Denim Garments Processing 1

8/8/2019 Denim Garments Processing 1

1/14

DIN EN ISO 9001 : 2000

Zertifikat 15 100 52977

CARE CHEMICALS

Fabric-Care

DENIM GARMENT

PROCESSING

Dr. Ravichandran. [email protected]

e-mail: [email protected]

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


2/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care

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 preparedfrom the stock vat.

Indigo 100% 80 gplCaustic soda 130 gplSodium hydrosulfite 60 gplTemp 500 CTime 30 min

The dye bath is prepared from the stock vat at room temperature with sodium hydrosulfite dehydrate andcaustic soda. During dyeing, since sodium hydroxide is consumed in the decomposition of sodiumhydrosulfite, 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.

Modified starch owg. Warp yarn 7 8%Binder (PVA,CMC, guar gum, acrylic polymer etc) 2.0 3%Dye fixative (polymeric fixing agent) 2.0 -5.0 %Lubricant 0.25 0.55%

The term "fixing agent" refers to any of a large number of chemicals used to improve the retention of adyestuff by a fiber. In most applications of dyestuffs to fibers, the dyestuff is fixed to the fiber by chemical orphysical 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 isincorporated in the first wet processing step. By holding more color on the fabric during the desize cycle, ahigher degree of contrast can be achieved between the highly abraded and lightly abraded areas of thegarment.Other specialty polymers possess both epi-polyamine and epi-polyamide functionality. This type polymercan be used to control both color bleed in wet processing and subsequent home laundering. However, higherusage 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 utilizedas pretreatments and fixatives.

Indigo stock vat preparation:

A typical denim size recipe would consist of add 10 % size on weight of warp yarn

The fixation of indigo dye stuff




3/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


Fastness of indigo dye stuff:

Garment streaks:

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 canbe treated with fixing agents to greatly enhance the wash fastness of the indigo dyestuff. The degree offixation required and the point at which the fixative is applied depends largely on the look desired in thewashed 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 followingillustrates 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 finishingoperation. This results in less cross staining and reduction of the tendency for the shade to get heavier as thecolor builds up in the finish bath.

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 thebottom of the bundles are creased along side seams due weight of the garment on top of the stack. Duringwet 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 onwhether 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 effectis 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.

Problems encountered during garment wet processing & precautions.




4/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


The lowest level back staining is achieved in between the pH levels of 6.5 to 7.5. Since the acid enzymeswork on acidic pH, the level of back staining will be much higher with these kind of enzymes. However itcan 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 backstaining. - Higher quantity of the water will give more space for the discharged indigo to distribute, and thelevel of re-deposition will be less. The amount of back staining can be reduced by lengthening the rinsetiming, or increasing the no. of rises. Lowering the bath temperature can help in the reduction of the returnedindigo. It is to be noted that new neutral enzyme formulations can work in 25C 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 wellmonitored 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 ofenzyme and equipment.




5/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


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 veryhard water can increase the level of back staining. Semi hard waters are the best ones. The stabilization of theindigo 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.

One of the key noxious by-products of urban photochemistry is ozone, and this can be reached dangerouslyhigh levels of 0.5 ppm. In presence of UV light, there is an interaction between hydrocarbons, oxides ofnitrogen and oxygen that causes of the release of ozone. The release is during day time due to the presence ofsun light.

Ozone induced yellowing is a major problem on denims. This is due to the sun's UV radiation. The increasedconcentration of NOx and SOx gases due to pollution can potentially react with ozone and reduce itsconcentration tremendously in the ozone layer. As a result a portion of the sun's UV radiation reaches to theearth's surface and generates ozone gas from the atmospheric oxygen. Ozone (O3) being a very strongoxidizing agent decomposes indigo dye in the following manner.

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

Ozone Fading:

Based on molecular weight calculation One gram of ozone could destroy 10.9 gramof indigo dye.




6/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


The factors influenced in the yellowing of indigo dyed garments:

Position of dyestuff in the fibre :

Absorption and diffusion of moisture in to the fibre :

Humidity :

Protective chemicals on the fibre :

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

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

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

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

The conventional oxidants such as Sodium Bisulfite, Ethylene Diamine Derivatives etc, will provide onlyshort 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 periodsof time in high ozone concentration.

Selected amine based softeners can provide the protection for ozone fading. Since the softeners are appliedsubstantially in large quantities as compared to anti oxidants, they can provide protection for an extendedperiod of time.




7/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


The usage rate of anti-ozone softeners are highly depened on the activity of the product. The rate at whichthe cationic softener exhausts on the cellulose is related to the pH of the softener bath. Anti-ozonates aresolubilized by lowering the pH of the product. Once in solution an increase in pH reduces the solubility ofthe softener and the exhaust rate increases significantly. As the pH of the bath reach certain point (pH 8 orabove), the softener exhausts so rapidly that it plates out on the surface of the fabric. The excess softener onthe surface has a clammy, tacky feel and will yellow severely when dried. For optimum exhaustion of this

oproduct on to the garment, the temperature should be kept in between 45 55 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 thecomplete control.

This is the yellow discoloration that textiles can develop during processing, use or storage. Since this yellowdiscoloration, 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;

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

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

The other reasons of denim garment yellowing:

Yellowing due to softeners;

Use of fluorescent whitening compounds;




8/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


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

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. Thisyellow colour fades when exposed to ozone. The yellow products are soluble in hot water and polar solventssuch as alcohols, and become colourless in acid medium at pH 5,0 or below. Plastic wrapping materials suchas poly bags contain Butylated Hydroxy Toluene (BHT) as an anti oxidant to prevent it from ageing. Thesecan be transferred to textile surfaces.

BHT reacts with nitrogen oxides present in the atmosphere and form nitro phenol compounds or stillbenequinone. These are yellow in colour and impart yellowness to the fabric. Alkaline pH is a must for thisprocess to take place. The sources of alkalinity on white or pale shaded fabrics are the residual chemicalsused in the bleaching or dyeing process, which are not properly neutralized.

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.

Phenolic yellowing :

General precaution to avoid yellowing and colour change after wet processing:




9/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


Bleaching of indigo by sodium hypo chlorite :

Parameters affecting bleaching;

Sodium hypochlorite :

Effect of pH on HOCl concentration

* 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.

Strongest oxidative bleachEffect of pH, NaOCl is a moderate base.

+ -NaOCl Na + OCl- + -OCl + H O HOCl + OH2Hypochlorite ion Hypochlorous acid

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

pH % of NaOCl on HOCl concentration10.0 0.309.0 3.08.0 217.5 507.0 736.5 916 96.05 99.7




10/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


* 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 Na CO2 3

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

* 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

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

2

HOCl +HCl Cl + H O2 2

+ +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

Effect of alkali and acid in the bleaching bath:

If Acid (HCl) is added to the solution

If additional HCl is added

Effect of Metal Cations :




11/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


Effect on time and temperature :

Fibers bleached with NaOCl:

Typical bleach formulation :

Shrinkage:

Testing:

oTemperature C Time of bleaching ( Minutes)

20 36030 13040 5050 2060 7

* 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 tochloramines).

* Cellulose bleached with NaOCl must be treated to reduce chloramines formed from proteinaceous

matter in space.

2.5% NaOCl bleach1% Na CO Buffer2 3

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 0-2% of other synthetic fibre. Warp yarn having been sized. The finished woven fabric will have a warpshrinkage varying from 5 -12% and 3-5% in the filling direction. If the term pre-shrunk is used then the warpshrinkage will be 3-5% and weft shrinkage will be 0-3%.

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)

0and drying in a conventional tumble dryer to a maximum dryness at a final max. Temperature of 71 C.usually drying time of 30 minutes is required.

Denim with spandex: precautions




12/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


Dryer heat:

Extraction :

Dryer heat does not shrink the garments. Shrinkage in the tumbler is caused by the tumbling action as thegarments hits the sides of the dryer. In fact the dryer heat has the opposite effect, as the garments loose themoisture it elongates slightly. But the drying process can damage fabrics made of natural fibres such ascotton, linen and wool, if too much moisture is removed. These fibres have natural moisture content, evenwe feel they dry.

The occasional over drying will usually not cause a problem. Later they will absorb moisture from theatmosphere. So dont try to extend drying timings assuming that low temperature and extended timing couldhelp to reduce garment shrinkage. It will shrink more because of the tumbling action on a longer period oftime.

The major portion of the shrinkage occurs in the washing process. The warmer the water, the greater theshrinkage. So temperature and wash timing have a great impact on the shrinkage. As a matter of fact, thedenim fabrics have shades because of the dye lots. So if the other process parameters are consistent, shadefactor cannot be clubbed with garment shrinkage. It only happens when there is a difference in processtimings, temperature, water level and loading.

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 temperaturewash, correct loading methods, better extraction for maximum removal of water, reducing drying timingetc.

The residual shrinkage has to be calculated in the fabric stage. Wash a trial lot before going ahead with bulkcutting. 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 donthave any idea about the fabric process parameters, we have to have certain R&D work with the fabric lots forthe particular wash. Also ensure that the fabrics are well relaxed in the layer before cutting.




13/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


Process precaution with spandex denim:

Some dos and donts in denim garment processing:

* 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

0than 47 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.

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

o* Cold bath enzyme process: Novowash E-10 can be used at temperature ranging from 35 -40 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 surfaceabrasion. The starch film on the garment is often broken or cracked during sewing when garments at ornear the bottom of the bundles are creased along side seams due weight of the garment on top of thestack. During wet processing, the areas of cracked size films abrade quicker than the protected reminderof the garment. The additional abrasion removes more dye, either on the out side or inside of thegarment depending on whether or not the garments are right side out. In any case the streakiness will bethe result.

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




14/14

DIN EN ISO 9001 : 2000


CARE CHEMICALS

Fabric-Care


For optimum exhaustion of this product on to the garment, the temperature should be kept in between 40o

50 C and pH in between 6 to 6.5. Usage of anti-ozone softener to prevent the ozone fading in indigodenim is not the complete solution. Thorough study for the reason for yellowing must be done beforegoing 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 protectivesoftener 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 oxidationtakes place at main structure.

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

For the removal of tarnish from zipper made of with copper, brass, tin, aluminium, alloys etcwash theozippers inside a mesh bag, with acetic acid and baking soda for about 10 min at 50 C temp. This couldeffectively remove the tarnish or oxide film. Then wash the zippers with a commercial detergent foranother 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 abouto

45 C 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. Thenwash 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.

.. THANKS .

Dr. Ravichandran. [email protected]



Denim Garments Processing 1

Documents

Transcript of Denim Garments Processing 1