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

ECO-FRIENDLY TECHNOLOGIES FOR TEXTILE PRODUCTION.

R.B.ChavanFormer Professor,

Textile Dept. IIT Delhi Consultant, MGIRI, Wardha

E-mail [email protected]

AbstractCradle to grave or womb to tomb is the most effective concept for cleaner production activities

including textiles. This concept has coined the terms such as production ecology, user ecology

and disposal ecology. According to this concept it is no longer adequate to have a finished

product to be safe only to human beings but the production processes and the product disposal

after use should be environment friendly. In the present paper attempt has been made to discuss

critically the cleaner production technologies such as use of organic cotton, naturally coloured

cotton, environment friendly Reactive, Vat, and Sulphur dyeing and finishing processes for

cotton, the use of synthetic thickener as a substitute for kerosene in pigment printing. Eco-norms

Eco-labels for identification of environment friendly textiles and the attempts made by the

Government of India, Ministry of Textiles to facilitate the use of eco-friendly textile production

are briefly discussed.

Introduction

During the manufacture of textiles very large number of chemicals are used e.g. during

the cultivation of cotton, the use of fertilizers, pesticides is quite common, during sizing one uses

size preservatives and during chemical processing a large number of chemicals, textile

auxiliaries, dyes, pigments, thickeners, finishing agents etc are used. Many of these agents are

responsible for problems during their handling, water and air pollution causing health problems

to 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 activities

in general and textile production in particular till recently Germany has put the ban on the use of

certain azo dyes, commonly known as German Ban.

Eco-friendly Textiles

The German Ban acted as catalyst to develop the concept of eco-friendly textiles. In

developing this concept "Cradle to Grave" or "Womb to Tomb" approach is followed. According

to this concept textile industry should take the environmental and health hazard aspects into

consideration right from the stage of fibre cultivation/manufacture to spinning, weaving,

chemical processing, apparel manufacture, packaging and disposal after use. The material flow

diagram during textile production is shown in Fig. 1

Fig. 1 MATERIAL FLOW ALONG THE TEXTILECLOTHING CHAIN

Synthetic Fibre

Basic chemicalspetrochemistryProduction of monomers /

Production

Fibre, yarn, fabric

Natural Fibre

- Cultivation .fertilizerspesticides

- Crop auxiliary agents

Textile Processing

e.g. desizing, mercerizing, bleaching,

dyeing, printing, finishing

Garment / Textile industry

UsePacking, washing, dry-cleaning

Disposal

In order to make the textiles totally environment friendly, not only the final product to be

used by the consumer be eco-friendly, but the production technology, packaging and disposal

after use should also be eco-friendly. Therefore, the production ecology, user ecology and

disposal 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 on

air, water, soil as well as human beings.

User Ecology

This refers to the aesthetics, performance characteristics and effects of textiles on human

body.

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-fibres

Organic Cotton Cotton is cultivated using pesticides, fertilizers and other crop related chemicals. The

residues of these chemicals remain on cotton bolls. These residues are removed during the preparatory processes and enter into the wash liquor resulting in water pollution. Therefore, in true sense, cotton cultivated by using such chemicals is not considered to be eco-friendly. A trend is started to cultivate cotton without the pesticides, fertilizers and other chemicals. Such cotton is considered 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 farming techniques may decrease the use of chemicals, pesticides, herbicides, fungicides, defoliants and harvest aid chemicals used for cotton cultivation. This would help to decrease soil pollution

during cultivation and water pollution during preparatory processes. The eco labels shown in fig. 2 identify the organic cotton

Fig 2 Eco-labels for cotton

Naturally coloured cottonNaturally coloured cotton of various colours particularly green and brown varieties were

cultivated since ancient times in many countries. However, such cotton did not gain commercial popularity due to low yield, short staple length, poor fibre strength, poor spinnability and possible contamination due to pollination. The present environment protection 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 dyeing operations.

Lyocell It is regenerated cellulose marketed by Courtalds. It is obtained by wet spinning of cellulose pulp dissolved 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 friendly

corn fibre under the trade name Lactron. It is produced from lactic acid obtained through the fermentation of corn starch. Strength, stretchability and other properties of Lactron fibre are comparable to petrochemical based nylon and polyester except lower melting point (175o C). The fibre is suitable for both textile and non-textile applications.

Environment Friendly Chemical ProcessingThe input/output analysis during chemical processing of textiles is shown in Fig 3

Large number of base chemicals, dyes, auxiliaries, and finishing agents are used during chemical processing of textiles as in put. As an out put we have air pollution, water pollution and problems of sludge disposal. There are two major pollution control strategies

Cleaner production techniques and processes End-of-pipe treatments

Cleaner Production Techniques and ProcessesSome of the cleaner production techniques with reference to cotton are discussed.

Fig. 3 Input / output analysis of Textile chemical Processes

Textile Auxiliaries

Dyes

Base chemicals(e.g. acid, Alkali, sodium chloride)

Textile EnergyNatural Fibres; 10-20 MJ/kgChemical Fibres: 5-50 MJ/kg

Water60-360 l/kg textile

Polluted Air

Water Effluent

WasteSewage sludge:

60-70 g/kg textile

Wet Processing (pre-treatment,

dyeing, printing, finishing.)

Dyeing

Different dye classes which are suitable for dyeing of cotton and the chemicals in the effluent stream is shown in Table 1

Table 1 - Chemicals in effluent streams

Dye Chemicals in effluent streams

Vat Residual dyestuff (5 - 20 %)Reducing agentsOxidising agentsDetergentsSalt

Reactive Residual dyestuff (20 - 50 %)Salt AlkaliDetergent

Direct Residual dyestuff (5 - 20 %)Salt Dye fixing agents

Sulphur Residual dyestuff (30 - 40 %)Sodium sulphideAlkaliSalt

Dyeing of Cotton with Reactive dyesAmongst the different dye classes suitable for dyeing of cotton, reactive dye class is the

most important.

The use of reactive dyes is predicted to rise by 50%. Presently, most of the reactive dye manufacturers are concentrating on addressing the following environmental problems associated with the reactive dyes: Colour in the effluent.Minimization of chemical usage.

Colour in the EffluentRemoval of colour from the effluent is one of the expensive approaches for the end of

pipe technology. Therefore, it is necessary to find suitable alternatives. In exhaust dyeing, the use of reactive dyes is the major source of concern. The vat, sulphur and azoic dyes exhibit a high degree of exhaustion and the insoluble unfixed dye can readily be removed as a part of the primary flocculation process. Whereas in case of reactive dyes, sometimes as high as 30% dye remains unbound during primary treatment and needs to be treated either on site as a secondary process after biological oxidation or at a municipal sewage works. The adsorption of hydrolyzed reactive dye on biomass is not as efficient as of other water-soluble dye classes. However, the amount of hydrolyzed dye in the effluent can be minimized through process innovations.

The government pressure for regulating industrial effluent discharge has led to the development of new reactive dyes, machinery and processes to minimize waste and colour in the effluent. The development of bifunctional reactive dyes is important from this point of view.

Bifuntional Reactive DyesBifunctional reactive dyes consist of two reactive groups capable of forming covalent

bonds 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 heterobifunctional reactive dyes presently marketed by main dyestuff manufacturers .

Fig. 4 Homo and Hetero Bifuntional Reactive dye

The characteristics of these dyes is their high exhaustion and high reactivity with the fibre so that there is less quantity of dye in the effluent.

Dye Liquor WastageMinimization of dye liquor wastage is a major environmental consideration in a

continuous dyeing to reduce colour in the effluent. At the end of every dyeing, there is liquor left in the pad trough as well as in the stock tank prepared as a precaution against running out before the dyeing is completed. A latest development from Monforts (Matex 3 bowl padder) has the feasibility 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 UsageSome of the approaches to minimize the use of chemicals are:

Dyeing at low liquor ratio.Right-first-time approach.Process innovations in continuous dyeing.Use of low-salt reactive dyes.

Dyeing at Low Liquor RatioThe 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. Apart from the easier handling of lower volume of effluent, the dosing of chemicals and auxiliaries in the dye bath is done on the basis of g/litre of liquor. This significantly reduces the quantities of chemicals and auxiliaries and finally the effluent load. In reactive and vat dyeing systems, a change of liquor ratio from 1:10 to 1:5 brings about a decrease in pollution load by about 40%.

Right-first-time ApproachCarefully following the dyestuff manufacturer’s recommendations for salt, alkali usage,

temperature, time, etc. to ensure optimum fixation levels and right-first-time production, thereby avoiding the need to make shading additions. The computer colour matching should help in this regard.

Low salt Reactive Dyes Substantial quantities of electrolytes, such as sodium chloride and sodium sulphate, are used

for the dyeing of cotton with reactive dyes. Exhaust dyeing with 10:1 liquor-to-material ratio needs 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 salt enters the environment on discharge of effluent treated water. High salt concentration in effluent has 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 salt concentration is too high, soil may become overloaded with salt, and making the land infertile and ultimately useless.

Low salt reactive dyes

Ciba Speciality Chemicals has introduced low-salt Cibacron LS dyes, which require only 20 g/L salt, whereas the conventional reactive dyes require 60-80 g/L salt for exhaustion. The dyes have 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.

Fig. 5 General characteristics of Cibacron LS dyes

As the salt requirement is reduced to ¼ of that required for conventional dyes, the saving in cost is observed. Another benefit is that rinsing step after dye application is much faster and less water consuming. Since the Cibacron LS dyes have a higher fixation rate than the conventional dyes, 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

Alternative Reducing Systems for the Dyeing of Cotton with Vat and Sulphur Dyes

Vat Dyes

Vat dyes are applied by using sodium hydrosulphite as reducing agent and sodium hydroxide as an alkali. A few of the byproducts formed are sulphur compounds like Na2S which pollute air through the formation of H2S. At the same time, the salts of sulphur in the form of sulphate and sulphites (Na2SO3, NaHSO4, Na2SO4, Na2S2O3) contaminate sewage, lower its pH and show corrosive action on concrete pipes. To overcome these problems, attempts were made by several

Chromophore Chromophorebridge

Reactivegroup

Reactivegroup

Conventional dyes60 % fixation

Cibacron LS (bireactive)80 % fixation

200 gm into the waste water

800 gm on the fibre

1 kg dye

+ 33% %

- 50% %

1 kg dye

600 gm on the fibre

400 gm into the waste water

researchers to develop alternate reducing systems, which are ecofriendly in nature. Such new systems 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 on

cotton. Residual sodium sulphide acts as contaminant in the effluent. Sodium sulphide causes no marked odour nuisance above pH 9 but in acidic pH, gaseous H2S is liberated, giving fowl smell of rotten eggs and is toxic when inhaled. Its odour threshold value is 10 ppm

Replacement of Sodium Sulphide

GlucoseGlucose has long been known as reducing agent for sulphur dyes. Sulphur black is almost

always reduced using glucose A considerable improvement is achieved when the dyeing is carried 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, glucose gives colour yield equivalent to that obtained with sodium sulphide. Century mill at Mumbai also established, on commercial scale, that sodium sulphide can be totally replaced with glucose obtained from hydrolysis of starch.

Synthetic Thickener for Pigment PrintingEmulsion thickener using kerosene oil or mineral turpentine oil was the ideal and most

popular thickener for pigment printing of cotton. However, emulsion thickener poses serious health hazards, fire hazards and air pollution problems. Attempts to recover and recycle kerosene or MTO were not successful. Synthetic thickeners based on polyacrylates have successfully replaced emulsion thickener in pigment printing. Many indigenous as well as imported products are readily available.

Easy care or Wrinkle free Finishes Majority of cross-linking agents used today are formaldehyde based including DMDHEU

and etherified DMDHEU, which have low formaldehyde level. Formaldehyde based cross-linking agents are cost effective and efficient. However, the release of formaldehyde vapours during finishing processes as well as during subsequent storage and consumer use of finished products has caused world wide concern on its impact on human health and environment because of the fears that it is carcinogenic and its well known dermatitis effects. The release of formaldehyde is restricted to 20-ppm level. Non-formaldehyde based cross linking agents is one of the approaches which has been explored.

Polycarboxylic acids (PCA) as cross linking agentsAn alternative approach has been based on the use of PCAs. In 1998 Welch reported that

cotton fabric treated with 1,2,3,4 butane tetra carboxylic acid (BTCA) in presence of sodium hypophosphite showed high level of wrinkle resistance and strength retention as well as good durability to home launderings. However, exceedingly high cost has prevented the use of BTCA

on commercial scale. Citric acid (CA), a low priced tri-functional carboxylic acid is less effective to 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 as wrinkle free finishing agents using sodium hypophosphite as catalyst. Most of these acids imparted DP rating of 4.3-4.7, and crease recovery angle 285-300°. However, the resultant finishes differed considerably in durability in alkaline laundering. The acids arranged in order of decreasing durability in terms of maximum number of washings and tumble drying cycles withstood were as follows

BTCA>CA>Maleic acid.>Succinic acid.

SoftenersFabrics and garments are usually comfortable to wear if they are soft to touch. Chemical

pretreatments remove natural cotton waxes rendering cotton harsh to handle. This is usually made worst after wrinkle free finishing. To compensate this; softeners are widely used. They also act as fibre lubricants decreasing both fibre-fibre and fibre-metal friction. The draping and, cutting properties are also enhanced. The trend is towards the use of silicone softener that provides a soft luxurious handle, thereby imparting a higher quality and added value to the material.

Silicone softeners Silicones have been used as textile softeners since 1960.

Currently available silicone softeners can be classified as 1. Non-reactive2. Reactive

Studies 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 wash effects on indigo dyed denim. The technology is well established and widely accepted as eco-friendly.

Identification of Eco-friendly Textiles

Eco Parameters and Norms for Eco-friendly TextilesIn the past textiles were considered primarily from economical, functional and fashion

points of view. More recently consumers are imposing demands on the safety of textiles for the health and also on the environmental soundness as decided by eco-parameters stipulated by well established organizations. These norms are based on the analysis of textile products entire life cycle commencing from cultivation of raw material (e.g. cotton), various production stages, packing, distribution, utilization and disposal after use. For formulating eco norms different classes of chemicals are considered. These are

Toxic Substance Process

Pesticides 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 Fashion

Steilmann Comitextil Indian ec0-lable

FormaldehydeBaby clothing 20 20 20 50 20 20Close to skin 75 75 75 300 75 75Outer Wear 300 300 300 300 300 300Toxic pesticides

1 5 1 1 0.1-1 1

Pentachloro phenol

0.5 - 0.5 Ban 0.05-0.5 0.5

Heavy metalsArsenic 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 3-100Cobalt 0.2-20 0.2-20 0.2-20 0.2-20 0.2-20Zinc 5-100 5-100 5-100 5-100 5-100Nickel 0.2-10 0.2-10 0.2-10 0.2-10 0.2-10Azo dyes containing carcinogenic amine

Ban Ban Ban Ban Ban 50

Halogen carriers

Ban - - Ban Ban 200

Chlorine bleaching

- - - To avoid Ban -

Eco Trade marks, Eco LabelsThere are large number of eco trade marks, eco labels are available for identification of

eco-friendly textiles. These eco labels are made available by associations, institutions and service companies of the textile industry. Most of these initiatives were originated in Gemany, but they claim validity for the whole Europe and in some cases for the whole world. Ministry of Environment and Forest under the certifying agency of Bureau of Indian Standards (BIS) has also developed eco label. Some of these eco labels are given in Fig.

Fig. 7 Eco labels

Republic of China–Taiwan European Union Eco-label “Flower”Green Mark

India Eco Mark Netherland Ecolabel Foundation

Commercial Activities Organic cotton is grown at several places in India. Naturally coloured cotton comes in

fawn brown and pista green colour. It was grown in India in olden days. Textile items made from organic and coloured cotton fetch considerable higher price. Green minded people are willing to pay high price for eco-friendly textiles, which are free from carcinogenic dyes and harmful chemicals.

Eco-friendly apparelsEco 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.

4. Coats Viyella : Astra brand sewing threads, free from carcinogenic dyes5. 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 IndiaTo meet the challenges posed by eco regulations by Germany and other countries, the

Government of India, through the Ministry of Textiles and the Ministry of Environment and Forests, charted two approaches, viz. regulatory and developmental. Some of the regulatory measures 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 available

to deal with the environment problems. Among these, clean production technology is more effective. Some of the clean production technologies for dyeing, printing and finishing of cotton are highlighted. Eco- friendly textiles are identified by means of eco labels which are based on eco norms. Government of India Ministry of textiles made serious efforts to popularize the concept of eco-friendly textiles and provided facilities in terms of setting up of eco laboratories and modernization funds to textile industry.