Cleaner production technologies for textiles iitd dec.10 12, 2008

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  • 1. ECO-FRIENDLY TECHNOLOGIES FOR TEXTILE PRODUCTION. R.B.Chavan Former Professor, Textile Dept. IIT Delhi Consultant, MGIRI, Wardha E-mail rbchavan@hotmail.com AbstractCradle to grave or womb to tomb is the most effective concept for cleaner production activitiesincluding textiles. This concept has coined the terms such as production ecology, user ecologyand disposal ecology. According to this concept it is no longer adequate to have a finishedproduct to be safe only to human beings but the production processes and the product disposalafter use should be environment friendly. In the present paper attempt has been made to discusscritically the cleaner production technologies such as use of organic cotton, naturally colouredcotton, environment friendly Reactive, Vat, and Sulphur dyeing and finishing processes forcotton, the use of synthetic thickener as a substitute for kerosene in pigment printing. Eco-normsEco-labels for identification of environment friendly textiles and the attempts made by theGovernment of India, Ministry of Textiles to facilitate the use of eco-friendly textile productionare briefly discussed.
  • 2. Introduction During the manufacture of textiles very large number of chemicals are used e.g. duringthe cultivation of cotton, the use of fertilizers, pesticides is quite common, during sizing one usessize preservatives and during chemical processing a large number of chemicals, textileauxiliaries, dyes, pigments, thickeners, finishing agents etc are used. Many of these agents areresponsible for problems during their handling, water and air pollution causing health problemsto human beings, aquatic life, plant and foliage. Thus giving rise to various environmental issues.In India no serious thought was given to these environmental issues caused by industrial activitiesin general and textile production in particular till recently Germany has put the ban on the use ofcertain azo dyes, commonly known as German Ban.Eco-friendly Textiles The German Ban acted as catalyst to develop the concept of eco-friendly textiles. Indeveloping this concept "Cradle to Grave" or "Womb to Tomb" approach is followed. Accordingto this concept textile industry should take the environmental and health hazard aspects intoconsideration right from the stage of fibre cultivation/manufacture to spinning, weaving,chemical processing, apparel manufacture, packaging and disposal after use. The material flowdiagram during textile production is shown in Fig. 1
  • 3. Fig. 1 MATERIAL FLOW ALONG THE TEXTILE CLOTHING CHAIN Synthetic Natural Production Fibre FibreBasic chemicals - Cultivation Fibre,petrochemistry .fertilizers yarn,Production of pesticides fabricmonomers / - Crop auxiliary Textile Processing e.g. desizing, mercerizing, bleaching, dyeing, printing, finishing Garment / Textile industry Use Packing, washing, dry-cleaning Disposal
  • 4. In order to make the textiles totally environment friendly, not only the final product to beused by the consumer be eco-friendly, but the production technology, packaging and disposalafter use should also be eco-friendly. Therefore, the production ecology, user ecology anddisposal ecology must be taken into consideration.Production Ecology This comprises of • Cultivation and harvesting of natural fibres • The manufacture of regenerated and synthetic fibres • Yarn and fabric manufacture • Textile chemical processing • Garment manufacture • Packing The production should be as environmentally sound as possible with regard to its impact onair, water, soil as well as human beings.User Ecology This refers to the aesthetics, performance characteristics and effects of textiles on humanbody.Disposal Ecology This refers to the disposal of textiles after use i.e. to recycling, composting, dumping,incineration in a manner that ensures that the least possible environmental impact.Eco-fibresOrganic 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. A trendis started to cultivate cotton without the pesticides, fertilizers and other chemicals. Such cotton isconsidered to be eco-friendly and is known as natural cotton, green cotton or organic cotton. The use of biotechnology to introduce disease resistant cotton and organic farmingtechniques may decrease the use of chemicals, pesticides, herbicides, fungicides, defoliants andharvest aid chemicals used for cotton cultivation. This would help to decrease soil pollution
  • 5. during cultivation and water pollution during preparatory processes. The eco labels shown in fig.2 identify the organic cotton Fig 2 Eco-labels for cottonNaturally coloured cotton Naturally coloured cotton of various colours particularly green and brown varieties werecultivated since ancient times in many countries. However, such cotton did not gain commercialpopularity due to low yield, short staple length, poor fibre strength, poor spinnability and possiblecontamination due to pollination. The present environment protection trends have given impetusto the revival of cultivation of naturally coloured cotton. Such cotton is not subjected to dyeingand thus is free from pollution caused by dyeing operations.LyocellIt is regenerated cellulose marketed by Courtalds. It is obtained by wet spinning of cellulose pulpdissolved in an aqueous solution of an eco-friendly solvent N-methyl morpholine oxide(NMMO). The solvent can be totally recovered, purified and recycled.Biodegradable Polyester (Corn Fibre) Kanebo spinning and Kanebo Gohsen of Japan, jointly developed an environment friendlycorn fibre under the trade name Lactron. It is produced from lactic acid obtained through thefermentation of corn starch. Strength, stretchability and other properties of Lactron fibre arecomparable to petrochemical based nylon and polyester except lower melting point (175o C). Thefibre is suitable for both textile and non-textile applications.Environment Friendly Chemical Processing The input/output analysis during chemical processing of textiles is shown in Fig 3
  • 6. Fig. 3 Input / output analysis of Textile chemical Processes Base chemicals (e.g. acid, Alkali, Textile Energy sodium chloride) Natural Fibres; 10-20 MJ/kg Dyes Chemical Fibres: 5-50 MJ/kg Water Textile Auxiliaries 60-360 l/kg textile Wet Processing (pre-treatment, dyeing, printing, finishing.) Polluted Air Waste Sewage sludge: 60-70 g/kg textile Water Effluent Large number of base chemicals, dyes, auxiliaries, and finishing agents are used duringchemical processing of textiles as in put. As an out put we have air pollution, water pollution andproblems of sludge disposal. There are two major pollution control strategies • Cleaner production techniques and processes • End-of-pipe treatmentsCleaner Production Techniques and Processes Some of the cleaner production techniques with reference to cotton are discussed.
  • 7. Dyeing Different dye classes which are suitable for dyeing of cotton and the chemicals in theeffluent stream is shown in Table 1 Table 1 - Chemicals in effluent streams Dye Chemicals in effluent streams Vat Residual dyestuff (5 - 20 %) Reducing agents Oxidising agents Detergents Salt Reactive Residual dyestuff (20 - 50 %) Salt Alkali Detergent Direct Residual dyestuff (5 - 20 %) Salt Dye fixing agents Sulphur Residual dyestuff (30 - 40 %) Sodium sulphide Alkali SaltDyeing of Cotton with Reactive dyes Amongst the different dye classes suitable for dyeing of cotton, reactive dye class is themost important.
  • 8. The use of reactive dyes is predicted to rise by 50%. Presently, most of the reactive dyemanufacturers are concentrating on addressing the following environmental problems associatedwith the reactive dyes:Colour in the effluent.Minimization of chemical usage. Colour in the Effluent Removal of colour from the effluent is one of the expensive approaches for the end ofpipe technology. Therefore, it is necessary to find suitable alternatives. In exhaust dyeing, the useof reactive dyes is the major source of concern. The vat, sulphur and azoic dyes exhibit a highdegree of exhaustion and the insoluble unfixed dye can readily be removed as a part of theprimary flocculation process. Whereas in case of reactive dyes, sometimes as high as 30% dyeremains unbound during primary treatment and needs to be treated either on site as a secondaryprocess after biological oxidation or at a municipal sewage works. The adsorption of hydrolyzedreactive dye on biomass is not as efficient as of other water-soluble dye classes. However, theamount of hydrolyzed dye in the effluent can be minimized through process innovations. The government pressure for regulating industrial effluent discharge has led to thedevelopment of new reactive dyes, machinery and processes to minimize waste and colour in theeffluent. The development of bifunctional reactive dyes is important from this point of view. Bifuntional Reactive Dyes Bifunctional reactive dyes consist of two reactive groups capable of forming covalentbonds with the fibre. There are two types: (i) those consisting of two similar reactive groups(homobifunctional reactive dyes) and (ii) those with two different reactive groups(heterobifunctional reactive dyes). Fig. shows various homobifunctional. and heterobifunctionalreactive dyes presently marketed by main dyestuff manufacturers . Fig. 4 Homo and Hetero Bifuntional Reactive dye
  • 9. The characteristics of these dyes is their high exhaustion and high reactivity with the fibreso that there is less quantity of dye in the effluent. Dye Liquor Wastage Minimization of dye liquor wastage is a major environmental consideration in acontinuous dyeing to reduce colour in the effluent. At the end of every dyeing, there is liquor leftin the pad trough as well as in the stock tank prepared as a precaution against running out beforethe dyeing is completed. A latest development from Monforts (Matex 3 bowl padder) has thefeasibility to decrease the pad liquor volume to 15 litres as the fabric comes to the end of the run.Ramisch Kleinwefers has also developed a padder with a minimum trough volume of 10 litres.2.2 Minimization of Chemical Usage Some of the approaches to minimize the use of chemicals are:
  • 10. Dyeing at low liquor ratio.Right-first-time approach.Process innovations in continuous dyeing.Use of low-salt reactive dyes. Dyeing at Low Liquor Ratio The average consumption of water per kilogram of finished fabric is around 80-100 litres.Lowering of liquor ratio bring down the volume of water used and the waste generated. Apartfrom the easier handling of lower volume of effluent, the dosing of chemicals and auxiliaries inthe dye bath is done on the basis of g/litre of liquor. This significantly reduces the quantities ofchemicals and auxiliaries and finally the effluent load. In reactive and vat dyeing systems, achange of liquor ratio from 1:10 to 1:5 brings about a decrease in pollution load by about 40%. Right-first-time Approach Carefully following the dyestuff manufacturer’s recommendations for salt, alkali usage,temperature, time, etc. to ensure optimum fixation levels and right-first-time production, therebyavoiding the need to make shading additions. The computer colour matching should help in thisregard. Low salt Reactive Dyes Substantial quantities of electrolytes, such as sodium chloride and sodium sulphate, are usedfor the dyeing of cotton with reactive dyes. Exhaust dyeing with 10:1 liquor-to-material rationeeds a salt concentration of 30-80 g/L. This corresponds to 300-800g salt per kg of dyed cotton.During effluent treatment, only a small quantity of salt is removed. Thus, a major quantity of saltenters the environment on discharge of effluent treated water. High salt concentration in effluenthas the following disadvantages :Rivers and lakes get polluted with effluent containing high salt concentration .Fresh water organisms can have toxic effects.In the regions with scarce fresh water resources, such water has to be used for irrigation. If saltconcentration is too high, soil may become overloaded with salt, and making the land infertileand ultimately useless.Low salt reactive dyes Ciba Speciality Chemicals has introduced low-salt Cibacron LS dyes, which require only 20g/L salt, whereas the conventional reactive dyes require 60-80 g/L salt for exhaustion. The dyeshave the general structure as shown in Fig. . The main features of these dyes are given below:• Bifunctional reactive dyes have medium reactivity, but high dye affinity and high dye fixation.• Stable dye-fibre bond• Less dye to be removed from fabric after dyeing.• Rinsing step is much faster.• Less water is needed for wash off.• Less dye effluent.
  • 11. Fig. 5 General characteristics of Cibacron LS dyes Chromophore bridge Chromophore Reactive Reactive group group As the salt requirement is reduced to ¼ of that required for conventional dyes, the saving incost is observed. Another benefit is that rinsing step after dye application is much faster and lesswater consuming. Since the Cibacron LS dyes have a higher fixation rate than the conventionaldyes, this leads to lower dyestuff concentration in the effluent. Ecological benefits of Cibacron LS dyes are summerized in Fig 6. Fig. 6 Higher fixation rate of Cibacron LS dyes Conventional dyes Cibacron LS (bireactive) 60 % fixation 80 % fixation 600 gm on the fibre + 33% 800 gm on the fibre % 1 kg dye 1 kg dye 400 gm into 200 gm into the waste water - 50% the waste water %Alternative Reducing Systems for the Dyeing of Cotton with Vat and Sulphur DyesVat DyesVat dyes are applied by using sodium hydrosulphite as reducing agent and sodium hydroxide asan alkali. A few of the byproducts formed are sulphur compounds like Na2S which pollute airthrough the formation of H2S. At the same time, the salts of sulphur in the form of sulphate andsulphites (Na2SO3, NaHSO4, Na2SO4, Na2S2O3) contaminate sewage, lower its pH and showcorrosive action on concrete pipes. To overcome these problems, attempts were made by several
  • 12. researchers to develop alternate reducing systems, which are ecofriendly in nature. Such newsystems include electrochemical reduction, use of organic reducing agents like hydroxy acetone,iron pentacarbonyl compounds and iron (II) complexes. Sulphur Dyes Sodium sulphide is commonly used for the reduction in the application of sulphur dyes oncotton. Residual sodium sulphide acts as contaminant in the effluent. Sodium sulphide causes nomarked odour nuisance above pH 9 but in acidic pH, gaseous H2S is liberated, giving fowl smellof rotten eggs and is toxic when inhaled. Its odour threshold value is 10 ppmReplacement of Sodium Sulphide Glucose Glucose has long been known as reducing agent for sulphur dyes. Sulphur black is almostalways reduced using glucose A considerable improvement is achieved when the dyeing iscarried out under strongly alkaline condition Chavan and Vhanbatte obtained glucose by acid hydrolysis of molasses and cane sugar.On the basis of detailed investigations of various parameters, such as concentration of glucose,caustic soda, temperature and time, they concluded that at dyeing temperature of 90oC, glucosegives colour yield equivalent to that obtained with sodium sulphide. Century mill at Mumbai alsoestablished, on commercial scale, that sodium sulphide can be totally replaced with glucoseobtained from hydrolysis of starch.Synthetic Thickener for Pigment Printing Emulsion thickener using kerosene oil or mineral turpentine oil was the ideal and mostpopular thickener for pigment printing of cotton. However, emulsion thickener poses serioushealth hazards, fire hazards and air pollution problems. Attempts to recover and recycle keroseneor MTO were not successful. Synthetic thickeners based on polyacrylates have successfullyreplaced emulsion thickener in pigment printing. Many indigenous as well as imported productsare readily available.Easy care or Wrinkle free Finishes Majority of cross-linking agents used today are formaldehyde based including DMDHEUand etherified DMDHEU, which have low formaldehyde level. Formaldehyde based cross-linking agents are cost effective and efficient. However, the release of formaldehyde vapoursduring finishing processes as well as during subsequent storage and consumer use of finishedproducts has caused world wide concern on its impact on human health and environment becauseof the fears that it is carcinogenic and its well known dermatitis effects. The release offormaldehyde is restricted to 20-ppm level. Non-formaldehyde based cross linking agents is oneof the approaches which has been explored.Polycarboxylic acids (PCA) as cross linking agents An alternative approach has been based on the use of PCAs. In 1998 Welch reported thatcotton fabric treated with 1,2,3,4 butane tetra carboxylic acid (BTCA) in presence of sodiumhypophosphite showed high level of wrinkle resistance and strength retention as well as gooddurability to home launderings. However, exceedingly high cost has prevented the use of BTCA
  • 13. on commercial scale. Citric acid (CA), a low priced tri-functional carboxylic acid is less effectiveto home launderings than BTCA. It also causes yellowing of fabric under curing conditions.Other 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 order ofdecreasing durability in terms of maximum number of washings and tumble drying cycleswithstood were as follows BTCA>CA>Maleic acid.>Succinic acid.Softeners Fabrics and garments are usually comfortable to wear if they are soft to touch. Chemicalpretreatments remove natural cotton waxes rendering cotton harsh to handle. This is usually madeworst after wrinkle free finishing. To compensate this; softeners are widely used. They also actas fibre lubricants decreasing both fibre-fibre and fibre-metal friction. The draping and, cuttingproperties are also enhanced. The trend is towards the use of silicone softener that provides a softluxurious handle, thereby imparting a higher quality and added value to the material.Silicone softenersSilicones have been used as textile softeners since 1960. Currently available silicone softeners can be classified as 1. Non-reactive 2. ReactiveStudies indicate that the silicone softeners are safe to environment as well as human health. Bio finishingCellulase enzymes are widely used for the bio-polishing of cotton and for producing stone washeffects on indigo dyed denim. The technology is well established and widely accepted as eco-friendly.Identification of Eco-friendly TextilesEco Parameters and Norms for Eco-friendly Textiles In the past textiles were considered primarily from economical, functional and fashionpoints of view. More recently consumers are imposing demands on the safety of textiles for thehealth and also on the environmental soundness as decided by eco-parameters stipulated by wellestablished organizations. These norms are based on the analysis of textile products entire lifecycle commencing from cultivation of raw material (e.g. cotton), various production stages,packing, distribution, utilization and disposal after use. For formulating eco norms differentclasses of chemicals are considered. These are
  • 14. Toxic Substance ProcessPesticides Cotton cultivationPenta chlorophenol SizingEmulsifiers, chlorinated solvents ScouringHalogeneted carriers Polyester dyeingSodium hypochlorite bleachingAzo dyes containing banned amines Dyeing, printingDyes containing traces of heavy metals Dyeing, printingFormldehyde as dye fixing agent Dyeing, printingFormaldehyde cross-linking agent FinishingChlorinated stain removers Garment manufactureInsecticides Packaging wooden boxes Some of the most important eco-parameters are given in Table Table 2 Comparison of norms/criteria stipulated for eco-lebelling of textiles Eco-parameter M.S.T OTN 100 Clean Steilmann Comitextil Indian Fashion ec0-lable Formaldehyde Baby clothing 20 20 20 50 20 20 Close to skin 75 75 75 300 75 75 Outer Wear 300 300 300 300 300 300 Toxic 1 5 1 1 0.1-1 1 pesticides Pentachloro 0.5 - 0.5 Ban 0.05-0.5 0.5 phenol Heavy metals Arsenic 0.1-0.2 0.1-0.2 0.1-0.2 0.1-0.2 0.1-0.2 Lead 0.04-0.8 0.04-0.8 0.04-0.8 0.04-0.8 0.04-0.8 Cadmium 0.005-0.1 0.005-0.1 0.005-0.1 0.005-0.1 0.005-0.1 Mercury 0.001-0.1 0.001-0.1 0.001-0.1 0.001-0.1 0.001-0.1 Copper 3-100 3-100 3-100 3-100 3-100 Cobalt 0.2-20 0.2-20 0.2-20 0.2-20 0.2-20 Zinc 5-100 5-100 5-100 5-100 5-100 Nickel 0.2-10 0.2-10 0.2-10 0.2-10 0.2-10 Azo dyes Ban Ban Ban Ban Ban 50 containing carcinogenic amine Halogen Ban - - Ban Ban 200 carriers Chlorine - - - To avoid Ban - bleaching
  • 15. Eco Trade marks, Eco Labels There are large number of eco trade marks, eco labels are available for identification ofeco-friendly textiles. These eco labels are made available by associations, institutions and servicecompanies of the textile industry. Most of these initiatives were originated in Gemany, but theyclaim validity for the whole Europe and in some cases for the whole world. Ministry ofEnvironment and Forest under the certifying agency of Bureau of Indian Standards (BIS) has alsodeveloped eco label. Some of these eco labels are given in Fig. Fig. 7 Eco labelsRepublic of China–Taiwan European Union Eco-label “Flower”Green Mark India Eco Mark Netherland Ecolabel FoundationCommercial Activities Organic cotton is grown at several places in India. Naturally coloured cotton comes infawn brown and pista green colour. It was grown in India in olden days. Textile items made fromorganic and coloured cotton fetch considerable higher price. Green minded people are willing topay high price for eco-friendly textiles, which are free from carcinogenic dyes and harmfulchemicals.Eco-friendly apparels Eco friendly apparels are manufactured by the following industries in India 1. Alps Textiles, ghaziabad: Produce vegetable dyes and fabrics dyed with vegetable dyes. 2. Reymonds : Green shops in most big cities. Products are free from banned dyes. 3. Arvind Mills : Eco-friendly denim using pesticide free cotton. Trade mark-Ecologically optimized fabric (EOF) issued by Eco-Tex, Germany. Specialized environmental stores in Switzerland like Globus and Jumoli are marketing arvind Mills EOF denim. Arvind mills also have plans to introduce EOF denim in US and European markets.
  • 16. 4. Coats Viyella : Astra brand sewing threads, free from carcinogenic dyes 5. Century Mills : Cool cotton and Eco-friendly fabrics and garments. Also developed eco- friendly process for dyeing of cotton with Sulphur dyes.Efforts Made by Government of India To meet the challenges posed by eco regulations by Germany and other countries, theGovernment of India, through the Ministry of Textiles and the Ministry of Environment andForests, charted two approaches, viz. regulatory and developmental. Some of the regulatorymeasures and development efforts include the following:Regulatory Measures• Prohibition on the use of 112 dyes, which are capable of releasing harmful amines.• Evolution of eco standards and logo for eco-friendly textiles.Developmental Efforts• Organization of educative seminars, workshops and camps to inculcate the eco-friendly concepts among the industry and consumer.• Assistance to be provided by Textile Research Associations and Textile Committee to textile units for securing ISO 9000 Quality System Certification and ISO 14000 Environment Management System Certification.• Keeping in mind the need for modernization on war footing, the Ministry of Textiles has announced the scheme called Technology upgradation fund (TUF), wherein the credit is available at concessional rate of interest to enable industry to take up modernization projects in a big way.• Similarly, as part to support textile industry for testing of eco-friendly textiles, the Ministry of Textiles took up a massive programme of setting up of eco testing laboratories. In this pursuit, the Textile Committee, a statutory body under Ministry of Textiles, is identified as a nodal agency.Conclusion Two approaches viz. clean production technology and end of pipe treatment are availableto deal with the environment problems. Among these, clean production technology is moreeffective. Some of the clean production technologies for dyeing, printing and finishing of cottonare highlighted. Eco- friendly textiles are identified by means of eco labels which are based oneco norms. Government of India Ministry of textiles made serious efforts to popularize theconcept of eco-friendly textiles and provided facilities in terms of setting up of eco laboratoriesand modernization funds to textile industry.