Denim Garments Processing 1

Fabric-Care CARE CHEMICALS

DENIM GARMENT PROCESSING Dr. Ravichandran. L [email protected]

e-mail: [email protected] www.atlanticchemicals.com

3545 Stonecutter Crescent, Mississauga, Ontario, L4M 7N7, Canada

DIN EN ISO 9001 : 2000

Zertifikat 15 100 52977


DENIM GARMENT - PROCESSING

A glimpse in to denim garment processing: Indigo dyeing is done at high alkaline medium. Initially indigo stock vat is prepared. Dye bath is prepared from the stock vat.

Indigo stock vat preparation: Indigo 100% Caustic soda Sodium hydrosulfite Temp Time

80 gpl 130 gpl 60 gpl 500 C 30 min

The dye bath is prepared from the stock vat at room temperature with sodium hydrosulfite dehydrate and caustic soda. During dyeing, since sodium hydroxide is consumed in the decomposition of sodium hydrosulfite, it is necessary to add more sodium hydroxide while dyeing. The yarns are dyed- dried- sized and wound directly in the warp beam for weaving.

A typical denim size recipe would consist of add 10 % size on weight of warp yarn Modified starch owg. Warp yarn Binder (PVA,CMC, guar gum, acrylic polymer etc) Dye fixative (polymeric fixing agent) Lubricant

7 – 8% 2.0 – 3% 2.0 -5.0 % 0.25 – 0.55%

The fixation of indigo dye stuff The term "fixing agent" refers to any of a large number of chemicals used to improve the retention of a dyestuff by a fiber. In most applications of dyestuffs to fibers, the dyestuff is fixed to the fiber by chemical or physical forces during the dyeing process. Hence no additional fixation is required. However, in some cases, particularly heavy shades, the dyed fabric does not have adequate fastness unless fixing agents are used. Epi-polyamines are commonly used to reduce color loss during garment wet processing. This is incorporated in the first wet processing step. By holding more color on the fabric during the desize cycle, a higher degree of contrast can be achieved between the highly abraded and lightly abraded areas of the garment. Other specialty polymers possess both epi-polyamine and epi-polyamide functionality. This type polymer can be used to control both color bleed in wet processing and subsequent home laundering. However, higher usage levels are required to achieve equivalent results. In the case of dyeing of fabric and garments, both the epi-polyamines and epi-polyamides have been utilized as pretreatments and fixatives.



DIN EN ISO 9001 : 2000




Fastness of indigo dye stuff: Due to the nature of Indigo dyestuff and the surface ring dyeing techniques used to apply the dyestuff, Indigo dyed yarns generally have poor wash fastness. However, if desired, indigo dyed yarns and fabrics can be treated with fixing agents to greatly enhance the wash fastness of the indigo dyestuff. The degree of fixation required and the point at which the fixative is applied depends largely on the look desired in the washed garment. In the process of manufacturing Indigo denim, there are two areas that offer the greatest opportunity for application of the fixative. These are the slashing of the yarns and finishing of the fabric. The following illustrates the possibilities for applying the fixative in those particular operations. Application of the fixative to the dyed yarns reduces bleeding of the indigo dyestuff during the finishing operation. This results in less cross staining and reduction of the tendency for the shade to get heavier as the color builds up in the finish bath.

Problems encountered during garment wet processing & precautions. Garment streaks: Inconsistent and ineffective desizing results in garment streaks and inconsistent garment surface abrasion. The starch film on the garment is often broken or cracked during sewing when garments at or near the bottom of the bundles are creased along side seams due weight of the garment on top of the stack. During wet processing, the areas of cracked size films abrade quicker than the protected reminder of the garment. The additional abrasion removes more dye, either on the out side or inside of the garment depending on whether or not the garments are right side out. In any case the streakiness will be the result. Back-Staining: Back staining is the phenomena of the re-deposition of discharged indigo from the process bath. The effect is reduced contrast, with bluish color evenly distributed all over, masking the desired white contrast look. The parameters which control the back staining level during wet processing are, • pH level of bath, during processing • temperature level • Rinsing time • No. of rinses after enzyme treatment • Quantity of dispersing agents used in the bath • Type of enzyme preparation used. • Additional treatment with a protease based enzyme detergent.



DIN EN ISO 9001 : 2000


Fabric-Care DENIM GARMENT - PROCESSING

CARE CHEMICALS

The lowest level back staining is achieved in between the pH levels of 6.5 to 7.5. Since the acid enzymes work on acidic pH, the level of back staining will be much higher with these kind of enzymes. However it can be resolved by using protease based enzyme detergent after the enzyme treatment. The quantity of water and temperature used during processing are another important factors of back staining. - Higher quantity of the water will give more space for the discharged indigo to distribute, and the level of re-deposition will be less. The amount of back staining can be reduced by lengthening the rinse timing, or increasing the no. of rises. Lowering the bath temperature can help in the reduction of the returned indigo. It is to be noted that new neutral enzyme formulations can work in 25°C bath also. The usage of a dispersing agent during the processing can minimize the re-deposition of discharged indigo. Fatty alcohols having chains of 40 - 60 molecules will have good results. However, the dosage has to be well monitored during processing to obtain the maximum efficiency. Over dosage can cause excessive foaming, which could badly affect the cellulase enzyme preparations, and further rinses. Optimum dosages can be 0,5 - 2 gpl. The use of antifoaming agents is not advisable because it could badly affect the performance of enzyme and equipment.



DIN EN ISO 9001 : 2000



CARE CHEMICALS

More alkaline specific enzyme could give better performance in lowering the level of back staining. Alkaline specific engineered cellulose is now available for the industry. The back staining level is also depending on the type of water and quality of indigo dye. The usage of very hard water can increase the level of back staining. Semi hard waters are the best ones. The stabilization of the indigo dye on the fabric also matters a lot in the level of indigo re-deposition. After treatment with protease based detergent and the usage of low heat, alkaline specific neutral cellulose can control and remove the re-deposited loosened indigo dye particles.

Ozone Fading: One of the key noxious by-products of urban photochemistry is ozone, and this can be reached dangerously high levels of 0.5 ppm. In presence of UV light, there is an interaction between hydrocarbons, oxides of nitrogen and oxygen that causes of the release of ozone. The release is during day time due to the presence of sun light. Ozone induced yellowing is a major problem on denims. This is due to the sun's UV radiation. The increased concentration of NOx and SOx gases due to pollution can potentially react with ozone and reduce its concentration tremendously in the ozone layer. As a result a portion of the sun's UV radiation reaches to the earth's surface and generates ozone gas from the atmospheric oxygen. Ozone (O3) being a very strong oxidizing agent decomposes indigo dye in the following manner.

Based on molecular weight calculation

One gram of ozone could destroy 10.9 gram of indigo dye.

The ozone induced oxidation of indigo produces certain compounds which are 'isatin, anthranillic acid, and the complex of the two products.' which is yellow in colour. This is the reason of yellowing due to ozone fading.



DIN EN ISO 9001 : 2000




The factors influenced in the yellowing of indigo dyed garments: * * * * *

Position of the dyestuff in the fibre Absorption and diffusion of moisture in to the fibre Humidity Protective chemicals on the fibre Ozone concentration;

Position of dyestuff in the fibre : The yellowing due to ozone is directly proportional to the amount of back staining generated in the wash process. Back staining is the re-deposition of indigo dye released during various wash process. Redeposited dye has more loose sites for oxidation resulting in the yellowing of denim garments, the use of anti re-deposition chemicals in the de-size and abrasion baths can prevent the re-deposition of the released dye by suspending the dye particles in the bath and not allowing the re-deposition to happen.

Absorption and diffusion of moisture in to the fibre : The increase in humidity accelerates ozone fading of indigo dye stuff as high humidity give rise to a surface water film that increases the ozone absorption rate. This is due to the increased surface concentration and also the increased rate of diffusion in the fibre. Fibres swell after the absorption of moisture and the swollen fibres are always in a more receptive condition. So the problem of ozone fading will be more prominent in high humidity regions

Humidity : High humidity raises the absorption rate since the fibre is more receptive due to swelling. With 0.2 ppm of ozone level, the time to fail (2.5 rating on AATCC –scale) increases substantially as the relative humidity increases. At the RH of 80, the time to fail would be 34 hours and this would fall in to 16 hours at RH 85.

Protective chemicals on the fibre : The conventional oxidants such as Sodium Bisulfite, Ethylene Diamine Derivatives etc, will provide only short term protection against ozone fading. This type of anti oxidants undergo very rapid chemical decomposition and do not provide the protection required when the garments are stored for extended periods of time in high ozone concentration. Selected amine based softeners can provide the protection for ozone fading. Since the softeners are applied substantially in large quantities as compared to anti oxidants, they can provide protection for an extended period of time.



DIN EN ISO 9001 : 2000



CARE CHEMICALS

The usage rate of anti-ozone softeners are highly depened on the activity of the product. The rate at which the cationic softener exhausts on the cellulose is related to the pH of the softener bath. Anti-ozonates are solubilized by lowering the pH of the product. Once in solution an increase in pH reduces the solubility of the softener and the exhaust rate increases significantly. As the pH of the bath reach certain point (pH – 8 or above), the softener exhausts so rapidly that it plates out on the surface of the fabric. The excess softener on the surface has a clammy, tacky feel and will yellow severely when dried. For optimum exhaustion of this product on to the garment, the temperature should be kept in between 45 – 55o C and pH in between 6 to 6.5. Usage of anti-ozone softener to prevent the ozone fading in indigo denim is not the complete solution. Thorough study for the reason for yellowing must be done before going for any remedial measures – for the complete control.

The other reasons of denim garment yellowing: This is the yellow discoloration that textiles can develop during processing, use or storage. Since this yellow discoloration, which appears on the fabric on low intensity, it can be visible only on white and pastel shades. Dark shades are also affected, as colour becomes dull. There are many reasons for this yellowing. 1. Yellowing due to softeners; 2. Use of fluorescent whitening compounds; 3. Phenolic yellowing;

Yellowing due to softeners; Cationic and silicone softeners are commonly used to impart a good handle to the fabric. Both these softeners generally contain primary, secondary and tertiary amines and some times amides also. All these groups contain Hydrogen atom attached to Nitrogen atom. The former is susceptible to substitution and can be replaced by chlorine and form chloramines. Chloramines being yellow in colour impart yellowness to the fabric. Most of the commercial detergents contain carriers of chlorine bleaches. So each domestic wash the fabric tends to yellow more. Also the amines and amides are nitrogen-based groups can very well oxidized to nitrogen oxides if the finished fabric is over heated. Even during the normal drying of the garment/ fabric these groups can be oxidized and can produce different oxides of nitrogen. Nitrogen oxides are brownish in colour and at very low concentrations they seem yellow.

Use of fluorescent whitening compounds; Fluorescent whitening agents are used to improve the whiteness of fabrics, these fluorescent whitening agents absorbs the UV light and emit it in a visible region. This emitted light is blue white in colour and mask the yellow colour of the material.



DIN EN ISO 9001 : 2000




These fluorescent whitening agents contain some un-saturation in their structure, which are responsible for absorbing the UV light and emitting it in a visible region. But these un-saturations are very sensitive to sunlight and oxidation or weathering. These compounds are not at all fast and loose their ability to work as fluorescent whitening agents. Hence the fabric yellowness becomes more prominent.

Phenolic yellowing : This is the most common type of textile yellowing and it generally occurs during storage. Phenolic yellowing is characterized by its bright yellow colour and has maximum absorption at 420 – 450 nm. This yellow colour fades when exposed to ozone. The yellow products are soluble in hot water and polar solvents such as alcohols, and become colourless in acid medium at pH 5,0 or below. Plastic wrapping materials such as poly bags contain Butylated Hydroxy Toluene (BHT) as an anti oxidant to prevent it from ageing. These can be transferred to textile surfaces. BHT reacts with nitrogen oxides present in the atmosphere and form nitro phenol compounds or stillbene quinone. These are yellow in colour and impart yellowness to the fabric. Alkaline pH is a must for this process to take place. The sources of alkalinity on white or pale shaded fabrics are the residual chemicals used in the bleaching or dyeing process, which are not properly neutralized.

General precaution to avoid yellowing and colour change after wet processing: • Prevent back-staining during de-sizing, enzyme wash or stone wash. Loose indigo on un-dyed weft is prone to yellowing. • Proper rinsing before finishing eliminating residues of surface – active agents and other chemicals which will interfere in protective action. • Removal of Mn+2 residues by treating with proper sequestering agent, if potassium permanganate is used for fading. • Avoiding softeners / finishing chemicals that accelerate indigo decomposition. Initial screening in laboratory is recommended. • Dry the garment as quickly as possible, as wet garments are more prone to yellowing. • Use suitable packing material to avoid phenolic yellowing. Avoid packing material contains BHT (anti oxidant). • Avoid exposure of garments to light and atmospheric ozone and Nox. • Have proper ventilation in store rooms to avoid the build up of NOx. Avoid fuel based trucks and fork lifts. Instead use electrically operated vehicles to avoid build up of exhaust fumes in warehouse • Avoid storing and display in highly polluted areas having higher petro- chemical smog.



DIN EN ISO 9001 : 2000




Bleaching of indigo by sodium hypo chlorite : Parameters affecting bleaching; * * * *

Bleach concentration Time of process Temperature of process pH of bleach solution ( very important in controlling concentration of active bleaching agent)

Bleaching degrades fibre. Must control conditions to maximize whitening and minimize fibre degradation.

Sodium hypochlorite : Strongest oxidative bleach Effect of pH, NaOCl is a moderate base. NaOCl OCl + H2O Hypochlorite ion -

Na+ + -OCl HOCl + + -OH Hypochlorous acid

HOCl is the active bleaching agent. Its concentration in the solution must be controlled.

Effect of pH on HOCl concentration pH 10.0 9.0 8.0 7.5 7.0 6.5 6 5

% of NaOCl on HOCl concentration 0.30 3.0 21 50 73 91 96.0 99.7



DIN EN ISO 9001 : 2000



* * * * * *

CARE CHEMICALS

Usually between 9 and 10 Very low HOCl concentration As HOCl is used it is replenished by the equilibrium Fibre degradation is minimized pH drops during bleaching Bleach solution must be buffered with Na2CO3

Effect of alkali and acid in the bleaching bath: If base NaOH is added to the solution * * * *

Equilibrium shifts to left HOCl concentration is reduced Bleaching is reduced pH >10 OCl is a major species in solution

If Acid (HCl) is added to the solution * * * * *

Equilibrium shifts to right HOCl concentration is increased Rapid bleaching occurs Fibre degradation may occur pH between 5 and 8.5, HOCl is a major species in the solution

If additional HCl is added * * * *

Chlorine gas is generate HOCl concentration is reduced Bleaching is reduced pH < 5.0 Cl2 is major species in solution.

HOCl +HCl

Cl2 + H2O

Effect of Metal Cations : Transition metal cations (Fe++, Cu++, etc) catalyze degradation of cellulose by sodium hypochlorite * Use stainless steel equipment * No rust spots or metallic pieces in fibers * Acid pre-treatment to dissolve metals preferred



DIN EN ISO 9001 : 2000



CARE CHEMICALS

Effect on time and temperature : Temperature o C 20 30 40 50 60

Time of bleaching ( Minutes) 360 130 50 20 7

Fibers bleached with NaOCl: * * * * *

Mainly cotton Polyester and poly / cotton, ok Do not use on fibers containing nitrogen ( polyamides, acrylic, polyurethane (spandex / lycra yarn) ) Chlorine reacts with nitrogen to form chloramines which will yellow fibers ( residual chlorine in the garments after bleaching could react with cationic softeners and change to chloramines). Cellulose bleached with NaOCl must be treated to reduce chloramines formed from proteinaceous matter in space.

Typical bleach formulation : 2.5% NaOCl bleach 1% Na2CO3 Buffer

Denim with spandex: precautions Shrinkage: Denim twill fabric are with a warp yarn consisting essentially off 20 -95% cotton and balance0 -5% other synthetic fibre based on the end use and the fill yarn consisting essentially of 20 -100% cotton and from 02% of other synthetic fibre. Warp yarn having been sized. The finished woven fabric will have a warp shrinkage varying from 5 -12% and 3-5% in the filling direction. If the term pre-shrunk is used then the warp shrinkage will be 3-5% and weft shrinkage will be 0-3%.

Testing: The fabric shrinkage is determined by measuring the dimensions of the fabric before and after three wash/ dry cycles. The wash/ dry cycle consists of washing the fabric according to the desired look (process recipe) and drying in a conventional tumble dryer to a maximum dryness at a final max. Temperature of 710C. usually drying time of 30 minutes is required.



DIN EN ISO 9001 : 2000




Dryer heat: Dryer heat does not shrink the garments. Shrinkage in the tumbler is caused by the tumbling action as the garments hits the sides of the dryer. In fact the dryer heat has the opposite effect, as the garments loose the moisture it elongates slightly. But the drying process can damage fabrics made of natural fibres such as cotton, linen and wool, if too much moisture is removed. These fibres have natural moisture content, even we feel they dry. The occasional over drying will usually not cause a problem. Later they will absorb moisture from the atmosphere. So don’t try to extend drying timings assuming that low temperature and extended timing could help to reduce garment shrinkage. It will shrink more because of the tumbling action on a longer period of time. The major portion of the shrinkage occurs in the washing process. The warmer the water, the greater the shrinkage. So temperature and wash timing have a great impact on the shrinkage. As a matter of fact, the denim fabrics have shades because of the dye lots. So if the other process parameters are consistent, shade factor cannot be clubbed with garment shrinkage. It only happens when there is a difference in process timings, temperature, water level and loading.

Extraction : Better extraction can reduce the drying time, thus the shrinkage due to tumbling action. The shrinkage factor can be controlled in the washing process. This can be achieved by low temperature wash, correct loading methods, better extraction for maximum removal of water, reducing drying timing etc. The residual shrinkage has to be calculated in the fabric stage. Wash a trial lot before going ahead with bulk cutting. The trial load pattern has to make as per the recommended shrinkage testing method. Rushing in to production with lycra fab. is like “stopping watch and saving time”. The norms and procedures can only bring consistency in shrinkage. This is purely physics. Since we don’t have any idea about the fabric process parameters, we have to have certain R&D work with the fabric lots for the particular wash. Also ensure that the fabrics are well relaxed in the layer before cutting.



DIN EN ISO 9001 : 2000



CARE CHEMICALS

Process precaution with spandex denim: * * * * * *

Keep a low and consistent temperature wash procedure. Standardize the time and M:L ratio. Try to remove maximum colour in de-sizing and enzyme procedures to avoid extended bleaching time. Carefully control the pH in bleaching. Should be kept in between 9.5 – 10 and temperature not more than 470 C. Give heavy extraction for removing maximum water- so as to reduce the beating action in tumbler. Remove complete chlorine residue by using proper antichlor.

Some do’s and don’ts in denim garment processing: *

Follow the de-sizing with hot water rinses: The cold water rinse may re solidify the sizing waxes and lubricating agents and tend to re-deposit unevenly on to the garment surface. This could create patches on the further enzyme process.

*

Cold bath enzyme process: Novowash E-10 can be used at temperature ranging from 35 -40o C (cold process). The back-staining will be very low and slight difference in cast will be the results. Dosages will be slightly higher for similar results.

*

Inconsistent and ineffective desizing results in garment streaks and inconsistent garment surface abrasion. The starch film on the garment is often broken or cracked during sewing when garments at or near the bottom of the bundles are creased along side seams due weight of the garment on top of the stack. During wet processing, the areas of cracked size films abrade quicker than the protected reminder of the garment. The additional abrasion removes more dye, either on the out side or inside of the garment depending on whether or not the garments are right side out. In any case the streakiness will be the result.

*

Antiozone softener: The conventional oxidants such as Sodium Bisulfite, Ethylene Diamine Derivatives etc, will provide only short term protection against ozone fading. This type of anti oxidants undergo very rapid chemical de-composition and do not provide the protection required when the garments are stored for extended periods of time in high ozone concentration. Selected amine based softeners can provide the protection for ozone fading. Since the softeners are applied substantially in large quantities as compared to anti oxidants, they can provide protection for an extended period of time. The usage rate of anti-ozone softeners are highly deepened on the activity of the product. The rate at which the cationic softener exhausts on the cellulose is related to the pH of the softener bath. Anti ozonates are solubilized by lowering the pH of the product. Once in solution an increase in pH reduces the solubility of the softener and the exhaust rate increases significantly. As the pH of the bath reach certain point (pH – 8 or above), the softener exhausts so rapidly that it plates out on the surface of the fabric. The excess softener on the surface has a clammy, tacky feel and will yellow severely when dried.



DIN EN ISO 9001 : 2000




For optimum exhaustion of this product on to the garment, the temperature should be kept in between 40 – 50o C and pH in between 6 to 6.5. Usage of anti-ozone softener to prevent the ozone fading in indigo denim is not the complete solution. Thorough study for the reason for yellowing must be done before going for any remedial measures – for the complete control. •

Novosoft AZ is a classic example of anti ozone softener. The amines are specially modified by pre hydrogenating to impart long lasting protection against ozone induced yellowing. This protective softener undergoes degradation sacrificing itself with ozone there by preventing destruction of indigo. Primary oxidation takes place at free amine group in the softener, where as the secondary oxidation takes place at main structure.

•

Zipper tarnishing: the zipper made of or coated with silver or copper, brass, tin, aluminium, alloys etc get oxidized in the presence of heat, moisture, sulphur, chlorine etc and form a black/ dark blue residue of oxides on the surface. This oxide film can create stains on the fabric in contact. The best solutions are either asking for tarnish protected zippers or use the following method to remove it before fastening on the garment.

•

For the removal of tarnish from zipper made of with copper, brass, tin, aluminium, alloys etc…wash the zippers inside a mesh bag, with acetic acid and baking soda for about 10 min at 50oC temp. This could effectively remove the tarnish or oxide film. Then wash the zippers with a commercial detergent for another 5 min and rinse well. Do proper rinsing to prevent further oxidation.

•

For silver or silver coated zippers: soak the zippers in a solution of soda ash at a temperature of about 45oC in the presence of aluminium foil. Insert the aluminium foil first and keep the zippers on top of it. The add chemical in hot water. Keep min. 15 min. the tarnish will catch on the foil by ionisation. Then wash with a commercial detergent and rinse well.

•

The oxidation can happen in presence of heat in chlorine bath or alkaline bath. Improper rinsing or removal of residual chemical can cause dulling of zippers due to oxidation while drying the garment.

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THANKS

……………….

Dr. Ravichandran. L [email protected]



DIN EN ISO 9001 : 2000


Denim Garments Processing 1

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