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Developments in environment friendly functional finishes



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  • 1. Developments in environment friendly functional finishes for cotton fabrics and garments R.B.Chavan Department of Textile Technology Indian Institute of Technology Hauz-Khas, New Delhi 110016Abstract Global awareness for environment protection combined with stringent legislation onindustrial effluents had led to the search for environment friendly chemical processes fortextiles. In the present paper an overview of environment friendly functional finishes forcotton fabrics and garments has been given. The developments in formaldehyde free wrinklefree finishing, silicone softeners, bio-finishing, water repellent breathable finishes, anti-microbial finishes, soil release finishes etc are critically discussed. Plasma treatment,finishing through fibre coating, the use of biotechnology for genetic modification of cottonare considered to be some of the emerging technologies for imparting functional finishes tocotton.Introduction "The polluters must pay" is the concept, which has been emerged recently forindustrial production. There are stringent legislations particularly in developed countries oneco-toxicological considerations, health and safety during storage, use and safe disposal ofchemicals in water, landfills or release in air during processing or during incineration. Inorder to meet these requirements an integrated pollution control approach is essential. Thishas necessitated having a re-look towards the entire textile production processes. As a resultof this some of the well-established chemicals, dyes, finishing agents and auxiliaries havebeen replaced by environment friendly substitutes for the production of textiles. Consumers particularly in developed countries prefer eco-friendly textiles. Therefore,the manufacturing of textiles in developing countries for the export market in developedcountries is oriented towards achieving this goal, though the cost of production is high. Among the various fibres used for apparels, cotton dominates the market due to itsseveral advantages. It is readily available at affordable price compared to silk and wool.Being natural it is considered to be eco-friendly. In the present article an attempt has beenmade to review critically the developments in functional finishes for cotton fabrics andgarments.Eco-friendly cotton Cotton is cultivated using pesticides, fertilizers and other crop related chemicals. Theresidues of these chemicals remain on cotton bolls. These residues are removed during thepreparatory processes and enter into the wash liquor resulting in water pollution. Therefore intrue sense, cotton cultivated by using such chemicals is not considered to be eco-friendly. Atrend is started to cultivate cotton without the pesticides, fertilizers and other chemicals. Such 1
  • 2. cotton is considered to be eco-friendly and is known as natural cotton, green cotton or organiccotton. The use of biotechnology to introduce disease resistant cotton and organic farmingtechniques may decrease the use of chemicals, pesticides, herbicides, fungicides, defoliantsand harvest aid chemicals used for cotton cultivation. This would help to decrease soilpollution during cultivation and water pollution during preparatory processes.Naturally coloured cotton Naturally coloured cotton of various colours particularly green and brown varietieswere cultivated since ancient times in many countries. However, such cotton did not gaincommercial popularity due to low yield, short staple length, poor fibre strength, poorspinnability and possible contamination due to pollination. The present environmentprotection trends have given impetus to the revival of cultivation of naturally coloured cotton.Such cotton is not subjected to dyeing and thus is free from pollution caused by dyeingoperations.Finishing Though attempts are being made to produce raw cotton itself as environment friendlyas possible. Nevertheless, to make salable consumer products, the fibre, yarn, fabric orreadymade garments have to go through various chemical-processing sequences such aspreparatory, dyeing, printing and finishing. Among these the finishing assumes considerablesignificance because the value addition is realized through functional finishing of cotton infabric or garment form to impart desirable properties. Some of the most important finishesare1. Easy care/Durable press/Wrinkle free finishes2. Softening3. Enzyme/bio finishing4. Water proof breathable finishes5. Soil release and stain release finishes6. Anti microbial finishes Some of the recent developments related to eco-friendliness of the above finishes arecritically described in the present paper.Easy care/wrinkle free finishes The primary function of clothing is to prevent the loss of body heat to allow the sweatto pass through it to the outside atmosphere. Cotton is good in each of these functions. Theseproperties together with its hydrophilicity, freedom from static charge generation andpleasant natural feel makes it excellent fibre for tropical wear. However one of the majorshortcomings of cotton fabrics/garments is that, it is prone to creasing during wear andwashing. A treatment with cross linking agent is given to impart wrinkle free properties tocotton. The process is traditionally known as resin finishing. This finish imparts creaseresistant properties to cotton and keeps shrinkage under control. However when the desirableproperties are imparted at attractive levels, the strength is reduced to unacceptable level. Ofthe several technological attempts addressing this issue a few have been able to achieve a 2
  • 3. favourable balance of wrinkle resistance and mechanical properties and have becomecommercially successful. The development of all cotton wrinkle free apparel in 1990s has raised consumersexpectations on the performance and appearance of cotton garments. The consumers expectthe wrinkle free performance to remain almost intact over at least 50 launderings. The rule ofthumb is that if the performance stands 10 washes (each of 10 minutes duration at 50-600 C inpresence of 1-5g/l detergent) it is likely to stand 50 washes. There are different routes for imparting wrinkle free/easy care properties to cottonfabrics/garments. The most important routes are1. Pre-cure and post-cure processes2. Dip and tumbling processesPre-cure process This is used for fabrics which do not require pleats. The advantages being uniformdistribution of chemicals and better process control. The steps involved are pad-dry-cure andare carried out at mill level.Post cure process In this pad-dry application is done at mill level to produce sensitized fabric which isthen transported to garment manufacturing unit. Care during storage of sensitized fabric isessential. Many ship the fabric by air and store under refrigeration. The time betweengarment sensitization and garment making followed by curing is kept minimum (not morethan 3 months). The typical steps involved arePad with resin recipe (60-70% pick up).Dry to 10-12% moisture content.Sanforize without moisture spray.Garment makingGarment pressing to introduce creases at desirable placesGarment curing at 150-1600C for 8-10 minutes.Finishing in garment form The principal benefits of wrinkle free processing in garment form are1. Permanent fixing of creases in garment at desirable places2. No risk of pre-mature cross linking during drying, storage and transportation.3. Puckering of garment seams is minimized. The following points must be considered.1. Careful selection of sewing thread buttons zips etc. since these are exposed to corrosive chemicals and heat during wrinkle free processing.2. Resin finishing offers only one chance. If there is any thing wrong it can not be corrected. This applies both to fabrics and garments. However the control may be more difficult in case of garments than fabrics. Stripping of resin and re-finishing causes more damage. There are two methods of garment finishing1. Dip process2. Tumbling process 3
  • 4. Dip process1. Dip the garment inside out in the finishing chemicals keeping MLR 1:5. Suitable washing machine may be used.2. Rotate the garments for 20 minutes.3. Hydro-extract to 70-80% pick up.4. Tumble dry at 700 C to moisture content 10-12%.5. Turn the garments right side out.6. Iron/steam press the garments to set the creases at the desired places.7. Cure at 150-1600C for 8-10 minutes. The solution recovered from the hydro-extractor can be reused.Tumble method In this process the garments are placed (inside out) into a machine with sealed (notperforated) drum and application of resin recipe by pumping or spraying. The drum is turnedfor 20 minutes. There should not be excessive dripping of chemicals from the garments andalso there should not be dry spots on the garments. This method is being used more and moredue to the fact that there is no wastage of chemicals. After saturation the garments are hydroextracted, tumble dry at 700C to 10-12% moisture content.Iron/steam press the garment to set the creases.Cure at 150-1600C for 8-10 minutes.Important featuresMLR should not be less than 1:0.85 for the garments weighing up to 600 gms/garment and1:1 for those weighing more than 600 gms.Minimum time of tumbling should be 20 minutes.Tumble rotations speed 28-30 rpm.Tumble drying temperature should not be more than 700CMoisture retention after drying 10-12%. If it goes below 10% re-dip and dry.Chemicals usedCross linking agent Low formaldehyde modified glyoxal based (DMDHEU) with externalor built in catalyst and buffered. Various brand products are available in the market.Catalyst Facilitates cross-linking reaction. Most commonly used is magnesuimchloride:citric acid systemWetting agent Helps to achieve quick wetting and even distribution of resin recipe.High-density polyethylene emulsion Imparts hand, improve tear strength, abrasionresistance and sewability.Amino silicone or reactive silicone softener Impart soft hand and slick surface feel.Improve wrinkle recovery and sewability. 4
  • 5. Silicone elastomer Impart springiness, improve strength.Acrylates Improve soil release.Typical application recipe Cross linking agent 40-120 g/l Magnesium chloride 10-25 g/l Citric acid 0.3 g/l Softeners combination (total) 40 g/l Wetting agent 1 g/l Acetic acid to pH 4-4.5 After resin application and drying turn the garments right side out. Steam press. Hungfrom non-staining hanger. The assembly is then transferred to moving rails. The rail takes thegarments through curing oven and then to packing.Important precautionsPre finishing stage1. Good water absorbency (<3seconds)2. Free from size.3. High tensile and tear strength (sufficiently high to remain acceptable even after 50% loss after resin finishing).4. Use mercerized cotton.5. Fabric pH 5.6. Fabric and garment should be free from softener.Resin finishing stage1. After drying the residual moisture content should not be <10%. Low moisture gives high dry crease recovery at the cost of heavy loss in tensile and tear strength. For wrinkle free performance both dry and wet crease recovery are important. Wet crease recovery is achieved when moisture content in dry fabric is high.2. Resin impregnated sulphur dyed fabric/garment deteriorates due to generation of acid from sulphur dye. The generated acid may cause pre mature curing of resin. Sulphur dye should be thoroughly oxidized.3. Addition of 1-2% urea to the finishing bath is often useful to minimize the release of formaldehyde from resin. Since urea would reduce the efficiency of the resin it may be necessary to increase the resin concentration by 10%. However, it is best to use low formaldehyde etherified DMDHEU.Garment stage1. Stone washing and other garment processes are done before wrinkle free finishes.2. Lower curing temperature is required for white to prevent yellowing. 5
  • 6. 3. Pockets, belt loops, labels, sewing threads, buttons, zippers etc. should be resistant to chemicals and heat. The resin recipe liberates acid during garment curing.Quality controlPhysical properties Efficiency of wrinkle free finishing is tested by wet and dry crease recovery angle,smooth appearance rating, resin add on, tear strength, tensile strength, abrasion resistance,dimensional stability etc.Cuen (1 N cupriethylene diamine hydroxide) test Pull the yarn from the backside of the finished garment. Fray the yarn. Put it onmicroscope slide. Wet out the yarn with 1-2 drops of Cuen. Put the cover slide and observethe swelling after15 minutes under the microscope. The Cuen rating is given by comparingthe standard photographs Swelling Rating Remarks None 5 Fully cross linked Slight or none 4 Good cross-linked Moderate 3 Moderately cross linked Moderate to heavy 2 Partially cross-linked Heavy, rapid 1 Low cross-linked Rapid and dissolves 0 No cross linking Rating 3-4 is normally taken as acceptable. Anything below 3 fails due to lack of resincure and anything above 4 fails due excessive loss of physical properties.Eco-friendly cross linking agents Majority of cross-linking agents used today is formaldehyde based includingDMDHEU and etherified DMDHEU, which has low formaldehyde level. Formaldehydebased cross-linking agents are cost effective and efficient. However, the release offormaldehyde vapours during finishing processes as well as during subsequent storage andconsumer use of finished products has caused world wide concern on its impact on humanhealth and environment because of the fears that it is carcinogenic and its well knowndermatitis effects. The release of formaldehyde is restricted to 20-ppm level. Some of the approaches to limit the release of formaldehyde are1. After wash of cured fabric/garment2. Addition of formaldehyde acceptors or scavengers such as urea, carbohydrizide to the finishing bath.3. Application of 10-30% urea solution with 5-10% add on by atomized spray technique using BASF fog chamber.4. Modification of DMDHEU with alcohol to produce etherified DMDHEU to decrease formaldehyde release e.g. treatment of DMDHEU with diethylene glycol or 2- propanediol. 6
  • 7. Zero formaldehyde derivatives of DMDHEU are more expensive and less effective thanDMDHEU at the same add on levels. More active curing systems are also often required.Polycarboxylic acids (PCA) as cross linking agents An alternative approach has been based on the use of PCAs. In 1998 Welch reportedthat cotton fabric treated with 1,2,3,4 butane tetra carboxylic acid (BTCA) in presence ofsodium hypo phosphite showed high level of wrinkle resistance and strength retention as wellas good durability to home launderings. However, exceedingly high cost has prevented theuse of BTCA on commercial scale. Citric acid (CA), a low priced tri-functional carboxylicacid is less effective to home launderings than BTCA. It also causes yellowing of fabricunder curing conditions.Mechanism of PCA cross linking The crease resistance performance of cotton fabrics treated with traditional N-methylol compounds is dependent on ether bond cross-linking with cellulose while BTCAand other PCAs are based on ester-links. In general the esterification reaction takes place intwo steps.Step 1 Two adjacent -COOH groups dehydrate and transfer in to cyclic acid and anhydrideunder high temperature curing conditions.Step 2 The acid and hydride undergoes esterification reaction with -OH groups of cellulose.Requirement for step 1 is that two adjacent -COOH groups should be located at the same sideof the main chain which is responsible for easy dehydration and creating cyclic anhydride. If O Othe two -COOH groups are located at the two sides of the main chain, cyclic anhydride willnot be generated and esterification of cellulose will not take place. Weakly basic alkali metalsalts of phosphorous containing mineral acids accelerate the formation of cyclic anhydride. C HC C OH HCAmong various phosphates sodium hypophosphite monohydrate (NaH2PO2.H2O) is found to V V - H2Obe excellent. The catalyst increases the rate of. anhydride formation as well as the rate of Ocross linking through esterification. HC C OH H C V C V O O Polycarboxylic aci Cyclic anhydride O O HC C O R HC C cellulose HO – R V V cellulose O Cellulose HC C HC C O H V V O O 7 Cyclic anhydride Polycarboxylic acid bonded to cellulose through an ester linkage
  • 8. Fig. 1. Reaction of polycarboxylic acid with celluloseOther carboxylic acidsPerformance of various PCAs has been compared with conventional methylol derivatives aswrinkle free finishing agents using sodium hypophosphite as catalyst. Most of these acidsimparted DP rating of 4.3-4.7, and crease recovery angle 285-300°. However, the resultantfinishes differed considerably in durability in alkaline laundering. The acids arranged in orderof decreasing durability in terms of maximum number of washings and tumble drying cycleswithstood were as follows:BTCA>CA>Maleic acid.>Succinic acid.Principle of PCA selection The principles on which PCAs can be used as non-formaldehyde finishes are asfollows:1. In terms of number of COOH groups, saturated Carboxylic acids should possess atleast three and unsaturated at least two COOH groups.2. Regarding the position of COOH, the two COOH in aliphatic PCA should be in cisconfiguration and two in aromatic PCA should be in adjacent position.According to above principles it may be possible to develop new low cost PCA finisheswhose DP rating is as good as or greater than BTCA. It has been thought that polymaleicanhydride (PMA) can be used as PCA finish but the reaction conditions should be strictlycontrolled. The DP of polymerization of PMA should be within the range of 4-6. CH CH n C C O O O Fig 2. Polymaleic acid anhydrideDemerits of PCA finishEco-friendliness of catalystsFor cross linking of cotton with BTCA or CA the catalysts used are weakly basic alkali metalsalts of phosphorous containing mineral acids. Some of the salts which act as catalysts are 8
  • 9. sodium hypophosphite, sodium dihydrogen phosphate, disodium hydrogen phosphate,trisodium phosphate, tetrasodium pyrophosphate etc. mono di and tri sodium citrate are alsoused in BTCA finishing. The most effective catalyst is sodium hypophosphite. But it hasserious disadvantages. For example:1 High cost2 Being reducing agent it brings about shade changes in most sulphur dyes and reactive dyes.3 Environment impact is also a major concern Compounds containing phosphorous can consume large amount of oxygen in water,deteriorate the quality of water and influence the reproduction of fishes. Recently attemptshave been made to replace sodium hypophosphite by trisodium citrate and a combination ofsodiun oxalate and sodium formate as catalysts. These catalysts do not have any effect onsulphur or reactive-dyed fabrics.Cost of BTCADue to extremely high price of BTCA, there are limitations in its industrial application. Twoalternative aspects may be taken in to consideration for cost reduction. 1. Cost of synthesis The synthesis process of BTCA is extremely sophisticated, therefore, one shouldstrive to seek an optimum production to decrease its cost. Industrially used BTCA may bemanufactured without purification. The solution of BTCA can be decolorized andconcentrated in the paste form for the application.2. Cost of Finishing One can incorporate other PCAs or catalysts in to finishing formulation to reduce theamount of BTCA in finish bath. Inexpensive citric acid may be used. Some auxiliary catalystssuch as triethanol amine (TEA) may be incorporated to lessen the finishing cost and toenhance the strength of finished fabric.Discoloration/yellowing effect of CA finished fabricsWhen CA is applied, as cross-linking agent discoloration of finished fabric is observe Thereason for discolouration is that unsaturated poly carboxylic acids are produced duringcuring, generating conjugated double bond system as a chromophore. Investigations showedthat major products formed during the curing process of CA treated fabrics are aconitic acid,citraconic acid and etaconic acid. H2C COOH H2C COOH HC COOH HO C COOH HC COOH H2C COOH H2C COOH Citric acid BTCA 9
  • 10. HC COOH CH2 CH3HOOC C C COOH C COOH H 2C COOH H2C COOH HC COOH trans – Aconitic Itaconic acid Citraconic Fig. 3. Formulae of PCAS used as crosslinking agents and of the unsaturated PCAS formed during curing process of CA-treated fabrics In order to minimize the yellowing, special additives such as triethanolamine (TEA),N,N-bisHydroxy ethyl) glycine, boric acid and polyethylene glycol may be incorporated inthe finish bath. It has been observed that TEA can suppress the yellowing effect efficiently.The mechanism of the yellowing suppression is suggested to be that, the OH in TEA canreact with OH in CA to form ester bonds which can block the OH in CA and prevents CAfrom hydrating and decomposing to unsaturated polycarboxylic acid when it is exposed toelevated temperature. As a result the formation chromophores responsible for discolorationis prevented. Poor wash fastness of finished fabrics The difference in structure of CA and BTCA is that one OH group exist in structure ofCA. Accordingly, the difference in easy care effects between CA and BTCA is attributableto the disturbance impact of the OH group in CA on esterification reaction between theCOOH in CA and OH in cellulose molecule. Due to this reason the hydrolysis rate of theester bonds formed by CA under alkaline conditions is greater, than those formed by BTCA.Thus the OH group in CA is the origin of the low wash fastness of CA finished fabrics. Inorder to improve the durability of the finish, OH group in CA must be modified. Investigations indicate that when PMA is incorporated in to CA finish bath, the OH inCA can undergo esterification reaction with the COOH in PMA to form extremelycomplicated molecules under elevated temperature curing conditions. As a result the OH inCA will he blocked and enhance the wash fastness of finished fabrics.From the above-mentioned drawbacks it can be seen that there are many problems associatedwith PCA based non-formaldehyde finishing. These include cost of the PCA, theenvironmental problem of catalyst containing phosphorous, the yellowing effect and the lowwash fastness of CA finished fabrics. All these problems are under investigation and some ofwhich have been overcome satisfactorily. It is believed that it will not be too long before thetraditional N methylol amide finishes are substituted completely by PCA non-formaldehydefinishes. A new approach to the production, of formaldehyde free DP finishes has been the 10
  • 11. recent work on the ester crosslinking of cotton by two polymers of maleic acid, namelyhomopolymer (PMA) and a terpolymer (TPMA) based on maleic acid, acrylic acid and vinylalcohol. The terpolymer approach showed a significant improvement in DP performance ofcotton fabric and retention of physical properties compared to the DMDHEU.Softeners Fabrics and garments are usually comfortable to wear if they are soft to touch.Chemical pretreatments remove natural cotton waxes rendering cotton harsh to handle. Thisis usually made worst after wrinkle free finishing. To compensate this; softeners are widelyused. They also act as fibre lubricants decreasing both fibre-fibre and fibre-metal friction.The draping and, cutting properties are also enhanced. The modem requirements are forsofteners of good durability to machine washing, and retain the wettability and absorbency aswell as properties against static charge under adverse conditions. The trend is towards the useof silicone softener that provide a soft luxurious handle, thereby imparting a higher qualityand added value to the material.Silicone softeners Silicone is a general term that refers to class of man made polymers based on theframework of alternate silicone and oxygen (Siloxane) bonds with organic substituentsattached to silicone. Methyl group (Me) is the most important of organic sustituents used incommercial silicones.The most dramatic changes in the field of softening have been the introduction of novelPolysiloxane softeners in both macro and micro emulsion forms. Softeners and elastomersbased on Epoxy and amino functional polysiloxanes provide an ultra soft handle to cotton.Such softeners generally increase the tensile resiliency and decrease the bending rigidity.Another aspect of elastomeric finishes is that they can be used to replace some of the crossLinking agents used in typical easy care formulations. When ethylene diamino functional siloxanes are cured for easy care finishing, yellowing can occur through the formation of azo and azoxy compounds as a result of oxidation of amine groups. Secondary amines such as cyclo hexyl amine and tertiary amines such as piperazine have been studied for use in polysiloxane softeners. Yellowing is greatly decreased but the finish is less hydrophilic and somewhat dryer than that obtained using primary amino functional siloxanes. Carboxy funtional, epoxy functional and amido funtional siloxanes have also been developed. The Later is prone to yellowing and more hydrophilic than amino functional siloxanes. Particularly, interesting is the research involving carboxy functional siloxanes which may improve resistance to oily soiling.The use of polysiloxane softeners modified to incorporate various organo functional groupswill increase in the next decade as cotton finishers strive to improve the strength retention ofeasy care fabrics.Silicones have been used as textile softeners since 1960. Initially, polydimethyle siloxane(PDMS) were used but in late 70s the introduction of amino functional PDMS opened newdimensions. Currently available silicone softeners can be classified in to following classes: 1. non-reactive 2. Reactive 11
  • 12. 3. Organo reactive.Non-reactive silicones These are based on polydimethyle siloxanes. They impart desirableproperties to fabrics due to their flexible polymer backbone, stable bonds and lowintermolecular forces. However, the softening effect is not very durable to washing due toabsence of reactive groups. - 2. Reactive silicones: these are PDMS polymers modified with silane hydrogen or silanol functional groups. Conventional reactive silicones form a cross-linked siloxane rework on the fabric surface in presence of water and Organo metallic catalyst. The durability is better than non-reactive PDMS. Silanol functional polymers are also the basis for silicone elastomers and textile finishes to improve hand and DP performance.3. Organo functional silicones: In this amino functional groups, which are bound to PDMSbackbone improve the orientation and substantivity on fibre. The improved orientation ofamino functional silicone leads to extremely soft hand which if frequently described as"super soft". In this Organo reactive groups such as amines epoxides and alcohols areintroduced in PDMS. Me Me Me Me Me3 SiO (SiO) Si Me3 Me3 SiO (-SiO) (-SiO) Si Me3 XMe3 SiO (-SiO) (-SiO)n Si Me2X n a b Me Me Me MeNonreactive silicon polymar Reactive silicone polymer Me Me Me3 SiO (-SiO) (-SiO) Si Me3 -HC CH2 - NR +Cl- , -COOH , NHCOR` , -O(EO) (PO) X a b 3 a b Me R O Y X = -OH or RO- Y = - NH2 Organo functional reactive silicone polymar Fig. 4. Examples of non-reactive, reactive and Organo functional reactive silicone polymersEco-friendliness of silicone softenersThe textile processing operations produce an aqueous effluent, which is discharged to wastewater treatment plant for purification. Silicones are a minor part of that discharge. PDMSbecomes part of the plant wastewater stream in the form of tiny dispersed droplets and attachto suspended solids. Because non-volatile PDMS fluid is essentially insoluble in water, thesematerials become a minor component of the sludge in the treatment plant. The specific route 12
  • 13. of non-volatile silicones in the environment depends on how the individual wastewatertreatment plants handle the sludge. If the sludge is incinerated the silicone gets converted toamorphous silica, water and CO2. Sludge, if used as a fertilizer it may introduce PDMS tosoil, where it is subjected to natural degradation processes. Similarly soil catalyzeddegradation is also expected to occur if sludge bound PDMS is land filled.Though PDMS materials are highly resistant to biodegradation they break down in to lowermolecular weight silaxonols and silanols during soil contact. The degradation products aresusceptible to biological decomposition eventually oxidizing to natural silica. Me Me Soil HO (-SiO) H Me3 SiO H y + Me3 SiO (SiO) Si Me3 Water x Me Me y = mainly 1 Fig. 5 Degradation of PDMSEffectsPDMS is ecologically inert and has no effect on aerobic or anaerobic bacteria. It does notinhibit the biological process by which the waste water is treated. No adverse effects ofPDMS were seen on seed germination or survival percentage of plants. Studies found noevidence that PDMS may inhibit the bacteria responsible for nitrogen fixation in some crops.If PDMS enters the aquatic environment they do not bio concentrate. Their molecular sizeprevents them from passing through the biological membrane of fish or other animals. PDMSfluids attached to particulate matter and are effectively removed by the natural cleansingprocess of sedimentation. They do not partition back in to water column. PDMS fluid exhibitinsignificant BOD. Testing on aquatic plants and animal life revealed no measurable adverseeffects even under highly exaggerated conditions of exposure. No significant change in thegrowth of algae or other marine organisms has been found. PDMS has not been found to posethreat to insect population and birds. While manufacturers across the world continue to seekenvironment friendly alternatives for many performance additives and finish chemicals in thetextile industry, the inherent eco-friendly silicones and their low concentration usage indicatethe likelihood of there sustained presence in textile manufacturing.Water resistant breathable finish Present trend is to impart water repellency without affecting water vapourpermeability of fabrics and garments for use in out door activities, foul weather-clothing etc.Improving the transpiration rate of perspiration through the textile materials is particularlyimportant in sports activities, where the relative metabolic rate is high. Water-resistantbreathable finishes are impermeable to water droplets but allow the escape of water vapour. Itis possible to achieve this property because of enormous size difference between liquid water 13
  • 14. molecule (100 microns in diameter) and water vapour molecule (0.0004 microns) i.e. there isfactor of 2,50,000) between two sizes. Such type of garments is designed for sports wear,skiwear, tracksuits, ram wear, clothing for mountaineering etc.Lightweight fabrics coated with poly (vinyl chloride) and polyurethane have becomeincreasingly popular for foul weather clothing. Such fabrics provide exceptional protectionagainst rain but considerable build up of moisture vapour inside the clothing may causediscomfort. This problem arises because of water vapour impermeability of the polymercoating. To overcome this problem breathable polymer coatings are now available whichhave greatly enhanced comfort properties of these clothing. Classification of breathable fabrics Breathable fabrics may be classified into three categories High density woven fabrics These are obtained by densely weaving fine smooth micro fibre yarns, this type ofweaving results in wind proof fabric with excellent water vapour permeability. However it isnot waterproof even after treating for water repellent finish. These fabrics are used forfashionable ski clothing, where water vapour permeability and wind proofing is moreimportant than water impermeability.Laminated fabricsIn this approach the fabric is coated with breathable adhesive with the help of rotary screen-printing or spray coating. It is than laminated with micro porous breathable barrier film likePTFE. The breathable films are made through biaxial stretching or by mechanical fibrillationto produce microscopic tears through out the film. Manufacturers claim that such PTFEmembrane contains 9 billion pores per square inch with a maximum pore size of 0.2 microns.Such PTFE membranes are used in Goretex two layer and three layer laminates of polyesterfabrics.Other commercial micro porous polymeric membranes include 1. Sympatex(hydrphilic polyester): Akzo 2. Bion II (polyurethane): Toyo Cloth 3. Excepor U (Poly amino acid/PU): Mitsubishi-Kasei 4. Thintech (Poly olefin): 3M companyCoated fabricsMicro porous coatingThe most important techniques used to produce micro porous coatings for breathable textilesare1. Solvent exchange2. Phase separation3. Phase inversionSolvent exchangeIn this process the polymer is dissolved in water miscible solvent and then thinly coated onto 14
  • 15. the fabric. Passing through a coagulation bath develops the porous structure where the solventis displaced by water.Phase separation The coating polymer is applied from a mixture of relatively volatile solvent with aproportion of higher boiling non-solvent. Precipitation of polymer as the micro porous layeroccurs as the true solvent evaporates faster during the subsequent drying process. e.g.Ucecoat 2000, a polyurethane based coating Here a low temperature boiling solvent (methylethyl ketone) evaporates preferentially as the fabric passes through oven, thereby increasingthe concentration of non solvent in the coating. When the concentration of the non solventreaches a critical level, the polyurethane precipitates out in a highly porous form and remainsin this form on complete dryingPhase inversionA solution of polyurethane containing a non-solvent is coated on the fabric. In a selectiveevaporation step, the solvent is eliminated first. The polyurethane then precipitates in a microporous way, the example is Ucecoat 2000 (S) of UCB specialty chemicals. Bio finishing Processing of cellulose fabrics and garments with cellulase enzymes is generallyreferred as bio finishing or bio polishing. The concept was started in 1980s. Presently majorindustrial application of cellulase enzymes is to produce wash down or worn out look (stonewash) on indigo dyed denim. This is known as biostoning. Cellulases are multi componentenzyme system that is commonly produced by soil dwelling fungi and bacteria. The mostimportant cellulase producing organisms are fungi of Trichoderma, penicillium andFusarium. Cellulase consists of at least three enzyme systems working togethersynergistically.i. Endoglucanases or Endo cellulases hydrolyze cellulose randomly along with thecellulose chains, preferentially the amorphous region.ii. Cellobiohydrolase or Exo cellulase attack the chain ends and primarily produce cellobioseiii. The cellobiose and the small chain oligomers produced by exocellulase are thenhydrolyzed by the third enzyme β-( 1,4 )-glucosidase into glucoseDepending on the pH of activity, there are three types of cellulase enzymes viz:Acid stable (pH 4.5-5.5)Neutral (pH 6.5-7)Alkali stable (pH 9-10)These enzymes can be used in the temperature range of 40-60° C. Biopolishing consists ofcellulase treatment so that there is partial hydrolysis of cellulose at the surface with a weightloss of around 3-5% and loss of strength of 2-7%. Short fibre ends are hydrolyzed and areremoved by additional mechanical treatment to prevent pilling particularly in case ofPET/cotton blends.Mercerization enhances the rate of enzymatic hydrolysis. Biostoning has achievedconsiderable importance for treating casual wear garments to give them a wash down or wornout look. Environmentally this is more acceptable because it replaces or decreases thequantity of pumice or synthetic stones that cause damage to machine. It also avoids 15
  • 16. occurrence of pumice dust in the environment and in the garments creating a harsher handle.Neutral cellulases are preferred for biostoning of indigo dyed denim trousers and othergarments. The bio finishing of cotton or PET/cotton blends reduces pilling, provides durablesoft handle, increased gloss or lustre. The cellulase treatment of cotton is now well established. Further refinements inprocess techniques would emerge. Developments such as the use of one or more specificenzyme types rather than three types working synergistically will depend on commercialseparation of the enzymes.Anti microbial finish Clothing and textile materials carriers of microorganisms such as pathogenic bacteria,odour generating bacteria and fungi. Because of the growth of micro organisms on the fabricsurface, anti microbial / anti bacterial / anti fungal fabrics gained significant importance inthe recent years due to its wide acceptance as surgical apparels, baby clothing, undergarments etc. There is growing concern all over the world on the dangers of microbialcontamination. Recent outbreak in diseases such as AIDS, Hepatitis B has increased theawareness of these health hazards and the need for protection against them. Anti microbialfinished fabrics for surgical apparel play an important role in reducing diseases transmitted inoperation theatre, as the bacterial and viral diseases are spread through air and blood. Antimicrobial agents in these fabrics prevent the proliferation of disease causing microbes orreduce their number by the action upon them by destroying their cell membrane. Antimicrobial surgical apparels act as physical barrier against the transfer of micro organisms. Asurgical patient is at greater risk because the wound created during the operation is open andeasily accessible to microorganisms and hence may become septic. For this reason thesurgical gowns used by patients should be free from microbes. The doctors and nurses arealso to be protected from the blood and other body fluids of the patients, which may containmicroorganisms spreading the disease to doctors and nurses. Anti microbial under garmentsis also useful in preventing skin related diseases, urinary track infection etc. Babys clothingare advised to be anti microbial and their thin skin may be permeable to microbes. Since theinternal intake of anti biotic for the infants is not desirable so protective action againstmicroorganisms should be taken through clothing. Taking all these factors into considerationdevelopment of anti microbial fabrics/clothing is important. Requirements in anti microbial finshing1. Durability to multiple launderings and dry cleaning.2. No toxic effects on wearer.3. Acceptable moisture transfer properties.4. Compatibility with dyes, auxiliaries and other finishing agents.5. Ready availability at reasonable price.6. Should not affect the fastness properties of dyes.Mechanism of protection There are three mechanisms by which treated fabrics are made resistant to diseasecausing bacteria Viz. Controlled release, regeneration model and barrier or blocking action.Controlled release 16
  • 17. This finish is considered effective when in the presence of sufficient moisture, the antibacterial agent is released from fabrics at a rate sufficient to kill or inhibit the growth ofbacteria.Regeneration modelThis model is based on subjecting the fabric to agency that would destroy the bacteria e.g.addition of bleaching agent during laundering or exposure to UV lightBarrier or blocking mechanismThis includea) insertion of physical barrier films or coatings that are simply impervious to transmissionof micro organisms through fabric ..b) Films or coatings that have direct surface contact activity against bacterial growth.Finishing techniquesFollowing processes can be used for imparting anti bacterial finish to cotton or PET/cottonblendsPad-dry-cure process for fixation of anti bacterial additive onto fabric with the help of crosslinking agentGraftingIncorporation of anti bacterial agent during fibre finishPad-dry-cure methodVarious chemicals, which can impart antimicrobial property to cotton, are shown in Table Table 2. Anitibacterial chemicalsName Chemical Nature Effective Concentration (g/l)Afrotin LC Na salt of heterocyclic compound 20Mysotox ELN Pentachlorophenyl laurate and Non-ionic emulsifying agent 2.5Mystox WFE Aqueous solution of Sodium Ortho phenylphenate 1Antibac MF An organic compound containing Nitrogen with no halogen 40Antibac MFB Combination of hetrocyclic Organic compound 80Fungitex OP Derivatives of bezimidazole 100Above agents can be applied along with cross linking agent by pad-dry-cure technique.However the wash fastness of the finish is not satisfactory.Chitosan and citric acid 17
  • 18. Chitosan and citric acid are used as durable press anti microbial finish cotton when appliedby pad-dry-cure process CA reacts with OH group of cellulose and NH2 of chitosan to formester cross links and inter ionic attractionPoly(hexamethylene-biguanide hydrochloride, PHMB)A new anti microbial finish called Ruptex 20 has been found to give durable finish to cottonand cotton blends. It is based on the active agent PHMB. It is applied by padding orexhaustion technique. The Finish can withstand 25-50 wash cycles depending on washconditions. Tulsi leaves (Ocium santum) One bath process for dyeing and simultaneous anti microbial finish by methanolicextract (1-5%) of Tulsi leaves on cotton has been investigated. It is believed that Urosolicacid (C30H48O3) is the active ingredient, which inhibits the growth of bacteria.GraftingPoly-(2-methyl-5-vinyl pyridine) was grafted onto cellulose followed by immersion inaqueous Kl solution. Such a technique produces idophor, a material that slowly releasesiodine to impart anti bacterial and anti fungal activity.Barrier coatingOrgano siliconeThe anti bacterial finish based on the concept of barrier coating (direct surface contactactivity) is Dow Corning 5700 (3-trimethoxy silyl propyl dimethyl octa decyl ammoniumchloride) Organo silicone polymer. Containing pendant quaternary ammonium group thatforms a bio barrier onto fabric. This finish is effective in inhibiting the growth of odourcausing bacteria and is durable to atleast 40 laundry washes.Soil release and stain release finishesSoil release and stain release finishes are particularlyimportant where leisure or sports wear activities may lead togreater incidence of soiling or staining. This type of finishwould become more important as standards of easy careincrease and consumer expectations become greater Anotherfactor is the trend towards lower temperature washing ofgarments where removal of persistent soil and stain removalbecomes more problematic. In general, the approach in textilefinishing has been to ensure that any soil that is deposited isless strongly bound to facilitate the removal of soil duringdomestic washing. Because most persistent soils are 18
  • 19. hydrophobic, the major trend has been to use finishes thatrender the fibre surface more hydrophilic. On this principlethree major groups of finishes are developed.Finishes containing carboxyl groupsFinishes containing oxy ethylene and /or hydroxyl groupsFluorocarbon finishes Finishes that contain carboxyl, oxy ethylene or hydroxylgroups may be incorporated within zero formaldehyde basedchemical cross-linking systems for cotton. Easy care finishesmake cotton more hydrophobic and can increase oily soiling.Whereas the introduction of hydrophilic carboxyl groups canimprove the release of oily soil dramatically. It is known thathydrophilicity, anti soiling and soil release properties are notusually associated with silicone softeners, and silicone based water repellent finishes do notprovide oil repellency.FluorochemicalsFluoro chemicals or fluorocarbons are increasing in use because of greater ability to engineerthe chemical structure to provide good water repellency and soil and stain release properties.Hybrid flouro chemical finishes have been introduced that contain per-fluoro alkyl containingpolymer segments and also hydrophilic segments. In air the fibre-air interface is dominatedby closely packed per fluoro alkyl moieties which promote soil repellency. In aqueous washliquor, molecular reorientation occurs, leading to. the hydrophilic segments being orientedtowards fibre-liquid interface, thereby promoting soil release. The use of perfluoralkylacrylate and methacrylate based copolymers modified to suit particular end uses is wellestablished.Emerging technologiesTraditionally chemical finishes are applied by padding or low wet pick up techniques such aslick roll, porous bowls, vacuum extraction or foam. Alternative methods include coating andlamination technologies. New application technologies are emerging. Some of these arebriefly mentioned.Nextec ProcessIt is patented by Nextec Applications Inc. USA. It is a novel process by means of whichindividual fibres within the fabric are encapsulated or wrapped with an ultra thin film ofpolymer. This can be utilized to provide a breathable barrier film within the fabric, preventingliquid water from penetrating while allowing moisture vapour to pass through at as close tothe same as original fabric. The handle of the fabric is relatively unaffected. It is also possible 19
  • 20. to introduce chemicals for imparting wrinkle resistance, soil release, stain resistance.Chemical and biochemical additives may be positioned on the fabric in order to provide waterrepellency, UV protection, flame resistance or viral barriers. So far this unique fibreencapsulation process has been applied using silicone-based polymers, polyurethane,polyacrylate and other polymers. This process would open up many opportunities forproviding multi functional finishes on cotton fabrics. Plasma treatment The plasma treatment is based on ionized gases produced by electrical discharges.The plasma treatment is highly surface specific and does not affect the bulk properties. Thesurface properties enhanced include wettability, adhesion, cross-linking, bio- compatibility,chemical affinity or inertness. Relative free radical intensity of the plasma treated fibresmeasured by ESR, increases in the following order Cotton > wool > silk > Nylon = PETPlasma treatment may enable to avoid pre-coating and pre-lamination preparation of thesubstrate, replacing some costly and environmentally polluting processes. The dry treatmentand environment friendliness for improved wetting, adhesion and bondability offer scope forimprovement in functional finishes for cotton.Use of biotechnologyThe use of biotechnology for the modification of cotton is at an exciting stage and the greaterapplicability of enzyme treatments as chemical pre treatments and finishing treatments isworth exploiting. The next decade should bring forward some interesting developments inthis field and the genetic manipulation of cotton gene may usher in new cotton varieties withimproved properties and performance that can be further exploited in chemical finishing toproduce innovative effects.UV protection The problems of ozone depletion in the upper atmosphere have led to increasedproblems of exposure of skin to UV radiations. The size and depth of Antarctic ozone holehas caused concerned, particularly in Australia. It has been suggested that a decrease of 1%ozone would lead to increase UV radiation at the earths surface and may eventually lead to a2-3% increase in skin cancer. Hats, sun screens, sunglasses and clothing can be used todecrease the exposure to UV radiation by a factor of 10 or more. The term UV protectionfactor (UPF) has been introduced such that a garment of UPF 15 will provide the sameamount of protection against solar UV radiation as a sun screen of SPF 15 (Sun protectionfactor). Garments with UPF value of 20-29 offer high protection (UVR transmission 5-3.3%).A UPF value of 30-40 (UVR transmission 3.3-2.5%) offers very high protection and UPFvalue of >40 offers maximum protection with UVR transmission of <2.5%This opens up another area of opportunity for cotton fabric and garment producers tomanufacture comfortable ranges of clothing for leisure and for out door work wear that offersignificant enhanced protection against UV radiation. The appropriate selection of dyes,fluorescent brightening agents and particularly UV absorbers should enable cotton finisher toprovide high level of UV protection. 20
  • 21. Conclusions Desirable properties can be imparted to cotton by the application of functional finishes. Thisnot only would improve the quality of cotton but also give value addition. Innovationsthrough R&D in chemical finishing will be necessary to stimulate the more demandingconsumer and to develop specialty and niche markets for cotton fabrics and garments. Thedevelopment of finishes with multi-functionality will be particularly interesting fieldespecially with regard to easy care finishing. Novel methods that minimize water and energy costs may be based upon plasma treatments, but such treatments for cotton are still in the development stage. Enzyme treatments also offer many promises. In general many innovative ideas are being explored in the field of functional finishes for cotton and in the next decade quite a few new concepts may be introduced for imparting desirable properties to cotton fabrics and garments. 21