metalized PET for bag-in-box liners for wine. Compared to LDPE, they have higher impact strength and elasticity, higher permeability to water vapour and gases and are heat-sealable over a wider temperature range. It functions better at lower temperatures as well as seals at a lower temperature. It is more permeable to gases and water vapour. EVA has good flexing properties so it is useful for hinged lids. Slip is low so anti blocking additives are used. EVA itself has very good stretch and cling characteristics and can be used, as an alternative to PVC for cling-wrap applications. EVA is generally used for stretch wrap, closures, liners for bag-in-box packages and meat wrap. Modified EVAs are available for use as peelable coatings on lidding materials such as aluminium foil, OPP, OPET and paper. They enable heat sealing, resulting in controllable heat seal strength for easy, clean peeling. These coatings will seal to both flexible and rigid PE, PP, PET, PS and PVC containers. Modified EVAs are also used to create strong interlayer tie bonding between dissimilar materials, e.g. between PET and paper, LDPE and EVOH. EVA is also a major component of hot melt adhesives, frequently used in packaging machinery to erect and close packs, e.g. folding cartons and corrugated packaging. Ethylene vinyl alcohol (EVAL / EVOH) EVOH is a copolymer of ethylene and vinyl alcohol. The typical composition of this copolymer is 66-82% by weight of vinyl alcohol. The melting point of EVOH is 185°C.

Due to its high gloss and low haze, it has excellent clarity. It has outstanding barrier properties, i.e. it has very low values of GTR, WVTR, and is a barrier to the transfer of odours and flavours. The barrier is better at lower levels of ethylene in the copolymer. This film has high oxygenbarrier properties, but hydroxyl groups make it hydrophilic, which increases its permeability. Thus, it must be sandwiched between materials with good water-barrier properties, such as PP of LDPE, to be effective. However, its oxygen-barrier properties make it a highly desirable film, competing with PVDC for this role. EVOH is more expensive than PVDC, but it is easier to process and is recyclable. It is related to polyvinyl alcohol (PVOH), which is a water-soluble synthetic polymer with excellent film-forming, emulsifying and adhesive properties. It is a high-barrier material with respect to oil, grease, organic solvents and oxygen. It is moisture sensitive and, in film form, is water soluble. At high RH, the barrier properties are reduced. It is resistant to oils and organic solvents but is affected by alcohols and strong acids. Due to the presence of alcohol molecule, its surface is polar and therefore can be printed without pretreatment. It is an expensive material, so it is generally used as a thin layer in a laminate or in a coextrusion. 34


Polyvinyl chloride (PVC) The term vinyl means that a halogen has been substituted for a hydrogen atom. PVC is made by chlorination of acetylene or ethylene forming the vinyl chloride monomer (VCM), followed by polymerisation under pressure in the presence of a catalyst. It is available in two forms, a rigid one known as UPVC and a flexible form known as PPVC, i.e. unplasticised and plasticised PVC.

It is a clear, transparent film which on its own is brittle. The addition of plasticizers and stabilizers to the polymer are necessary to give it flexibility and reduce its processing temperature. The plasticizers used are generally high boiling point organic chemical in the liquid form or dioctyl phosphates. These work by reducing the interchain forces of attraction in the polymer, acting as a lubricant. The plasticizer affects the strength, density, flexibility and elongation of material. It makes it easier to mould the plastic into various shapes when the heat is applied. Properties PVC has low crystallinity (so has good transparency when pure), but higher interchain bonding than PE due to the Cl halogen, so is harder & stiffer. For this reason, plasticizers are added during manufacture. PVC has good feel and printability. It is highly inert. It is glossy and resistant to moisture, fats, and gases. UPVC or lightly plasticised grades have good rigidity and thermoformability, giving good mould detail. Density is higher than that of polyolefins at 1.35o 1.45 gm/cc. It has a softening point of less than 100 C. At low temperatures it has poor impact resistance, which can be improved by orientation. It has good barrier properties, which includes low GTR. WVTR is higher than for the polyolefins. Odours and flavours are also well retained and it is an excellent barrier to the transfer of oils and alcohols. It has good mechanical properties. Its permeability to water vapour, gases and volatiles depends on the type and amount of plasticizers added to the polymer. These properties decrease with increasing plasticiser content. It is resistant to acids, alkalis and many solvents except esters, ketones, aromatic hydrocarbons and aldehydes. It heat shrinks after stretching and can be thermoformed. It is a cheap plastic but there is a chance of migration of plasticizers from the plastic into the food. It is essential that PVC film used in food packaging contains only permitted additi ves to avoid any hazard to the consumer. Density of PPVC is in the range of 1.2-1.7 gm/cc. It has an elongation value of 200-450 whereas the rigid form is only 2-40. It has better impact strength but lower tensile strength. Applications PVC is used in the biaxial-stressed form, e.g., for shrink wrapping of cheese and meat. It is also used for thermoformed containers, e.g., for chocolates as well as for plastic pipes and to ys. UPVC is moulded into trays, bottles and other containers where it provides a better barrier and clarity than PE. PPVC is generally used in film form. It has a higher WVTR and is used to pack fruits & vegetables as it eliminates the risk of condensation by allowing the moisture and respiration gases to escape. It is suitable for stretch-wrapping and shrink-wrapping, where it has better transparency than PE.

Polyvinylidene chloride (PVdC) Polyvinylidene chloride (PVdC) is made by further chlorination of vinyl chloride in the presence of a catalyst, followed by polymerisation. It is also known by its trade name as Saran. 35


Properties It is a very transparent, glossy and tough material, with good impact strength except at low temperatures, and good abrasion resistance. It has excellent barrier properties, with very low GTR (especially to O2), WVTR, and it also retains flavours and odours. Resistance to oils and waxes, alcohols, strong acids and alkalis is good but it is attacked by ketones and ethers. It is difficult to cut as it lacks stiffness, so is hard to machine by itself and is too expensive for use as a pure monofilm. It has high chemical stability and is hydrophobic. It has a sharp melting point which can lead to problems in heat sealing so it is often used with PE which provides a heat seal layer. PVdC cannot be reprocessed because it degrades (melting point, 162°C). This makes coextrusion lamination difficult as well, although it can still be easily used in coating from solution. When used in coextrusion, it must be copolymerized first (for e.g. with vinyl chloride) to give better temperature stability. Applications It is used in flexible packaging in several ways as monolayer films, coextrusions and coatings. Generally, it is used as a thin film or coating as it is expensive. Due to its elasticity, it is used for shrink and stretch wrapping, and as a twist wrap for candy as it has excellent cling properties. Its main use is as a barrier layer in a laminate structure, applied as a coating. As a result of the high gas and odour barrier, it is used to protect flavour and aroma sensitive foods from both loss of flavour and ingress of volatile contaminants. PVdC is a widely used component in the packaging of cured meats, cheese, snack foods, tea, coffee and confectionery. It is used in hot filling, retorting, low-temperature storage and MAP as well as ambient filling and distribution in a wide range of pack shapes.

Comparison of barrier materials: PVdC and EVOH PVdC is best for where a water vapour barrier is required. It is heat sealable and a good barrier to gases, vapours and odours. EVOH is moisture sensitive so it is best used for dry products. It is an excellent barrier to gases and odours, and in dry condition it is ten times better than PVdC. It also has good chemical resistances and transparency. The barrier improves as the vinyl alcohol content in the copolymer increases. It is often used in coextrusions in very small amounts. Ionomers Ionomers are basically the copolymers of ethylene and methacrylic acid, with some of the acid groups present in the form of a metal salt. The polymerisation process is similar to that of LDPE. It is also known by its trade name as Surlyn. In Ionomers, there are ionic forces between the polymer chains, in addition to the normal covalent (chemical) bonds between the separate atoms in each chain. These ionic bonds strengthen and stiffen the polymer without reducing its melt processability. The ionic forces also make it much clearer than LDPE, by eliminating the traces of visible spherulites that make LDPE hazy. It has very high puncture and abrasion resistance. It has high melt strength and gives more uniform thermoforming, i.e. it has stronger corners. Its main advantage is its ability to seal through the contaminated sealing surfaces. This is very useful in packing of messy 36


products, which spill onto the sealing area of the pack. This material will seal at a lower temperature than LDPE, i.e. the packing machine can work faster. GTR is similar but WVTR is higher. Chemical resistance to alkalis is good but it is slowly attacked by acids. At room temperature, it has a greater resistance to oils and grease; at higher temperature its performance is equal to LDPE. They are most widely used as components in laminates with other films, such as PC or PET, for packaging cheese and meat products. It is used to pack dry products that have sharp edges because of its puncture resistance. It is also used for skin packages due to its clarity and for meat packaging as it can seal through contamination such as grease or blood. Polystyrene (PS) Polystyrene (PS) is produced by reacting ethylene with benzene to form ethyl benzene. This is dehydrogenated to give styrene which is polymerised at a relatively low temperature, in the presence of catalysts, to form polystyrene. Its structure thus has a benzene ring attached to each alternate carbon.

PS is an odourless, tasteless, colourless, very transparent and glossy material. It is hard, rigid and o brittle with poor impact strength. Due to a low softening point of 78-95 C, it is not suitable for hot filling applications. Density ranges from 1.04 – 1.07 gm/cc. There is a problem of static in the build up that makes it attract dust and cling to itself. It is easily scratched so the packing machines must be smooth to prevent the damage to the surface. This is a stiff material so it handles well on automatic equipment. It is a poor barrier to gas, moisture, odours and flavours. Chemical resistance is good for acids and alkalis; but it is soluble in toluene, ketones, such as acetone, chlorinated hydrocarbons like carbon tetrachloride, higher alcohols and esters. PS is widely used in the form of thermoformed semirigid containers and can be easily moulded into jars, trays, containers and screw on caps, used for dairy products, salads, etc. Due to its high transmission rates, it is suitable for fruits, vegetables and baked goods. Oriented PS (OPS) is stronger and tougher and is used as an overwrap for meat and vegetables. Copolymers of PS using acrylic and rubber compounds, e.g. butadiene are called High Impact PS (HIPS). These have better impact strength and flexibility, but the plastic is translucent as some clarity is lost. It is used for pots and tubs, especially for low temperature applications such as ice cream. Expanded PS (EPS) is produced by expanding the volume of the PS with pentane gas to produce a high volume, low weight material with excellent insulating and cushioning properties. It is used to produce cups for hot or cold beverages, shock absorbing trays for fruit, eggs, meat, etc. and cushioning to protect sensitive equipments such as television in transit. PS film is produced by extrusion. It is stiff and brittle with a clear sparkling appearance. In this form it is not useful as a food packaging film. Biaxially oriented polystyrene (BOPS) is less brittle and has an increased tensile strength, compared to the non-oriented film. BOPS has a relatively high permeability to vapours and gases and is greaseproof. It shrinks on heating and may be heat sealed by impulse sealers. For this, it is coextruded with EVOH or PVdC/PVC copolymer. 37


Polyethylene Terephthalate – Polyesters - PET or PETE Polyesters are condensation polymers formed from ester monomers, resulting from the reaction of a carboxylic acid with an alcohol. There are many different types of polyester, depending on the monomers used. When terephthalic acid reacts with ethylene glycol and polymerises, the result is polyethylene Terephthalate (PET). PET can be made into film by blowing or casting. It can be blow moulded, injection moulded, foamed, extrusion coated on paperboard and extruded as sheet for thermoforming. PET can be made into a biaxially oriented range of clear polyester films produced on essentially the same type of extrusion and Stenter-orienting equipment as OPP. Film thicknesses range from thinner than 12µm for most polyester films to around 200 µm for laminated composites. No processing additives are used in the manufacture of PET film. Properties It has good sparkle and clarity. Impact and tensile strength and puncture resistance are good. Due o to its high softening point of 245-270 C, it performs well over a wide range of temperature o ranging from -60 to +150 C, so it can be used for boil in the bag. It is not good for heat sealing and if this is required, it is usually coated with a layer of polyethylene. Density ranges from 1.38 – 1.395 gm/cc. If molten PET degrades, acetaldehyde can be formed. This compound occurs naturally in citrus fruits. Even if the quantity is not enough to risk toxicity, it can lead to taint in products such as coca-cola. It provides a good barrier to gases and odours, and has a moderate WVTR, which is reduced to zero at freezing temperatures. It has good resistance to grease and oil, as it is chemically resistant to weak acids, alkalis, alcohols, hydrocarbons, ketones and esters. It is attacked by strong acids, alkalis and phenols. Applications As it has high strength and can withstand the carbonation pressure, it is used in bottle making. However, the GTR may not be low enough in some bottle designs to prevent the carbonation gases escaping. It is often used in laminates with PVdC and PE for coffee, meat, etc. in gauges as low as 12 m. Because of the wide temperature range, it can be used for boil in the bag,

microwave and ovenable applications. Polyamides (PA) - Nylon Polyamides (PA) are commonly known as nylon. These are made from condensation of a diacid (e.g., adipic acid) and a diamine (e.g., hexamethylene diamine). These are distinguished by numbering them according to the number of carbon atoms in the parent. Hence, Nylon 6, 6 is produced from adipic acid and hexamethylene diamine. Nylon 6, 10 is made from hexamethylenediamine and sebacic acid. They can also be produced from amino acids in which case the number is that of the number of carbon atoms in the parent, i.e. Nylon 6 is made from caprolactam whereas Nylon 11 is made from aminoudecanoic acid. The most common grades of nylon used in packaging are nylon 6, 6; 6, 10 and 6, 11. Properties Polyamides have high crystallinity, strength, impact strength puncture and stress-crack resistance, flexibility, and melting and softening points. It is slightly hygroscopic and is thus not a good moisture barrier but it is very good gas barrier. Nylon is a tough material, very resistant to abrasion with a high tensile strength. It can be biaxially oriented to give it improved strength and o o toughness. It has high melting point, 185 C for Nylon 11 and 265 C for Nylon 6, 6. Chemically, it is resistant to most inorganic solvents but it is attacked by oxidizing agents and concentrated mineral acids. It is unaffected by alcohols, ethers, benzene, acetone, carbon tetrachloride and 38


many mineral oils. It is resistant to grease and oils. It is an excellent material for printing and thermoforming. They are stable over a very wide temperature range. They can be heat-sealed but o at a high temperature, 240 C. They do absorb moisture and their dimensions can change by 1–2% as a result. Nylon films may be combined with other materials, by coating, coextrusion or lamination, in order to facilitate heat-sealing and/or improve their mechanical and barrier properties. Polyethylene, ionomers, EVA and EAA are among such other materials. Their functional properties may be further modified by vacuum-metalizing. Applications Polyamides are used for boil-in-the-bag-type products, frozen foods, fish, meat, vegetables, and processed meat and cheese, always in lamination for vacuum packaging. It is also used in coextrusion as barrier layer.

Polycarbonate (PC) These are formed from condensation of carbonic acid in the presence of aliphatic or aromatic dihydroxy compounds. They are amorphous in nature and process by all conventional processing techniques. Polycarbonates are tough, stiff, hard, durable and transparent (high clarity), with high softening points, and therefore can be cooked in oven or sterilized. They are mechanically strong and grease-resistant. They have relatively high permeability to vapours and gases and cost three times o o as much as PP, and are stable over a wide temperature range, from –70 C to 130 C. It has excellent dimensional stability, rigidity and impact resistance at high temperature. It makes an excellent structural layer in co-extruded or laminated packaging for hot fill, retortable pouch, and frozen food products. PC can be sterilized by γ- and electrobeam radiation with good stability. They are not widely used for food packaging but could be used for ‘boil in the bag’ packages, retortable pouches and frozen foods. They are also used for plastic tableware and fruit juice containers. They are mainly used as a glass replacement in processing equipment and for glazing applications. Their use in packaging is mainly for large, returnable/refillable 3–6 litre water bottles. They are used for sterilisable baby feeding bottles and as a replacement in food service. They have been used for returnable milk bottles, ovenable trays for frozen food and if coextruded with nylon could be used for carbonated drinks. Styrene butadiene (SB) SB copolymer is also a packaging polymer. It is tough and transparent, with a high-gloss surface finish. Blown film has high permeability to water vapour and gases. It is heat sealable to a variety of surfaces. The film has good crease retention, making it suitable for twist wrapping sugar confectionery. Injection-moulded containers with an integral locking closure have a flexible hinge, similar in this respect to PP. It is known as K resin in the USA. It is used to pack fresh produce. It can also be used to make thermoformable sheet, injection and blow moulded bottles and other containers with high impact resistance and glass-like clarity. The relatively low density gives SBC a 20–30% yield advantage over other, non-styrenic, clear resins. Acrylonitrile butadiene styrene (ABS) ABS is a copolymer of acrylonitrile, butadiene and styrene, with a wide range of useful properties which can be varied by altering the proportions of the three monomer components. It is a tough material with good impact and tensile strength and good flexing properties. ABS is either translucent or opaque. It is thermoformable and can be moulded. A major use is in large shipping and storage containers (tote boxes), and it has been used for thin-walled margarine tubs and lids. 39


Polymethyl pentene (TPX) TPX is the trade name for methyl pentene copolymer. It is based on 4-methyl-1-ene and possesses the lowest density of commercially available packaging plastics (0.83 cm3). It is a clear, heatresistant plastic which can be used in applications up to 200°C. The crystalline melting point is 40°C (464°F). TPX offers good chemical resistance, excellent transparency and gloss. It can be extruded and injection moulded. The main food packaging use is as an extrusion coating onto paperboard for use in baking applications in the form of cartons and trays for bread, cakes and other cook-in-pack foods. This packaging is dual ovenable, i.e. food packed in this way may be heated in microwave and radiation ovens. The surface of this plastic gives superior product release compared with aluminium and PET surfaces. TPX coated trays must be formed by the use of interlocking corners as they cannot be erected by heat sealing. High nitrile polymers (HNP) HNPs are copolymers of acrylonitrile. They are used in the manufacture of other plastics such as ABS and SAN. The nitrile component contributes very good gas and odour barrier properties to the common gases, together with good chemical resistance. HNPs therefore offer very good flavour and aroma protection. Polyvinyl acetate (PVA) PVA is a polymer of vinyl acetate which forms a highly amorphous material with good adhesive properties in terms of open time, tack and dry bond strength. The main use of PVA in food packaging is as an adhesive dispersion in water. PVA adhesives are used to seal the side seams of folding cartons and corrugated fiberboard cases and to laminate paper to aluminium foil. Cellulose-based materials Plain cellulose is a glossy transparent film which is odourless, tasteless and biodegradable (within approximately 100 days). It is tough and puncture resistant, although it tears easily. However, it is not heat sealable and the dimensions and permeability of the film vary with changes in humidity. It is used for foods that do not require a complete moisture or gas barrier. The original packaging film was regenerated cellulose film (RCF). Pure cellulose fibre derived from wood is dissolved and then regenerated by extrusion through a slot, casting onto a drum and following acid treatment, is wound up as film. It is commonly known as Cellophane, though this is in fact a trade name. Regenerated cellulose varies from other plastics in that it is derived not from petrochemicals but from plants, generally woodpulp or cotton liners, thus are biodegradable. Its main advantage is that it can be tailormade to meet product requirements with a variety of coatings and barrier properties. Properties It has excellent clarity, glossiness, sparkle and transparency. It can be printed. Density is in the range of 1.27-1.34 gm/cc. It has good tensile and impact strength as is stiffness which is needed for high speed machine applications. It tears easily and is suited for easy opening applications. It has low slip and dead folding characteristics. It remains unaffected by static build up, i.e. suitable for shrink wrapping, and is also insoluble in organic solvents. It has low GTR and high WVTR. It has excellent barrier to gases and odours, oils and grease. However, it is affected by humidity, being slightly hygroscopic. As the RH decreases, it becomes brittle and shrinks. It is flammable and is not resistant to strong acid and alkali. It can be coated with PVdC to improve its moisture barrier and can be made heat sealable if required. It doesn’t have same tensile strength as plastic films. Cellulose is widely coated with other plastics, some of which are: 40


 Nitrocellulose cellophane – coated with nitrocellulose to i ncrease moisture barrier  PVC coated cellophane – for excellent machineability  PVC-PVdC coated cellophane – superior product protection in terms of aroma, flavour lock

and decreased oxygen permeability  LDPE coated cellophane – to increase heat sealable properties, has low GTR and high WVTR, and used for fresh meat There are various grades of cellophane. In order to identify the various grades, a coding system is used, which is as follows: A - Anchored (lacquer coating), gives better moisture resistance /A - Copolymer coated from dispersion B - Opaque C - Colored D - Coated one side only, moisture proof on one side onl y F – Flexible grade for twist wrapping applications M – Moisture proof on both sides L – Less moisture proof than M P - Plain (non-moistureproof), uncoated material Q – Semi-moistureproof QM – Not as moisture proof as M S - Heat sealable /S - Copolymer coated T - Transparent U - For adhesive tape manufacture X – Copolymer (PVdC) coated on one side XX - Copolymer coated on both sides MXXT/A – Double coated with PVdC applied as an aqueous dispersion MXXT/S – Same but applied by a solvent dispersion The code is preceded by a number which corresponds to the weight of ten square meters of the material, e.g. 350 MS refers to a material which is heat sealable and moisture proof of which ten square meters will weigh 350 gm, i.e. 35 gsm. Applications Product requirements vary from one another. Leafy vegetables that are respiring need to let the water vapour out to prevent the condensation fogging up the film, while cakes need to let the moisture out to prevent mold growth and the crusty bread need to let the moisture out or it will become soft. The P grade is used to give protection from dust or grease where a barrier is not required. M grade is used for hygroscopic products such as biscuits, crisps, etc. QMS is popular for meat wrap. DMS is used for fresh meat. The uncoated side in contact with the meat is moistened and its permeability to gases rises helping to maintain the desired red colour. Additives There are many different additives used in the manufacture of plastics in order to improve their characteristics or performance. These include:  Plasticizers to improve flexibility  Antistatic agents such as ammonia compounds or glycol derivatives are used to reduce static which makes the layers cling to each other, attracts dust and can give electric shock to the machine operators 41


 Slip agents such as fatty acid amides, are used to achieve better running on the machine  Antioxidants may be organic sulphides, which prevent oxygen causing decomposition

especially at high processing temperatures of polyolefins, etc  Colorants used are titanium oxide, zinc oxide, chromium oxide and calcium sulphide  Fillers are used to reduce cost or improve strength and stiffness. They may be in the form of talc, chopped glass fibres and other inert materials  An anti-blocking additive to prevent bags sticking together, coats the material with a very fine powder such as silica with a diameter of 1-7 m, which gives the material a microscopic surface roughness.

Other additives include antifogging agents to prevent internal condensation which could obscure the product visibility and easy peel additives to make the pack easier to open. For food use, all the additives must be approved for food contact, and must not migrate into the food products in unacceptable amounts. Converting plastics into packs Plastics are generally produced as pellets or granules of polymer known as resin. To convert this into a plastic material for use in packaging, it must go through a series of conversion process. There are various conversion processes available depending on the form of the material required. Flexible films are usually cast or blown in extrusion process while rigid containers are manufactured by moulding or thermoforming them. Extrusion The first major step in the conversion of plastic resin into films, sheets, containers etc., is to change the pellets from solid to liquid or molten phase in an extruder. Extrusion is used to produce film or sheets of material, to coat paper or other substances or to feed moulding machines. It is a continuous process. The general sequence of the process is:  Feeding of the plastic material to the extruder hopper o  Plastification of the plastic granules in the barrel by application of heat between 140 C and o 350 C depending upon the polymer  Uniform plastification of the molten material in the barrel by a single or a twin screw  Metering of the platicised material through a die that forms it to the desired shape  Setting of the plastic (plus calibration) into the desired shape and size  Winding or cutting into desired lengths

Fig: Extruder In the manufacture of film and sheet, the molten plastic is forced through a narrow slot or die. In the manufacture of rigid packaging, such as bottles and closures, the molten plastic is forced into shape using a precisely machined mould. The properties of plastic films and sheets are dependent on the plastic(s) used and the method of film manufacture together with any coating or lamination. In film and sheet manufacture, there 42


are two distinct methods of processing the molten plastic which is extruded from the extruder die. The flexible film can be produced by two methods, which are: a. Slit die or cast film extrusion process In this process, the molten material is extruded through a T-die (also known as a slit or a coat hanger die) and onto a chilled highly polished metal roller. The die consists of two lips, one of which can be adjusted to vary the output. The gap between the die lips determines the film thickness. From the die, the material is extruded onto a chilled metal roll to quench the melt and produce a workable web of film. The rapid cooling of the hot film leads to the formation of small crystallites, giving excellent clarity and shine to the film. It also reduces the tendency of the material to “neck in”, i.e. it prevents contracting at the edges due to surface tension with a resultant loss in width. The cooling process can be carried out by two methods: Quenching in water bath: In this method, the film formed is cooled by passing through the cold water bath. This method has the following drawbacks:  Water remaining on the film leads to the problem in post film treatment and subsequent printing process because total removal of water is very difficult and expensive.  There is a chance of presence of detergent residue on the film as water contains detergent.  Wave stability is less, i.e. not uniform packaging thickness, which can be minimized by keeping the gap between the die and the water surface as small as possible. Generally, the gap is 10-40 mm.  Chance of steam contamination on the die and formation of wave in the bath. Casting on a chilled metal roll: In this process, the molten plastic is extruded through a straight slot die onto a cooled cylinder, known as the chill roll. A chill roll has water inside which keeps the surface cool. The roller surface is chromium plated to achieve a high optical quality film.

In both the processes, the molten polymer is quickly chilled and solidified to produce a film which is reeled and slit to size. The advantages are excellent clarity, uniformity of thickness, superior physical and mechanical properties and higher outputs. Orientation can be done to improve the film properties of tensile strength, stiffness, barrier properties and visual appearance at the loss of stretchability. Machine direction (MD) orientation is achieved by feeding the material thorough a series of rollers, which are of different diameters, temperatures and rotating at different speeds. Initially the material is preheated to just below its melt temperature as it passes through slow speed rollers. It then passes through some high speed rollers of small diameter which stretches it pulling it through a faster pace than that at which it is being fed. The final stage is heat setting stage to stabilize the material by passing it through a series of large diameter fast driven rollers. For biaxial orientation, the material must also be stretched in transverse direction. 43


This is achieved by the use of stenter which grips the edges of the film in an endless chain. The film is preheated before the chains at either side begin to diverge thereby stretching the material. An annealing stage follows to heat set the film, so it retains its new dimension. After it has cooled, it is released from the chains and the thicker edges are trimmed off and recycled. It the surface is to be printed, a corona discharge can be applied at this stage to activate the film surface so the inks or adhesives can adhere to it. b. Circular die – blow film extrusion process In this process, the molten plastic is continuously extruded through a die in the form of a circular annulus, so that it emerges as a tube. The tube is prevented from collapsing by maintaining air pressure inside the tube or bubble. This tube is expanded into a bubble by blowing air through the mandrel, the blow-up ratio being 1 : 2.5 to 3 and up to 7 or 8 for special materials like HM-HDPE. The size of the bubble and the film thickness are controlled by die gap, air pressure, extrusion and take-off speeds. The air is contained in the bubble by pinch rollers at one end and by the die at the other. The tube is pulled upwards, being collapsed as it reaches the top by a series of guide rollers that reduces its diameter. The film emerges out as a flattened tube at the top. This tube can be split at the edges to form two rolls of film that are wound onto separate reels. For tubular containers, the edges are not split. For increased strength and improved barrier properties, film can be stretched to realign, or orient, the molecules in both the machine direction (MD), and across the web in the transverse direction (TD) or cross direction. With the blown, or tubular, film process, orienting is achieved by increasing the pressure inside the tube to create a tube with a much larger di ameter. Film stretched in one direction only is described as being mono-oriented. When a film is stretched in both the directions, it is said to be biaxially orientated. Packing the molecules closer together improves the gas and water vapour barrier properties. Orientation of the molecules increases the mechanical strength of the film. The materials most commonly used for monolayer films are LDPE, LLDPE, HDPE, HM-HDPE, PP, PVC, etc. The factors that govern the properties of blown film are: - Monoaxially oriented films of PP - Biaxially oriented films of PS, PP, PET - Monoaxially oriented slit films of PP, HDPE, LLDPE for woven fabrics - Sheets for thermoforming - Extrusion coating - Foamed sheets Potential defects from this process include wrinkling of the fil m, hazy appearance, low impact and tensile strength. Temperature control is important. If the temperature at the pinch roll is too cold, then the material will stiffen and wrinkle. On the other hand, if the temperature is too high, the material will tend to block. A high melt temperature will result in a tough and transparent 44


material. A low one gives better slip and antiblock properties. The air pressure within the bubble must be uniform. Comparison of blown versus cast extrusion Blown film extrusion is cheaper. The tube produced can be readily converted to bags, without need of making an extra seam, by just sealing the base. This film has better mechanical properties. Cast film extrusion has very high output rate. The film produced is clearer. However, the cost of the chill rollers is high and the material needs to have the edges trimmed after manufacture. Extrusion coating It is a technique used for coating a wide range of substrates such as paper, aluminium foil, duplex board, textiles, woven fabrics of HDPE/PP, dry bond laminates, etc. with LDPE, LLDPE, HDPE, PP, etc for improving the barrier and sealing properties. Rigid and Semirigid Plastic Containers Many of the thermoplastic materials can be formed into rigid and semirigid containers (such as bottles, drums, crates, gallons, etc), the most common being LDPE, HDPE, PVC, PP, PET and PS, singly or in combinations. Acrylic plastics are also used for this purpose, including polyacrylonitrile and acrylonitrile-butadiene-styrene (ABS). Urea formaldehyde, a thermosetting material, is used to make screw cap closures for glass and plastic containers. Construction of Rigid Plastics This can be achieved by injection moulding, blow moulding and thermoforming.

Injection Moulding This is a batch process, in which the polymer pellets are softened in a heated chamber and then injected under high pressure into the closed mould through the nozzle of the moulding machine and into the mould through a gate, sprue and runner system. It cools and hardens by circulation of water in both parts of the mould, which is then opened and the item is ejected by ejector pins, stripper plate or by compressed air. To reduce the cycle time, the material can be pre-plasticised and the injection rate can be increased. The mould must be vented so that the air trapped in the mould can escape. Otherwise, the air will overheat and lead to localized scorching of the plastic. The pressure used, the temperature and the type of plastic and also the design of the mould will determine the cycle time.

The injection moulding process produces products having excellent surface finish, very good dimensional consistency and close tolerances. The mould design must allow for shrinkage in the mould as the plastic contracts. High production rates can be achieved, especially if multi cavity moulds are used, i.e. more than one moulding is made per cycle. 45


It is not possible to make items with reverse tapers or undercuts as the item could not be ejected from the mould, i.e. the openings can’t be narrower than the body. Injection moulds are expensive because of their massive construction & expensive materials of construction, which are necessary since they have to withstand high temperatures and pressures. So, this method is economical for long production, high volume items. There may be problems with brittleness if the temperature is too low, or distortion due to ejecting at too high temperature, and weld lines if there is insufficient pressure or cold mould, detracting from the appearance. All thermoplastics and special grades of thermosetting resins can be processed by this process. Injection moulding is mainly used to produce wide-mouthed containers, but, narrow-necked containers can be injection moulded in two parts which are joined together by a solvent or welding. PS is the main material used for injection moulding, but PP and PET may also be processed in this way. Applications include containers, cups and closures, base cups for PET stretched bottles, crates and pallets, thin walled disposable cups, etc. Blow Moulding Many plastics are shaped using a process called blow molding. This is a process for producing hollow items with openings narrower than their body and is primaril y used to make plastic bottles. Air under pressure is forced into a sealed molten body or plastic parison, surrounded by a cold split mould, causing it to expand to fill the container thereby being moulded to its shape. The material cools on contact with the cold mould walls and solidifies. The mould opens and the item is ejected. Blow moulding is mainly used to produce narrow-necked containers. LDPE is the main material used for blow moulding, but PVC, PS & PP may also be processed in this way. Food applications include bottles for oils, fruit juices and milk and squeezable bottles for sauces and syrups. Variations on blow molding include extrusion blow molding, injection blow molding, and injection stretch molding. Labeling can also be done in the mold. a. Extrusion Blow Moulding An extruded tube is produced either continuously or by batch process. A predetermined length of this tube is then trapped between two halves of a split mould. Both ends of the mould are sealed and the hot trapped parison is inflated by compressed air to take the shape of the mould. It cools and solidifies before it is ejected. The neck has to be manufactured subsequently. The excess material where the mould closes around the tube at the top & base, known as fl ash is trimmed.

46


Methods of increasing the production include the use of more than one mould. This being a low pressure process, the moulds can be of aluminium and are, therefore, comparatively low cost. The bottle will show a thin line in the position where the two parts of the mould are joined. Corners of the containers formed by this process tend to be weaker as the material is stretched most at that point. Blow moulding is used for milk bottles (HDPE) and wide mouth jars. b. Injection Blow Moulding In this method, the molten plastic material is first moulded round a parison stick inside a conventional injection molding machine. This stick constitutes the core of a split mould, the cavity of which is machined to accurately determined dimensions so as to give the required thickness profile, after blowing to form the finished bottle. While still molten, the parison and the blowing sticks are transferred to a second (blowing) mould, where it is blown into its final shape by passing compressed air down the blowing stick. The blown bottle is cooled, the mould opens and the bottle is ejected. Multi cavity injection moulds have also been developed.

The main advantage of this process is that it is possible to achieve accurate control of the wall thickness and neck calibration. The wall thickness of the finished container is controlled by the shape of the parison mould. The container will not have thin walls or base. Also, this produces fully finished bottle because the parison is fully enclosed and formed in the blow-mould, unlike in extrusion blow-moulding, where flash occurs at the parison pinch-off positions requiring a secondary operation. However, the equipment is expensive as two sets of moulds are required. It is a slower process due to the time required for transfer between the two sets of moulds and a longer cooling time. Injection moulded items are recognized by a pinhead-sized protrusion, known as the gate, on the surface, indicating the point of entry of molten plastic into the mould. With injection blow moulding, the gate mark on the preform is expanded in the blowing action to a larger diameter circular shape. Injection blow moulding is mainly used for the production of vials and small bottles even though commercially machines up to 5 L capacity are available. This process is more versatile in terms number of plastics that are possible to be processed such as PS, SAN, PC, etc which are not easily blown on a conventional extrusion blow moulding machine. c. Stretch Blow Moulding A variation of injection and extrusion blow moulding is the stretch blow moulding. It involves stretching the parison in the axial direction before blowing it to the required shape and size, which stretches it in the transverse direction. The stretched preform is then blow moulded which results in biaxial orientation of the polymer molecules, thereby increasing strength, clarity, gloss and gas barrier. It enables a thinner material to be used and is excellent for carbonated beverages. Injection stretch blow moulding is used to make PET bottles for carbonated beverages. 47


Aseptic bottles are formed by this method. The parison is extruded, blown to the required shape and size, filled and sealed in the same machine. Thinner film can be used as the carbonation pressure provides rigidity and strength. Multilayer (Coextrusion) Blow Moulding No single polymer can ever meet the complete requirements of a particular product to be packed, and in such cases, a combination of various polymers to form a composite structure is used. All the basic blow moulding processes are used with some differences. First, there are additional extruders for extruding one layer each and secondly, a very specially designed die to form a laminate composite structure of the bottle wall is used. All the polymers can’t form bond with each other and, therefore, an adhesive or bond layer is required to create the bond, which doesn’t delaminate. As a result, three or more extruders are required. With the HDPE/EVOH, for e.g., five layers are actually required: HDPE | Adhesive | EVOH | Adhesive | HDPE. EVOH is a relatively more expensive material but with excellent barrier properties, but is sensitive to water, which can deteriorate its properties. So, it can sandwiched with HDPE or PP, which are comparatively low priced, have excellent water vapour barrier properties, and are approved for food contact applications, though they are poor oxygen barriers. Thus, EVOH and HDPE/PP supplement each other to produce an economical package with excellent barrier properties.

Thermoforming This method uses sheets or reels of plastic films. The material is clamped in position above the mould. The sheet is heated until it softens and then made to take up the shape of the mould by either (a) Having an air pressure greater than atmospheric applied above the sheet, (b) Having a vacuum created below the sheet, or (c) Sandwiching the sheet between a male and female mould, i.e. matched die.

Fig: Thermoforming, filling and sealing 48


The sheet cools through contact with the mould, hardens and is ejected from the mould. The pressurized system gives better mould definition than the vacuum system whereas the matched die is excellent for complex shapes but is more expensive as two dies is required. Thermoforming tends to give thin corners as the film is stretched most there. However, compared to other methods of moulding, the moulds are relatively cheap so it is suitable for short runs. It is hard to control thickness but a good design of the mould helps. The shapes that can be made by this method are limited. There are no weld lines. Plastic materials that are thermoformed include PS, PP, PVC, HDPE and ABS. Thermoforming is used to produce open-topped or wide-mouthed containers such as cups and tubs for yoghurt, cottage cheese or margarine, trays for eggs or fresh fruit and inserts in biscuit tins or chocolate boxes. Compression Moulding Compression moulding is used from thermosetting plastics, such as u rea formaldehyde, as well as for materials like ultra-high molecular weight HDPE. The plastic powder is held under pressure between heated male and female moulds. It melts and takes up the shape of the mould. The mould is cooled by water circulation, opened and the cooled item is removed from the bottom half of the mould, i.e. female mould. The main application for this method is to produce screw caps. Multilayer Films Each type of plastic has its own role in the field of packaging. A single material may be suitable for some products, but in certain cases it will need to be so thick that it would become uneconomical. In some cases, no one material can achieve all the requirements. In such case, a composite material is needed, different layer contributing to the overall performance. This can be achieved by lamination or coextrusion. In the form of laminates and multilayer coextruded films, they are expected to dominate the field because of some distinct advantages:  Meeting the exact performance requirement by selection of different layers of the composite structure  Considerable economy because of lower consumption of raw materials through lower weights, for e.g. a 1 kg pouch weighs 8 gm as compared to at least 40 gm of an HDPE blown container  Retailing in smaller unit packs gives protection from adulteration and convenience to the weaker sections of the society  Ease of handling and storage  Ease of disposal and total prevention of reuse with spurious materials causing a major health hazard. Lamination Lamination is a combination of several different materials to form a multilayer material that utilizes the advantage of each component to optimum effect at minimum cost. It creates a composite material of the required properties by letting the weakness of one be compensated for by the strengths of another. Lamination increases the physical properties (puncture resistance, tensile strength, and impact strength), barrier properties (decrease GTR and WVTR), sealability, printability, product compatibility, economy and appearance (gloss, clarity, etc). For e.g. polyethene is an excellent heat seal medium and has a good moisture barrier but is permeable to gases. At thicker gauges, this permeability is reduced but the cost increases. PVdC has a very low gas transmission rate but is not so good at heat sealing. It is also a lot more expensive than polyethylene. Nylon is strong, thermoformable with puncture r esistance, but needs 49


to be protected from moisture. By combining nylon, PVdC and PE, a laminate is formed with each layer contributing to the overall performance. Similarly, aluminium foil is an excellent barrier material but is easily damaged by puncturing on its own. It can be protected by sandwiching it between polyester, which has good puncture resistance & polyethene to give a heat sealable material. Economy is achieved by using minimum weights of each material or by using cheaper materials for rigidity or stiffness. Paper is cheap, printable and has good dead fold properties. It can be coated with polyethene for moisture resistance, laminated to foil and polyethene to form a barrier, heat sealable material. By combining the qualities of choice from the raw material films, a laminate can be tailor-made for its particular application. Each layer in the resulting laminate may exhibit different properties from its free state, such as mutual layer reinforcement in which cracks in a brittle layer are prevented from propagating by a high elongation (elastic) layer. This effect depends on good adhesion between the layers. Three factors affect the adhesion between layers: 1. Viscosity/shear rate match during melding of layers. To be coextruded, the melt flow viscosities should be similar (a ratio of within 3:1), otherwise one of the plastics will flow with respect to the other, preventing bonding. 2. Temperature, pressure, and period of contact, to build the bond. 3. Functionality of adjacent resin layers, i.e., that they are sufficiently similar in structure to mix at the contact surfaces. Properties of some common components used for laminates Components Uses - Moisture vapour barrier 1. Low density polyethylene - Moderate barrier to gas (LDPE) - Excellent heat sealing medium - Low temperature performance - Moisture vapour barrier - Low and high temperature performance 2. High density polyethylene (HDPE) - Grease resistance - Barrier properties superior than LDPE - High transparency 3. Oriented polypropylene - Excellent clarity (OPP) - Barrier properties similar to HDPE - Outstanding water vapour and gas barrier properties 4. Polyvinylidene chloride (PVdC) - High grease resistance - Gas barrier properties - High strength 5. Polyethylene Terephthalate (PET) - Grease resistance - Low and high temperature performance - Excellent clarity and printability - Good gas barrier properties - Moderate water vapour barrier properties 6. Polyester - Excellent grease resistance - Can be metalized for use as a substitute for aluminium foil - Properties similar to LDPE 7. Ethylene vinyl acetate - Superior grease resistance (EVA) - Printable 50


8. Nylon

9. Regenerated cellulose

10. Ionomer (Surlyn)

11. Paper

12. Aluminium foil

13. Paraffin wax

-

Low and high temperature performance Excellent grease resistance Low gas permeability & can be used for vacuum packaging Tough Excellent gas barrier properties Moisture vapour barrier when coated Transparent and printable Generally similar to LDPE but superior grease resistance Stronger with better clarity and printability Can perfectly seal through even a contaminated layer Stiffness at low cost Opacity and printing Very good barrier (100% barrier to gas and water vapour) Decorative effects Excellent printing impression aids to the sales appeal Non-toxic & can be used in direct contact with food products Can be used at deep freeze & elevated temperature condition As adhesive Improves water vapour barrier properties

Materials selection based on package requirements 1. Opacity: Aluminium foil, metalized PET/BOPP films, paper and pigmented plastic films can be used. 2. Transparency: Cast films of HDPE, PET and PP have good clarity. 3. Gas barrier properties: Aluminium foil and MET-PET/BOPP films are almost complete gas barriers. The other films that meet the requirement in most cases are nylon, PVOC, EVOH. 4. Low temperature performance: Nylon, PET, BOPP and HDPE have good temperature resistance. Aluminium foil is also excellent. 5. Heat sealability: LDPE tops the list. 6. Grease resistance: Nylon, EVA, HDPE, PP, PET, PVC and PVdC have good resistance. 7. Printability: Films like nylon, PET, etc have good printability. Lamination Techniques The most commonly used techniques for the preparation of laminates are:  Adhesive lamination – wet lamination and dry lamination  Thermal or heat lamination (fusion method)  Wax or hot-melt lamination  Extrusion lamination (melt lamination)

Wet lamination This method is used when one or more of the substrates is permeable to the passage of coating solvents. The process is widely used to produce laminations of paper/foil, film/paper, and paper/paper. It may be necessary to prime-coat the non-porous substrate prior to lamination to ensure adequate adhesion. Wet lamination uses solvent- or aqueous-based adhesives, including silicates, resin emulsions, rubber lattices as well as water-soluble glues. The solvents must be able to evaporate without causing web deformation. Wet lamination is not usually successful with plastic films when laminating them to paper. However, wet lamination using organic solvent-based adhesives has 51


been carried out in some instances, and even aqueous-based adhesive lamination can be carried out for films such as cellulose acetate when bonded to paper. Cellulose acetate is fairly permeable to water vapour and hence aids drying out of water after laminating. Wet lamination method is more popular with paper laminates. In any case, the finished laminate must run through a drying oven to speed up the drying of the solvent.

The No. 1 ply is preheated along a section of the heating and combining drum, while the No. 2 ply is coated on an adhesive applicator which then travels to the la y-on roll mounted on the surface of the combining drum. By using a low fusion temperature plastisol adhesive, the films can be bonded below the critical film temperature. Dry lamination This method is used for bonding two impervious webs and is more suitable for the lamination of plastic films to other substrates. This method consists of applying the adhesive to the inside face of one or both webs. Rubber based adhesives, aqueous emulsions and heat-seals t ype formulations can also be used for dry bonding. Solvent drying can cause some problem. Solvent based adhesives also present fire hazards. The dry bonding process incorporates either: - The use of an aqueous or solvent based adhesive film that is dried prior t o laminating, or - A hot-melt adhesive, based on wax or one of a range of polymers. In the first case, the aqueous or organic solvent based adhesive is applied in precise amounts to the inside face of one web. The coated web is then passed through the oven, to remove all water or solvent. The second layer is applied to the sticky surface and the t wo are bonded under pressure by passing through a nip roller, which may sometimes be heated.

The success of this lamination when used for plastic films i ncludes factors such as tension control, accurate adhesive application and accurate control of drying. Tension control is very important. If it is too low, there will be wrinkles in the film, and if too high, it could stretch the film beyond its elastic limit. Film tension should normally be kept to a minimum and will depend on the distance the film has to be pulled through the laminating equipment and on the sharpness of any change in direction as it passes over the various rolls. The amount of adhesive applied must be controlled; 52


the dose must be accurate & applied uniformly. The oven must operate at the correct temperature and residence time in it must be sufficient to dry the solvent or the material could delaminate (which is a process where the individual layers separate). Excessive solvent remaining in the adhesive at the nip stage is the major cause of delamination. Thermal or heat lamination (fusion method) Heat lamination is used to combine coated materials by simply running them together between rollers, one of which is heated. The equipment is very simple and relatively inexpensive. The process involves passing two films through heated pressure rolls with the resultant heat sealing. The heat during lamination can cause the film to become brittle because moisture is removed. In order to prevent the loss of moisture, two different techniques are employed as a supplement to thermal lamination. One method utilizes a specially designed laminating head which preheats the film (the degree depending upon the thickness) and injects steam prior to lamination. The heat causes softening of the coating and allows for better moisture penetration and a softer and more durable lamination. Great care must be taken to control the temperature, since it is easy for a sheet to become overheated causing web failure or melt off; or on the other hand, to become too cool and perhaps give only a superficial bond. The other technique employs the use of a water nip. Water is added at the nip point. A well of water from 2 to 2.5 cm high must be maintained in the nip between the metal & the rubber roller. It is also important that the introduction of the webs is made properly to avoid air entrapment that would tend to form bubbles between piles. The degree of preheat required is determined by the film thickness as well as the production speed. In the case of materials that have distinct melting points (such as polyethylene, polypropylene, etc), the proper control and regulation of temperature and speed is more important. Other problems involve bond strength and ink compatibility. Inks must be heat sealable, and as an aid in thermal lamination, they may be applied in-line or separately. Wax or hot-melt lamination It is used to produce materials such as cellophane/wax/foil, cellophane/wax/cellophane, etc. This method uses wax instead of adhesives. Microcrystalline waxes are most popular. The equipment used for roll application of hot melts consists of a reverse kiss coater, a pneumatically loaded rubber roll with a fixed steel roll to combine the substrate, and an adequate chill roll section to set the adhesive.

The hot melt is applied by a reverse kiss coater to one of the webs. The two webs are brought together at the nip between a pneumatically loaded rubber roll and a fixed steel roll. The laminate again passes through a cooling section and is then wound up. The advantage of this method is that the solvent drying or recovery is not required after laminating and therefore the laminator machine can operate at a faster rate. The addition of 53


polymers to the waxes produces tougher films, better cohesive and adhesive characteristics, and good moisture barrier properties. This type of lamination lends itself to the production of moisture proof wrappers of all types, liners and pouches, and carton overwraps. A limitation exists in heat sealing temperature. The heat sealing temperature of the finished laminate is generally higher than the melting point of the laminate. This results in the movement of the wax or hot melt away from the seal area. Extrusion lamination (Melt lamination) This method is used to produce coated materials like paper/polyethylene, foil/polyethylene, paper/polyethylene/aluminium foil or paper/polyethylene/cellulose film. Due to its excellent heat sealability, polyethylene is coated onto paper, aluminium foil, cellulose, etc. polyethylene resin is used as the adhesive between two substrates in extrusion lamination. The type of plastics that can be extruded are limited and about 90% of the extrusion is done with LDPE, or compounds in which polyethylene is the principle ingredient. Polyethylene gives a laminate greater ability to withstand impact stocks than conventional adhesives. The other materials used are HDPE, PP and nylon. Extrusion laminates are good barrier to water and water vapour and are usually tough and flexible. It can be used as a lamination process where the extruded layer acts as the adhesive layer for applying the third material, e.g. in structure such as paper/polyethylene/aluminium foil. Extrusion lamination is a form of dry bonding but without the use of any solvent in the lamination medium. A flat die extruder discharges a molten curtain of polyethylene, polypropylene or some other thermoplastic into the nip between the two webs to be laminated. The heated adhesive is cooled by passing the laminated sheet over a specially designed combining & cooling roll section. This cooling section replaces the drying section generally needed in wet adhesive bonding. Pressure is applied to ensure that the two materials stick together.

Temperature and pressure must be controlled very carefully in each zone of the extruder to get a uniform flow and avoid degradation of the material due to overheating. The extrusion die must also be well designed, carefully maintained and accurately adjusted throughout its length to get consistent results. Laminating weights are usually between 20 to 40 gsm of LDPE. Common examples of Laminates MXDT/LDPE – for dry foodstuffs, where gas and water vapour barrier is required Nylon/LDPE – vacuum packs for cheese, meat, coffee, nuts PET/LDPE – vacuum packs for cheese, meat, coffee, nuts Coated OPP/LDPE – gas and vacuum packs for bacon, cheese, cooked meat Paper/POLYETHYLENE/Al/LDPE – dried foods, milk, coffee, soup, cake mixes PET/Adh/Al/Adh/PP – retort pouches, goods requiring long shelf life under extreme conditions 54


Factors affecting adhesion between layers 1. Viscosity/shear rate match during melding of layers. To be coextruded, the melt flow viscosities should be similar (a ratio of within 3:1), otherwise one of the plastics will flow with respect to the other, preventing bonding. 2. Temperature, pressure, and period of contact, to build the bond. 3. Functionality of adjacent resin layers, i.e., that they are sufficiently similar in structure to mix at the contact surfaces. Components of lamination machine Lamination machine or process consists of the foll owing components:  Continuous feed roll with a feeder “on-the-fly” splicer, which can cut off the old roll and join on the new (there may be several rolls feeding film into the machine at once)  Tensioning rollers – to give exact control over the tension in t he plastic  Lamination stage – where the primary and secondary webs are combined  Compression rollers – to push the layers together  A take-up (rewind) roller – to collect the final laminate Comparison of extrusion coating and adhesive lamination In adhesive lamination, excessive drying temperatures often lead to “shinning” where the solvent is superficially dry and permeates through the “skin” after a period of time. Spoiled food, product loss and delamination result from solvent odour incurred during adhesive lamination. However, this is not present in adhesive techniques not involving solvents. Extrusion coating permits coating of a very thin gauge. It not only strengthens the bond but also helps in filling up pin holes and other pore found i n paper and thinner gauge of foil. Coextrusion No single polymer can meet very exact performance requirements of packaging materials – flexible, semi-rigid or rigid. As such, the process of combining two or more polymers by coextrusion to manufacture multilayer films was developed. In this method, two or more extruders are used to produce a composite film/sheet using different polymers for achieving the desired properties. Two or more (up to seven) extruders are coupled to a single die head and the die is so designed that what emerges out is a well bound multil ayer film/sheet, which appears as one single composite film/sheet. Three and five layer constructions are common, with the alternate layers of adhesive known as tie layers. A typical structure is LLDPE/tie layer/EVOH/tie layer/LLDPE. The tubular film produced can be formed into bags or subsequently moulded into bottles. The selection of the polymers is based on the salient features of each polymer to meet the requirements. The polymers most commonly used for films are LDPE, LLDPE, EVA for the outer layer; bonding agent or tie layer of CXA or Primacor; barrier layer of nylon, EVOH, etc. and the sealant layer of Surlyn or Primacor. In sheet production, the polymers used are HIPS, EVOH, PET, etc. Coextrusion helps to develop a tailor-made package while reducing the manufacturing costs, particularly the raw material and energy costs. Coextruded materials are not subjected to delamination. However, they can’t be sandwich printed as laminates. They can only be surface printed which leads to problem if the surface is scuffed off. They can use materials in much thinner gauges than laminates. Each ply in a laminate must be stiff enough to feed through the laminator but in a coextruder it can be used in very small amounts such as 3 micron. Waste from the coextruder can’t be easily recycled as it is not a pure material. It is sometimes recycled and used as the core of the structure. Both laminates & coextrusions are not easy to recycle but their environmental advantage is that they use minimal quantities of materials. 55


Coextrusion processes There are five principal manufacturing processes utilizing coextrusion techniques. They are:  Cast-film extrusion  Blown-film extrusion  Coextrusion coating (extrusion coating)  Coextrusion lamination  Cast sheet coextrusion

Lamination versus coextrusion Lamination 1. Chance of delamination. 2. Paper and aluminium foil can be used for lamination. 3. Interior printing may be done. 4. Can be recycled (pure form).

Coextrusion 1. No chance of delamination. 2. Takes place between plastics only. 3. Surface printing can only be done. 4. Can’t be recycled.

Major advantage and disadvantages of multilayer films Advantages  Multiple properties are achievable on a single converting operation with resultant economy  No solvents are used in the process & as of such no problem of polluti on or odour on the film  Thin layers of films that will be difficult to handle separately can be produced by lamination  Pigmented layers could be sandwiched without affecting the sealability  To reduce cost, it is sometimes possible to recycle reclaimed materials, if they are compatible  Gas barrier resins could be introduced into structure eliminating the need for further coating  A sandwiched layer could be of reprocessed material for effective economy  A choice of various polymers to meet the product requirement with respect to compatibility, sealing, barrier properties and cost. Disadvantages  It is necessary to balance melt viscosities and the chemical properties of the resins to be coextruded  Equipments are quite expensive  There is no chance to bury printing within a coextruded film  Make-ready costs are high so the coextrusion process require longer production runs to be cost-effective Shrink Wrapping Shrink wrapping is a method of shrinking transparent plastic around a product, container or group of containers to give a tight fitting pack. Shrink film packaging involves the use of thermoplastic films that have been stretched or oriented during manufacturing and have the property of shrinking with the application of heat. It involves passing a package wrapped in a loose envelope of film through a heated tunel on a conveyer belt. In the heat, the material shrinks and forms a tight wrap around the package, keeping it clean, dry and intact.

Manufacture Extrusion is the most common method and either annular or slot dies are employed, depending on the materials used and the subsequent methods of orientation. Both center-fed, spider dies or sidefed, crosshead dies are used to produce polymer tubing. Calendering is sometimes used to produce PVC films. The third method of casting from a polymer solution is also used for PVC, but less frequently. Both of these processes normally yeild films with better thickness distribution 56


compared to extruded films, but the capital investment for calendering or casting is very high, and for the solution cast process, operating costs are almost prohibitive. Shrink film is oriented by stretching the polymer sheet or tube at a temperature above its softening point, whereby the polymer chains are alligned in the direction of stretch. After stretching the polymer, alignment is locked in the film by cooling. When the oriented film is subsequently heated to temperatures in the vicinity of the stretching temperature, the frozen-in shrinkage stresses become effective and the film shrinks, reflecting strains and stresses related to the degree of orientation and the forces applied during stretching. The orientation can significantly change some of t he basic properties of a polymer. Properties Generally, orientation improves the tensile strength, impact strength, clarity, transparency, and flexibility at both ambient and low temperatures. The degree of shrink and shrink derive from the orientation process and it becomes difficult to tear. In certain cases, gas and moisture permeability are also lowered. On the other hand, orientation generally has a detrimental effect on elongation, ease-of-tear propogation and sealability of a film. The heat sealing range is narrowed and film properties may vary with age. Advantages The various advantages of shrink packaging include the following:  Contour fit : Shrink film readily conforms to irregular shapes and product configurations  Multi-packing: Groups of products can be attached to the basic product  Appearance : A shrink-wrapped product has a transparent sparkling sheen that enhance merchandising and display characteristics  Protection and cleanliness : Shrink film packaging reduces pilferage, increases shelf-life, and provides environmental protection  Immobilization: Shrink film can lock one or more products in place, protecting against movement that can cause scuffing or breakage  Economy: Packaging with shrink film can eliminate more costly materials such as corrugated, kraft or chip board. Applications Shrink packaging is used for a wide range of industrial applications for tray pack, bundling and pallet load utilization. Tray pack is widely used by beverage and canned goods industries as a means of eliminating corrugated shippers. Shrink film i s also used with corrugated board for what is called a suspension pack . This process is used to suspend breakable products on a corrugated Upad, eliminating dunnage. Stretch, Cling and Twist-Wrap Films Stretch-Cling Film Stretch wrapping can be used similarly to shrink wrapping as outer packaging or can be in direct contact with the food. Stretch wrapping doesn’t use heat, but relies on the elasticity of the material. The material, generally LLDPE, is wrapped around the packages and stretched for a revolution and half. When the tension is released the material clings to itself and retains its shape to hold the good tightly in place. This is used to overwrap trays of food or to secure a stack of pallet of boxes so that they do not move about in the vehicle while it is moving. Stretch wrapping is a cost effective and highly efficient means of utilization. It is applied by hand dispenser or by machine to the load or pallet load and is ideal for any type of regular or irregular sized product. Its chemical composition gives it high tensile strength and memory providing a 57


rubber band effect. Consequently, stretch cling film holds loads securely in place, regardless of handling conditions and adjusts to loads that shift or settle after packing. Stretch wrapping is an alternative to shrink wrapping as no power or heat energy is required to pr ovide the secure effect. It can be divided into: 1. Standard stretch: A tough film for use in applications where cling properties are not required. 2. Cling-stretch: A tough film for use in applications, with good stretch and cling properties. 3. Super stretch cling: A linear low density polyethylene film with exceptional stretch and cling properties. Areas of application  For lighter loads up to 350 kg: for protection without crushing such as potato crisps where the packed load requires protection against dust, pilfer-proofness to humidit y during storage.  For assorted loads between 350 kg and 750 kg: for users demanding high load security at lower unit cost.  For loads from 700 kg up to 1 ton: as protection for general applications.  For loads exceeding 1 ton: for palletized goods and heavy irregular loads providing extra holding force and toughness. Household Cling-Catering Film For packaging and preservation of cooked food and as a protection towards insect contamination, cling film is used by airlines, fast-food stores and to cover cooked food & vegetables to be stored in refrigerators/freezers. The applications include the packaging of meat, fruits and vegetables, cheese and dairy products and for catering films for use in homes and hotels as covering material for cooked food to be stored in refrigerators or under ambient temperature conditions. The commonly used combinations are EVA/LLDPE/EVA or LLDPE/LLDPE/EVA. Twist-Wrap Film Sweets, toffee, candies, chewing gums, etc utilize cellophane, PVC film, and wax coated paper as over wraps. Cellophane is undoubtedly the traditionally used film for wrapping of hard boiled sweets but is expensive. PVC film is utilized by the small scale units where there are no self/buyers regulatory controls. Wax coated paper is utilized in the lower price range of sweet/toffee products. The industry therefore needs an alternative to cellophane, which can work at fast operational speeds on twist-wrap machinery providing economy in production. The PP twist-wrap film is the alternative as it provides high clarity with good printability characteristics and speeds of operation reaching as high as 1000 wrappings per minute.

General requirements Raw materials requirements for:  Stretch-film production: LDPE, EVA, PVC, LLDPE  Cling-wrap film: EVA, LLDPE, PVC  Twist-wrap film: PP-cast homopolymer  Additives: PIB, atatic PP, anti-block, clarity modifier Functional property requirements for:  Stretch-cling films: - High values for puncture energy - Tear strength - Tensile strength - Elongation - Cling property 58


 Twist-wrap films:

- Tear strength - Ability to retain twist - Clarity and gloss - Good surface printing property - Knife cuttability - Stiffness - Anti-static  Process of manufacture: - Blown - Cast - Monolayer - Multilayer Generally, the use of PIB is preferred to provide the cling effect. Selection of PIB grade depends on the production process as also its performance on the processed product. Selecting a higher molecular weight PIB (for a given level) provides a stretch-wrap film with the following properties:  High cling value  Film feels less greasy  Cling takes longer to develop pumping pib to extruder more difficult noise on film unwinding increases Stretch-Film Equipments Stretch film can be prepared by the use of any of the following equipments. 1. Rotary pallet wrapper This is a general term for those machines that are based on a turntable combined with a fixed frame to which the film is attached. As the film moves along the frame, the turntable rotates resulting in a spiral winding of the pallet load. This type of equipment is most common with added sophistication to be automated and with the provision for a top sheet inserter which ensures water proofing. Equipment capacity varies between 15 and 80 pallets per hour. The suitable stretch film to be used is 15-20 microns. 2. Full-width wrapper This is also based on the rotary wrap principle with the only change that the film used has sufficient width to cover the load in one rotation. The suitable film thickness is 50-100 microns. 3. Curtain wrapper This equipment was the first type developed for the use of stretch films. The principle involves allowing the load to pass between the two rollers rotating around individual vertical axes where the film is kept stretched for the wrapping operation. As the pallet passes between the rollers, the film is stretched along the sides of the pallet. When the entire pallet is enclosed, two welding jaws come together and seal the stretched film. This film is retained mechanically until the joint has cooled and reached full strength. 4. Horizontal wrapping machine This differs markedly from other machines. Instead of pallet rotating, the film is allowed to rotate around the load. The machine is intended for wrapping long loads that do not fit into a pallet. 5. Wrapping paper reels The latest addition to stretch film dispensing equipment is the innovation to wrap paper reels by radial and axial winding simultaneously. The suitable film thickness is 30-120 microns. 59


6. Hand wrapper The hand wrapper is the simplest implement for stretch-film wrapping. The film rolls are mounted on a frame where unwinding of the film can be slowed down by turning a handle. This allows a certain degree of stretch control. This device is excellently suited to tasks as the re-sealing of loads that have already been opened or repairing damaged wrapping as also normal wrapping not subjected to any load capacity requirements. The suitable film thickness is 15-20 microns.

Comparison of shrink and stretch wrapping Shrink wrapping requires heat, which makes it more expensive as a heating tunnel is required, and less flexible as it cannot be used everywhere. It uses more m aterial than stretch wrapping. It is not suitable for heat sensitive food products. It uses power whereas stretch wrapping can be done manually. However, it will shrink to shape of the product which is very useful for irregular shaped items. Metalizing Metalizing of paper and plastic films is done for improving the barrier properties as well as for enhancing the visual appeal. The metalizing machine is similar to a conventional coating machine. A roll of paper or film is passed over a sprayhead, the coating is applied and the web is wound on a core. The paper/film roll is then loaded on an unwind stand and threaded over rollers to a windup stand. In this case, the coater on which the roll passes consists of evaporator pots containing molten aluminium, opposite a chill roll. The whole process takes place in a vacuum chamber. In this process, the aluminium is melted, vaporized and condensed on the substrate containing a prime coat of adhesion. The amount of deposition is controlled by (i) temperature of the aluminium – higher temperature implies more metal, (ii) running speed – slower speed gives more metal, and (iii) the number of plating stations – more stations will give more metal. The amount of coating is determined by the percentage light transmission, electrical resistance, & optical density. Plastic films that are mostly metalized are PET, BOPP, PS, and to lesser extent, PVC and nylon. Package Design Retortable Pouch Retortable flexible packaging materials are defined by the ASTM as “those capable of o withstanding specified thermal processing in a closed retort at temperature above 100 C.” Initially, only metal containers were used. Nowadays, plastics are being used. Retorting is done above boiling point (for low-acid foods) to increase shelf life. Retorting a can has certain disadvantages. It requires openers and may cause injury. Plastics, on the other hand, have low weight, lower production cost and several other advantages. The pouch has narrow profile (cross-section thickness) and heat penetration is quicker (shorter process time). Consequently, this results in better product quality and control over microorganisms. The desirable characteristics include toughness, puncture resistance, good barrier properties (against oxygen, water vapor, light and microbial penetration), high temperature resistance (110-114°C), heat sealability. Retortable pouches have several plies of laminates, e.g., two-ply laminate, 3-ply laminate, etc. The outer film should have good strength and flex resistance (flexural rigidity = stiffness), resistant to heat-seal temperature, ability to withstand retort temperature without bursting, shrinking and delamination. A very common example of retortable pouch is polyethylene terepthalate (PET). Some of the important product considerations include: 60


1. Exact filling: accurate measurement and dosing 2. Clean filling: contamination in the seal area weakens the seal (low seal strength) 3. Removal of headspace before sealing: by exhausting residual air content in the pouch. Should be < 2% of pouch capacity by volume 4. Good seal integrity 5. Use of overriding pressure: (air pressure of 3-10psig). This minimizes pressure differential inside and outside of retort. This is done as a counter-pressure during retorting. Semi-rigid containers (tray or tub type) have the advantage over flexible package of ease and speed of filling. Hot fill pouch It is a flexible plastic container. The product is filled in hot condition. It is normally used for acid food or acidified food. The filling temperature is about 70-93°C. The usual process is to fill hot, seal, and hold for 1-3 min to achieve commercial sterility. The package may be in the form of i) Flat type or ii) Stand-up type. These are made from PET/Al-foil/PE; PET/PE; Metallized PET/PE. Plastics for vacuum, gas and modified atmosphere (ma) packaging For vacuum packaging, the air/gas is expelled from the package before sealing. In the case of gas packaging, inert gases like N 2 and CO2 is introduced into the package by different means and sealed. Today, machines are available for combined vacuum and gas packaging. The materials commonly used in such packaging are PVdC (polyvinylidene chloride)-coated PET or PE; PVdCcoated PP; and metalized PET or PE. Ovenable plastic container Ovens can imply either conventional oven or microwave oven. The characteristic of the packaging material can differ in this aspect. The desirable properties include: 1. Resistance to high temperature (200-250°C for ovenable containers) 2. Permeable to microwave radiation for microwavable containers 3. Good impact strength at freezer temperature (= good deep-freeze performance) 4. Good printability The following materials can be used for both types of ovens: PP, high impact polystyrene (HIPS), crystallized PET (CPET). The package may be in the form of tray or board. Plastic tubes They are used for paste, sauce, ketchup, etc. They are available as metal tubes or plastic tubes. Plastic tubes do not collapse but retain the full length, shape, etc. throughout the life of use. They are crush-proof. They have stronger seal and are corrosion less. The commonly used plastic materials for tube manufacture are low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE) and linear LDPE. Colored polyethylene granules are mixed and blended to produce a continuous length of tubing offering the required characteristics of color, density, circumference and wall thickness. This tubing is cut to correct length. Shoulder and nozzle are molded. The complete molding is subjected to offset machine for color printing. Lacquering is done to give glossiness. A UV-light system is used to dry the printing ink. Laminated tubes It contains additional plastic layer, paper and aluminum foil. It has superior barrier properties. Consequently, the product quality is better. The outer layer is LDPE with antistatic agents (prevents static electricity). The agent is used as print carrier. Then come LDPE, printing ink, 61


pigmented white LDPE, paper, LDPE, ethylene acrylic acid copolymer, aluminum foil, ethylene vinyl acetate (EVA), and LDPE (innermost layer). The advantages include: 1. Easily squeezable (so, eliminates waste) 2. Cracking, creasing and denting do not take place 3. Since printing is done prior to tube formation, it has a superior eye appeal and the printed matter is scratch-proof 4. Superior barrier properties 5. Corrosion-free Edible coating This is a new form of packaging. The food is coated with a thin film of edible package. For a heterogeneous material, coating of individual component is done to serve as a boundary within the bulk (demarcating film). Protective edible coating controls deterioration (microbiological, physical, and chemical). The coating contains certain agents, e.g., antibiotics and preservatives. Thus, edible coating can also be used as part of active packaging. Chocolate and sugar coatings, gelatin coatings, etc are some of the well known examples of this category. Edible coatings can be applied by two methods, viz., i) coating formation, and ii) applying the coating on product. Advantages/characteristics of edible coating include: Edible, Waste reduction and pollution control, Low cost, Improves organoleptic and nutritional properties, Solubility, and Barrier property (to moisture, oxygen, and solute movement). Coating can be done by i) normal coating or ii) solution coating. Drying can be done in IR radiation or in air. Films are prepared as coating or over-wraps. The basic preparation for overwraps entails concentration of the mix, extrusion, and wrapping. The coating techniques are: 1. Hand spreading with paint brush 2. Spraying 3. Falling film enrobing 4. Dipping and subsequent dripping 5. Distribution in a revolving pan 6. Bed fluidizing or air brushing Plastic Bags Bags are formed from sheet or film plastic by folding and heat sealing as required. Some bags have folds in the base so that when packed, they expand to a rectangular shape. Handles may be inserted during folding and heat sealed into the folds. The bags must be strong enough to resist breakage under the design load, but also must not break when being loaded. Bags may be preformed, in which case they may be “wicketed,” or formed from the source plastic sheet during packaging (usually by forming tubes from the plastic). Wicketing is the process of punching small carry holds at one end of the bag with which to hold the bag during loading. The holes must be carefully designed to carry the load of the product entering the bag, yet must tear off easily so that the next bag becomes available. Plastic Closures A closure must perform five functions: 1. Contain, to the same level as the remainder of the package. 2. Allow access, so that the consumer can retrieve the product in a convenient way. The ability of the package to be functional in this regard is an important marketing consideration. 3. Restrict access, e.g., tamper-evident and child-resistant caps. 4. Protect the product, keeping out dirt, moisture, etc. 5. Be economic. 62


The closure may also be used for advertising or bar-coding. A plastic screw cap lid has three main components: 1. The cap itself 2. A linear (HDPE wad), adhesively attached to the cap in most cases 3. The screw, which interlocks with connecting lugs in the finish of the container but does not provide a good barrier seal The closure must be applied with the correct torque. Insufficient torque leads to leakage, whereas too much torque makes removal by the consumer difficult. Tamper-evident attachments to the screw cap are commonly used with plastic beverage bottles, consisting of a ratchet ring under the cap, which becomes detached when the customer removes the lid. A dispensing closure is one that allows the product to be dispensed without removing the closure. Examples of dispensing closures are lids such as flip-tops, pump action, aerosols, and opening pourers, which allow small amounts of the product to be removed easily.

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�� Introduction The American Society for Testing Materials defined glass as ‘an inorganic product of fusion which has cooled to a rigid state without crystallizing’. Glass is a popular and traditional packaging material used for milk, jams, soft drinks, wines, beer, and spirits, and for many food products, pharmaceuticals, etc. Glass containers used to be and still are considered a prestigious means of packaging, and serve for the most expensive wines, liqueurs, perfumes, and cosmetics. Advantages 1. It is highly inert – neither affecting nor being affected by the product, no change in colour and flavour 2. It is a rigid inflexible material that can support a lot of weight – strong as compared to plastic and paper 3. Glass doesn’t deteriorate or change over time – not degraded by light 4. Easily available, easy to mold and cheap 5. Glass is impervious - has almost perfect barrier properties (including barriers to odors) 6. Suitable for recycling, reuse and reclosing, it is made from renewable resources 7. In its normal state, it has the advantage of transparency, but where required it can be given different desired colors – attractive appearance 8. It has complete as well as selective light protection properties 9. A variety of sizes and shapes are available - amenable to the most diverse shaping 10. May be heat processed, hot filled and microwaved 11. High speed automatic lines can be used to fill glass containers 12. Smooth surface – easily cleanable Disadvantages 1. It is brittle (breakable) and there is the danger of contaminating the product or injuring the consumer with splinters or chipped edges and there is also the chance of product loss 2. It is heavy which leads to high transportation costs 3. It is subject to thermal shock 4. It is noisy material in use at the filling stage 5. Light sensitive product can’t be stored 6. Not printable – requires additional label 7. Occupy large volume 8. High energy requirement during manufacturing Composition Glass is manufactured by a continuous process in huge machines, which may take up to 2 days from the input of raw materials to the output of finished containers. It is important to have a good quality control throughout the process to ensure that the quality will be acceptable.

The composition of glass can be broken down as follows: Silica oxide (from sand) : 73.0% Lime as calcium oxide or carbonate : 11.0% Soda ash (sodium oxide or carbonate) : 14.0% Alumina (Al2O3) : 1.0%

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Additives such as selenium and cobalt are added for decolorizing. Colours are made by adding various additives. For e.g.: Pale green: add 0.2% iron oxide Dark green: add chromium oxide Blue: add cobalt oxide Amber/brown: add iron oxide + sulphur + carbon for UV protection Opal/white: add calcium fluoride that scatters the light to give a white appearance For glass to resist thermal shock, a high silica and low alkali blend is used. Cullet is the term given to recycled glass which is broken down and added to the fresh raw materials to make glass of a similar composition. The cullet is added in the ratio of 25% cullet to 75% raw materials to assist the melting process and to achieve a homogenous melt. Manufacture The raw materials used for the manufacture of glass are SiO2: 68-73% Calcia, CaO: 10-13% Magnesia, MgO: 0.3-3% Soda, Na2O: 12-15% Alumina, Al2O3: 1.5-2% Fe2O3: 0.05-0.25% Sulfur trioxide, SO3: 0.05-0.2% Silica is combined with other flux. Sodium and potassium carbonate are added to lower the fusion temperature and viscosity of silica. Calcium and magnesium carbonates act as a sterilizer, preventing the glass from dissolving into water. Lead gives clarity while alumina increases the hardness and durability. Addition of borax up to 6% reduces the leaching of sodium which is loosely combined with silicon from the glass by forming the boro-silicate. The raw materials and cullet are mixed and fed into the melting chamber of the oil or gas fired o furnace. The operating temperature is about 1500 C and the capacity is 4-400 tons. Small amounts of minerals are added for color or strength. The soda ash melts first and acts as solvent for the sand. The raw materials react, fuse and circulate until they become a homogenous molten liquid. Gas bubbles are given off and set up currents that improve the mixing. If they are not given sufficient time at this stage, the gas bubbles will be trapped in the mass and will not be vented, leading to the occurrence of small bubbles in the finished container, known as seeds. Another potential fault is the occurrence of stones that are crystalline inclusions in the glass, which are imperfections due to the raw materials being insufficiently melted. As the mixture melts, the compounds fuse & become easy to shape. From the furnace, the molten liquid is fed through a throat or restriction that prevents the passage of impurities, into the working chamber, which is fired by a small number of burners. The main aim is to ensure uniform temperature distribution throughout the depth of the glass. Glass in a continuous and viscous stream is cut by rapidly moving horizontal blade to form a gob (gob formation). A gob is a piece of material of the right size and weight to form the required container. The gob falls by gravity into the former. There are two sets of moulds; the first is the parison mould where the shape of the finish (the opening) is formed and it determines the distribution of the material and the wall thickness of the container. The second is the blow mould where the inverted parison is blown to its final size and shape. The parison mould can operate using pressure or by blowing air. So, there are two methods, viz. Press and Blow (P & B) method, which is used for wide mouthed containers 65


such as jars and the other is the Blow and Blow (B & B) method, which is used for narrow necked containers, such as bottles.

Fig: Blow and Blow (B & B) method

Fig: Wide neck Press and Blow (P & B) method An alternative, for lightweight bottles, is the narrow neck press and blow process. The press and blow process is generally best suited to produce jars with a neck finish size of ≥35mm (≥1.25′′); the other two processes are more suited to produce bottles with a neck finish size of ≤35mm. The narrow neck press and blow process offers better control of the glass distribution than the blow and blow process, allowing weight savings in the region of 30% to be made.

Fig: Narrow neck press and blow forming process o

The temperature of the moulds is important. Molten glass enters at a temperature of about 1000 C o and the moulds should be about 500 C. If the mould is too cold, the glass will not flow properly as it will tend to cool and solidify, whereas if the moulds are too hot, the glass will stick to the mould surface. The moulds are made of fine grained cast iron with a highly polished surface, to a specified size. Lubricants are used on the moulds but these contain graphite and leave a deposit of a fine film of carbon on the mould surface that is oxidized by heat. This must be regularly removed, which tends to enlarge the mould cavity. o After moulding, the glass is at a temperature of about 450 C. If allowed to cool at ambient temperature, there would be internal stresses in the container as the exterior wil l cool at faster rate than the interior. This differential rate will lead to contraction and the container may shatter. To prevent this, the containers are fed into the annealing tunnel. Annealing is a process of reheating the glass, and then gradually cooling to remove stresses. At first, the temperature is raised to about o 600 C at which stresses are removed as it is near the softening point of glass. Then the temperature is gradually reduced to ambient temperature. Inspection is the next stage. The containers are examined for defects; their dimensions are checked and compared to the specification, which includes height, diameter, weight, capacity, color, etc. If there is an out of specification bottle, it would not be sealed on the machine and can lead to downtime, breakages, faulty seals, etc. 66


Design parameters One of the design parameters to be borne in mind when looking at the functionality of a glass container is that the tilt angle for a wide-mouthed jar should be ≥22° and that for a bottle ≥16°. These parameters are indicative of the least degree of stability that the container can withstand. Surface treatments Glass just formed has non-lubricant surface and may lead to abrasion. Once formed, surface treatment is applied to the container in two stages, which are:

Inner surface treatment This can be carried out by two methods: o

a. Sulphur dioxide or ammonium sulfate is injected into the container at 550-600 C. The gas reacts with sodium atom to form a haze deposit of sodium sulfate on the surface, which is then subsequently washed off by the filler leaving the surface which is extremely resistant to chemical attack. This method is not commonly used. b. This method involves the use of fluorocarbon gas in place of sulphur dioxide. In this case, sodium fluorite is formed, which is then removed by volatilization process. The fluorine atoms enter into the glass structure and immobilize the sodium ion. As a result, no residual film is formed on the surface. This technique is valuable and is generally used for colour glasses. Outer surface treatment This method consists of two essential steps: a. Hot end treatment: The purpose of hot end surface treatment is to prevent surface damage whilst the bottle is still hot and to help maintain the strength of the container. This is done prior to annealing process. In this process, vapour containing tin or titanium in the form of tetrachloride is brought in contact with the outside of the container forming a thin metal oxide layer which improves the adhesion of the subsequent post annealing coating. This treatment tends to generate high friction surfaces; to overcome this problem, a lubricant is added. b. Cold end treatment: This step is applied after the container has been annealed. This step involves the spraying of an organic material in an aqueous base containing wax, silicon, oleic acids, or polyethylene onto the surface of the container to increase the lubricity by providing a surface with low coefficient of friction. The purpose of the cold end treatment is to create a lubricated surface that does not break down under the influence of pressure or water, and aids the flow of containers through a high speed filling line. Components of glass bottles (Nomenclature) The in sweep hill prevents the damage at the corners as it is less likely to hit off any object. Thread is the protruding part on the neck of the bottle which the lid connects giving a seal. CT refers to the continuous thread, commonly used for screw on lids. There are many styles of finish available depending on the type of closure required. Thread engagement and thread pitch are important. Thread engagement is defined as the number of turns given to the lid from the point of first engagement to the point where the sealing edge of the bottle makes contact with the liner. It must be at least equal to one. Greater than one is better for a secure closure. Thread pitch is the number of turns of thread per unit travelled in the transverse direction. It thereby measures the steepness or slope of the thread. A low number means that the thread is steep, giving a more rapid screw on and off. However, it requires a deeper cap to achieve thread engagement. 67


Although glass can be made into a wide variety of shapes, particularly f r marketing high-value products such as liqueurs an spirits, simple cylindrical shapes are stro ger and more durable. Sharp corners and abrasion o glass surfaces weaken the container, and d sign features such as a protruding ‘shoulder’ which inimizes contact between containers during handling, or protection by a plastic sleeve are used to reduce the risk of damage. Alternatively glass surfaces ay be treated with titanium, aluminium or z irconium compounds to increase their strength and lso enable lighter containers to be used. ouis (1998) described potential advances in glass-m king technology using plasma-arc crucibles to melt raw ingredients. The molten glass could then be co-extruded in a similar way to that currently used for plastic containers to produce jars or ottles of any shape, size or thickness. Thermal shock For pasteurized and sterilize products, the glass container will need to be able to withstand a o temperature difference of more than 45 C. Ordinary glass will shatter because it is a poor conductor of heat and there ore is not suitable for these applications. Thicker glass is more vulnerable to thermal shock s it will have a higher temperature differential across it and being more stressed, it will crack. Types of glass containers The main components of the container are the cylindrical main part, the ottom, the neck (called the finish), the closure (the screw cap), and the label. The cylindric l shape is chosen for maximizing strength for a given volume (the sphere is a better shape but not convenient for packaging). Glass is not well suited for sharp corners as stresses tend to concentrate in areas of sharp curvature. The main co mponents of the cap are a lacquer, wad, liner, and cover. Caps may be plastic or metal, and the t pe of closure might be thread, lug, friction, snap-cap, roll-on, cork, crown, twist-off, etc. The various types of glass containers have a range of names: 1. Bottles (most used) – round, narrow neck to facilitate pouring and losure, for liquids and powders 2. Jars (wide-mouthed bottles ) – neckless, allowing fingers or utensils to be easily inserted; used for liquids, solids, and non-po urable liquids such as sauces, jellies, and pas tes 68


3. Tumblers (open-ended jar ) – shaped like drinking glasses; used for jams, condiments, and jellies 4. Jugs (bottles with carrying handles) – short, narrow necks designed for ouring 5. Carboys (shipping contain rs) – shaped like short-necked bottles, usually used with a wooden crate holder 6. Vials and ampoules (smal l glass containers) – occasionally used for spices, etc., but mainly used by the pharmaceutical in dustry The main uses of glass for p ckaging are in milk bottles, condiments, ba y foods, instant coffee, and drinks. Glass is not use for frozen products, or for ground or ro sted coffee because of breakage costs and the difficu lty of vacuum flushing. Design of containers It is important to achieve t e best distribution of glass to maximize strength without being excessively heavy. The redu ction in weight of glass containers leads o savings in both raw materials and in transportatio costs. The strongest shape is the sphere bu t this is not feasible for containers that must have a lat base for stability. The most practical shape is the cylinder. An ellipse is half as strong as cylinder. Bottles having square cross sections w ith rounded corners will have quarter of the strength s cylindrical bottles, while with square corners will have only onetenth strength as compared to the cylindrical ones. Here the corners must be reinforced. Thus the shape plays a large part in the strength of the container. Sharp corners a d changes of direction should be avoided, the smoot er the radius, the better.

A returnable bottle such as b er bottle is known as multi-trip container. to the container to which it will be exposed, it will be thicker and returnable container.

ue to the extra hazards eavier than a one-trip

Sealing of glass containers Although glass is a complete barrier to moisture vapour, gases and odou rs, the product can still deteriorate if the sealing of th bottle is faulty. The main features of a good bottle closure are: 1. It should prevent the loss f the contents or any constituents of the con ents 2. It should prevent penetration of any substance from outside the contain er 3. The closure material shou d not react with the contents of the container 4. It should be easy for the c nsumer to reach the contents 5. If may have to make a go d re-seal 6. It may have to be pilfer -proof, i.e. it must be obvious, visually, if the closure has been removed and replaced 7. It should harmonize with the container. A well-designed closure can add considerably to the sales appeal of the pack

There is a wide range of clo sures available for the sealing of glass cont ainers, but they can be divided into 3 main groups:

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a. Normal seals: These are closures whose main function is to give a good seal when internal and external pressures are approximately equal. They are able to withstand reasonably small change in pressure, such as might be caused by changes in ambient temperature. Normal seals, that is those used for non-vacuum/non-pressure filled products, comprise composite closures of plastic/foil, for products such as coffee, milk powders, powder and granular products in general and for mustards, milk and yoghurts. b. Pressure seals: These are designed to withstand high internal pressures, such as those occurring in carbonated beverages. Pressure seals can be metal or plastic with a composite liner to make the seal, and can either be pressed or twisted i nto place. They include: - preformed metal, e.g. crown or twist crown - metal closures rolled-on to the thread of the glass - roll-on pilfer proof (ROPP) - preformed plastic screwed into position with or without a tamper evidence band. c. Vacuum seals: These are designed to give an air-tight seal where the pressure inside the containers is appreciably lower than those outside the container. The seal is usually maintained by the higher external pressure so that if there is a loss of vacuum inside, the closure may leak. Vacuum seals are metal closures with a composite liner to seal onto the glass rim. They can be pressed or twisted into place, at which time a vacuum is created by flushing the headspace with steam. They lend themselves quite readily to in-bottle pasteurization and retort sterilization and sizes range from 28 to 82 mm. For beverages, sizes are usually in the 28–40 mm range. Finishes and closures The part of the glass container that takes the closure is called the finish. Wide mouth containers have an opening almost as large as the body of the bottle. Liquids are usually put into the narrow neck containers for convenience in pouring. The neck may be threaded for screw cap or rounded for crown cork. It may have an interrupted thread to fit a lug type of cap, also known as quarter turn closures. Metal caps may be used, made of tinplate or aluminium and are usually coated with organic compounds. Screw cap is widely used and is made of tinplate with a liner of cork or pulp-board laminated with a layer of plastic film, vinylite and other plastics or with a rubber gasket (for vacuum seal). Defects in Glass Containers More than 60 defects occur in glass container ranging from minor defects, major defects and critical defects.

Critical defects Critical defects are hazardous to the user and do not meet the requirements. The containers are completely unsellable. The following are the criti cal defects occurring in the glass containers: 1. Unfilled finish: A depression on the surface above a thread not filled out 2. Check : A shallow surface crack usually wavy and generally in a straight line. Groups of checks are called crizzled finish. Bruised checks occur near the shoulder or heel areas. Mould checks are deep and run from the bottom to the sides. Panel checks are found on the flat areas of the bottle. 3. Filament : Hair-like strings inside the bottle. 4. Split : Open crack starting at the finish and extending downwards. 5. Spikes : Long thin strands inside the bottle which would break when the bottle is filled. 6. Over-press : A rim inside the final which may be sometimes sharp. 70


7. Freaks : Odd shapes which render the bottle unusable. 8. Soft blister : A thin blister near the sealing surface or anywhere in the bottle. 9. Cracks : Partial fracture in the heel or shoulder. 10. Cord : A strain not relieved by annealing. 11. Finish marks: Lines on the sealing surface. Major defects Minor defects reduce the usability of the container or its contents. The following are the major defects found in the glass containers: 1. Chipped finish: Broken edge. 2. Stone: Non-glass material in the container. 3. Rocker bottom: A sunken center portion in the base. 4. Fin: A seam on the top surface along the parting line. 5. Flanged bottom: A run of glass around the bottom at the parting line. Minor defects Minor defects do not affect the usability of the container but render them unattractive to the user. The following are the minor defects occurring in the glass containers: 1. Hard blister or droplet : A projection on the glass. 2. Sunken shoulder : Improper blowing. 3. Long neck : Taken out from mould when too hot 4. Heel tap: Heavy glass on one portion of the base. 5. Mark : Caused by oil accumulating in the mould. 6. Dirt : Non-glass material like oil, carbon, rust, etc coming from the mould. 7. Seeds: Small bubbles in the glass. 8. Wavy bottles: Irregular surface on the inside. 9. Stuck bottles: Two bottles sticking when hot and leaving a rough spot on pulling apart. Physical Properties of Glass

1. Mechanical properties Because of its amorphous structure, glass is brittle and usually breaks because of an applied tensile strength. The fracture of glass originates at small imperfections or flaws, the large majorit y of which are found at the surface. A bruise or contact with any hard body will produce very small cracks or checks on the glass surface that are invisible to our naked eye. However, because of their extreme narrowness, they cause a concentration of stress that may be many times greater than the nominal stress at the section containing them. It is the ultimate strength of a glass surface which determines when a container will break. The fracture formula is: Tensile stress + Stress concentrator = Fracture The mechanical strength of a glass container is the measure of its ability to resist breaking when forces or impacts are applied. Glass deforms elastically until it breaks in direct proportion to the applied stress, the proportionality constant between the applied stress and the resulting strain being Young’s modulus E. It is about 70 GPa for normal glass. The following four aspects are important: a. Internal pressure resistance This is important for bottles produced for carbonated beverages, and when the glass container is likely to be processed in boiling water or in pressurized hot water. Internal pressure produces bending stresses at various points on the outer surface of the container. 71


b. Vertical load strength The design of shoulder is important in minimizing breakage during high speed filling and sealing operations. c. Resistance to impact Two forms of impact are important – a moving container contacting a stationary object (as when a bottle is dropped) and a moving object contacting a stationary bottle (as in a filling line). In the latter situation, design features are incorporated into the sidewall to strengthen contact points. It is also be lowered by the development of surface treatments (including energy absorbing coatings). d. Resistance to scratches and abrasions The overall strength of glass can be significantly impaired by surface damage such as scratches and abrasions. This is especially important in the case of reduced wall thickness bottles such as one trip bottles. Surface treatments involving tin compounds provide scuff resistance, thereby overcoming susceptibility to early failure during bottle life.

2. Thermal properties The thermal strength of the bottle is the measure of its ability to withstand sudden temperature changes. This property is important because glass has the least resistance to temperature changes. The resistance to the thermal failure depends upon the type of glass employed, the shape of the container and the wall thickness of the container.

When a glass container is suddenly cooled (e.g. on removal from a hot oven), tensile stresses are set up on the outer surfaces, with compensating compressional stresses on the inner surface, as shown in fig(a). Conversely, sudden heating leads to surface compression and internal tension. In both situations, the stresses are temporary and disappear when the equilibrium temperature has been reached. Because glass containers fracture only in tension, the temporary stresses from sudden cooling are much more damaging than those resulting from sudden heating, since the potentially damaged outer surface is in tension. It is found that the amount of tension produced in one surface of a bottle by sudden chilling is about twice as great as the tension produced by suddenly heating the outer surface, assuming the same temperature change in both cases. 3. Optical properties Because glass has no crystalline structure, when it is homogenous and free from any stresses, it is optically isotropic. The optical properties of glass relate to the degree of penetration of light and the subsequent effect of that transmission, transmission being a function of wavelength. The spectral transmission is determined by reflection at the glass surface and the optical absorption within the glass.

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Factors affecting glass container strength  Shape  Surface condition  Glass weight  Applied stress

The shape, surface condition, applied stresses and glass weight all combine to determine the strength of a glass container. Carbonated beverages and vacuum packed foods develop internal pressure stresses, predominantly circumferential and longitudinal. Typical pressure inside a carbonated beverage bottle at ambient temperature is 400 kPa, rising to o about 700 kPa at 40 C and 1000 kPa at pasteurization temperatures. Bottles for carbonated beverages have target bursting strengths well in excess of the equilibrium pressure of a carbonated beverage. Vertical load stresses are generated by stacking containers on top of each other or by applying closure; these compressive forces produce tensile stresses in the shoulder and heel region of up to 690 kPa. These stresses can be lowered by decreasing the diameter difference between the neck and the body, by increasing the shoulder radius and by reducing the diameter difference between the body and the bearing surface. During hot filling or pasteurization of glass containers, the rapid temperature changes lead to the development of tension stresses on the cold surface and compression stresses on the hot surface with additional bending stresses being generated by expansion and contractions of the container. Thermal stresses can be reduced by minimizing the temperature gradient from the hot to the cold side, decreasing the glass thickness, and avoiding sharp corners, especially in the heel. Stresses caused by steady-state thermal gradients may or may not cause failure depending on the degree of constraint imposed by some parts of the container on others, or by the external mounting. Consequently, under minimum constraint and maximum uniformity of gradient through the thickness, very large temperature differences can be tolerated.

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�� Introduction A wide range of paper and paperboard is used in packaging today – from light-weight infusible tissues for tea and coffee bags to heavy duty boards used in distribution. Paper and paperboard are found wherever products are produced, distributed, marketed and used, and account for about one-third of the total packaging market. Approximately 10% of all paper and paperboard consumption is used for packaging and over 50% of the paper and paperboard used for packaging is used by the food industry. Today, examples of the use of paper and paperboard packaging for food can be found in many places such as supermarkets, traditional markets and retail stores, mail order, fast food, dispensing machines, pharmacies, and in hospital, catering and leisure situations. Uses can be found in packaging all the main categories of food such as:  Dry food products – cereals, biscuits, bread and baked products, tea, coffee,  Sugar, flour, dry food mixes etc.  Frozen foods, chilled foods and ice cream  Liquid foods and beverages – juice drinks, milk and milk derived products  Chocolate and sugar confectionery  Fast foods  Fresh produce – fruit, vegetables, meat and fish. Packaging made from paper and paperboard is found at the point of sale (primary packs), in storage and for distribution (secondary packaging). Paper and paperboard are sheet materials made up from an interlaced network of cellulose fibres. These materials are printable and have physical properties which enable them to be made into flexible and rigid packaging by cutting, creasing, folding, forming, gluing etc. There are many different types of paper and paperboard. They vary in appearance, strength and many other properties depending on the type(s) and amount of fibre used and how the fibres are processed in paper and paperboard manufacture. 2 The amount of fibre is expressed by the weight per unit area (grams per square meter, g/m , or lbs. per 1000sq. ft), thickness {microns, µm or 0.001mm, and thou (0.001 inch), also referred to as points} and appearance (colour and surface finish). Paper is defined as sheets of material thinner than 0.23 mm and lighter than 220 g/m2, or grammage of less than 150 gsm (grammage per square meter), whereas paperboard is thicker than 2 paper and has a higher weight per unit area. Paper over 200 g/m is defined by ISO (International Organization for Standardization) as paperboard or board. However, some products are known as 2 paperboard even though they are manufactured in grammages less than 200 g/m . Properties 1. Paper in its basic form is a cheap material 2. It is recyclable and biodegradable 3. It is derived from plant source and is thus renewable 4. It is easy to print 5. It has stiffness, rigidity and good fold properties 6. It is opaque and can be produced with different degrees of opacity 7. It has light weight and is flexible 8. It can be produced in many grades and converted to many different forms, especially boxes or cartons 74


9. It is non-toxic – directly b used in contact with food surfaces 10. It is easily combined with other materials to make coated or laminated packs 11. It has high GTR and WV R; without treatment, it provides a poor barrier to gases & moisture 12. It is sensitive to moisture content and RH; at high RH, it is likely to url at the edges, which can affect operation on hi h speed packing lines 13. It is not grease-proof except certain grades that have been specially tre ted 14. It is easily torn and punct red Composition of Paper Paper is derived from cellulo e, which is found in wood, bamboo, cotton, straw, etc. Some waste paper is also recycled when urity and strength are not essential. Additiv s are added to improve its characteristics. Of the total world paper prod ction, 97% is from wood, of which 85% is btained from firs, pines and spruces. Wood contains about 50% cellulose fibres, which is held together in bundles by lignin. The lignin makes u about 30% of the composition with the remainder being 16% carbohydrates and some 4% f other materials such as proteins, resins a d fats. It is principally the cellulose which is eventually made into paper. The individual cellul se fibers are finer than human hair, and a few mm in length. The type of raw material influen es the fiber length and thickness. Depending upon the chemical constituents, wood is divided into two gro ups, viz. soft wood and hard wood. Components Soft wood Hard wood Cellulose 42≤2% 45≤2% - long chain, unbranched m olecule Hemi-cellulose 27≤2% 30≤5% - branched, short chain mol cule Lignin 28≤3% 20≤4% - three dimensional phenoli polymer network

Cellulose – moderately resistant to action of chlorine and dilute NaOH solution under mild condition, resistant to oxidati n, i.e. bleaching can be done without physic l damage Hemicellulose – largely resp nsible for hydration and development of bo nding during beating of chemical pulps. So, hemicellu lose must be rejected as possible Lignin – intracellular substa bundle. It has no fiber formi hydroxide with the formatio thus thermocoupling can be d

ce responsible for joining/cementing cellul se fibres together in a g properties, i.e. undesirable. It is attacked y chlorine and sodium o of soluble dark brown derivatives. It softens at about 160 C, and ne.

Soft wood is especially preferred for paper manufacturing. Hard wood produces finer and smoother but less strong shee . Manufacture of Paper

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Pulping Paper and paperboard are sheet materials comprising an interlaced network of cellulose fibres derived from wood. Cellulose fibres are capable of developing physico-chemical bonds at their points of contact within the fibre network, thus forming a sheet. The strength of the sheet depends on the origin and type of fibre, how the fibre has been processed, the weight per unit area, and thickness. The type of fibre also influences the colour. To be useful to the papermaker, the raw material must be reduced to fibrous state. This method is called pulping. The main objective of pulping is to separate cellulose fibers without damaging them. The presence of lignin may deteriorate paper in terms of colour and strength. There are two basic methods of pulping, mechanical and chemical pulping. In both the process, the bark is stripped from logs cut to a suitable length at appropriate stage in their growth.

Mechanical Pulping Logs for mechanical pulping may be used directly in 1.2 m lengths or, alternatively, they may be chipped into pieces of uniform size about 15-20 mm long. Two methods of mechanical pulping are used. In one, the logs are pressed against the surface of large revolving grindstone, kept wet by a stream of water which also removes the fibers. In the other system, the wood chips are passed between the two plates of a disc refiner with specially treated surfaces, very close together and rotating at high speed. In this way, the wood chips are reduced to individual fibers and the water soluble impurities are removed while most of the lignin remains. Many fiber bundles and some damaged fibers are also left in the pulp. Mechanical pulp is normally made from softwood, typically spruce. The yield of pulp is higher, in the range of 70-80%. Much grinder and disc-refined wood pulp is used for newsprint, magazine, folding and molding cartons, although substantial quantities are employed as a mixture with chemical pulp for making certain kinds of board. Bundle fibers are only removed, and hence, the bundle is stiff and bulky which do not collapse as chemical pulp. Paper made from this type of pulp is relatively weak and dull compared to the alternative chemical pulp. This method is not as efficient as chemical method. Properties  Low cost requirement  Quick ink absorbing property  High bulk  Excellent opacity  Stiffness  Low mechanical strength  Mechanically separated fibre retains the colour of the wood though this can be made lighter by mild chemical treatment. Chemical Pulping Chemical pulping starts from chips, but removes all materials other than the cellulose fibers by chemical action and solution, the chemicals converting the lignin to a soluble form that can be removed by washing. This type of pulping produces cellulose fibers of higher purity than those produced by the mechanical process. They are generally much less damaged and, in addition, the fiber bundles are fewer. Some mechanical pulp may be added to chemical pulp for paper manufacture, but such paper is not usually used in direct contact with foods. Several chemical pulping processes exist, and the quality of the pulp depends upon the process, as well as the kind of wood fiber used. For packaging purpose, any of the following processes are used: 76


a. Alkaline process Chemical pulp is produced by digesting wood chips in an alkaline solution followed by washing. This method involves the direct or indirect use of NaOH to degrade and dissolve the lignin from the wood to separate the fibers. This is further divided i nto two methods: Soda process : This method involves the direct use of NaOH in the range of 4-6% w/w and the o temperature is maintained at 170 C. Sulphate/Kraft Process : In this process, the wood chips are digested in a solution of caustic soda and sodium sulphate for some hours. This dissolves the lignin, which can be recovered and reused, and leaves the cellulose fibers to be used. This method produces the strongest papers, which are brown in colour and strong due to their long fibers. The name comes from the Swedish word “Kraft” meaning “strong”. Kraft paper has a blotchy appearance due to it being non-uniform with varying length of fibers.

b. Sulphite process This process uses sulphur dioxide and calcium bisulphate, which are mixed with the chips in o aqueous solution and heated to about 140 C. The lignin is dissolved out leaving the fibers, and after digestion the mass is washed with water and then bleached with another chemical, such as calcium hypochlorite and pressed into pulp sheets. This gives a very pure cellulose fiber, although the resulting pulp is not as strong as that from the Kraft process. c. Semi-chemical process This method is a combination of mechanical and chemical pulping. In this process, the wood chips are partially treated with chemicals and partly mechanically to reduce them to fibers, hence the name semi-chemical. It consists of soaking the wood chips in caustic soda to soften the lignin before grinding. It is commonly used for hardwoods. The material obtained has strength and stiffness and is used for the manufacture of the fluting medium for corrugated board. Chemically separated fibre is brown but it can be bleached to remove all traces of non-cellulosic material. Pure cellulose fibres are translucent individually but appear white when bulked together. Sulphate paper is strong and hence used for paper sacks for flour, sugar, fruits and vegetables. Sulphite paper is lighter and weaker and is used for grocery bags and sweet wrappers, as an inner liner for biscuits and in laminations. Digestion The digestion process essentially consists of the treatment of wood in chip form in a pressurized vessel under controlled conditions of time, liquor concentration and pressure/temperature. o Digestion is carried out under pressure of 1000 KPa, at the temperature of 170 C for 1.5 hours. The main objectives of digestion are:  To produce a well cooked pulp free from non-cellulose portion of wood (i.e. lignin and to some extent hemicellulose)  To achieve a maximum yield of raw material from wood with pulp quality  To ensure a constant supply of pulp of uniform quality

After digestion, the liquor containing the soluble residue from the cook is washed out of the pulp, which is then screened to remove knots and fiber bundles that have not fully disintegrated. The pulp is then sent to the bleach plant or paper mill. Bleaching Pulps vary considerably in their colour after pulping, depending on the wood species, method of processing and extraneous components. The whiteness of pulp is measured by its ability to reflect 77


monochromatic light in comparison with a known standard. Brightness is an index of whiteness, measured as the reflectivity of paper sample using light at 457 nm. Unbleached pulps exhibit a range of brightness values from 15 to 60. Cellulose and hemicellulose are inherently white but do not contribute to colour. It is the chromatic groups on the lignin that are largely responsible for the colour of the pulp. Bleaching is done to improve the colour and appearance of the pulp, i.e. increase whiteness. It can be carried out by two methods:  Oxidative bleaching – use of H 2O2, NaOHCl  Reductive bleaching – use of sodium hydrosulphite As bleaching reduces the strength of the pulp, it is necessary to reach a compromise between the brightness of the finished sheet and its tensile properties. Beating After the pulp has been produced, it may have to be bleached to make it white, or coloured, or treated in other ways. One of the most important processes used in the pre-preparation of fibers for paper making is the beating process. After pulping, the water content is 96%, and the pulp is beaten to rub and brush the individual fibers. This causes them to split down their length, producing a mass of thin fibrils which will enable them to hold together in the matted paper more strongly. This method is called fibrillation. The greater the degree of fibrillation, the stronger will be the paper. Different pulps respond differently to this treatment. Softwood fibers will fibrillate to a greater extent than hardwood fibers, and hence softwoods are potentially able to produce stronger papers. The main objective of beating is to improve the strength and other physical properties of the finished sheet. Beating increases the surface area of the fiber, and also makes fibers flexible causing them to become relatively mobile and to deform plastically on the paper machine.

However, beating also cuts the fibers, which is undesirable, because in excess, it will lead to a loss of tear strength. A compromise must be reached to optimize the performance of the paper. Fibrillation increases its tensile & burst strength while too much cutting lowers its burst strength. This can be represented by the alongside diagram: Furthermore, beating breaks up any fibre clumps and refines them into individual cellulose fibers. The art of breaking packaging pulps is to maintain a high proportion of fibrillation and a low proportion of cutting in the pulp, to give the desired properties in one finished paper. Paper and board making machines The modern paper making instrument is the Fourdrinier machine. It has two sections, each with four basic parts, known as the wet end and the dry end.

Wet End 1. Stuff chest It holds slurry of pulp containing about 97 parts of water to every 3 parts of fibre. The pulp is diluted from 96% to 99.5% water content so that it is not too heavy to form a sheet. 78


2. Head box The diluted pulp from the stuff chest passes into the head box, which is both a means of agitating the slurry and a turbulence reducer. The pulp is agitated to form a uniform fiber suspension, known as the stock, which is fed to the slice. 3. Slice The slice is a part of the head box and consists of a narrow slot in its front face through which the stock flows onto the wire. Adjustments can be made in the opening to the slice, and it can be raised or lowered to adjust the flow. 4. Fourdrinier wire The Fourdrinier wire carries the stock from the slice up to the place where the sheet is removed at the so-called “couch” roll. The wire allows some water to drain away, helped by rollers underneath it and by suction boxes to remove the water, to get the mat of paper fibers into a sufficiently strong sheet to transfer to a felt which will move into the drying section. At this stage the mat of fiber consists of 75-80% water by weight. It is transferred from the wire onto a felt or woolen carrier that absorbs moisture as it carries the sheet into the drying section.

Dry End 5. Presses The presses may be either plain, which just catch the water in trays, or fitted with suction to help to remove the water by pulling it through thousands of tiny holes in the suction roll. The sheet still contains 60% water, which is then passed into the dryers. 6. Dryers The dryers consist of long train of heated cylinders which come into intimate contact with the paper and dry it by heat. The moisture content is r educed to 4-6%. 7. MG dryer In certain cases, the paper may require to be machine glazed . A MG dryer is a special dryer which gives the paper a ‘machine glaze’ or a gloss finish, by use of a highly polished cylinder. 8. Calendar stacks Machine finished (MF) papers are smoothed in what is called a calendar stack . This consists of a series of rolls which iron the sheet by slippage. The degree of machine finish is controlled by the number of rolls through which the paper passes, and it may be increased by applying a certain amount of surface water (from water box) to increase it. The MF papers are less stiff. Finally the paper passes to the reeler and winder, and is wound up into a giant roll, ready to be sent to the converter to convert it into cartons, wrappers, bags, etc. The furnish, the degree of beating, the amount of filler, binders, sizes, etc together with the operating variables of the particular paper-making machine and specific finishing processes, can be varied to produce many types of paper.

Finishing The large diameter, full machine width reels of paper and board are then slit into narrower reels of the same or smaller diameter or cut into sheets to meet customer and market needs. Sheets may be guillotined, pile turned, counted, ream wrapped, palletized, labeled and wrapped securely, usually with moisture resistant material such as PE coated paper or PE film. Surface sizing can be carried out, usually with a solution of gelatin in water containing small quantities of other chemicals to make the surface more water-resistant and to improve its printing properties. Paper and board are often coated with a layer of mineral pigment to improve their appearance and printing properties. 79


Board Making Paperboard is thicker and the basic idea behind the production is to form the paper web more rapidly and usually between two wires so that the drainage can take place from both sides. The twin wire former is in principle a method of letting the fibre suspension come out of the slice into a converging gap between two wires. Water is expressed from both sides of the sheet by the tension in the wire, and scraper blades pressing on the underside of the wires assist. To manufacture board of 4-5 mm thickness, it is necessary to use a c ylinder machine using several vats of stock, each adding a layer to the web. Rollers are used to squeeze out the excessive water and to dry it. The better quality papers are put on the outside while the cheaper, semi-chemical or recycled papers are put inside. Types of Paper and Paperboard Paper Types There are many types of paper available to meet the different requirements.  Kraft/sulphate Papers

Kraft papers are generally made from sulphate pulp on softwoods (e.g. spruce). These are heavy duty paper used for 25–50 kg multi-wall sacks, board liners, etc. They are usually used in several layers or ‘plies’, to give the required strength. They may be bleached white, printed, or used unbleached (brown), and may be wet-strengthened or treated to make water repellant. Bleached varieties are used for packaging where strength is required. Typical grammages are in the range of 70-300 gsm.  Sulphite papers

They are lighter and weaker than sulphate papers. These are usually bleached and generally made from mixture of softwood and hardwood. They are clean, bright paper, excellent for printing. It may be glazed to improve its wet strength and oil resistance, when it is known as MG (machine glazed) sulphite paper, which is used for labels. They can be coated with polythene to make it heat sealable, used in laminates. These are generally used for smaller bags, pouches, envelopes, waxed papers, labels and for foil laminating, etc. Typical grammages are in the range of 35-300 gsm.  Vegetable parchment

It is made from a pure cellulosic material (waterleaf) by treating pure sulphite pulp with concentrated sulphuric acid, after which it is washed in dilute sulphuric acid and water before drying. This closes the pores and fills voids in the fibre network to make the surface more intact than kraft paper, and thus makes the paper resistant to grease and oils and gives greater wet strength properties. Glycerol may be added to make a soft, flexible paper. It is odourless and tasteless, used to pack butter, cheese and fresh fish or meat. Typical grammages: 35-300 gsm.  Grease-proof papers

It is often used instead of the more expensive vegetable parchment for baked and greasy foods. It is made from sulphite pulp in which the fibres are more thoroughly beaten to produce a closer structure. It is a close-textured paper with greaseproof properties under dry conditions. It is not as white, strong nor as grease resistant as the parchment and will decompose if immersed in boiling water for several hours. It is widely used for wrapping fish, meat and dairy products. Typical grammages are in the range of 70-150 gsm.  Tissue

It is light and has an open structure. It is a soft non-resilient paper used to protect the surface of fruits, soft wrapping for silverware, jewellery, flowers, hosiery, etc. Typical grammages are in the range of 20-50 gsm. 80


 Glassine papers

It is similar to greaseproof paper, but is given additional calendering to increase the density and produce a close-knit structure and a high gloss finish. It is more resistant to water when dry but loses the resistance once it becomes wet. It has good oil and grease resistance and provides an odour barrier. It has a higher density and grammage of 40-150 gsm.  Waxed papers

It is a high grade sulphite paper coated in wax to give it a better moisture barrier, grease resistance and heat sealability. Generally, paraffin wax blended with microcrystalline wax or polyethylene is used. Coated Papers Paper and board both have the disadvantage from packaging point of view, of being susceptible to changes due to moisture. There are many methods of impregnating, coating and laminating paper with other materials in order to improve the resistance to water. The simplest and best method is waxing, which can be carried out by two methods. The first is the dry waxing, in which the paper passes through a bath containing the wax, and then through a heated section or hot nip rollers, which assist the wax to penetrate right through the paper. The wax is impregnated uniformly and doesn’t from a surface film. The second method is the wet waxing, which is used when it is desirable to have a film of wax on the top of the sheet. After the wax film has been applied to the surface of the sheet, it passes into a bath of cold water, which immediately sets the wax before it has time to penetrate into the sheet. Wax provides a moisture barrier and allows the paper to be heat sealed. However, a simple wax coating is easily damaged by folding or by abrasive foods, but this is overcome by laminating the wax between layers of paper and/or polyethylene. Waxed papers are used for bread wrappers and inner liners for cereal cartons. The paper or board web may also be coated with many kinds of emulsions, varnishes, lacquers and may also be laminated to other materials such as plastics, either using adhesives or by direct extrusion. The objective of all these methods is to improve the resistance of the basic sheet to water, water vapour, gases, greases or oils. Coatings can be applied:  from aqueous solutions (cellulose ethers, polyvinyl alcohol) to make papers greaseproof  from solvent solutions or lacquers  from aqueous dispersions (e.g. polyvinylidene chloride)  as hot-melts (e.g. microcrystalline wax, polyethylene and copolymers of ethylene and vinyl acetate) to increase gloss, durability, scuff and crease resistance and permit heat sealability)  as extrusion coatings (e.g. polyethylene) Although they are not affected by temperature, all papers are sensitive to humidity variations, and coated papers in particular may lose moisture from one face and are therefore prone to curling. Smooth papers block if pressed together in a stack. The optimum storage conditions for papers are about 20ºC and a relative humidity of approximately 50%. Paperboard Paperboard is a generic term covering boxboard, chipboard and corrugated or solid fiberboards. Typical paperboard has the following structure:  a top ply of bleached pulp to give surface strength and printability  an underliner of white pulp to stop the grey/brown colour of middle plies showing through middle plies of lower grade material  a back ply of either low grade pulp or better grade pulp if strength or printability are required 81


All plies are glued together with hot-melt or aqueous adhesives. Boards are made in a similar way to paper but are thicker to protect foods from mechanical damage. They normally are made on the cylinder machine and consist of two or more layers of different quality pulps with a total thickness in the range 300-1100 m. The main characteristics of board are thickness, stiffness, the ability to crease without cracking, the degree of whiteness, surface properties, and suitability for printing. Board Types The types of paperboard used in food packaging include:  White board

It is suitable for contact with food and is often coated with polyethylene, polyvinyl chloride or wax for heat sealability. It is used for ice cream, chocolate and frozen food cartons.  Chipboard

It is made from waste or recycled paper and is not used in contact with foods. It is cheap but unattractive due to its mottled appearance. It is difficult to print and has no strength or stiffness. It is often lined with white board to improve the appearance and strength.  White lined chipboard

It is popular for secondary packaging. It is a chipboard with an outer lining of chemical pulp, which gives a good printing surface, better foldability, and a better appearance. However, the interior is an unattractive mottled gray colour and is unsuitable for direct food contact. It is often used for products which are protected by an inner bag.  Duplex board

It has two layers. It has surface outer layer of bleached virgin chemical pulp and internal layers of mechanical pulp while the inner surface in contact with the product is a bleached (white) or semibleached (cream colour) chemical pulp layer. It is a popular material for folding box board cartons and may be hard sized to allow it to be used for chilled or frozen products.  Solid bleached board

It is a bleached virgin chemical pulp material that is relatively thick. It is used for ice-cream and frozen foods, etc. when it has been hard sized to prevent moisture ingress. Applications Primary Packs Paper is used in many different package formats, either alone or in combination with other materials. Bags are used to contain items in an easy to handle low cost form. Boxes are used to give the product a better presentation, stackability and greater rigidity. Bags are normally made from kraft paper which may be bleached for a white appearance when strength is required. If an attractive appearance is the main criteria, it is common to use MG sulphite paper. There are different styles of bags from a simple satchel type with a folded and glued base, or a similar design with a gusset to give greater capacity. A block bottomed bag is used for products which need to be displayed upright as it gives them a flat base so they can stand upright. A self opening bag is a block bottomed and gusseted bag. Folding bags are boxes made from board 300-1100 micron thick, 200-600 gsm, which are delivered in a flat collapsed state to be erected at the filling point, usually by automatic erecter/ gluer/filler/sealer machines. They may be of cheap recycled material – but this doesn’t perform well on automatic machines and would be suitable for hand pack operations, - or pure sulphite board, or duplex board, or it can be coated with plastic, wax or laminated with another paper 82


depending on the application. For e.g. it may be wax coated for moisture resistance, laminated to polyethylene for heat sealability or to glassine for grease resistance. Manufacture The board is manufactured and cut into sheets of the appropriate width and length for converting machines where it is printed and made into cartons. Usually, several boxes are made from one sheet depending on size, the individual box designs being arranged on the sheet to minimize board wastage. The machine also creases it where the board will fold to form the box, slits it to the desired shape and size and strips the excess board before passing the flat box to another machine where the side seam is glued and the creases are prebroken to ensure that they will fold easily on the fillers equipment. Each design is specific to a product and there are many variations available offering different shapes, opening features, reclosable features, display windows to allow the consumer to view the product, with punch holes or hooks so that the product can be hung for display etc. The design in improved from a handmade sample to suit the inner container or product. The crease must be of the correct depth. If it is too shallow, the box will not open easily as it will be stiff. If it is too deep, it will cut into the board, causing it to delaminate or split. The box may have opening flaps or bowing panels as a result. The pattern is supplied to the graphics department for artwork origination which will then be transferred onto stereos or plates for printing the boxes at the converters. A varnish is often applied to achieve a glossy appearance.

Dimensions are always specified: length x width x height Setup boxes differ from folding boxboard boxes in that they are not supplied in flat form to the packers but are pre-erected. For e.g. shoe box, match box, etc. These are used for low volume where the expense of an automatic filling system could not be justified. They have the advantage of greater rigidity but are less efficient in terms of storage requirements and material costs.

Composite containers This is another type of paper based primary package. It is called a composite container as it is made from more than one material, generally a paperboard body with metal or plastic ends. It is often used for dry foods such as salt, spices, custard, etc and can also be used with liquids if the interior is lined with a suitable material such as vegetable parchment, polyethylene or foil. There are two types of composite containers, based on two manufacturing methods, the spirally wound and the convolutedly wound. The spiral winding method is used to produce cylindrical containers only. It superimposes two or more plies of board and glues them together as they are wound about a stationary cylindrical mandrel in a spiral manner. Each ply is applied at an angle. When the cylinder so formed is of the required length, it is cut and edged from the mandrel. The weakest point in this structure is at the joint of the plies so these end need to be well butted with proper overlaps. The convolutedly wound container can be of different shapes; square, triangular, rectangular or oval. By this method, the container is formed by the mandrel rotating, pulling paper from the reel over glueing rollers and around the mandrel forming the tube. After each cycle, the paper is cut to separate it from the parent reel, the partly formed tube is pushed up along the mandrel and the next piece is formed behind it until it reaches the required length. The strength of the container depends on the board thickness and the number of plies. It is generally 250-500 micron thick. Two thin plies are better than one thick one. Materials used include chipboard or kraft, lined with parchment for liquid products, wax for hygroscopic products such as biscuits. Aluminium foil is non-toxic, opaque, water and grease resistant, and a barrier to volatiles. Polyethylene coated paper is used for ice-cream products while glassine is 83


used with oily, greasy foods like butter. For very hygroscopic products such as milk powder, a laminate of paper, foil and aluminium is used. The base is usually applied b y the manufacturer, by double seaming. Dif erent styles of closures are available, for example:  Slip on lids which are not airtight  Plug in lids which have a flush engagement so while not airtight ar more secure  Lever lid, with or without a diaghram, good for reclosability and h groscopic products  Plastic perforated to to aid dispensing product, e.g. salt. Init ially sealed to prevent spillage in transit  Double seamed end as used in canning, which is leakproof  Membrane closure (foil or plastic) with plastic snap on lid for reclosability after use Comparison of composite co tainers versus Metal can The composite container is v rsatile, strong, rigid and light weight. It is cheaper to produce and can be handled on the same filling equipment as a conventional metal c n. However, due to its paper content, it can be affect d by high humidity with a resultant loss of s trength. Other containers made of co posite materials include paper laminate cart ns such as tetrapak and purepak used to pack liquids l ike milk, juice, etc. Secondary Packages Traditionally, wood was us d for secondary packaging applications, but nowadays use of fiberboard is more popular s it is cheaper, lighter and automatable. he two main types of fiberboard are solid and corru gated fiberboard.

Solid fiberboard consists of a series of plies of paper. The inner plies are generally a cheap material such as chipboard hile the outer plies are often kraft or test as these have a more attractive appearance. The pl ies are laminated together under pressure u ing adhesive making a sheet of board of overall thickness 0.8-2.8 mm. The sheet is creased, slotted and printed in the flat form before it is converted into boxes by cutting it and gluing the side se m. Its strength depends on the material used in the v rious plies, its thickness and the type of ad hesive used. In general, two to six plies are used. Soli fiberboard is rigid and resistant to puncturi g. Corrugated fiberboard consi ts of liners, usually kraft or test grades, nd fluting medium or corrugated sheet which is us ally of a lower grade such as semi-chemic l or straw, sandwiched between the liners. The flutes or corrugation run parallel to the depth, i .e. down the side wall, when converted into a box a d increases its strength by increasing the su rface area on which the load is acting, thereby reduci g the effective load being supported by the box. As a result, it can be stacked higher. The liners rammage varies from 185 to 440 gsm while the fluting medium can be 113, 127 or 150 gsm, depe ding on the compressive strength required.

Components of single walled corrugated fiberboard

Triple walled corrugated fiberboard 84


There are various constructions available, from single faced board which consists of a liner and a fluting which is used to wrap articles, to single walled board which has one fluting medium sandwiched between two layers. For heavier loads it may be necessary to use double walled board which has three liners and two sheets of fluting arranged in alternate order, while very heavy loads will require the strength offered by triple wall board which uses four liners interspersed with three sheets of fluting. The fluting medium is available in different grades denoted as A, B, C and E fluting, which all have different characteristics and applications as outlined below: -1

Grade Flutes/m (m ) Flute Height (mm) A 104-125 4.5-4.7 B 150-184 2.1-2.9 C 120-145 3.5-3.7 E 275-310 1.15-1.65

Description Coarse, good compression resistance Fine, best impact & crush resistance, folds easily Medium-good stiffness & compression resistance Very fine, good printing surface, very automatable

Combinations of fluting used for boxes are AB, BC, AA and AC for double wall and AAB, CCB, BAE for triple wall. The finer grades will be on the outside as they provide a better printing surface and fold more easily. In testing the flat crush resistance grade B is best, 25% better than C and 50% better than A. Applying the force in another direction to test the rigidity will reveal that grade A is the strongest, 15% more than C and B is a further 25% behind. E grade has a good flat crush resistance but not a lot of strength. So, it tends to be used for display boxes for on shelf display of products. In transit to retailers, it is protected by a stronger outer carton. Manufacture of corrugated board The corrugation is achieved by subjecting the board to a steam shower and preheating rollers to make it flexible before passing it through the corrugated rollers. The tips of the flutes on one side are then coated with adhesive such as cornstarch, the liner is preheated and brought into contact with the flutes to produce single faced board. To convert this to single walled board, the other fluted side is passed over an adhesive applicator and a second liner i s attached.

For double walled board, two single faced boards are combined and a backing liner is added to complete the structure. The board is then dried, cut to the required width of sheet to be converted into boxes and passed through the converter where it is printed, scored (i.e. creased where the folds are required) and slit (to remove excess board where the flaps have to turn in) before it is cut to the required size. Then the side seam is glued, stitched, taped or stapled. These are available in many styles and in order to achieve standardization, the styles are all denoted by a code, whose first two digits tell the basic nature of the style. For e.g. the 02 code refers to a group of boxes which are one piece slotted blanks whose sides are folded. 85


The 03 groups are two piece boxes with a lid which fits over the body. The 04 groups have a hinged base with a lid which folds down. Economical packaging can be achieved by minimizing the amount of board used while maximizing the enclosed volume. The most economical ratio of dimensions has been found to be L:W:H :: 2:1:2 When the product is being palletized, the size should be designed to optimize the pallet, i.e. to maximize the number of boxes per pallet. Comparison of Solid versus Corrugated boxes Solid is better for damp environment but the corrugated board can be treated to make it more moisture resistant. It is more puncture resistant and not so easy to crush as corrugated so it is less likely to lose its strength. However, it is less rigid. The waste paper content of solid fiberboard may contain salts which can affect the corrosion of metal packages. Corrugated board is light in weight for equivalent strength so it is more economical. The corrugations act as cushioning for the product, being more shock absorbing. Comparison of Fiberboard versus Wood Fiberboard is cheaper, lighter more flexible in design, easy to automate on a packaging machine, easier to print, with no danger of splinters. It can be transported and stored flat until required thereby needing less storage volume.

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�� Introduction Wood had been traditionally used for secondary packaging in pallets, crates and boxes as it is a strong, rigid, and indigenous material. However, in developed countries, environmental concerns about deforestation have reduced the acceptability of wood packaging. As it is heavy, likely to splinter, not automatable, neither easy to open not to close, requires a lot of storage space and has a high labour requirement its use has been reduced. It is still popular material in the developing countries where it is available and labour is cheap. Wooden packaging does not require high capital investment in equipment as it is unsophisticated so it suits some small scale industries. It is difficult to dispose of and is bulky which makes retailers unhappy to accept it. It has a bad cost to weight ratio compared to fiberboard, which is its main rival. There are some applications for wood as a primary pack, mainly for the gift market as a presentation pack for tea, spices etc. Classification of Wood Wood can be categorized as hard or soft wood. Hardwood comes from deciduous broad leafed trees. It has shorter fibres than that from softwoods such as coniferous or needle bearing trees, which have greater strength. The properties which are important from a packaging aspect include the density which indicates the strength of the wood, its resistance to extraction of nails and how 3 much it will shrink in the drying process. Wood that has a density of less than 400 kg/m is not 3 suitable as it is not strong enough. Wood with a density of more than 750 kg/m is also not suitable for packaging applications either as it is too heavy or will distort. Wood with a density in the range 600-750 is suitable for use as load bearing member in a crate or as an edge bearing plank in a pallet. If the density is between 400-600 it should be used in lower stress applications such intermediate members, side and end panels etc. Other factors that are important are the woods bending and compressive strength, its nail holding power, resistance to splitting, ease of working and resistance to decay. For best results wood should have a moisture content of about 15%. There should be no knots more than one third the width of the plank and none in the nailing area. There should be no splits, decay nor insect damage.

For classification wood can be subdivided into four groups: Group 1: This contains some soft and hard woods including cedars, chestnut, firs, pines and willows. This group does not split easily when nailed, has moderate nail holding capacity, moderate strength as a beam and moderate shock resistance capacity. It is soft, lightweight, & easy to work and to dry. Group 2: This includes heavier coniferous species that have a noticeable difference in the colour of their wood grown during the spring (which is light) and the summer (dark) season, such as the larch, Douglas fir etc. These have greater nail holding capacity than Group 1 but are more inclined to split. The summer wood is harder and tends to deflect nails causing them to run out at the sides of the cleats. Group 3: This includes medium density hardwoods such as ash, elm, maple and sycamore. Similar to Group 2 for nail holding capacity and beam strength but less inclined to split or shatter on impact. Suitable for box ends and cleats.

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Group 4: These are the heavy hardwoods of highest density, e.g. beech, birch and oaks. Resistance to shocks and nail holding capacity is greatest but their hardness makes them difficult to nail and they tend to split at the nails. These are generally used for load bearing members. Styles of wooden containers Wood is used to make nailed wood boxes, wire bound boxes, crates, barrels, casks and baskets. Considering the main types:

Nailed wooden boxes are available in different styles depending on the strength required. The type of nail, size and spacing are very important as they affect the strength of the box. The location of the nail with respect to the grain of the wood is also relevant. If the nail is too large it will split the wood. The nails should be staggered, i.e. should not be in a straight line to give maximum strength. On a 100 mm wide board there should be a minimum of two nails 25mm from either end, if more than 100 wide then there should be at least three nails. The side grain is nearly three times stronger than the end grain so nails in the end grain should be closer together. Steel bands can be used to reduce the stress on the nails and reduce bulging. This allows a reduction of one third in the thickness of the wood used, and it also discourages theft. The steel bands should be placed one sixth of the box length in from either end for maximum effect. Wirebound boxes can take load of up to 225 kg. They are made of thinner hardwood and have wires secured around their girth at frequent intervals to add strength. Wooden cleats are placed at the ends for reinforcement. The advantage of this style of box is that it can be stored flat (known as “shooks”) until required so it takes up less storage space. The ends are fitted at that point. These boxes use less wood, half as much as the nailed box. However they are not even, due to the wire so they do not stack well. They require more sophisticated equipment to attach the wires and ends, and have a poorer resistance to puncture. They also need to be ordered in larger quantities as they are made to a specified size, but for longer production runs they are economical. Crates are used for transporting large items. They may consist of an open framework of cleats and battens that take the load, or they may be closed vial sheathing. Steel bands may be used to reinforce the corners. It should be large enough to completely enclose the product, i.e. no part should be protruding as it may be damaged. The contents should be secured within it so they do not move about during transit. The use of diagonal planks from corner to corner greatly reinforces the container. Shipping Containers This is the name given to packaging used to transport commercial quantities of material, also known as transport or transit packaging. Shipping containers which contain and protect the contents during transport and distribution, but have no marketing function. It includes wooden boxes, crates, drums, fiberboard shipping containers, textiles, paper and plastic sacks. More recently, intermediate bulk containers (IBCs), including combi-bins, large boxes made from metal, plastic or corrugated fiberboard, and large bags made from woven plastic fabric, have been introduced to increase handling efficiencies and have largely displaced wooden crates and cases.

The choice of shipping container will depend on the handling method and type of transportation used, costs and the product requirements. Ideally a shipping container should be returnable, as in crates from the dairy or for beer and coke bottles. These are designed to maximize transport and storage areas ideally when they are empty they fit into one another or stack well. Shipping containers play a vital but less glamorous role than the primary packaging that it contains and protects on the journey from the manufacturer to the retailer. Identification is another 88


main function of these contai ers to ensure that they arrive at their intended destination and are in good condition. To achieve th is, there are several international symbols used to tell people how to store, stack and handle the co tainer. Unlike sales packaging, transport packaging is removed after transport t the trader (wholesaler, retailer etc.) and the goods are sold on to the consumer or other third par ty without the transport packaging. Packaging which is delivered to the consumer and in which the consume r has no interest is also classed as transport packagin . Examples of transport packaging are: •

Paperboard trays and ilms as packaging for beverage cans

•

Boxes for capital goods, such as machinery, engines etc.

•

Cartons and films acti g as packaging material for furniture

Cartons holding a rel tively large number of individual items, s ch as toothpaste tubes, canned foods Some types of transport/shipp ing containers used are: •

Wooden containers These are used for perishable (moisture content =12-18%) and machineries. Poplar or pine wood is preferred. The surface is p inted to prevent moisture loss. Such a pack ging requires provision for aeration in order to dissi ate heat evolved from the produce. The material has high stacking strength and dimensional stab ility. Fungal growth does not occur even at high RH. Corrugated fiberboard boxes (CFB) These are made of paperboar liner and corrugated medium. Unbleached, virgin, coniferous kraft is suitable for liner. Waxing may be done to retard entry of moisture. C rrugated boards can be either single lined or double lined. Corrugated fiberboards are designate as per the number of plies, the flute height, and n mber per 30cm. A “3-ply A flute” refers t fiberboard made of 3 plies with every 30cm length aving 32-38 flutings of 4.5-4.7mm height. The adjacent figure shows a tri-wall corrugated board. It consists of three plies of fluted paper which are glu d together by two plies of paper or cardboard and the outer surfac s of which are likewise each covered with one ply of paper or card oard. Inserts in the box These are used for cushionin g very delicate items. They come in variou s forms, viz., cell pack (partitioning), paper honey comb, molded pup tray, expanded polystyre e inserts, plastic foam mat, paper wool or wood woo l, thermoformed PVC trays. Barrels and drums They are made from metals o wood. Steel and aluminum are extensively sed. Inner lacquer may be used in some cases. Wooden barrels are made by binding staves with hoops. Fiber drums are light, have rubber or plastic gasket and may or may not be line or coat d. Plywood drums are made of 3-ply veneer. Polye hylene drums are also available. Other drum types include liquidtight drums and plain drums. Sacks These are made from jute, textile, paper and plastic material. Sacks can not provide support for products against superimpose loads. Because of the coarse weaving, ther is possibility of sifting and spillage. Paper sacks are f 2 or more plies. They have 70 gsm substa nce are made from pure sulfate paper. 89


Plastic sacks are made from PVC, polyethylene, polypropylene, etc. They are lighter in weight and have a thickness of 0.12m. Quite often, a combination of plastic and jute can also be used for making sacks. Multiwall paper sacks These have traditionally been made of kraft paper for its strength but modern technology has been applied to improve its strength but modern technology has been applied to improve its performance. Coatings such as PE and bitumen wax have improved the water resistance of these materials. Bag in box The bag as such is flexible. It is supported by an outer rigid container of paperboard, fiberboard, etc. A wide range of expensive foods are paper in such containers. There are two types of production method of bag in box package, viz., (i) lined carton system, and (ii) coated and laminated carton system. Textiles Textiles in packaging were dominated by jute but other fibr es used include kenaf, cotton, sisal and figue. Jute is a strong, non stretching material, easy to sew. Textiles allow the contents to breathe, which is very important for cereals, etc. Traditionally used as sacks and bales, these materials have been overtaken by plastics due to the latters hygienic appeal and lower cost. Plastics are also heat sealable and water resistant so they are better suited to large scale use.

Plastics are being used as sacks, as rigid bulk containers and as large collapsible shipping bags holding up to a tone of products such as cereals. The collapsible bags are reusable. Plastic crates are popular for returnable bottle crates, and it is also used for pallets instead of wood. Plastic films are being used to line the interiors of drums, boxes and sacks. The choice of which material to use will depend on the level of protection required, the economical aspects of each material, the handling facilities at the destination and on any regulations that may apply. Solid and corrugated fiberboard cases are probably the most widely used shipping containers. They combine convenience with economy and hygiene. The most common type is the one-piece (or regular) slotted container, although open tray and wrap-around styles are used extensively. The normal range of weight which corrugated and solid fiberboard cases carry lies between 5 and 20 kg, but fiberboard cases can be made to hold loads of up to 50 kg without any special fittings being used. If specially reinforced containers are made, they are capable of being produced to carry loads of powdered or granular material up to 500 kg weight. The main purposes of a shipping container can be listed as follows:  It must contain products efficiently throughout the journey  It must provide protection against the external climatic conditions and contaminants.  It must be compatible with the product.  It must be easily and efficiently filled and sealed.  It must be easily handled by the appropriate mechanical or other means.  It must remain securely closed in transit, open easily when required (as for customs inspection), be capable of efficient and secure reclosure.  It must carry information for carriers, wholesalers, and manufacturers about contents, destination, and how to handle and open the pack.  Where the product is dangerous or potentially harmful (as for chemicals and acids), the package must be virtually unbreakable. 90


 It must have minimum cost.  It must be readily disposable, re-usable or have another use.

Outline of Industrial Packaging As large scale industries are becoming the norm, the level of sophistication in the handling of materials has increased, to improve efficiency and productivity. One of the biggest advances in this process was the introduction of the pallet. This is a wooden or metal framework, which has a flat surface on which boxes, sacks, etc. can be stacked, supported by a base that keeps it clear of the ground. The base consists of wooden beams in an open lattice and through the open spaces the prongs of a forklift can fit, enabling it to extend under the pallet and lift it safely, to put it into a truck or into a storage rack. The forklift can be attached to a truck or be hand operated with a pneumatic device for raising the pallet a few inches off the ground so it can be moved easily. The truck type can lift the pallet six or even ten meters high, enabling efficient utilization of the height of the store. The advantage of pallets is that the manufacturer and wholesaler, etc. will have the same handling equipment and racking and so will not need to transfer it from the delivery truck manually into the store, etc. Racking means that the pallets are not stacked one directly on top of another which would severely compress the lower pallets but are individually placed into the rack and each pallet is supported individually by the rack, a metal framework like scaffolding to the required dimensions for pallets. The standard sizes of pallets are 1200 x 1000 mm and 1200 x 800mm. In some countries handling is sophisticated with cranes loading special metal containers into the hold of a ship or onto a train. Other types known as intermediate bulk containers (IBC’s) which can be metal, fiberboard or woven material, are reusable, the board and woven ones return in a collapsed form to the producer to be refilled. To maximize efficiency of handling, standard sizes were adopted internationally. This means that the handling equipment and storage facilities used internationally will be compatible and cheaper due to higher volumes.

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�� There are many new techniques being developed to extend the shelf life of the product or to package it in a new, more efficient or cost-effective way. Some are developed to find new markets or applications for materials. Aseptic Processing and Packaging It refers to the filling of a commercially sterilized and cooled product into p re-sterilized containers under aseptic conditions and sealing with a pre-sterilized closure in an atmosphere free of microorganisms. It is used to produce high quality, long life products such as fruit juices, soups and UHT milk. The basic operation in aseptic packaging consists of: o  Heating the product to sterilization temperatures (140-170 C)  Maintaining the sterility of the products till they are cooled  Filling into sterile containers and sealing aseptically

Many physico-chemical and optical properties are considered in packaging materials and forms to be suitable for aseptic packaging from total packaging system and marketability criteria. The main characteristics, which are essential from the basic functional view point, are as follows:  Low water-vapour transmission rate; very low or nil for long term storage  Low gas transmission rates, especially to oxygen. This is important to preserve the colour, flavour and nutritional constituents in the products  Good physical or mechanical strength, sufficient to resist any falls, shock and puncturing during manufacture and distribution.  Good sealing characteristics to prevent ingress of external contaminants and other deteriorative factors  Capability to perform well on machine; ability to being handled on automatic fabricating and filling equipment  Resistance to withstand the temperatures encountered during filling of the product as well as that during storage and distribution  Chemically resistant to the product packed and ability to withstand sterilization conditions – gas, liquid or radiations  Resistance to microbes, insects or other t ypes of biological hazards  Compatibility with the type of food product packed. The packaging material should not taint the product packed. Further, the material constituents and additives, etc should be inert with low migration levels  Economical in cost in commensurate with the packaged product and its free availability in the market Aseptic blow moulding It is a process where the bottle is extrusion blow-moulded in a commercially sterile environment with highly modified equipment. In many cases, the product filler is combined with the blow moulders. Aseptic blow moulders are generally divided into two sub-groups, viz. blow-and-hold method and blow-fill-and-seal method. All the operations take place in the same environment, which is aseptically maintained. In general, the modifications to the equipment include the use of special stainless steel and plated materials throughout. The moulding/filling area of the machine is enclosed in a cabinet. Sterilized air with positive pressure and laminar flow characteristics is maintained inside. All internal 92


surfaces, passage ways, hoses, blow pins, valves, and so forth are sterilized with special “clean-inplace” fixtures. Once the process begins, nothing can be touched with the human hand. Although bottles as large as 10 liters have been aseptically moulded, the process is generally used for bottles and vials of small sizes. Aseptic Packaging Applications

Rigid Plastics Containers Aseptic packaging in rigid plastic containers is developing considerably due to advantages such as ease of forming, low unit cost of containers, ease of handling and filling of multiple containers in even small sizes, ease of opening and dispensing the product. Containers in the form of cups, trays, portion packs, blisters, press-through packs, etc are aseptically filled and packaged for a number of food items. Form-fill-seal system may be used, in which container manufacturing, product filling and lid sealing are all performed in a single unit. The body of the container could be of any plastic materials with a lid of peelable thermoplastics or aluminium foil laminated film structure or fitted with a reclosable snap-on-closure. Flexible Packaging Systems The use of flexible laminates with PET/BOPP/foil, etc coextruded multilayer film structures, aluminium foil, and/or paper board combinations with these for aseptic food packaging applications has increased rapidly due to logistic advantages. In unit containers, the films used may be of paper coated with wax, PE, BOPP, PET, and EVA blends or other combinations depending on the product characteristics and the shelf-life r equired. The Brik-Pak System This system consists of a sterile rectangular block shaped paperboard carton, especially designed for liquid milk and fruit juices. Generally, a combination of hydrogen peroxide and high temperature air is used for the sterilization of the container. A laminate used for Brik-Pak unit packages is 12 micron PE for general & special food-products requiring longer shelf-life. Another laminate is made of 18 micron PE/kraft board/25 micron PE for milk packaging, formed, filled and sealed into a brick-shaped carton. The filled containers result i n considerable savings in space over metal cans or glass bottles of equivalent volume. Bag-in-Box System This system is specifically designed for high and low acid products such as fruit juices, fruit syrups and dairy related products. It combines all the producer, retailer and consumer advantages of bag-in-box with high integrity aseptic filling and packaging. This system is easy to install, simple to use, eliminates the risk of product contamination during and after filling, and provides totally sealed, longer life packs. Its salient features are:  Used for fruit juices, syrups, concentrates, dairy related products, etc  No risk of product contamination during or after filling  No need for artificial environment – positive sterilization at the point of fill, no chemical sterilants used  Totally sealed pack is not dependent on ‘friction-fit’ components  Aseptic fill needs no product preservatives  Filling system is easy to install and simple to use  Minimal energy requirements  Used for bag-in-box packs from 1 to 30 liters The sealed membrane reduces the oxygen permeability of the pack by isolating the product from the dispensing fitment. The pre-sterilized bag has a double membrane seal around the gland which 93


enables transfer sterilization, filling and resealing to take place within the fill head of the filling machine. The product is then not exposed to potentially contaminated surfaces of air during or after filling cycle. Positive, high pressure steam sterilization at the time of filling eliminates the need for filtered air workstation technology. As a result, it provides a convenient and easy-tooperate filling method which offers total aseptic packaging efficiency, overcomes the need for preservatives, and also provides a totally sealed pack for longer shelf-life. Bag-in-Box System for Bulk Packaging This is an important development for bulk packaging of various food products. It consists of a bag, which is made of a packaging material having high strength and excellent barrier properties and could be pre-sterilized by suitable means. The bag-in-box packages are generally of the capacity from 1 to 1000 liters. Bags are also available as liners for 200 liter capacity containers. Bags are mostly of laminates of substances such as foil, nylon, PET, BOPP, LDPE/LLDPE, EVA, etc. The box in the system in bag-in-box is generally made of corrugated fiber-board of suitable construction with optimum strength and cushioning properties. The box not only provides physical protection for the bag, but also stacking strength and a means for transportation and handling. The advantages of bag-in-box system of aseptic packaging are:  It occupies less storage space, since the empty package is transported in a knocked-down condition  The transit weight of containers is reduced as both the empty and filled containers weigh less than metal, glass or rigid plastic containers  Filled pallet loads are stable because the square shape of the filled package makes standard stacking patterns possible  Packaging material cost is lower than other types of packages The product being packed are edible oils, fruit juice concentrates, non-carbonated beverages, alcoholic beverages, mineral water, etc. The Tetra Pack System In the Tetra Pack system, a sterile product is packed under sterile conditions, which remains sterile until it is opened. To achieve this, the following conditions must be fulfilled:  Product sterilization  Packaging material sterilization  Sterile surrounding while forming and filling the cartons The products mainly packed are milk, edible oils, non-carbonated beverages, etc. The Packaging Material The main function of packaging material is to protect the sterility of the product & be compatible with the product itself. The Tetra Pack system uses paper-plastic laminates for the purpose. Apart from providing protection to the sterilized product, the paper and plastics play important roles in the package. Paper helps in shaping the pack and keeping the shape, while giving mechanical strength to the pack. Paper is cheaper, lighter, easily storable and provides an excellent printing surfaces. The plastic layer on the printing side provides protection to the print, while the inner plastic layer imparts the heat sealability property. Both layers of plastic act as gas barriers. Product Sterilization The product sterilization is carried out by the in-process or on-line sterilization, which is popularly known as ultra high temperature (UHT) or high temperature short time (HTST) depending on the product treatment. 94


The packaging machine installed in a room is kept under positive pressure. In a common system, the process takes place as:  Sterilization: In order to ensure a sterile path for the product, the product path in the machine is sterilized by passing hot air.  Cooling: It is essential as the system will not be in a position to take the product directly due to high temperature during sterilization. It is done by passing cooled sterile air through the path.  Production: The packaging material in the form of paper reel is fed into the filling machine. The material web passes through a bath containing hydrogen peroxide. Most of the liquid is squeezed out by a pair of rollers. After passing a blending roller, the material web travels downward; a tube is formed and sealed longitudinally. Following this, the sealed tube passes the tube heater by which the inside of the tube is heated up. This results in evaporation and disintegration of the remaining hydrogen peroxide into oxygen and water. This completes the sterilization of the packaging material. The sterilized product flows into the tube, while transversal seams are produced by a pair of jaws, which simultaneously pulls down the packaging material and produces the cartons. Vacuum and Gas Packaging Many products, particularly foodstuffs, are adversely affected by oxygen and the shelf life can be increased by the exclusion of oxygen from the package. This can be done by vacuum packaging, in which the air is removed from the package by vacuum pumps. It also requires a packaging material with very high barrier properties and such barrier properties can only be achieved by the use of multi-layer webs. Another method is inert gas packaging. The gases normally used are nitrogen and carbon dioxi de. Nitrogen is completely inert & when used to replace air inside a package, it prevents the oxidation of oxygen sensitive products. Carbon dioxide also acts in a similar way but additionally it inhibits bacterial growth within packages when stored at low temperatures. This property of carbon dioxide has led to its use both alone and in combination with other gases in the form of modified atmosphere packaging. There are two basic methods of gas packaging:  Modified atmosphere packaging (MAP) which uses gas mixtures, usually containing carbon dioxide to prevent bacterial growth, which would lead to putrefaction.  Single gas flushing with nitrogen or carbon dioxide to prevent oxidation of the product and subsequent deterioration. The multi-ply materials will provide the necessary gas barrier properties. Single gas flushing is mainly used to prevent oxidation of the fat content of certain powders, granules and small-piece solids, such as dried milk, coffee and roasted peanuts. Controlled Atmosphere Packaging (CAP) The shelf life of highly perishable foods can be increased by the use of flexible packaging materials with a wide range of permeabilities to gases and vapours. By replacing the air surrounding the food with an optimum mixture of nitrogen, carbon dioxide, and oxygen prior to sealing at atmospheric or reduced pressure, shelf-life can be extended from days to week. The factors affecting the cost-effective use of controlled atmosphere packaging are:  Chemical and biological activity of foods  Microbial contamination  Product formulation  Storage temperature  Susceptibility of the product to chilling injury 95


 Susceptibility of the product to ethylene  Consumer packaging preferences  Product tolerance to high and low oxygen and carbon dioxide concentrations

The level of packaging and the chemical and biological activity of foods can be organized in a matrix to show how modified and controlled atmosphere can be used to extend shelf-life of perishable foods. Packages can be grouped as: impermeable, selectively permeable and highly permeable systems. Foods can be grouped as having minimal chemical activity, chemically active, and biologically active foods. The significant features of controlled atmosphere packaging are:  Prolongs high quality, doesn’t improve or enhance qualit y.  Slows down the natural respiration rate of fresh product, causing lowered oxygen levels, elevated carbon dioxide levels and lowered temperatures.  Results in either equilibrium between the respiration rate of the product and the influx and escape of gases through the package, or, at least, a predictable rate of change of the levels of different gases inside the package.  Only the macro-environment within the package can be controlled, and there is possibility that different micro-environments can exist.  The product system (i.e. combination of product, package, atmosphere, temperature and all probable micro-organisms and parasites) is unique for virtually every food product and should be completely evaluated before the product is offered to sale.  Final condition of the package and its controlled atmosphere can only be determined safely by careful studies of the packaged product, including microbiological determinations and sensory testing panel evaluations.  In order to maximize the potential for extending retail shelf life of fresh food products, it is likely that major changes to the distribution chains for these products will be required. Modified Atmosphere Packaging (MAP)

The function of this packaging system is to extend the shelf-life of the product and, in some cases, allow it to be presented in more palatable manner. The shelf-life can be extended by modifying the atmosphere inside the structure. Generally, this is achieved by injecting gas mixture inside the container- either carbon dioxide, nitrogen, oxygen or a combination before sealing. The kind of film used in MAP also affects the shelf-life. In most MAP applications, conventional multilayer, high barrier films such as 5-layer LDPE blown with EVOH, nylon or PVdC is used as the barrier layer. Vacuum packaging also uses similar packaging material as both need low gas transmission rates, for vacuum packs to keep the atmosphere out and for MA packs to keep the gases in. These techniques are often used with meat & other fresh produce to maintain their fresh character, which is lost in other processes such as dehydration and canning. The normal composition of the atmosphere is 78% nitrogen, 21% oxygen & 0.3% carbon dioxide by volume, with minute quantities of other gases. MAP changes this composition to prolong the shelf-life of the product, by slowing down the rate of degradation, i.e. preventing oxidative rancidity by reducing the oxygen content. It is also known as gas flush packing, as the air inside the package is removed and replaced by flushing it with the mixture of gases to achieve the required atmospheric composition. MAP differs from CAP as the composition of the atmosphere inside the pack changes with time as the product respires or absorbs gases. CAP maintains the composition of the internal environment at a constant level. 96


The principal factors of MAP are:  Choice of gas or mixture of gases  Control of temperature  Choice of suitable packaging material The gases involved in modified atmosphere packaging, as applied commercially today, are carbon dioxide, nitrogen and oxygen. The gas or gas mixture that replaces the air depends on the product and how it deteriorates. If oxidation is the problem, then the oxygen level can be maintained very low by this method. It also protects against aerobic microbial growth. Carbon dioxide inhibits the growth of many micro-organisms, so 20-30% carbon dioxide levels have been found to be effective in aerobic systems and 100% concentrations in anaerobic systems. In general, the higher the concentration of the gas, the greater is its inhibitory power. However, this gas is readily absorbed by water and oils and will therefore be absorbed by the product until it comes to equilibrium. This can lead to the pack collapsing as the volume of gas reduces. The solubility of carbon dioxide increases as the temperature is reduced. Carbon dioxide reacts with water in the product to form carbonic acid which lowers the pH of the food. The effect of carbon dioxide is to increase both the lag phase and the generation time of spoilage micro-organisms. Bacteria in the lag phase of growth are most affected by th e gas. Nitrogen is an inert gas, and has no direct effect on microorganisms or foods, other than to replace oxygen, which can inhibit the oxidation of fats. As its solubility in water is low, it is used as a bulking material (filler gas) to prevent the collapse of MAP packages when the carbon dioxide dissolves in the food. Nitrogen is used to purge the air from the pack and to reduce the concentration of other gases in the pack. This is also useful in packages of sliced or ground food materials, such as cheese, which may consolidate under vacuum. Oxygen is used to prevent anaerobic spoilage or to maintain the red colour in some meat products, which is due to the oxygenation of the myoglobin pigments. It is also included in MAP packages of white fish, to reduce the risk of botulism. Other gases have antimicrobial effects. Carbon monoxide will inhibit the growth of many bacteria, yeasts and moulds, in concentrations as low as 1%. However, due to its toxicity and explosive nature, it is not used commercially. Sulphur dioxide has been used to inhibit the growth of moulds and bacteria in some soft fruits and fruit juices. In recent years, there has been concern that some people may be hypersensitive to sulphur dioxide. So called noble gases, such as argon, helium, xenon and neon, have also been used in MAP of some foods. However, apart from being relatively inert, it is not clear what particular benefits they bring to this technology. Temperature is a critical parameter as it affects the rate of deterioration of the product, whether deterioration is by enzymatic, chemical or biochemical reactions. To achieve the required shelflife, the temperature must be carefully controlled. MAP is often applied to pasteurized and chilled products so in this context, temperature control is important. The packaging material must have a suitably low rate of gas transmission and be strong enough to withstand the hazards of distribution, etc. MAP packages are either thermoformed trays with heatsealed lids or pouches. With the exception of packages for fresh produce, these trays and pouches need to be made of materials with low permeability to gases (CO 2, N2, and O2). Laminates and coextrusions are popular, using PVdC, EVOH or foil as the barrier layer, polyester or nylon for toughness and puncture resistance and polythene for heat sealability. The oxygen permeability of 3 –2 –1 these laminates should be less than15 cm m day at a pressure of 1 atm (101 kPa). 97


Typical MAP Applications Fresh meat : High oxygen systems are used to extend the colour stability and delay microbial deterioration. Alternatively the pack can be flushed with nitrogen. This results in a reduction in the formation of metmyoglobin on the surface. However, the nitrogen also dilutes the carbon dioxide produced by tissue respiration, prolonging the time required for the concentration to reach levels sufficient to inhibit the growth of spoilage bacteria. Fresh red meat packaged in an atmosphere consisting of 80% oxygen and 20% carbon dioxide or 70% oxygen, 20% carbon o dioxide and 10% nitrogen have a shelf life of 7–12 days at 2±1 C. Poultry: Poultry can be MA-packaged in a mixture of nitrogen and carbon dioxide. However, this is not widely practiced because of cost considerations. Cooked and cured meats may be packaged in a mixture of nitrogen and carbon dioxide. Packaging in a 20% carbon dioxide atmosphere will o give one week shelf life at storage temperatures of 2 C; higher levels will extend the life further. Fish: Fresh white fish, packaged in a mixture of 30% oxygen, 30% nitrogen and 40% carbon o dioxide, have a shelf life of 10–14 days at a temperature of 0 C. Such packages should not be o exposed to a temperature above 5 C, because of the risk of botulism. Fatty fish require low oxygen concentrations to prevent rancidity and are thus packaged in mixtures of carbon dioxide and nitrogen. Fruits and vegetables : Respiration in such products leads to a build-up of carbon dioxide and a reduction in the oxygen content. Some build-up of carbon dioxide may reduce the rate of respiration and help to prolong the shelf life of the product. However, if the oxygen level is reduced to 2% or less, anaerobic respiration will set in and the product will spoil. The effect of the build-up of carbon dioxide varies from product to product. Some fruits and vegetables can tolerate high levels of this gas while others cannot. Each fruit or vegetable will have an optimum inpackage gas composition which will result in a maximum shelf life. Selection of a packaging film with an appropriate permeability to water vapour and gases can lead to the development of this optimum composition. For fruits with very high respiration rates, the package may need to be perforated. Cheese : Portions of hard cheese may be packaged by flushing with carbon dioxide before sealing. The gas will be absorbed by the cheese, creating a vacuum. Cheese packaged in this way may have a shelf life of up to 60 days. To avoid collapse of the package, some nitrogen may be included with the carbon dioxide. Mould ripened cheese may be packaging in nitrogen. Bakery products and snack foods : The shelf life of bread rolls, crumpets and pita bread may be significantly increased by packaging in carbon dioxide or nitrogen/carbon dioxide mixtures. Nuts and potato crisps benefit by being MA-packaged in nitrogen. Pasta: Fresh pasta may be MA-packaged in nitrogen or carbon dioxide. Other foods: Pizza, Quiche, Lasagne, and many other prepared foods may benefit from MAP. It is very important to take into account the microbiological implications of MA-packaging such products. Maintenance of low temperatures during storage, distribution, in the retail outlet and in the home is essential.

Comparison of Vacuum Packaging and MAP Vacuum packs take up less volume, less weight and use less material than MAP. They give good product visibility and don’t have drip, blood, etc. moving about in the pack. However, irregular size and shape can make them less easy to handle, stack, etc.

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The following table shows typical gas mixtures, packaging materials used and additional days of life required. Food type Red meat

Gas mix (% O 2 /CO 2 /N 2 )

Typical Packaging Material

Shelf Life

70/20/10

PVC tray; PET/PVdC/PE lid

2-10

Poultry

40/40/20

PVC tray; PET/PVdC/PE lid

3-14

Bacon/Ham/Sausages

0/40/60

PVC/PE tray; PET/PVdC/PE lid

2-30

White fish

20/45/35

PET tray; PET/PVdC/PE lid

3-6

Oily fish

0/60/40

PVC tray; MXXT/A lid

3-5

Cheese

0/50/50

PVdC/OPP/PE coextrusion

6-30

Cakes/Pastries

0/70/30

PS/ PVC tray; PVdC/OPP/PE

7-90

Salads

2/10/88

OPP overwrap

3-14

Composite Packs

Composite packs offer a number of advantages over other types in packaging of many food products. It allows the production of a wide variety of shapes and sizes. The composite pack consists of four basic elements: body, base, membrane-lid and cap. The main body comprises of a composite material consisting of a light weight high impact core of expanded polystyrene in the thickness range of 0.6-12 mm. Externally, the core is coated with a printed plastic film. The inner face is coated with a plastic film or a combination of a film and aluminium foil, which ensure optimum barrier properties against moisture, oxygen, etc. A wide choice of materials is available, such as PET, PVdC or EVOH. The base, like the lid and snap-on-cap, are generally moulded from high impact polystyrene (HIPS) coated with a PET or other film to enhance barrier properties. The base is a solid moulding, whereas the lid incorporates a membrane which is pierced to give access to the contents. Typically, the membrane lid comprises a heatsealed paper/plastics film laminate. The cap is of snap-on type with reclosability. For security, a tear cap can be provided between the snap-on-cap and body of the composite. Also, a hinge can be fitted to link the lid and end cap. The fact that the bodies, bases and caps can be supplied as flats gives considerable saving in the cost of storage and transport.

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�� Introduction Packaging is an integral part of food processing industry. However the food will be processed and preserved, it requires a suitable form of packaging. Several types of foods have their own packaging requirements. The various types of packaging used for different food types are briefly explained below. Sterilized Food Products Sterilized food products can be packed in cans, retort pouches, and aseptic packs. Cans can be made from tinplate, aluminium or tin free steel. Lacquers may be used to prevent corrosion affecting the product. The material needs to be heat resistant. A retort pouch is like a flexible can, made of a laminate structure. It generally incorporates aluminium to prevent light and oxygen causing the product to deteriorate. Typical structure is: PET/Aluminium foil/HDPE.

Aseptic packaging is based on the principle that the product and the package are both sterilized separately. It is generally a laminate structure like PET/PE/Aluminium foil/PE, or PET/Aluminium foil, or a plastic coated paperboard (LDPE/paper/LDPE) as in milk and fruit juice packages. Tetrapak uses a similar material but is supplied to the filling factory as a reel to be formed into a carton, filled and sealed in one operation. It can be tetrahedral or rectangular. Foil may be incorporated to provide a barrier to gases, volatile loss, light, etc. when it is to be used for aseptic packaging. Dried powders This category includes soup mixes, spices, salt, sugar, flour, milk powder, breakfast cereals, etc. Most of these have low moisture contents and tend to be hygroscopic. So, the packaging material must prevent moisture from entering into the pack. Some of these are also sensitive to ox ygen and light, which catalyse rancidity. Volatiles need to be retained. Dried products have hard or sharp edges usually, so a tough material is required. Vacuum packing or gas flushing with nitrogen ma y be used for products such as milk powder. Therefore, the material should have low gas transmission rates. Packages suitable for this type of product range from simple paper/PE bags to maximum protection offered by metal cans, glass bottles and foil based laminates. Soup mixes are often packed in paper/PE/foil/PE laminates. Dried foods are packed in OPP/LDPE. Dried products The most critical factors for dry products in relation to packaging are moisture uptake leading to loss of crispiness and oxidation of fats resulting in development of rancidity. Other modes of deterioration include oxidation of vitamins, breakage of products, loss of aroma, discoloration, mould growth, staling, and fat bloom depending on the product. Thus, the most important requirements for the packaging materials include high moisture, oxygen, and light barrier properties and high mechanical strength.

Most dry products are packaged under atmospheric conditions. Packaging materials for dry products include: underground pits or containers, piles of bagged grains and storage bins of different sizes, shapes and construction types for grains; bags, bulk bins, multi-walled Kraft paper bags, sometimes with an LDPE liner for flour; paperboard carton with a plastic window (cellulose acetate), OPP or coated LDPE films for dried pasta; LDPE bags in which the end is twisted and sealed with a strip of adhesive tape or perforated LDPE bags for bakery products; regenerated cellulose films coated with LDPE or PVC/PVdC co-polymer and often with a layer of glassine in 100


direct contact with the product if it contains fat, for biscuits; cookies and crackers, aluminium foil/LDPE sometimes containing a layer of paper, either between the foil and the LDPE or on the outside of the foil, PVC/PVdC copolymer/LDPE, molded PVC trays wrapped in aluminium foil or placed inside paperboard boxes or metal or glass containers for chocolate. Dried Snacks This includes nuts, popcorn and potato crisp type products. The most common modes of deterioration of snack foods are loss of crispiness and development of fat rancidity. Thus, low water vapour and oxygen permeabilities are of the utmost importance. Mechanical strength is required of packages for snack foods and the exclusion of light has also been suggested.

Most snack foods are packaged by form fill sealing. For some snack products the air is removed and packages are flushed with nitrogen gas to protect against moisture absorption and retard the development of rancidity. Fried, extruded, and puffed snack foods are typically packaged in multi-layer structures. Packaging materials are usually pigmented, metalized, or placed inside paperboard cartons. Spiral-wound, paperboard cans lined with aluminium foil or a barrier polymer are used for e.g. chips and nuts. In addition, metal cans are used for fried nuts; the container usually being gas flushed with nitrogen. As a result of the requirements for low permeability towards water, these require a very good moisture barrier. They often have been fried or roasted and so they require protection from oxygen, which would make the oil rancid. Gas flushing may be used for some products. PVdC coated cellophane or OPP will give several months shelf life for most products, and foil based laminates will be better for the more oxygen sensitive ones. Bakery Products The requirements vary from item to item. Biscuits have low moisture content and need protection from moisture and oxygen due to their high fat content. MXXT/A cellophane, OPP, PVdC coated cellophane or waxed paper are commonly used. Bread has high moisture content and this needs to be retained to prevent staling, by packing it in LDPE, OPP or HDPE. Crusty bread however needs to let moisture escape to maintain its crustiness. So, it is wrapped in a simple paper wrap or perforated OPP. Cakes and pies also need to let moisture escape or else they will go moldy, while retaining enough moisture to prevent them from drying out and tasting stale. MAP can be considered for cakes. QMS cellophane is ideal for cakes and pies. Confectionary These include sweets, chocolate, toffees, etc. Moisture would soften toffees and make boiled sweets go sticky or crystallize. Moisture can also lead to ‘fat bloom’ on chocolate. The high fat content of chocolate also makes it vulnerable to rancidity. Foil wraps are popular and laminates are also being used, e.g. paper/foil/PE. OPP wraps and bags are popular or MXXT cellophane overwraps for boxes of sweets. Tins give the ultimate protection and are popular for larger size gift packs. Dairy Products

Milk, cream, fermented milk products, and processed cheese require low oxygen permeability packaging to avoid oxidation and growth of undesirable microorganisms. In addition, light initiates the oxidation of fats in dairy products and leads to discoloration, off-flavour formation and nutrient loss, even at temperatures found in refrigerated display cabinets. The oxidative reactions initiated by light may continue even if the products are subsequently protected from light. Dairy products should be protected from water evaporation, absorption of odours from the surroundings and high storage temperature to maximize shelf life. 101


Different packaging technologies apply to different products. Thus, cold filling is used for milk, cream and fermented products, aseptic packaging is used for UHT milk, hot filling is used for butter and yoghurts, MAP packaging is used for milk powder, MAP packaging and hot filling is used for cheese. A high fat content requires an oxygen barrier to prevent rancidity. Solids such as cheese products need to be prevented from losing excess moisture, which would lead to hardening and yellowing of the surface. Vacuum packaging or gas flushing is popular for hard cheeses. A PVC wrap is suitable for short shelf life or PVC/OPP/LDPE for longer life. Soft cheeses are wrapped in Saran or PVC. Liquid milk is available in a variety of packages. Milk can be packed into glass bottles that are reusable but are heavy; HDPE plastic pouches are also used and flexible LDPE plastic pouches. These usually have two layers of polyethylene, the inner one being black to prevent UV degradation. Alternatively, polyethylene coated paperboard cartons such as Tetrapack are used. Long life UHT milk can be packed into PE/paper/PE/foil/PE cartons. Cans are used for dried milk, sweetened condensed milks, creams and milk based puddings. Butter can be packed in vegetable parchment or foil tissue, which provides maximum protection against flavour change. Yoghurt and ice-cream can be packed in HIPS or PE tubes. Coated papers are also used for ice-creams. Fruit Beverages Factors limiting the shelf-life of beverages include microbial growth, migration/scalping, oxidation of flavour components, nutrients and pigments, non-enzymatic browning, and, in the case of carbonated beverages, loss of carbonation. Oxygen can cause flavour changes in these drinks. Thus, requirements of the packaging materials for beverages include low gas transmission and light permeabilities and resistance towards scalping (migration from food product to package). Packaging materials with high water vapour barrier properties are required to prevent penetration of the beverage through the package.

For packaging of acidic beverages the material must be resistant to acids. Packaging methods for packaging of beverages include aseptic packaging with or without nitrogen injection, hot and cold filling. The packaging materials commonly used include: glass, HDPE, PP, PC, PET, PVC, PE/paper/PE/Al/PE, PE/paper/PE/Al/special coating (gable top packaging types) for water; glass, metal, HDPE, PE/paper/PE/EVOH/PE, PE/paper/PE/SiOx/PE, PE/paper/PE/Al. Purepak and other cartons are used for fresh juices. For longer shelf life and UHT products, foil is included in the construction. Carbonated beverages The container must be able to withstand the high internal pressures of carbonation. The closures must also be suitable. They are generally packed in glass bottles with crown caps or in tinplate or aluminium cans with a suitable lacquer. Plastic bottles, usually PET, PVC or PE, are becoming popular due to their light weight and non breakability. However, there occur problems with maintaining the carbonation due to the high GTR of some materials.

Beer must be pasteurized in the bottles so thermal shock must be considered. It must also be protected from UV light so amber bottles or cans are used. Coffee/Tea

These products need to be protected from loss of flavour and odour volatiles, from moisture and rancidity. Packaging materials used include glass jars, metal cans, metalized or foil based laminates. Tea is not so susceptible to volatile losses and may be protected in a paper bag or box overwrapped with MS cellophane. 102


Fresh Fruits and vegetables Fruits and vegetables continue to respire, transpire and produce the ripening hormone ethylene even after harvesting with the result that the concentrations of carbon dioxide, oxygen, water and ethylene change over time inside storage packs. Changes in gas composition may have a positive influence on the colour and flavour of the products, but they may also induce negative effects on texture, colour, shelf-life and nutritional quality.

Short-term preservation by reducing respiration and transpiration rates can be obtained by controlling factors such as temperature, relative humidity, gas composition (ethylene, oxygen and carbon dioxide), light, and by applying food additives and treatments such as waxing and irradiation. Physical damage (e.g. surface injuries, impact bruising) may stimulate respiration and ethylene production and accelerate the onset of senescence. To protect from physical damage, they are often packed in contoured trays to keep them separate or with cushioning in the form of paper or single faced board. The choice of proper packaging material is complex because it depends on the specific respiration and transpiration rates of the different products and the conditions in the supply chain. If the chosen packaging material is impermeable to CO 2, O2 and H2O, an anaerobic environment inside the packaging will develop and lead to microbial fermentation and product deterioration. If the packaging material is too permeable to water vapour, the products will dr y out and the atmosphere in the packaging will contribute to a reduced storage life. Moisture must be controlled to prevent wilting and mold growth. Condensation and respiratory gases must be allowed to escape. The ideal packaging material has a permeability that takes the respiration processes of the products into account so that the atmospheric balance (CO 2 /O2 ratio) inside the packaging is optimal. The packaging material should retain desirable odours, prevent odour pick-up, provide protection from light and give sufficient protection against mechanical damage. Reduction of the O 2 content to less than 10% by using a passive or active modified atmosphere in the packaging (e.g. rigid tray wrapped in or sealed with plastic films) provides a tool for controlling the respiration rate and slowing down senescence although an adequate O 2 concentration must be available to maintain aerobic respiration. Packaging with bags, incomplete sealing or perforation of packages, individual shrink wraps, or bulk display where the consumers pick the product themselves, are used for fruits and vegetables. Among the packaging materials used for fruits and vegetables are: monolayer PVC, perforated thin LDPE, LDPE/MDPE with EVA, kraft paper, LDPE, HDPE, white pigmented PVC or PP, expanded (foamed) PS, LLDPE, shrinkable film, regular net stocking or expanded (foamed) plastic netting, PET, moulded paper pulp with a thermoformed plastic liner, sleeve packs, PE bags with small holes punched in them and PVC trays overwrapped by PVC. Fresh Meat and Fish Two factors are critical in the packaging of red meats: colour and microbiology. In order to preserve the red colour of fresh meat, attributed to oxymyoglobin, a high oxygen level over the product surface is required. This level can be obtained by using oxygen permeable films in the packaging process. On the other hand, oxygen also supports the growth of bacteria, and discoloration, attributed to the brown pigment metmyoglobin, occurs rather quickly. This surface discoloration is even more pronounced in ground meats where the exposed surface area is hugely increased. As a result of its high water activity, unprotected chilled meat will lose weight by evaporation and its appearance will deteriorate. Thus, low water vapour permeability is important in packaging of fresh meat. In cured meat products the pigment nitrosylmyoglobin oxidizes rapidly in the presence of light and oxygen. The onset of oxidative rancidity is also accelerated in 103


the presence of light and oxygen. Thus, low permeabilities to oxygen and light are required of packaging materials for cured meat products. Raw poultry support microbial growth due to its high pH (5.7-6.7). Hence, packaging in modified atmospheres with a high level of CO 2 or vacuum extends shelf-life considerably. Fresh meats are typically packed in oxygen permeable packs, vacuum packs or modified atmosphere packs. Where residual oxygen must be maintained at a very low level, vacuum packaging minimizes the colour and flavour defects associated with oxidation of muscle myoglobin and lipids, respectively. Modified atmosphere packaging (MAP), with 70-80% O 2 to maintain oxymyoglobin and 20-30% CO 2 to inhibit microbial growth is commonly used to package fresh red meats. ”White” meats, such as poultry meats, are often packed in a mixture of CO2 and N2. However, some authors point out that more than 25% CO 2 may cause discoloration and off-flavour formation in poultry. The “snug-down” effect obtained at high CO 2, when the CO 2 is dissolved in the water phase, is undesirable for several products giving the package a vacuum packaged look. It is possible to prevent the “snug down” effect by using N 2 in the gas mixture. Fresh meats and fish are usually sold chilled in portions of varying sizes. MAP packaging using high barrier laminates, is popular to slow the deterioration and to preserve the red colour of red meats. Short shelf life meat is sold on HIPS or PVC trays, overwrapped with pPVC. Vacuum packaging such as the Cryovac bag is popular for joints of meat. Thermoformed vacuum packs can have nylon/PVdC/PE bases and PET/PVdC/PE tops. Rigid bases for MAP packs can be of PVC/PE or PET/PE. Conventional packaging materials include permeable films (PVC, PE-based, polyolefin based), PS, expanded PS, PETG, PA or PET or PVC/PVC or PVdC coating/LDPE or EVA or ionomer, Saran (copolymer of PVdC and PVC). Frozen Foods The common modes of deterioration in frozen foods are pigment and vitamin degradation and oxidation of lipids. Thus, requirements of packaging materials for frozen products include a high moisture barrier property to reduce moisture loss and freezer burn and oxygen and light barrier properties for protection against oxidation. The packaging material should be resistant to tearing and puncturing. For common polymeric films, satisfactory water vapour transmission rates are obtained at freezer temperatures below -20°C. However, at the low temperature mechanical properties may be affected making the polymeric materials more brittle and sensitive to mechanical forces.

The rate of oxidation is much reduced at low temperatures so only vulnerable products such as fatty fish require protection from oxygen and are vacuum packaged or packaged in nitrogen. A barrier to the loss of volatiles may be required. Freezer burn due to moisture loss is the major problem leading to whitening and wrinkling of the surface and loss of texture. This can be prevented by using a good moisture barrier, which will also prevent atmosphere moisture penetrating the pack and forming an ice layer on the inside. Frozen foods can have sharp edges, i.e. bread crumbed or bone products so puncture resistance must be good. The material must also perform well at low temperatures. The majority of frozen fruits and vegetables are packed in polymeric films the major component being LDPE. Some films contain white pigments to prevent light penetration. Other conventional materials include waxed carton-board wrapped in a moisture-proof regenerated cellulose film and folding cartons with a hot melt coating of PVC/PVdC copolymer. Films and wraps used for meat and seafood include cellophane, aluminium foil, PVdC, PE, and PS trays surrounded by films and wraps, and coated paper and cartons. LDPE and LLDPE bags are popular as they are easy to print, 104


seal and are economical. Some products are sold in paperboard cartons, waxed for moisture resistance. Other products are sold as a convenience food that can be prepared by immersing it in boiling water to defrost and heat it known as “boil in the bag”. For this application PVdC/PET/LDPE and HDPE bags are popular. Foil and CPET trays (ovenable polyester) are used for food to be prepared by heating in an oven. Fats and Oils The fatty parts of foods, foods made chiefly of fats and oils, and fats and oils themselves are subject to chemical spoilage and microbial attack. The chief types of spoilage are oxidative rancidity produced by chemical or microbial oxidation, and hydrolytic rancidity, due to lipases naturally present or to micro-organisms. Fats subjected to either or both of these changes may contain fatty oxy-acids and hydroxyl acids, glycerol, other alcohols, aldehydes, ketones and lactones, in the presence of lecithin (e.g. butter & margarine) may include trimethylene with fishy odour. Also, some of the pigments produced by micro-organisms are fat soluble and therefore can diffuse into the fat, producing discolouration ranging through yellow, red, purple or brown. Because of the low moisture content of fatty materials, the growth of mold is favoured more than that of bacteria, which can also cause oxidative and hydrolytic decomposition. The oxidation of fats and oils may be catalysed by various metals (e.g. copper) and by irradiation and moisture as well as micro-organisms. The packaging materials used in margarine manufacture must fulfill two principal functions: (a) to protect the product from spoilage during transit, storage and use, i.e. from microbial spoilage, oxidative changes, water and oil transmission, and odour and flavour changes, and (b) provide sales appeal and convenience to the consumer. Packet margarines (and other fats such as lard) are normally wrapped in vegetable parchment, greaseproof paper or wrapper consisting of aluminium foil laminated to parchment or greaseproof paper. All must accept printing sufficiently well to give an attractive pack. The materials used include PVC, polystyrene, and acrylonitrile butadienestyrene (ABS). These materials are normally thermoformed, although injection-moulded high density polyethylene and polypropylene tubs are also used. Tubs in coextruded plastics and combinations of board and plastics are also used. Thermoformed PVC is the most common material in use for lids. Frying oils and salad oils for domestic consumption were originally packaged in glass bottles, but now plastics bottles are used. Glass offers many advantages such as impermeability, cleanliness, durability, rigidity and its lack of susceptibility to mold growth, but it is brittle and breakages in transit can ruin a complete caseload. This has led to the development and use of moulded thermoplastic containers of high and low density polyethylene, PVC and polystyrene. The choice of material is, however, governed by cost, chemical resistance, permeability and ease of processing and degree of clarity or opaqueness needed. Plastics containers for oils must be reasonably rigid, resistant to microbial attack, and to transmission of water and oxygen. Oils for the catering industry are usually packed in aluminium cans.

105


�� Introduction Shelf life is the time between the product being harvested or processed and packed until its quality has deteriorated to an unacceptable level. This may be due to organoleptic reasons such as a loss of texture or flavour or to microbial reasons such as mold growth, etc. Therefore the shelf life is the time during which the product can be consumed. Canned foods are shelf stable at ambient temperatures for several years due to the sterilization process, whereas fresh foods such as milk and bread have a relatively short life and are often described as perishable. Packaging must be suitable to protect the product from the external hazards, such as moisture, light, oxygen, microbial contamination, impacts, drops, etc. In selecting a suitable packaging material, consideration must be given to the hazards to which the product will be subjected. The food products may deteriorate due to rancidity, staling, microbial spoilage, enzymatic reactions, etc and of the processes used to retard deterioration include sterilization, pasteurization, freezing, and aseptic processing. In some of these processes, the packaging plays a major role in the actual processing such as in canning. In all of them, packaging is meant to protect the food from further contamination by preserving the micro environment inside the package in which the quality can be maintained for the duration of the shelf life. Several methods such as vacuum packaging, modified atmosphere packaging (MAP) and aseptic packaging can be used to extend the shelf life of food products. Factors affecting shelf life Shelf life is affected by the product, the packaging material and by the environment. It depends on many factors such as:  The mechanism of deterioration of the product, e.g. loss of volatiles, rancidity, moisture loss or gain, etc  The factors that are responsible for controlling the rate of deterioration, e.g. presence of antioxidants, vacuum, preservatives, etc  The initial quality of the product when packed. If the product is not in good condition, the packaging can’t improve it. Therefore, shelf life will be reduced as deterioration will have started.  The minimum acceptable quality standard for the product will determine the shelf life. For e.g. if biscuits become unacceptably soft at 4% moisture content then that means that the shelf life is the time taken for the biscuits to reach 4% moisture content.  The barrier properties of the primary pack will determine the rate at which the volatiles, moisture, etc can permeate the pack. This is particularly relevant for plastic and composite materials whereas glass and metal are complete barriers. However, if the seams on a metal can or the seal on a glass jar are faulty then gases, etc can permeate.  Defects in the material, such as pinholes in aluminium foil, will affect the theoretical value of the shelf life  The shape and size of the pack will affect the surface area, which greatly affects the rate of permeation of gases and moisture through the packaging material. The shape affects the material distribution. A poor design may cause thin corners, etc where the material is most stretched and there the permeation rate will be higher  The effect of conversion processes such as thermoforming plastic sheet into trays or pellets into bottles may affect the result. For e.g. if the temperature is not correct the trays might be thinner or thicker which greatly affects the permeation rate 106


 The protection offered by the secondary packaging is a critical factor in reducing the

deterioration  The climatic variations likely to be encountered during the life cycle of the product are very relevant. This includes issues such as a chilled product being left in the sun for a few minutes during loading, which causes condensation to build up, weakening corrugated packaging  The mechanical hazards of distribution and storage will put stresses on the packaging and product that may cause it to fail earlier than the theoretical value for the shelf life  The environmental controls such as for refrigerated products if very variable will have a different effect than if tightly controlled. Permeability Permeability is the ability of vapours, gases or volatiles to pass through a material. Permeation through glass and metal is zero but all plastics and paper are permeable to some extent. This can be good for some products while detrimental to others. For e.g. if moisture or oxygen permeates a packet of potato crisps, then the moisture will affect the texture or crispiness while the oxygen will catalyse the oxidative rancidity of the cooking oil in which the potatoes were fried. On the other hand, a product such as cake, which has high moisture content, will need to let some moisture escape to prevent mold growth.

The rate of permeation will depend on the nature of the packaging material, the conditions of temperature and relative humidity, the area of the pack, the thickness of the material, and the concentration or pressure difference between inside and outside of the pack. The difference in crystallinity will also affect the rate depending on the material characteristics. This was seen in comparing the differences in permeability between low and high density polyethylene, or between oriented and non oriented polypropylene. The presence of any micro cracks or permeation will affect the rate. The process of permeation is that the gas or vapour goes into solution at the film interface, diffuses through it and evaporates from the other side. This reaction is driven by the concentration gradient and the desire to come to equilibrium. Fick’s law of diffusion can be applied. This states that the quantity of gas permeating (Q) depends directly on the area of the film exposed (A), the time (t), and the concentration gradient across the film (dc), and is inversely proportional to the thickness (X). The constant of proportionality is given by D, the diffusion constant. Mathematically,  .  .  .  Q =  The gas concentration can be expressed in terms of its pressure (P) and Henry’s law can be applied to convert c to Sp where S is the solubility coefficient. However, the product of D x S is b, the permeability coefficient, which is a constant for each material under given conditions of temperature and relative humidity. Therefore, we have  .  .  .  Q =  This equation holds well for ideal gases such as oxygen, nitrogen, hydrogen and carbon dioxide which is almost an ideal gas.

107


Shelf Life Estimation

Introduction There are at least three situations when shelf life estimation might be required:  To determine the shelf life of existing products  To study the effect of specific factors and combination of factors such as storage temperature, packaging materials, processing parameters or food additives on product shelf life  To determine the shelf life of prototype or newly developed products Several established approaches are available for estimating the shelf life of foods: a. Literature study : the shelf life an analogous product is obtained from the published literature or in-house company files. b. Turnover time: the average length of time that a product spends on the retail shelf is found by monitoring the sales from retail outlets, and from this the required shelf life is determined. This doesn’t give the actual shelf life. It is assumed that the product is still acceptable for sometime after the average period on the retail shelf. c. End point study: random samples of the product are collected from retail outlets and then tested in the lab to determine their quality. From this, a reasonable estimation of shelf life can be obtained because the product has been exposed to actual environmental stresses encountered during warehousing and retailing. d. Accelerated shelf life test : lab studies are undertaken during which environmental conditions are accelerated by a known factor so that the product deteriorates at a faster than normal rate. This method requires that the effect of environmental conditions on product shelf life can be quantified. Techniques to estimate shelf life The shelf life does not only depend on the permeability of the packaging material but also on the product itself, how it deteriorates in time due to enzymatic reactions, etc. Therefore bottled and canned products also have a shelf life. The best method to evaluate shelf life is to do storage trials. However, these are time consuming as the packed product must be kept in controlled environment for the expected life and beyond, being evaluated periodically both organoleptically and bacteriologically. This may take several months or even years for canned foods. An accelerated test can be conducted at higher temperatures but its result must be interpreted carefully. A mathematical method of predicting shelf life would be advantageous especially if it could be used to predict the effect of changes in a material, or to compare alternate materials, but it can’t replace full scale testing. Mathematical and computer modeling is being used to predict the shelf life of products. The issue is complicated by the fact that the deterioration is generally by more than one factor. The accuracy of the result will depend on the accuracy of the data known about the agents of deterioration. For this purpose, we shall only consider the effect of moisture loss and gain on shelf life, as the mathematical model is not too complicated and it demonstrates the principle. In general, all the systems come to equilibrium with their surroundings. This applies to the product which wants to come to equilibrium with the environment by the transfer of moisture either to or from the product. The packaging opposes this tendency, i.e. it provides resistance thereby retarding the deterioration. The shelf life will depend on the effectiveness of resistance. Consider a packet of crisps containing 20 gm of potato, i.e. starch, which is hygroscopic, 10 gm of oil which is hydrophobic, and about 0.3 gm of bound water in the product. The packaging must keep out the moisture to prevent the crispness of the product but only for a reasonable amount of 108


time. It is technically possible to keep out the moisture for years but this type of packaging would be excessively expensive for a simple packet of crisps. Management will decide the reasonable shelf life to allow for the product to be produced, stored, sold and consumed before the quality deteriorates. In general, for crisps this is 6-8 weeks. Case I: Consider a simple case where the shelf life is known for a given material and it is proposed to replace it with a new material to achieve a longer life (e.g. use a foil based laminate) or to achieve a cost reduction (e.g. use a thinner gauge of material). The following equation can be applied:     Shelf life for new material = shelf life for the old x      Case II: To estimate the shelf life based on the rate of permeation The packaging technologist collects data to evaluate the performance of the material. The crisps are packed in the proposed packaging material and weighed. They are stored in a controlled atmosphere to prevent fluctuations that would affect the accuracy of the results and loose the pattern in the graph. The packs are weighed daily and the increase in weight due to the permeation of moisture is measured and graphed over time. The graph shows that the weight increases every day but at a decreasing rate, until equilibrium has been attained. A point will be reached when the product has absorbed so much moisture that it has lost its texture and become unacceptable. The equilibrium moisture content can be found quickly by opening the packet and letting the contents come to equilibrium. Similar curves are found for other products, but in opposite direction for products like bread that will dry out. However, by moving these to a common zero (by plotting the difference in weight against time), it is found that the curves are very similar and can be plotted as the change in weight to the change when the pack is opened. Typical curves:

Fig: Crisps weight gain wrt time Fig: Crisps/Bread curves The resultant curve is analogous to the curve representing the voltage rise across a capacitor with a time constant CR. Circuit diagram:

Here, CR represents the capacity of the pack for moisture gain in storage by the effective resistance of the packaging. This curve is simplified by a binomial curve that corresponds to the equation: 109


��

� � − � � � Where d is the weight gain in time t by the sealed pack and c is the ultimate weight gain of the pack on exposure to the atmosphere. =

Consider the following examples: 1. A packet of biscuit gained 0.25 gm weight on day one, and when left open, it ultimately gained 20 gm. It has been found that at a water gain of 5 gm, the product becomes unacceptable. Calculate the shelf life of the biscuits in this material. st fl 1 case, To calculate the effective resistance R, d = 0.25, C = 20 and t = 1 We know,

��

=

� �

−

  

or,

� � 

=



.

.

−



or, R = 4 nd

2 case, To calculate the shelf life, let t be unknown   

or,



=

 .

−

. 

or, t = 21.3 days. Suppose these results are reported to the sales manager who insists on a six-week shelf life. How can this be achieved? fl There

are several options, the material thickness could be increased, i.e. doubled, or a better barrier material could be used, or the surface area of the pack could be reduced. The most economic option is to be chosen. 2. A packet of cigarettes was exposed to a dry atmosphere where it lost 0.3 gm in 7 days. The pack was then opened and came to equilibrium losing 2.7 gm. If the maximum loss than can be tolerated by the product is 1 gm, find the shelf life. st fl 1 case, To calculate the effective resistance R, d = 0.3, t = 7 and C = 0.3 + 2.7 = 3 We know,

�� or,

=

� �

 

−

=

� �  .

−

. 

or, R = 23.1 nd

2 case, To calculate the shelf life, let t be unknown or,

  . 

=

 

−

 

or, t = 25.98 days. \ t º 26

days.

Real life complications arise due to the fluctuations in temperature and humidity, secondary causes of deterioration like oxidation, and the effect of secondary packaging that can reduce the rate of moisture penetration. The theoretical results should be checked by a storage trail. Changes 110


in weight, colour, odour, taint, and cracks should be noted. Conditions of storage should be representative of expected market conditions. Product should be periodically purchased from shops and checked to see if it has performed satisfactorily. Seal integrity is also critical as if it is a poor seal then the thickness of the material will be irrelevant and the calculated shelf life will be meaningless. Packing equipment should be kept in good condition, well maintained and must be regularly checked. Sensory evaluation Regardless of the methods chosen or the reasons for its choice, sensory evaluation of the product is likely to be used either alone or in combinations with instrumental or chemical analyses to determine the quality of the product. The instrumental and chemical analyses are neither prone to fatigue nor subject to the physiological and psychological functions that characterize human performance. However, because human judgment is the ultimate arbiter of food acceptability, it is essential that the results obtained from any instrumental or chemical analysis correlate closely with the sensory judgments for which they are to substitute. Other problems with sensory evaluation are high cost of using large testing panels and the ethics of asking panelists to taste spoiled or potentially hazardous samples. Three experimental designs are commonly used for the purpose of shelf life estimation: the paired comparison test, the duo-trio test, and the triangle test. Descriptive methods are used to measure quantitative and qualitative characteristics of the products and require specially trained panelists. Affective methods are used to evaluate preference, acceptance or opinions of products and do not require trained panelists. The selection of a particular sensory evaluation procedure for evaluating products undergoing shelf life testing is dependent on the purpose of the test. Acceptability assessments by untrained panelists are essential to an open dating program, while discrimination testing with expert panels might be used to determine effect of a new packaging material on product stability. However, an expert panel is not necessarily representative of consumers, much less different consumer segments. Even if that assumption can be made, a cutoff level of acceptability has to be decided. The time at which a large (but predetermined) percentage of panelists judge the food to be at or beyond that level is the end of shelf life.

111


�� Introduction The main functions of package are:  Protection of the product  Safety in storage and handling  Sales appeal by creating a brand image

The various BIS (Bureau of Indian Standards), BS (British Standards), ASTM (American Society for Testing Materials), ISO (International Organization for Standardization), and institutions like IIP (Indian Institute of Packaging , NCL, and the CFTRI (Central Food Technology Research Institute) provide guidelines for the development and testing of package suitable for any particular product. This field is continuously enlarging with respect to polymers, conversion methods, forms and applications. Therefore, it is necessary to continuously upgrade the test methods, and design tailor-made methods for each new end-use. Naturally all the test methods evolved for testing of packages and packaging materials need to be precisely taken care of for the above mentioned functions of a package. Materials and Package Testing Testing is necessary at different stages, especially before the product can be launched onto the market, to ensure that it will be satisfactory. Tests help to reveal how the pack will perform in practice, and also help to evaluate the alternatives. It can be decided what quality is required, for e.g., what grade of board or gauge of plastic is required. Routine tests are carried out to check the quality of new deliveries of material to ensure that it complies with the specification. The test condition must be realistic as possible to ensure a good correlation between the test results and actual performance. To achieve this, the test material should be conditioned (brought into equilibrium) with the conditions of use. For e.g., a corrugated box being stored in the dry raw materials store will behave differently in the humid atmosphere of a finished goods refrigerated store. Similarly, the permeability of a plastic film is dependent on the temperature and relative humidity. Therefore, tests should be carried out under known conditions & to approved standards that can be repeated for testing. Methods of Evaluation Evaluation may be carried out on complete packs (filled or empty), on pack components or materials, or on the product to be carried. The methods of testing can be classified as:  Physical tests: Physical tests look at factors such as puncture resistance, tear resistance, stretch, shrinkage, impact, density, tensile and compression strength, coefficient of friction, fragility factor, thermal shock, etc  Biological tests: Biological tests consider resistance to microbial attack, pests and rodents, etc  Chemical tests: chemical tests consider the effect of the pack on the product and of the product on the pack. Therefore, it looks at corrosion and migration issues, and chemical resistances to acids, alkalis, oils, solvents, etc. Also, GTR and WVTR are measured.  Visual tests: Visual tests look at issues such as clarity, print quality, gloss, haze, shape and electrostatic attraction which can cause problems with dust clinging to the pack.

Some of these tests are carried out on the finished pack while others will be on the packaging material. The type of test carried out and the quantity of frequency will depend on the situation, and the degree of confidence that there is in the quality of the supplier. A manual packaging line will have fewer critical parameters than an automated one. 112


Classifying methods of evaluation in another way, there are basically four avenues of approach:  Comparative testing: To compare the unknown pack, component, material or product with one

whose performance is known. This is the simplest approach and can determine not only whether the unknown is better or worse than the known but also provide a measure of the degree of difference.  Assessment testing : To simulate the events likely to be experienced in service and deduce,

from the results, what may happen.  Investigational testing: To determine whether the strength or weakness of the packaged

product lie.  Observational testing: To observe and/or record the performance in field trials or actual

distribution. Purposes of Testing Generally, the testing is carried out for the following purposes: 1. Selection of packaging material 2. Comparison of two or more different packaging materials 3. As an aid in designing of package 4. Assure quality and conform specification Test Procedures There are different tests and procedures based on different packaging materials used. A. Paper Testing The test of paper and paperboards can be divided into two groups, viz., (i) mechanical properties and (ii) physicochemical properties. A summary of tests is outlined as follows: TEST OF PAPER AND PAPERBOARDS MECHANICAL PROPERTIES (STRENGTH) Tensile strenght Static tensile strength Dynamic tensile strength Elongation Bursting strength Tear resistance Edge tearing resistance Internal tearing resistance Puncture resistance Abrasion resistance PHYSCOCHEMICAL PROPERTIES Thickness Basis weight Water absorptiveness Chloride content pH Moisture content Alkali staining Wax coverage Grease resistance Resistance to insect penetration Flute height Flat crush test Static bending test Resistance to glue bond to water Gas transmission rate (GTR) Water vapor transmission rate (WVTR) 113


Static Tensile Strength Tensile strength test gives an indication of the resistance of paper when subjected to a pulling force applied parallel to the plane of the sample. The tensile strength is influenced by (a) composition of material, (b) formation on the machine, (c) moisture content, and (d) other parameters like coating, creeping and calendaring. The beating of the cellulose fibers during pulping has a great effect on the tensile strength of paper. Excess beating will break the long cellulose fibrils and weakens the paper. The relationship of beating time (and extent) with paper properties like bursting strength, tensile strength, and tear resistance is shown below. bursting strenght tensile strength tear resistance Beating time

Tensile strength is important in tapes, wrapping paper, lining paper and bags. Instrument An instrument called Good Brand Tensile Tester is used for this purpose. The specimen is clamped between jaws and pulling force is applied. The force at which the specimen breaks is noted as kg/15mm. A schematic diagram of the instrument is given below: Elongation scale Pullling jaw 15mm width

Paper specimen 2 inch length

Elongation is a strength property. It is the length at the breaking point over the original length multiplied by 100%. It gives the % of change in length. The material should be tested in both the machine and cross directions. It is measured by the same instrument on a calibrated scale (having a pointer) and the result is expressed as: % Elongation = (reading×100) / (2 inch) Dynamic Tensile Strength This measures the energy required to break a specimen of specified dimension by subjecting it to an impact stress. The paper is clamped in a sigmoid shape. A pendulum is released to cut the paper. This test is important for construction of multiwall paper bags as it gives an index to the capacity of the sample to absorb impact shock. Instrument Van der Korput Baarn Tensile Tester is used for this purpose. The specimen is clamped between jaws in sigmoid shape. The pendulum is released and the impact (kg.cm) as registered on the scale is noted.

Pendulum

Specimen 114


Bursting Strength Test This test is also known as Muller test. It is the measure of the resistance offered by the material to a steadily increasing pressure applied at right angles to its surface. The burst pressure is the pressure at the point of rupture. The bursting strength test gives an indication of tensile strength and stretch of paper. The instrument may use hydraulic or pneumatic pressure. This test is used as a control test in the paper mill. The bursting strength is largely accepted as a specification for boards used in container construction and also for all types of papers. The specimen is fixed in the testing equipment and the pressure (pneumatic or hydraulic) is 2 applied. The pressure (psig or kg/cm ) at which the specimen ruptures is noted. The diameter of the disc affects the results, a smaller one being more difficult to burst. This test is generally carried out for paper, board and plastic packages. A high bursting strength is required for packing products that can move inside the pack such as dried peas, which can apply a concentrated pressure on a small area of material. pressure bursting

circular paper

Tear Resistance There are two types of tear resistance tests, viz., edge tearing and internal tearing; the latter is more widely used. Tear stain is usually measured in glassine, vegetable parchment paper, waxcoated paper and kraft paper. The test is designed to determine the force (gm x cm) required to continue, for a fixed distance, a tear already started. This is also known as internal tearing resistance. In edge tear resistance, the force needed to start a tear is measured. The tear resistance depends on grain direction, fiber length, degree of beating, density, surface treatment, etc. An instrument called Elmendorf Tearing Tester is used. A tear is made in the specimen and is subjected to a pulling force that continues the tear for a fixed distance and the force is measured. High tear resistance is useful for heavy packages and many industrial applications. A low tear strength is beneficial in easy-opening packages. Puncture Resistance Test This is also called Beach Puncture Test. It is used in paperboards. Puncture occurs in transportation, storage and handling due to nails, fork lift truck, lumber, etc. The test gives a combined assessment of stiffness and tearing resistance of boards. The instrument is called Beach Puncture Tester. The equipment is provided with different scales containing weights. The specimen is clamped between jaws and the pendulum with sharp edge pointer or head is released. The pointer is allowed to clearly and completely go through the specimen. The energy required to make puncture is measured as inch-once per inch of tear as shown on the scale or as Joule/m. Weight Pendulum

Penetration Sharp head

Specimen

115


Abrasion Resistance This test is designed to measure the ability to withstand surface wear during rubbing and friction. The test consists in abrading the sample with a wheel of standard abradant for a definite number of revolutions and finding the volume loss as: Volume loss = weight loss/specific gravity Rubbing wheel

Specimen

Caliper Caliper is the term used to describe the thickness of the sample. It is measured with a micrometer or vernier caliper. This should be tested, especially to check its uniformity throughout the sample. For corrugated fiberboard, this figure will be reduced due to the compressibility of the material. Yield Yield should be calculated. This is the value that determines how many packages can be made 2 from a kilogram of material. It is measured in units of m /kg. Basis Weight To calculate the grammage or gram per square meter (gsm), a known area is weighed and the weight is divided by the area and converted to the standard units. For corrugated fiberboard, this can be done for each component, i.e. for each liner & fluting medium & also for the total sample. Density It is the weight per unit volume, so it can be calculated from the gsm divided by the caliper. Chloride Content The standard method for the determination of sodium chloride is used. The sample is boiled in water to prepare an aqueous extract, which is then neutralized with acid or base. Chloride content is determined as NaCl by titrating with silver nitrate. H

P H P of the sample is measured by first preparing and aqueous extract as described before. Alkali Staining In order to qualitatively asses the degree of staining of paper by alkali, an alkaline extract of the sample is prepared by boiling it with suitable alkali and the color formed is compared with potassium dichromate-congo red standard. Wax Coverage This test is done for wax papers and is done to determine the amount of wax impregnated in the given sample of paper. Wax from the sample is first removed using suitable solvents and weighed. The difference in weight between the original sample and the treated sample, expressed as percentage gives the wax content in the sample. Grease Resistance It is determined by turpentine test. It gives an accelerated comparison of relative rates at which ordinary oils and greases, commonly found in foodstuffs may be expected to diffuse or penetrate through the papers like uncoated or unimpregnated greaseproof, glassine or vegetable parchment paper. It is easier to see if a sheet of blotting paper is placed under the sample paper. A varnish on board will increase its grease resistance so test a piece that is unvarnished. 116


The sample paper is placed on a sheet of book paper which is rested on a smooth glass surface, below which an adjustable mirror is provided. A 1-inch glass capillary is allowed to stand on the sample and filled with sand (5g). The capillary is removed after it has been filled with the sand. With a dropping pipette 1.1ml colored turpentine (red) is poured over the sand and noted the first time (transudation time) required to observe the first stain appearing in the book paper as seen from the mirror. Cobb Size Test It is a way of evaluating how resistant a material is to ingress of moisture. This is very important for packages intended for wet applications such as chilled and frozen products. 2 Take a 100 cm circle of paper. Weigh it and expose it to 100 ml of water for 120 seconds. Blot off the excess water and reweigh the sample. The better the sizing, the lower the weight increases. Moisture Content Moisture content determination is very important for printing, laminating, coating, curing, machineability, conformance to the specification, etc. It can be determined by various methods, including hot air oven, Infra Red moisture meter, and other methods. Resistance to Insect Penetration The test determines the strength of paper to resist insect penetration. Two to three week old, as far as possible uniform size test insects ( Sitophilus oryzae, Rhizopertha dominica, Tribolium castanum, Oryzophilus surinamensis) are kept under starvation for 24 hr. Place 5g food in a Petri dish 914.5cm dia) and cover it with the test packaging material. Put 100g test insects and cover the dish. Place the dish under the test conditions (a) 25-28°C and 50% RH, (b) Room temperature and 505 RH, (c) 21.1°C and 70% RH, and(d) 37.8°C and 95% RH for 3 weeks. The test material is examined every day for any penetration by the insects. The insects either die or reach the food after chewing and penetrating the test packaging material. Inverted Petri dish

Insects

sample

Food

Petri dish, 14.5cm dia

Flute Height Increase in flute height gives increased stiffness and compression-bearing strength. The flute height is measured by a traveling microscope. Flute Flute height

Flat Crush Test This test is used for fiberboard. It is the measure of resistance of flutes in corrugated fiberboard to a crushing force applied perpendicular to the surface. The test is useful for determining stacking strength of corrugated fiberboard. Force

Adhesive bond

Edge crush test o It measures the compression resistance in the opposite direction, i.e. at 90 . A small, vertically placed sample of board is loaded and the force it can withstand is measured. Thus, the rigidity of the board and its resistance to compression can be measured. 117


Static Bending Test A plot of load versus bending (deflection) is made. It is the measure of stiffness of board and gives indication of the quality of component and adhesive bond. Load

bending

Sample specimen

90 60 30 0

Load

Water Resistance of Glue Bond The test determines water resistance of glue lines of corrugated fiberboard. This property is particularly important where high degree of bond strength is required. Water makes the glue bond weak. Gas Transmission Rate (GTR) O2, N 2, and CO2 are generally used for GTR studies. The test measures the permeability of gases across the packaging material. This is an important test because penetration of O 2 is detrimental to most foods. Permeability of CO2 and N2 is tested for material used in inert atmosphere packaging, such as those used in meat products, milk products, fish, fats and oils, instant coffee, etc. GTR is defined as the volume of gas flowing normal to two parallel surfaces at steady-state conditions, through unit area of the material in unit time, under unit pressure differential and und the conditions of the test. The material being tested is arranged in a clamp so that it separates the test cell from an evacuated manometer. The pressure across the film is one atmosphere. As gas penetrates the sample, the mercury in the manometer is depressed. Conditions are controlled to give a constant rate. The height of the mercury is plotted against time giving a straight line whose slope is the GTR for those conditions of temperature and relative humidity. Hg column

Pressure difference

Steel disc Gas

Water Vapor Transmission Rate (WVTR) This is a very important property. It decides the shelf life of foodstuffs. It is used for packaging materials intended for packaging frozen foods, dehydrated foods, instant coffee, fresh food, etc. The measurement is expressed as: 2 WVTR = gram of water permeated/day/m at 37.8°C and 90% RH 118


WVTR operator filled with known weight of desiccant (water absorbing material such as silica gel or anhydrous calcium chloride) is taken. The packaging material is fixed on the dish. After the weight is noted, it is placed in the test chamber at 37.8°C (100°F) and 90% RH for 24hr. the weight is taken for some successive days. The weight gain (in gram) versus the number of days is plotted and the slope is found. WVTR is given by: 4 2 WVTR = (average slope×10 ) / 50, where 50 denotes 50cm , the area of the dish.

Slope

Specimen Controlled condition Seal

Calcium chloride Petri plate

Days

This method is suitable for materials with a rate of at least 1gm/day/sq. m. Accuracy is ≤10%. A more accurate method is required for high barrier materials. The film is clamped in a test cell. One side is exposed to a high humidity atmosphere while the other is dry air. As moisture permeates the film, it is detected by a resistor or an infra red absorption cell. The time taken for a standard change in the RH on the dry side is measured. B. Plastic Material Tests

Plastic Packages Plastic packages can be broadly classified as: Rigid packages: These include injection-moulded and blow-moulded containers and bottles as well as those made by powder sintering and thermoforming processes. Semi-rigid packages: These include mainly collapsible tubes and laminated tubes. Flexible packages: This is a very wide field ranging from simple polyethylene bags to the heavyduty woven sacks, and includes laminates of PE to paper, PET/BOPP films, aluminium foil, cellophane, strip packages, shrink packages, skin packages, multilayer films, etc. Collect a variety of plastics packages and check to see if it is a single material or a composite one by tearing it gently. A laminate will be obvious as the individual layers will tear at different rates. Identification of Plastic Infra red spectroscopy It is the best method to use as each material has distinctive set of absorption peaks. PE: Peaks at 3.4, 6.8, 7.4 and 14 m PP: Peaks at 3.4, 7.0, 8.0 and 12 m PS: Peaks at 7.0 and 9.5 m PVC has broad band at 14.5 m, and PVdC peaks at 9.3 and 9.6 m However, spectroscopy equipment is not always available and alternate techniques are used. Density tests

The material is placed into water to see if it floats. If it floats, then it is lighter in density than water and must be a polyolefin. To decide the exact family of polyolefins, prepare solutions of methyl alcohol to known densities as follows: % Concentration of methyl alcohol Density 74 0.88 62 0.90 50 0.92 44 0.93 119


38 0.94 26 0.96 The sample is put into each solution and observed to see if it floats or sinks. Therefore, the density can be found. The sample may also be scratched with a fingernail. If it scratches easily, it is LDPE, a slight scratch on a glossy surface suggests HDPE, whereas scratching PP will leave no mark. Burning tests

The sample is held on a spatula in the flame of bunsen burner and the flame is observed for colour and smell. When the sample is removed from the flame, it is observed to see if it continues to burn. If the material doesn’t burn and retains its shape, then the presence of thermosetting resins, such as phenol formaldehyde, urea formaldehyde, or melamine formaldehyde may be suspected. If the substance burns in the flame but this flame is readily extinguished on removal from the flame, then the substance suspected may be PVC and related polymers. If the substance continues to burn after removal from the flame, then the colour of the flame should be observed for identification. The polyolefins burn with a yellow or orange flame, about which there is a blue mantle. PP will burn and smell like paraffin wax. HDPE burns and drips like wax. PS burns with an orange flame and lots of dark sooty smoke. A yellow flame may be nylon, which burns with the smell of burning vegetation or hair, due to its nitrogen content. PET burns with a slightly sweet odour and melts into pearls. Halogenic materials such as PVC are readily identified by the copper wire test. A piece of copper wire is placed in the flame of a bunsen burner until it glows. It is then contacted with the plastic material before being returned to the flame. The colour of the flame will change to a blue/green if halogen is present. Solubility tests

Different types of plastics have various solubilities in various solvents and this property can be used to identify them. Polystyrene is soluble in toluene, carbon tetrachloride, acetone and ethyl acetate but not in methyl alcohol. Polyethylene is soluble in hot toluene and benzene. PVC is soluble in cyclohexane, dioxane and tetrahydrofurane. Put 15 ml of the required solvent into a 50 ml beaker and cut the material to be tested into required size (6 mm x 6 mm x 1.5 mm thick). Other solvents can be used to double check the result based on the polarity. For e.g. PA will also dissolve in formic acid. For polyolefins, the toluene should be heated. Therefore, initially put the sample into water to see if it floats or sinks. If it floats, it is likely to be polyolefin and so heat the toluene. Heating tests

This test is carried out by heating the substance in a small dry test tube, at first over a small flame and finally to ignition. Particular attention should be paid to the odour, acidity and alkalinity of vapours that are given off. For e.g. PVC gives fish-like odour, nylon gives the odour of burning vegetation, cellulose acetate butyrate gives the smell of rancid butter and so on. General Test Methods Testing of blown-moulded containers Plastic bottles should be evaluated for the following in addition to other tests: Stress Crack Resistance It depends mainly on the container design, resin, processing conditions, post-treatment, etc. 120


The commonly used method is the “Teepol method” in which the test containers are filled, sealed o and stored at 80 C immersed in 10% solution of Teepol in water. The containers are checked visually for cracks after 8 hours and then every 24 hours, for a period of 360 hours. Up to 50% failure at the end of the test period is an acceptable level. The probable causes of failure are:  Non-uniform wall thickness  Inadequate wall-thickness  Degradation of the polymer during processing  Poor container design  Improper polymer grade selection Container Breakage The test is intended to determine if the container finally designed has adequate strength to withstand drop tests. A common test method consists of filling the container to shoulder level o with water at 27 C, capping and dropping it from a height of 1.5 m. The initial drop is on the bottom edge of the container, the second drop on the wall, and the third drop so that the point of impact is on the flat area on the bottom of the sample. Container Collapse It is caused by the loss of the product contained in the container leaving a vacuum which draws in the container walls. This loss results initially from the absorption of the product into the container wall, which on continued use cause the product to diffuse through the walls and finally evaporate from the outside. Another possibility is that the product is filled at a high temperature in liquid form the filledsealed containers are transferred to low temperature chambers for solidification in fine crystal form. The reduction in volume on solidification creates a vacuum within, resulting in collapse, called the ‘panelling’ of containers. Wall collapse is essentially a visual observation and is governed by factors like resin density, wall thickness, container design, and filling techniques. Neck and Thread Dimensions The closure fittings must be correct and within close tolerances as they are produced separately and from different polymers. As with the overall dimensions, these are checked manually on a random sample basis, using maximum and minimum gauges for dimensions and templates for the threaded profiles. Weight and Material Distribution The weight of the blown container and the uniformity of the wall thickness are important considerations. The random samples must be checked for this factor. Container Volume and Weight These factors are important for confirming that the containers supplied pose no problem on the production line. The weight determines the wall thickness which in turn affects the container properties like strength, permeability, wall thickness, etc. Testing of Heavy Duty Packages The particular reference is to woven sacks, which are used for the packaging of fertilizers, chemicals, animal feeds, etc. The important requirements are: Fabric Strength A piece of sample is cut from the sack and wrap-way and weft-way are tested on tensile testing machine. 121


Seam Strength A cut sample from the seam is tested on a tensile testing machine for the breaking strength. Drop Test A filled sack is dropped vertically on the bottom from a height of 1.5 m and there should be no failure in three drops. Testing of Laminates The major problems with laminates generally are:  Delamination  Odour  Printing adhesion  Sealing properties

Type Tests Storage Tests The representative samples of the pouch material should be tested individually for storage properties with the edible oil to be packed into them. The storage tests should be carried out both o o at accelerated conditions (90 ≤2% RH & 38≤1 C) & standard conditions (65 ≤2% RH & 27 ≤1 C). The change in free fatty acid (FFA) as a % of oleic acid, moisture content and rancidity of the contents should be noted at intervals of 8 days and 15 days for testing under accelerated and standard conditions respectively. The pouch material is acceptable if the edible oil doesn’t show rancidity or increase in the values of the moisture content and FFA above the permissible limits specified at the end of 40 days storage period under accelerated conditions and 120 days under standard conditions. Overall Migration Tests Representative samples of the pouch material are subjected to overall migration test with no heptane at 25 ≤2 C for 30 minutes. The maximum extraction value for the material should not 2 exceed 10 mg/dm .

Stack Load Test Four pouches should be filled with the edible oil and sealed in the usual way. The pouches after filling and sealing with edible oil should be allowed to cool down for at least 4 hours before selecting them for this test. These pouches should be subjected to a uniformly distributed load for 72 hours at ambient temperature. The pouches should be laid in flat position. The application of load should be through a flat wooden plank or steel plate which should be placed on the pouches in such a way that load distribution is equal on each pouch. After completion of the test, the pouches should be examined for any leakages at the seams or bursting. Drop Test Ten pouches should be selected form 1 hour production or a lot of 100 pouches filled and sealed in the usual way. The sample pouches should be allowed to cool down to ambient conditions for at least 4 hours. Five pouches should be tested first. Each pouch should be dropped 4 times, one drop on each flat surface (upper and lower), and one drop on each longer side. The pouches should be dropped on a flat, smooth, hard surface, such as a concrete floor or a steel plate, from a height of 1.2 m. Each pouch should be examined for any leakages after the test. The lot can be considered as ‘passing’ if none of the five sample pouches fails in the drop. If any of the samples fails in the drop, then the other set of five pouches should be tested in the similar way. 122


Vibration Test The vibration table should be of adequate size to accommodate 110 pouches kept in a single layer and provided with an arrangement to prevent the falling down of the pouches during testing. The amplitude and frequency of vibration should be 254 cm and 120 cycles per min respectively. The pouches after filling with edible oil shall be left for at least 1 hour under ambient conditions o to attain the room temperature. The ambient condition is 65 ≤5% RH & 27 ≤2 C. The operating table surface should be clean and dry. A sheet of blotting paper may be spread on the surface and should be replaced after each test. The filled pouches are placed on the table in single layer, touching each other. The samples are subjected to vibration test for 40 min by running the motor. Observe any leakage of oil through the seams of the pouches during or after the test. The lot may be considered ‘passing’ if not more than one pouch shows leakage in the test. In the case of leakage from more than one pouch, retest must be carried out on a sample of another 10 pouches from the same lot. The lot may be considered ‘passing’ if in the retest, not more than one pouch shows leakage; otherwise, it should be rejected. Optical Tests One of the outstanding advantages of plastic film in packaging is its transparency. Hazy films often are not aesthetically pleasing. A film exhibiting a significant degree of gloss may be advantageous in certain packages and harmful in other applications. Gloss Gloss refers to transparency, shining or sparkle seen in the packaging material. High gloss is desirable in most applications. The film exhibits consumer appeal due to its inherent sparkle. Gloss is assessed subjectively or objectively with gloss meter. Gloss is the measure of the ability of the material to reflect light and is expressed as the fraction of original light (white light) at an angle of 45° falls on the surface of the test material. It is measure by gloss meter equipped with photosensitive cell which measures the amount of reflected light. A high reading on the meter indicates high amount of light reflected and the consequent increased gloss. Photocell

45o

Haze The haze measurements are conducted on specially designed haze meter, which measures light that is scattered from the incident beam. It consists of a light source and an integrating sphere capable of detecting transmitted light. The sample is placed between the light source & the sphere. By turning the sphere, a measure of scattered light is obtained. Percent haze at angles greater than o 2.5 is obtained. Low readings indicate less scattered light and clear films. Clarity This is the see-through property of packaging material. This is a subjective test and based on visual appearance. The specimen is compared with set of eight standard photographs for the measurement of clarity. Objective tests are also done, using the clarity meter, in which the light is allowed to pass through the sample and specular transmittance is measure using the expression: Ts = 100Is / I0 Where, Ts = specular transmittance; Is = Ts with specimen; I0 = Ts without specimen 123


Mechanical Tests The mechanical tests relate to the basic characteristics of the film. Overall film performance and strength are mechanical properties. Tensile strength, Elongation, Tear resistance, Burst strength, Puncture resistance, Gauge or Caliper, Yield, GTR and WVTR – See test of paper packaging Yield Strength st Yield strength is the tensile strength at the 1 point on non-elastic deformation, divided by area. Impact Test These tests are designed to measure the ability of films to withstand fracture by shock. The test is a measure of toughness of the material. It is a combination of deformation and braking properties. A dart is dropped vertically at the center of sample film which is held flat. The weight of dart can be increased using attachable weights. The weight for with 50% of the specimens fail is reported as impact failure weight. Another test used is the pendulum impact tester. A hammer-pendulum is allowed to swing through a sample. The difference in energy between the pendulum at maximum height and after sample rupture is known as the impact strength. Stress Flex The ability of the film to be continually exposed to severe stresses is of great importance. Various methods are available for the test and the suitable method is based on the end use. A flex tester measures the folding of a film backwards and forwards at a given rate. A recording of the number of cycles necessary for film fracture is obtained. Flex testing can be conducted in freezing or humid environments. Heat Seal Strength It measures the strength of the welding of sealed points of heat sealable plastics and laminates. This is the test of efficiency of heat sealing. The test can be done by tensile tester. The two sides are clamped in jaws and the force that breaks the seal is noted. Coefficient of Friction (COF) Two pieces of films are placed on an inclined plane with a weight on top. The angle of inclination is increased until one layer slips. The COF is the tangent of the angle of inclination at which this occurs. Softening Point It is the temperature at which the plastic begins to flow or to be deformed, i.e. where it softens. It is measured by the Vicat test which expresses the results as the temperature at which an indentation of 1 mm occurs when the test specimen is subjected to pressure by a standard needle with a 1 sq. mm surface area, under a standard load of 1 kg. Melt Flow Index (MFI) It is used instead of the molecular weight of the material as it is easier to measure. It is defined as the rate of flow in grams of a thermoplastic material at a given temperature extruded in 10 min under a constant pressure through an orifice of a set size. For a pressure of 300 KPa, a load of 2160 gm is used, whereas with a 700 KPa pressure, a load of 5000 gm is used. For polyethylene, o o the given temperature is 190 C, whereas for polypropylene it is 230 C. A high value of MFI means it flows easily. The MFI is inversely proportional to the molecular weight. The test procedure involves placing a sample of t he material in a cylinder, preheating it to the required temperature and lowering a piston of the given weight then measuring the rate of flow of the molten material. Typical values range from 0.1-50 gm in 10 minutes. 124


Test for Tinting (of Printing Inks)- product resistance to printed pouch Tints can solubilize in fats and oils. The test is performed by smearing edible oil to be packed on printed portion and rubbed firmly after one hour with tissue paper for 10 times. There shall be no significance removal of print and the printed material shall still be readable. Test for Ink Adhesion of Printed Pouches - Decoration The test assesses the strength of ink adhesion on printed plastic or pouch. Apply two strips of 25 mm wide transparent pressure-sensitive tape or cellotape to the printed area of the pouch, one piece down the length and the other along the width of the pouch. Press the tape firmly onto the pouch and leave for at least 15 s. o Remove the tapes by pulling slowly at about 1 cm/s from one end at about 90 to the pouch surface. There should not be significant removal of the print from the surface of the pouch and the printed material should still be readable.

Chemical Resistance Plastics have resistance to chemicals and solvents in varying degrees. This can be tested by completely immersing a sample of plastic in the chemical or solvent. Any change in appearance and other properties must be noted. Environmental Stress Cracking Cracks are sometimes found in plastic materials due to it being stressed in the presence of a particular chemical environment, e.g. certain polar organic compounds. The polyolefin plastics are particularly susceptible to this phenomenon. For the test procedure, take a strip of plastic material, 3.8 x 1.3 x 0.32 cm thick. Score along the o central 1.9 cm to a depth of 0.05-0.064 cm. Bend the strip along its long axis through 180 with the scored line on the outside and hold it in this position with a pin. Put it into a test-tube o containing the product and keep at 50 C. The time it takes until failure is noted and can be compared to other grades of material. C. Glass Testing For adequate performance on fast filling machines, glass container dimensions are critical and must fall within the set limits known as tolerance. The major dimensions to be measured are the height, body diameter, wall thickness, capacity, bore diameter and the finish. Thermal Shock It can be tested by immersing the container in hot water and letting it come to equilibrium for about half an hour before plunging it into cold water, for which the temperature difference of o 45 C is recommended. The container should be emptied of any hot water before it is transferred to the cold water to prevent rise in temperature. Thermal shock is important for containers that will be retorted or heat processed. Finish Details Thread engagement is defined as the number of turns given to the lid from the point of first engagement to the point where the sealing edge of the bottle makes contact with the liner. It is greater than or equal to 1. It can be measured by marking the bottle neck and finish at the point of initial engagement & then counting the number of revolutions until it reaches the sealing surface. Thread pitch is the number of turns of thread per unit travelled in the transverse direction, i.e. per cm. It measures the steepness or slope of the thread. A low number means that the thread is steep, giving a more rapid screw on and off. This can be measured by a caliper and reported as the vertical distance down travelled by the lid in one revolution of t hread engagement. The glass containers should also be observed for any defects, viz. critical, major and minor. 125


D. Metal Testing To determine the quantity of tin coating on a sample of tinplate A sample of tinplate is cut out of the container and its area is measured and it is weighed. Take 250 ml of conc. HCl in a beaker and add 5 gm of antimony trioxide (Sb 2O3) to it. Immerse the metal sample in the solution and leave for at least 1 min after all the hydrogen gas has been given off. This process may take several hours for completion. The chemical reactions that occur are as follows: Sb2O3 + 6 HCl Ø 2SbCl3 + 3H2O

2Sn + HCl + 2SbCl 3 Ø 2SnCl4 + 2 Sb + H 2Æ The metal is then removed from the solution and washed carefully under the tap. The solution should be disposed of carefully after neutralizing with sodium hydroxide. The surface of the m etal is carefully wiped with cotton wool or clean cloth to remove the loose antimony. Dry the sample and reweigh it. The difference in weight so obtained is the weight of tin coating for that area of metal. This should be converted to the standard units of grams per square meter. An allowance should be made for the small amount of iron that is also dissolved. This is recommended to be 0.33 gm for plate that has been electroplated with the same amount of tin on each side and 0.67 gm for that which has been differentially electroplated. Alternatively, the edge of the tinplate sample may be slightly dipped in wax to cover the exposed surface from where i ron may be dissolved in the solution. Package Testing Other tests include transit testing. This can be in a laboratory that simulates hazards such as vibration, compression, impacts, etc. It is important that the package is tested on each face and corner to find the worst possible case. Shock is a stress induced by sudden deceleration, i.e. if the vehicle stops abruptly. The resistance to shock is known as the fragility factor (ff). It is defined as the maximum deceleration that can be tolerated under specific conditions. It is measured by putting the package on a shock testing machine which drops it from a known height on a retarder which gives it a known deceleration. The height is increased until failure occurs, and the ff is measured in g, i.e. acceleration due to gravity. The test is repeated for each surface of the pack to ensure that t he weakest point is found. The compressive strength of the box depends on its cross sectional area over which the load is distributed. This value is found by placing a box between two metal plates. The upper one descends, subjecting the box to an increasing compressive force until it fails. Impact testing of filled containers is used when testing a new design or material for plastic bottles. It will reveal any weakness that could lead to leakage in transit. The bottles are filled with water and dropped down an unplasticised PVC tube onto a level rigid base plate. The distance dropped can be varied. The height at which half the samples fail is taken to be the maximum impact that the bottle can sustain. Compatibility Testing One of the most important parameters in selecting a particular material for packaging of a product is its compatibility with the product to be packaged. The tests should be carried out by storing the products for the expected shelf-life to ensure that the contents and the container have no adverse affects on each other. Accelerated tests are possible. o These are based on the theory that a rise in temperature of 18 F corresponds to a doubling of the o rate of reaction. An accelerated test is carried out at 50 C for 28 days. At the end of the test period, the containers are examined for change in weight, leakage, cracks, panelling, etc. The 126


temperature and duration of a test has to be selected depending on the product and the product requirement. This is useful to give an indication of the likelihood of a compatibility problem. However, a long term test programme under standard conditions should be carried out to confirm compliance with the regulations. Migration of constituents of the packaging material into the product is important. An overall migration limit has been set to ensure that the health of the consumer is not at risk. The overall limit is that a maximum of 60 mg of constituents may be released per kg of food for plastic containers. For film or packages that have a surface area that is easily measured, the overall limit is 10 mg per square decimeter of the surface area of the material. The determination of these minute quantities requires very specialist facilities. The results may be obtained by standard methods so that they may be compared on an equal footing with others. A schedule has been established, stating which solvents are to be used with each type of product. In some cases, a reduction factor can be used. The test conditions must reflect the conditions of use of the product. So, products cooked in contact with the material must be tested at high temperatures. If the contact time with the material is more than 24 hours at temperatures less than o o 5 C, the test should be carried out for 10 days at 5 C. If the storage temperature is between 5 and o o 40 C, the test should be conducted at 40 C. A contact time of less than 2 hours at temperatures o o between 100 and 121 C must be tested for 30 minutes at 121 C. Shelf Life Testing To estimate the shelf life based on the rate of permeation The initial moisture content of the product is measured. The product is packaged in the proposed packaging material and weighed. A control pack of the product in the standard packaging material is also tested. They are stored in the controlled atmosphere. The packs are weighed daily and the increase in the weight due to permeation of moisture is measured and graphed over time. The graph shows that the weight increases everyday but at a decreasing rate, until equilibrium has been attained. A point will be reached when the product has absorbed so much moisture that it has lost its texture and become unacceptable. The equilibrium moisture content can be found quickly by opening the packet and letting the contents come to equilibrium. Plot the change in weight to the change when the pack is opened. The typical curves are:

The general formula applicable is:



=



−



   Where d is the weight gain in time t by the sealed pack and c is the ultimate weight gain of the open pack on exposure to the atmosphere. A theoretical value for the shelf life may be calculated by taking the standard for the maximum moisture content allowable for organoleptic or for legal reasons. For e.g., in Nepal, the maximum moisture content of biscuits is 6%. This can be substituted in the equation as the maximum ‘d’ to calculate t. 127


Other Tests Product Change Product evaluation for the expected storage life after packaging is necessary to ensure that the product has remained unchanged. For e.g. tomato ketchup may turn blackish because of oxidation, or an instant coffee powder may form lumps because of absorption of moisture.

Product Loss During storage, there may be product loss due to permeation. Permeation is defined as the quality of being penetrated or allowing other substances to pass or diffuse through. Product loss testing can be carried out at room temperature and at elevated temperatures for accelerated test results. The critical factor is to test for a sufficiently long period that product loss occurs at a constant rate so that shelf-life calculation becomes meaningful. A minimum of three containers (in the case of film and sealed bags) are weighed at room temperature and filled up to 80% of the volume capacity with the test product, capped and reweighed. The containers are exposed to the test temperature and inspected periodically to ensure proper test environment and observe any changes. In addition, the samples are weighed every other day to arrive at constant rate of weight loss per 48 hours. After the completion of the test, containers are emptied, cleaned and dried, and the containers with caps (or bags) weighed again. Product loss % =

         

Saturation solubility % =

x 100

         

x 100

Permeability factor = Weight loss in grams in 24 hours per 100” surface area per mm thickness. Climatic testing This test is designed to test the resistance of package to extreme climatic conditions. Some specifications (ISO 2233 and British Standard 4826 pt. 2) are: Extreme cold temperature: 50°C and 40% RH Very cold: -18°C and 40% RH Cold and dry: -10°C and 40% RH Hot and dry: 65°C and 40% RH Normal temperature, UK: 20°C and 65% RH Normal temperature, USA: 23°C and 50% RH Wet temperature: Warm and moist:

20°C and 85% RH 38°C and 85% RH

Wet tropical:

38°C and 95% RH

Water spray test The test simulates rain and drain water. Water is sprayed on the package at a defined pressure, time, drop size angle of cone, and position of package. Water consumed is noted and the strength of package is noted before and after treatment. The strength properties related to this test are (i) bursting strength, (ii) puncture resistance, and (iii) water absorptiveness. Taste and Odour It is important that no taste or odour is imparted to the contents by the plastic material from which the container is produced. The only possible test is to smell the empty container before filling to determine, if there exists any unpleasant odour. Leakage A package has to be tested for leakage through the seals or caps. 128


�� Introduction A specification is the document used to communicate the necessary information or details about a product or a process, etc. According to the Oxford dictionary, it is “a detailed description of construction, workmanship, material, etc. of work to be undertaken. For e.g., it could detail the various components of an item, the relevant performance parameters, or how a process should be run, i.e. the time & temperature profile in a pasteurization process. In packaging, the specification is used as the basis of a contract between the supplier and the consumer so that all are aware of what is required.

The purpose of the specification is:  To inform all the relevant parties what has been agreed  To form a part of the contract, specifying what is required  To provide a checklist of data against which the supplied item can be tested for compliance  To prevent any misunderstandings  To provide a basis for settling any claims due to unacceptable quality  To provide a basis by which to compare the products offered from different suppliers The specifications must be clear, concise and unambiguous. Test methods should be standard, i.e. using international standards such as ISO methods and reproducible. Tolerances should be clearly stated, e.g. reel width to be 510 ≤1 mm means that the reel width can only be between 509-511 mm, and a reel of width 508.8 mm is unacceptable. Where possible a plus and minus tolerance should be given. All details should be discussed with the supplier and acceptable to him. If he is incapable of meeting the requirements, he should state so. The tighter the tolerances (i.e. less deviation, for e.g., ≤0.5 mm) allow the higher degree of control of the manufacturing conditions and a corresponding higher level of rejects can be expected at the supplier in order to meet the specifications. Hence, the product will be more expensive. However, modern packaging equipment is highly automated and the machines will only accept a certain degree of variation in the dimensions, reel widths, etc. So, a reasonable specification must be agreed. For packaging materials, there are two main types of specifications, viz. material and performance specification. The material specification describes in detail the material type needed to achieve the required performance. For e.g. a glass bottle specification would specify the type of glass, its colour, dimensions with tolerances, capacity, weight, and coatings required, etc. A performance specification is less concerned with which type of material is used but more with how it performs. It leaves to the supplier to choose the material and specifies the required strength or performance. For e.g. in the case of corrugated box outer case, a compression strength of 300 kg is required. The supplier can decide to use a high weight single walled board or thinner gauge double walled board, to use A, B, or C fluting, etc. The decision is based on the cost of either option as well as on the availability of the board. Many companies use a combination of both types of specification, for e.g. a material specification for the glass bottle (as above) with the performance parameters that it can withstand thermal shock or a certain internal pressure, specified. In general, the specifications must include the following information:  The type of the product and its characteristics, e.g. PH, carbonation pressure, etc  Quality or grade of raw material to be used in making the packaging material, e.g. food grade or recycled 129


 Quantity or volume to be packed  Relevant dimensions including tolerances, a drawing is often supplied to show the exact        

shape required Details of special features such as easy opening, peelability, tamper evidence, etc Graphic design details such as the number of colours ad their pantone references Details of packing methods, e.g. equipment used and conditions in the packing hall and in storage such as temperature and RH Delivery time, i.e. lead time and method of delivery, e.g. by truck, rail, etc. details such as the quantity per reel, quantity per pallet, height and weight of pallet Information to be supplied on the pallet label, delivery note, invoice, etc should be agreed Quality control procedures, test methods and schedule of testing Classification of defects and allowable levels Price

Information specification This is used internally in the factory detailing all the primary, secondary and tertiary components necessary to make up the retail unit. For e.g. to make a case containing 12 packets of soup will require 12 lengths of laminate to make the primary pack, plus the outer retail case plus the shrinkwrap and label. Similarly, 12 cans of baked means require 12 can bodies, 24 ends, 12 labels, glue to attach the labels, the outer case, its label and shrink-wrap. This information is used by the storekeeper who issues the material to production, based on the production schedule. It assists production who needs to know what to use in order to make the product. The account department uses this information to produce a costing of how much it costs to pack the product and hence to prepare budgets based on sales forecasts. The buying department uses it to predict stock requirements and quality assurance uses it to check that all is in order on the finished pack. The specification is usually originated by the packaging technologist and approved by the buying manager, and the production, technical and marketing departments. It is updated as necessary. Grading of defects – critical, major and minor There always occurs a degree of variability in the quality of any mass produced item. In the specification, these defects are classified as being critical, major or minor and an agreed level of defects will be accepted. Otherwise, the supplier would have to carry out a 100% quality inspection and this would be expensive resulting in more rejects and a more expensive product. A critical defect is unacceptable in all instances. It means that the item is unsuitable for the required purposes. A major defect is outside the agreed tolerances but could be used if the machine were altered slightly or if not affecting too high proportion of the batch. A minor defect is aesthetically unattractive but is usable. The end use will determine what is acceptable. For e.g. a glass bottle intended for use for squash will have lower standards than one intended for an expensive bottle of spirits. As it is not desirable to have too high quantity of defective material, an agreement is m ade. The acceptance quality level (AQL) is set. By this method, each type of defect in a given sample size is given a score and a maximum score is set as being allowable. If a critical defect is 10 on such a score system and a major defect is 5 while a minor defect is 2, then it is possible to set the AQL equal to 9 and say that if the sample contains any critical faults, 2 major faults, or 5 minor faults, etc, the entire delivery will be rejected. Examples of defects for various types of packaging: Glass Critical: broken, contaminated or cracked bottles 130


Major: dimensions outside tolerances but usable Minor: rough mold marks, seeds, etc Metal cans Critical: incomplete lacquer, leaking seams Major: out of round shape, dents > 25 mm Minor: dents < 25 mm, scratches, etc Labels

Critical: wrong colour, wrong text, serve curl Major: print out of register, rough cut edges Minor: slight curl, colour deviation from standard PE bags Critical: holes, tears, faulty seam Major: gauge below specification, foggy film, poor print Minor: rough cut edges, wrinkled appearance

A good inwards QC inspection is essential to prevent discovering that there is a problem only when the defective material reaches the production line, causing downtime and high levels of wastages and rejects. Records should be maintained of a supplier performance. It is important to have a good working relationship with the suppliers, involving them in development programmes looking at future requirements and investigating new materials and trends. The suppliers should be of a high quality with their own effective quality programmes. Verification Specifications In order to ensure that the good supplied meet the requirements; there should be a verification specification against which the various parameters should be checked. It should detail the parameters to be checked, the test methods and the degree of variation allowable. It will also include details of the AQL, and procedure to be followed if a problem is detected i.e. holding the suspect batch or quarantining it and further steps to be taken. Quality Quality can be best defined in relation to perfection. Perfection is something which can be very rarely, if ever, attained and the quality is the distance away from perfection that any particular specimen happens to be. In simple words, quality is the measure of distance away from perfection of an item. The level of quality must be determined by the particular product involved. It is not necessary to produce a quality higher than that required to do the job. The second important aspect of quality is the consistency of the quality throughout the job, and this is particularly important inters of packaging standards. It is of course; very important to realize that quality is something that is built in at the time of manufacture. We must remember the two aspects of quality for which we must cater: first of all the level of quality required, and secondly, the variation about that level throughout the batch. Setting a level higher than necessary normally means that costs will be increased for two reasons; firstly, the maintenance of the higher quality level on the production machines will mean that more rejects will be produced, and secondly, the requirements for a higher quality level will almost inevitably mean that the variation will become more obvious over a smaller range than if the level were lower. Quality Control Quality control is the measurement of quality by statistical methods to assist the control of production. Quality control involves deciding what is acceptable & how consistent are the results, 131


how much variation should be allowed. It is the application of statistical techniques as an aid to the control of quality at the point and time of manufacture. It covers two aspects, that of the product and of the process. This can also be applied to the goods inwards inspection procedures, i.e. the inspection of incoming raw materials. The degree of inspection can range from 0-100%, depending on how critical the application is. Quality control is often known as Statistical quality control or even Q.C. Another term frequently used, or misused is specification, and this also means different things to different people. There are six possible motives for writing a specification, and each of these give a different result. The six are:  To invite tenders on a like-for-like basis  To improve the product  To assist the supplier to judge what he has made  To allow the supplier to know more about what he should be tr ying to produce  To make one’s own staff better judges of what they accept or use  For use in case there is an inquest later on. However, the only valid use for a specification is as a document jointly drawn up by the user and supplier so that each knows as clearly as possible what is required. Sampling As some quality control tests are destructive and most are expensive, it is not reasonable to inspect every item and the principle for taking a representative sample has been established. The art of sampling is to select a sample from a population so that the quality of the sample is representative of the quality of the population from which it was taken. The sample should be taken in as random a manner as possible to give each container an equal chance of being selected. The larger the sample taken, the more representative it will be of the batch from which it is taken, and hence the lower the risk of not detecting serious fault. There are 3 methods of sampling. The first is called single sampling, because the result is decided on the examination of a single sample. The second is called double sampling and the decision can be reached following the examination of a smaller first sample, provided that the quality is either very good or very bad. If the result is intermediate, this indicates borderline quality, and in this case, a second sample is taken and the decision is based on the results of the combined sample. The third type of sampling is called multiple sampling. This is an extension of double sampling where successive samples are taken until a decision is finally reached to accept or reject. Assessment of quality Variability occurs in a batch due to factors such as lubrication, temperature, pressure, speed, density variations, etc. in the production process. The quality assessment should be accurate. Very accurate dimensional measurements are affected by surface texture variations. Similarly, geometric shape, straightness, etc have to be taken into account. Considerations of errors arising from measuring techniques points to the need to establish (a) the appropriate number of significant figures for recording the test results, and (b) whether, in determining the last figure, the result should be rounded up or down. Despite taking every precaution with our measuring equipment and our techniques, there is no such thing as a completely accurate measurement. It is possible, however, to find out by experiment how accurate any measuring process is. This determination covers all the aspects, the instrumentation deficiencies and observer errors. The measurement has to be repeated a number of times with several different observers. From the results, it is possible to calculate a mean value and a figure called the standard deviation. This is a measure of the variability of the results and is 132


designated s (sigma). When this has been determined for a given set of conditions, it is possible to state the mathematical risk of inaccuracy of a particular measurement exceeding a certain value. These chances are indicated by the normal distribution, as shown in the figure below:

As seen from the graph, in this pattern, there is a central value encountered most often with a range on either side. The Poisson distribution is a distribution of unlikely results which allows for the chance of a rogue (one not following trend) result in the sample t aken. Variability can be taken as that between successive items, or over a longer period of time as a trend or long term variation. There are two things which will be examined, namely the variables of an item such as its colour, length and other measurable features, and its attributes which are judged on a discrete scale such as odour, texture and flavour. A control chart is used to monitor results. It reveals the operating level, the normal variability to either side, the trend and any freak or rogue results. The size of the sample taken depends on the QC system. Four is a common size but it must be remembered that if there are four sealing stations, then four samples should be taken from each one. As the size of the sample taken increases, so does the cost of the quality control system. On the control charts, the average is plotted to see the trend and if it is within acceptable limits. Plotting the range will reveal the variation around the average value. The maintenance of QC records is a legal requirement. These records should be maintained until after the products shelf life has expired in case of customer complaints. Factors affecting quality in packaging Modern packaging lines, whether they are fully- or semi-automatic or manual, often contain highly complex pieces of engineering equipment. It is important for packaging efficiency the packaging material or containers to be processed are of right and consistent quality. Sub-standard material or containers will cause hold-ups and reduce the speed of the packaging operation. Nowadays, emphasis is placed on functional aspects, both during manufacture and in the preceding design stage. There are four key decisions on controlling the quality of any packaging or packaging container. They are:  What are the packages intended for?  What properties of the materials used control the requirements?  How can we measure these properties?  When and how will the operators of packaging machines use the measurements we have made? To summarize;  Measurement is needed to quantify quality  No measurement is completely accurate  Inaccuracies can be minimized by properly calibrated and sufficiently accurate equipment used with a proper understanding of the inherent problems in measuring  The probable extent of inescapable inaccuracies can be calculated where necessary. 133


�� Package selection criteria A number of criteria must be considered when selecting a packaging system for a food. These include:  The stability of the food with respect to the deteriorative chemical, biochemical and microbiological reactions which can occur. The rates of these reactions depend on both intrinsic (compositional) and extrinsic (environmental) factors.  The environmental conditions to which the food will be exposed during distribution and storage. The ambient temperature and humidity are the two important environmental factors and they dedicate the barrier properties required of the package.  The compatibility of the package with the method of preservation selected. For e.g. if the food is being thermally processed after packing, then the packaging must be able to withstand the thermal process.  The nature and composition of the specific packaging material and its potential effect on the intrinsic quality and safety of the packaged food as a consequence of the migration of components from the packaging material into the food. This is of major concern in the selection and use of plastic materials for food packaging. However, migration of components from the packaging to the food occurs with other materials as well. Migration The term migration is used to describe the mass transfer of substances from the package to the food. Substances that are transferred to the food as a result of contact or interaction between the food and the packaging material are known as migrants. Migration is a two way process because constituents of the food can also migrate into the packaging material. In addition, compounds present in the environment surrounding the packaged food can be absorbed by the packaging material and migrate into the food. It depends on the nature of the packaging material and the time of exposure. It is important to distinguish between overall migration (OM) and specific migration (SM). OM, also referred to as global migration is the sum of all (usually unknown) mobile packaging components released per unit area of packaging material under defined test conditions, whereas SM relates to an individual and identifiable compounds only. OM is therefore a measure of all compounds transferred into the food whether they are of toxicological interest or not, and will include substances that are physiologically harmless. Although the transfer of substances from packaging materials into foods is undoubtedly a complex process, diffusion resulting from the spontaneous natural molecular movements that occur without the assistance of external forces such as shaking, mixing or even convection current in liquids, is thought to be the main controlling mechanism. Regulatory considerations Concern about the wholesomeness and safety of foods has increased dramatically nowadays. Increasing understanding of & interest in technological matters on the part of consumers and organized consumer groups, coupled with a recognition that neither government nor industry can guarantee the safety of food, have lent support to this concern.

Safety is an emotive issue, and because everyone must consume food to live, the safety of food is especially emotive. Most concern usually focuses on food additives, both those added intentionally to the food and those ending up in the food from processing equipments or others. 134


It is important to note that it is not the toxicity of the chemical at the concentration at which it appears in the packaging material that is at issue here, but rather the toxicity of the chemical at the concentration at which it appears in the food from the packaging material. The toxicity of a substance is its inherent capacity to produce injury when tested by itself. A chemical may be toxic (i.e. inherently capable of producing injury when tested by itself) without being a hazard (i.e. likely to produce injury under the circumstances of exposure as in a diet). The concern, therefore, is not directly with the intrinsic toxicity of a particular chemical component of a food, but rather with the potential hazards of those materials when the foods in which they are present are eaten. Benefit can be defined as anything that contributes to an improvement in condition, which risk can be subdivided into two categories; vital and non-vital. A vital risk is one essential to life, while a non-vital risk usually doesn’t involve a threat to life but may lead to injury, loss or damage. Risks can also be divided into voluntary and involuntary risks. An example of voluntary risk is cigarette smoking, where the risk of lung cancer is likely but no one is compelled to smoke. An example of involuntary risk is a food additive in staple item of the diet, the additive having being shown from animal tests to be carcinogenic. The consumption of a chemical that has migrated from a packaging material into a food is classified as involuntary risk. The toxicity assessment of the food additives usually follows a decision-tree approach. Acute, subchronic and chronic toxicity tests are normally required. The final phase of toxicological evaluation involves assessment of the potential risk to humans and, in particular, the extrapolation of high-dose experiments with animals to low-dose risk assessments of humans. Manufacturer package foods in a variety of packaging materials to achieve certain benefits such as extending the shelf life of the food, making its storage and preparation for consumption more convenient or reducing the cost of the food compared to its cost if another type of packaging material were used. The fact that a component of the packaging material may migrate into the food and pose a risk to the consumer requires that the benefits arising from the use of the particular material be balanced against the risk arising from the consumption of the component. Quantifying the risks and benefits and then arriving at a decision that a certain packaging material should be permitted for use because the benefits outweigh the risks is extraordinarily complex, and because it is ultimately subjective, there will always be some consumers (and manufacturers) who will disagree with the final decision. The way in which the decisions are made about the migration of components from food packaging materials into foods differ to varying degrees in various countries around the world. The legislations vary from one country to another with regard to developed and under-developed countries.

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�� Introduction The packaging cost must be minimized within reason as it is the product which is being bought and not the package. However, it is the benefit to be optimized. It is responsible for protecting and preserving the product and helps it to sell it. Inferior packaging will make a product look cheap and unattractive, and it may mean that the product is damaged. Some products are sold as commodities and do not need fancy packaging, others such as expensive confectionary or premium spirits need to be packed in material suggesting that it contains a premium exclusive product. Hence, the packaging selected should be appropriate. Minimising the packaging to such an extent that the product is damaged is meaningless and false economy. Likewise, using excessive packaging to protect the product from all the conceivable hazards is wasteful and uneconomical. The resulting product will be so expensive that no one will buy it. A low level of damaged goods is acceptable for most food items. Costs

Cost comparison is a major exercise to set out, quantify and cost all the factors relating to a packaging system. Costs which must be considered include the actual materials used, the labour and equipment costs, services and overheads. Savings can often be made on material costs due to the technical improvements being made in materials science, especially with the application of computers to optimize the design. Thinner gauges of materials can achieve better results than traditionally. Comparing materials on the basis of yield may lead to cost savings. There are different barriers available and different combinations of materials to achieve the required performance at optimum cost. The combinations can be achieved by laminations and coextrusions. Reuse of packaging material also leads to cost saving. The labour cost will depend on the degree of automation in the packing line, which in turn depends on the volume of production, the cost of equipment and the labour charge. The efficiency of the machinery in converting the packaging material into containers with minimum waste and rejects is an important factor. Storage and distribution costs must be considered. Fireboard cases can be stored flat, taking up less space than fabricated wooden boxes. Plastic polymer pellets or reels of sheet which can be moulded or thermoformed, take up less space than preformed bottles and containers. Plastic bottles are lighter than wood and this leads to cost savings in the distribution of the product. The damage caused in distribution must be assessed to decide on the level of protection required, both for primary and secondary packs. In export packaging, the volume of the material can have a large affect on the costs as space is at a premium. Overheads include the rent, heating costs, administration, storage, waste, R&D, etc. Services required can include vacuum, gases such as nitrogen for gas flushing, power, water for cooling, etc. Depreciation affects the stocks of materials that are being held and the minimum order quantity. Once the material is purchased and in store it ties up money that could otherwise be used or invested, to earn interest for the company. Depreciation also applies to the buildings and equipment, etc. Contract packaging is an option to be considered, which involves sending the product in bulk to another company to be packed for retail. It is useful for test market production trials, for coping with seasonal demand, lack of production capacity, or if there is a labour dispute at the factory. Quite often, the contract packer employs casual labour and thus has lower labour costs. 136


Principles of good management 1. Correct specifications help to minimize costs. 2. Good quality suppliers should be used where possible. 3. Economic order quantities (EOQ) should be placed and advantage taken where appropriate of bulk discounts. 4. The number of colours used in printed design should not be excessive as this will lead to higher costs. 5. Where possible, standardization of pack sizes can lead to the use of standard boxes and reel widths, which reduces the number of different items to be stored and enables the bulk buying of standard items. 6. Stock rotation must be enforced to ensure that the material is used on a “first in, first out” basis and doesn’t sit in the store deteriorating. 7. Size the pack carefully, and do not use excessive material. This involves minimizing scrap such as in the trim and in the seal width. 8. Over-packaging should be avoided. 9. The environmental impacts of packaging cannot be ignored. Recycle and reuse the packaging materials where possible. 10. Finally, the equipment must be well maintained to achieve optimum performance.

Finally, to reinforce the above views, a quote from John Ruskin: “It is unwise to pay too much but it is worse to pay too little. When you pay too much you lose a little money, that’s all. When you pay too little you sometimes lose everything, because the thing that you bought is inadequate of doing the thing it was bought to do. The law of business balance prohibits you paying a little and getting a lot……....it can’t be done. If you deal with the lowest bidder, it’s well to add something for risk you run, and if you do that you will have enough for something better.”

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�� Introduction Marketing is a very important function in every business. The marketing department is responsible for identifying, anticipating and satisfying customer requirements, profitably. It is the marketing department who determine the market requirements, by market research and analyzing the supply & demand equation. They are responsible for informing consumers about the products virtues and persuading them to buy the product. Advertising, publicity in the form of positive public relations (PR), organizing sales promotion and motivating the sales force, are all part of the marketing department activities. The supply and Demand Equation In a demand oriented or consumer driven marketplace, it is necessary for each company to try to supply what is required by the consumer. The goods must be available in a huge variety of sizes, shapes and with different features. Mass production makes the product cheaper but it is useless unless there is also mass consumption. It is the marketing department who analyze the demand, determine what is required, in what form, by whom, when, where, at what price, and how it should appear and be packaged. Then it will be considered if this can be achieved at profit. If the product goes into production, the marketing department will use the mass media to inform the consumers. The advertising campaign will inform the consumers of the products existence, its features, applications and advantages over the other products. Then try to influence the consumers buying habits, persuading them about the needs of the product and to try to buy it.

Role of packaging Packaging plays a major role in the marketing process as it acts as an oh-shelf advertisement for the product in the shop and in the home, reminding the consumer of the brand. It must attract attention to itself and be distinctive, outstanding from other packages on the shelf by its strong graphics, imagery, shape, etc. The packaging identifies the product and must reinforce the image of it given in the advertisements. Graphics are not only feature that is important. The shape of the pack, the materials used, the convenience it offers in terms of ease of holding, dispensing, closing, etc. are all important. Features such as reusability may make it appeal to the consumer, for e.g. the horlicks jug or coffee jars being reusable as storage containers. Sales promotion, such as money off coupons, competitions, new improved product, extra product free offers, etc. are advertised on the packaging. Sometimes the packaging has to be returned as proof of purchase, e.g. crown caps from coke. The packaging draws attention to the promotion and gives details about it. Brand names In today’s marketplace, there is intense competition between products & the consumer is confused over which one to choose. Each company tries to gain sales volume. A brandname is a valuable asset to a company as it enables their products to be distinguished. A brand is a form of identity of a product, and can be protected by the copyright or trademark. There are some unbranded products that are generic, often commodity products such as sugar, salt, etc. Cola is a generic name while Coca Cola and Pepsi are brand names. Other examples include Cadburys & Nescafe. Brand identity is a vital asset to a company. A good brand is respected by the consumers who associate it with quality. The brand consists of the product, the packaging, the name, the advertising and its overall presentation. It is a combination of the physical, aesthetical, rational and emotional aspects as perceived by the consumer. 138


Checklists of Marketing Considerations

Market Analysis Factors  What is the size of the market, its volume, value and trends?  Competition – what other producers are there, what is their share of t he volume?  Is the market regional, urban/rural, north/south, etc?  Is it seasonal – dependent on weather, holidays, festivals, etc?  Who are the consumers – age, sex, socio-economic group? Product Factors  What is a suitable size or range of sizes of retail pack?  What is the price range in the market currently?  What advantages/disadvantages does our proposed product have over the opposition?  What levels of advertising will be required? Packaging Factors  What style, shape, colour, texture are suitable?  Is visibility necessary, does the consumer need to be able to inspect the product?  Does it maximize the shelf restrictions, optimizing storage requirements?  Is it easy to open, dispense, close and reuse?  Is it environmentally acceptable, recyclable, etc?  What shelf life is required?  How does the product deteriorate – what protection is required?  What are the likely distribution hazards?  Should this product be packed on existing equipment or can new formats be considered? Graphic/copy Factors  What are the legal restrictions – weight, sell by date, nutrition declarations, etc? This will affect size and location of some information.  What instructions are required – storage, cooking, serving, etc?  Does this design have to blend in with other varieties in the product range?  How many colours are to be used?  Are there special colours to be used, i.e. for the logo, t rademark, etc?  In a varnish to be included?  Which print process is suitable, i.e. high quality gravure print or flexographic which is adequate for simpler designs?  If date/price coding is to be applied by another machine, what are the restrictions on size and location of coding boxes?

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Packaging Technology.pdf

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