Indian Journal of Fibre & Textile Research Vo1.26. March-June 200 I, pp.116- 124

Environment-friendly processing of protein fibres

S R Shukla"

Di vision of Technology of Fibres and Textile Processing, Department of Chemical Technology, University of Mumbai , Matunga. Mumbai 400019, India

The various practi cal and theoretical approaches adopted during the last decade toward ~ the environment-fri endl y chemica l processing of woo l and si lk are hi ghli ghted. The ways and means are available at the disposal of a chemical processor to evolve an ccofriendl y wool/silk product, even wi th des ired value additi on. However. certaIn processes lI ke ultrasound and plasma treatment need to be ex plored at the bulk processing level.

Keywords: Ecofriendly processi ng. Protein fibre. Silk , Wool

Introduction Environmental issues have so far never rece ived

the importance they should have, although the industry always seemed to be aware of it. It is the quest of common man in last about two decades that these iss ues have come to the surface and are being addressed to with greater concern. The envi ronmental pollution has long since ceased to be the sign of progress, which it was in the earlier part of the 20lh

century. With increas ing indust ri ali za tion , the poll uti on and its impact on nature and human culture has crossed limits and hence the seri ousness about its abatement.

Chemi ca l processing of textil e materials involves the max imum poss ibilities of polluting chemical s being used. A number of chemicals and dyestuffs, which are being used liberally in order to en hance the so-ca lled quality, contain toxic and hazardous su bstances. These may be the chlorinated scouring and bleac hing chemicals , the banned amine-based dyestuffs, heavy metal traces present in dyestuffs, sta in removers, formaldehyde-based dye fixati ves, softeners, crosslinking agents, preservatives, etc. These are now known to not only damage the environment, but also to affect the consumer of texti le products. From the point of view of being environment fri endly, one approach is to switch over to purely mechanical fini shes instead of chemical or ass isted finishes, but this may not be feasible all the time. In dyeing, the use of natural dyes has been boosted, but with inherent limitati ons.

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Among the various fibres used in the making of textiles, the classification broadly categorizes them into those procured from natural sources direc tl y or indirectly and those fully synthesized from the petrol eum products. The latter are more or less non­biodegradable as they are synthetic. However, the former being natural (including ce llulosics and anima l protein fibres) are full y biodegradabl e. Hence, it is a minimum ex pec tati on of anybody hav ing concern about environmental pollution abatement that at least in the case of nat ural fibres, the use of polluting chemicals should be avoided as far as poss ible.

With such an approach, the thinking has given rise to the principles of pollution abatement as: • Use minimum to start so that less is wasted and,

therefore, will cause least di scharge to the environment.

• Reuse and recycle the products wherever poss ibl e so that their use ful life is enhanced and the period to di scard them to environment is delayed.

• Change, replace or redes ign the processes in order to be more environment friendly by use of ecofriendly chemica ls, energy conserving routes, etc.

Among the different natural tex tile fibres in use today, wool and silk are the two hi gh priced protein fibres known to mankind for ages.

Si lk is a smooth , lustrous and elastic filament of small diameter, which is obtained from the cocoons of the silk worm. When unwound from cocoons . silk is obtained as a continuous filament. It combines strength with li ghtness , durability with beauty and

SH UKLA: ENVIRONMENT -FRIENDLY PROCESSING OF PROTEIN FIBRES 117

cleanliness with lustre. Silk is the most beautiful continuous fil ament and the fabrics made out of it have exceptionally pleas ing lustre, soft handle and comfort.

Wool possesses unique phys ica l and chemical properties. Its bil ateral structure causes crimpiness to the hair, giving ri se to a large number of air pockets, which are capable of retaining warmth . Its draping qualities are outstanding due to its high extensibility. It absorbs a large amount of moisture, leading to comfort. The general chemical process sequence for wool consists of carboni sing, scouring and bleaching, dye ing and fini shing.

2 Processing of Silk Silk is mainl y composed of fibroin - the textile

filament - and sericin , the outer gummy matter adhering to the fil ament and compri sing of 20-25 % of the total mass.

The main chemical process sequence for silk , in general, includes degumming, bleaching, dyeing and fini shing.

2.1 Degumming of Silk

Main impurities in silk are sericin , lubricants and softeners (added during throwing or during preparation for weav ing/ knitting), dirt and oil picked up incidentally during process ing and the undesirable colouring matter. Remova l of sericin (degumming) is essential so as to make the silk material soft and supple with requi site lustre. It needs to be removed uni fo rml y otherwise it gives non-uniform results. Thi s sericin is removed to various degrees and gives ri se to different commercial varieties of silk such as ecru , soup Ie and cuit each with increasing level of degumming.

Essentially, degumming of silk is hydrolysis of protein seriCin and it may be carried out conventionall y by acids or alkalies. Normall y, the chemica ls used in degumming are not harsh on environment as they compri se weak alkali , soap, etc. Non-i onic detergents are preferred over soap due to their better efficiency under neutral conditions, stability to hard water, lower cost and more effi cient cleaning. However, from the point of view of better results in terms of appearance and fee l of the degummed si lk fil ament, the use of enzymes is gain ing importance.

The proteolyt ic enzymes are soft on fibre and they hydrolyse the peptide bonds formed by amino acids in

silk. The va rieti es available are trypsin , papain and bacteri al enzymes. Trypsin is a serine protease, active at room temperature and pH 7 - 9. Seri cin is a polar and less crystall ine protein with hi gh lys ine and arginine content, which can eas il y get hydrolysed by trypsin . On the other hand , the fibroin, being less polar, hi ghly crystalline and low in lys ine and arginine, is not affected by thi s enzyme!. Another enzyme papain is sulphydryl enzyme, act ive at 70-90°C and pH 5 - 7.5, whereas the bac teri al enzy me alcalase is ac ti ve at 60°C at pH 9.

Gulrajani et at? have shown that degummase improves the wettability and whiteness of the silk fabric without affecting its strength .

Gulrajani and Gupta3 carried out enzymat ic processing of waste silk fabric. Such fabrics have good drape and durability for upholstery and furni shings. Spun silk used in such fa brics contains many impurities including cellulos ic ones . By use of the cellulase enzyme from Trichoderma reesei along with a proteol yti c enzyme degummase J OOL, they obtained complete removal of impurities, at the same time improving the wettability.

2.2 Bleaching of Silk

Although the naturall y present colours in different silk varieties are the most des ired ones, sometimes there is a demand for white materi al or it becomes a necess ity for getting pure shades. In such cases, bleaching is essential and it is carried out using either reducing or oxidi sing bleaching agents. Among the different ox idi sing agents, hydrogen perox ide has been shown to be the best bleaching agent for mulberry and tasser sil k varieties fro m the point of view of better whiteness and lower loss in moisture regain and tensile strength4

. Among various types of bleaches, this is the only ecofriendly bleaching agent.

2.3 Dyeing of Silk

Silk can be dyed conventionall y using acid , metal complex, basic and direct dyes . Other than in case of metal complex dyes, the wet fas tness of dyed sil k is un sati sfac tory. From environmental safety point of view, it is essenti al to select the dyestu ffs based on va ri ous criteri a. The very first is to opt for the dyestuffs which are not based on any of the twenty banned amines as per the guidelines of German Ban. Most of such dyes belong to direct and acid applicati on classes of dyes, hence the caution. Once these are thrashed out, among the rema ini ng ones, and

11 8 INDIAN J. FIBRE TEXT. RES, MARCH-JUNE 200 1

thi s applied to all the dyeings, the selection should be based on high exhaustion of dyes on the fibres as far as possible. Thi s precaution will tend to let out onl y a limited amount of dye into the effl uent di scharge, whi ch requires further treatme nt for po llution control. Any amount of dye di scharged into effl uent increases the BOD, COD load as well as the unpleas ing appea rance to water strea ms and he nce, littl e is bette r.

Lewis and Shaos used sulphatoethyl sui phone type (Remazol by Hoec hst) reac ti ve dyes for dyeing silk to obtain high brilliancy and better wet fastness properties. These dyes can be app lied at pH 7 - 8 and 80°C in the presence of 30 -50 gil salt. They improved the dye exhausti on considerabl y, thereby e liminating the use of salt for ex hausti on. The degree of fixation

was also enhanced. The process ca lled B-elimination to yie ld vinyl sui phone dye with least hydrolysis was optimi sed at pH 7 fo r 10 min at lOOoC, followed by dye ing at pH4 - 4.5 using buffe r system.

An atte mpt was made to dye s ilk with cationic, ac id and metal complex dyes at low temperature in the presence of ultrasoni c e nergy fo r re lat ive ly shol'l durations. When the results were compared wi th those of the conventional dyei ng processes which are carri ed out at higher temperature and for longer dye ing times, it was found that the ultrasound e nergy cou ld give good fas t dye ings, many times comparable with the conventi onal dye uptakes . The process is energy effic ien t since it conserves energy as well as time6

. In another attempt, certain se lected dyes of direct and ac id classes were dyed under the weak ultrav io le t radiations in the presence of UV radiati ons and a photo initi ator. Not a ll dyes, but only those, which could form free radical s, could respond to thi s energy conserving process of dye ing7.

2.4 Silk Industry Health Hazards

A German study has indicated that nearly 50% of 130 workers of the si lk industry in 1984-1988 had undergone illness, mainl y respiratory ailments, followed by cardiovascular di sease, nervous system disorders , e tc8

.

2.5 Silk Industry Waste Water Treatment Zhu9 indicated that the use of bentonite containing

BT composite coagulant and propenamide polymer fo r treating high strength silk finishing wastewater gave COD and colour removal rates greater than 90%. Subsequent contac t oxidation produced colourless effluent with COD <150 mg/L.

3 Processing of' Wool Wool, another important prote in hair fibre, is

covered by the outer cuticular layer or the sca les. Although the function of these sca les is to protec t the hair from wea ther, abrasion , e tc ., it is the main hindrance during efficie nt and uniform c hemical process ing of wool. The scales offer hydrophobicity, decreased absorbance to dyes and c he mi ca ls, felting tendency in aqueous baths , non-easy care properti es and harsh fee l. Complete re moval of the sca les is detrimental to the fibre properties. However, parti al and uniform re mova l is essential for gett ing better out of the wool c harac teri sti cs. Earli er non-ecofriend ly method was to make use of chlorinat ion. The wool grease obtained after scouring process is of grea t va lue and hence, it is a lways advisable to recover it. Caboni sation of wool re moves the cellul os ic and alli ed impurities from wool material by acid trea tment.

Wool has been used to produce floo r coverings since time imme moria l and recentl y there has been a rev iva l in the popularity of wool for ca rpets and rugs'o. The unique molec ul ar st ructure of wool gives it advantages over other fibres . The usc of woollen carpets in an interior environmen t can reduce allergenic and harmful substances such as nitrous ox ide and formaldehyde. W ool is "green" be ing a renewable resource and biodegradable. Being naturally res istant to dirt, wool does not req uire the use of anti-soiling agents and has a red uced requirement for cleaning substances. Wool is ex tremely durable but is susceptible to moth damage.

It was observed by Shaw" that organoc hl orine pesticides in contaminated raw wool are not completely removed by the scouring process and may po llute process ing effluents.

Wool tech Group, Ita ly , has developed a non­aqueous wool scouring and process ing system '2. It uses no water and , therefore, leaves behind no effluent or unwanted waste. It cleans w ithout entanglement, increases tensile strength of the fibres , and is capable of producing cleaned wool that can be successfully spun on the rotor sys tem. It makes use of lCI's Triwool solvent as the cleaning agent, be ing non-flammable and non-carcinogenic with no depletion of the ozone or production of green house gas.

E nzymes have begun to assume increasing importance in texti le finishing. One of the main

SHUKLA : EN VIRONM ENT -FRI ENDLY PROCESSING OF PROTEIN FIBf{ES 11 9

reasons for thi s wider appli cati on of enzymes has been the steady inc rease in e nvironmental awareness on the part o f consumers as well as the legislati ons regarding the environmenta l protecti on. T he subst rate specific reacti ons of enzymes offer the poss ibility to cont ro l a che mi ca l reac ti on in such a way that no undesirable side reac ti ons take pl ace.

E nzymes are biocatalysts. Catalysts partic ipate in a chemica l or bioc he mical reaction in such a manner that they emerge fro m it unchanged at the end of the reac tion. Enzyme ac ti on is spec ific and they will only participate in very indi vidua l reac ti ons or substrates. Because of the ir complex compos ition, the e nzymati c reac ti ons of prote in fibres are ex tre me ly var ied.

Proteases are mult i-enzymatic systems, whi ch catalyse the hydro lytic degradation of prote in fib res. Protei nase splits the large molec ular protein molec ules to polypeptide chains or ind iv idual polypeptides. E ndopeptidase hydro lyses the peptide bond both at the end of the mo lecule as we ll as inside the molec ule, whereas exopeptidase exc lus ive ly breaks down the cha in ends.

Ying and T ian 13 observed that the additi on o f enzyme to the scouri ng bath considerably en hances the scouring effec t for wool. T he opti ma l scouring conditi ons were: enzy me concentration 0.0 15-0.02%, temperature 55°C, pH 10-11, and (NH~)2S04 or Na2C0 3 as auxili ary agent.

Enzyme treatment of the fibre considerabl y improved dyeabili ty due to degradation of the hydrophobic barrier by the lipoprotein lipases. As a result, the access ibility of the fibre to the aqueous dye liquor increased. ' Moreover, the degradati on of prote ins within the fibre a ll owed greater access ibility and mobility for the dye molecules. Even a mild enzyme treatment of wool marked ly improves dyeability without causi ng s ignificant fibre damage l4.

A novel cutic le-degrading enzyme for degrading cuticle on the surface of animal hair is prepared fro m the culture of Bacillus cereus stra in NS- 111 5. The enzyme is useful in process ing animal hair fibres like wool to improve the ir qua lity by increasing water absorbancy, decreas ing sta tic property, dec reasing shrinkage, e tc. T he enzyme exhibits a pH optimum 8 and temperature optimum 45°C.

Another enzyme, Proteinase-NH is isolated from the cu lture of Aeroll/onas hydrophila st rain and it is able to hydrolyse water-insoluble protein kera tin

during process ing of wool16. The enzyme ex hi bits a pH optimum 7-9 and temperature optimum 50-60°C.

The use of low-pressure/ low-temperature pl asma for pretreating wool is shown by Fuc hs and Hocker

l7

to offer small and medium sized companies an ecofri endly acceptable and economi ca ll y optimum way to dye the materia l. The wool, however, has a somewhat harsher handle and rougher surface as a resul t. Thi s is due to the removal of fa ts . Dye ing behav iour is much improved and effluent is reduced. Colour fastness is better and dye f ixing times are red uced.

3.1 Bleaching or Wool T he two-s tage bleac hing fo r wool is unsurpassed in

its bl eac hing effec t but new bleac hing agents and processes permit more rapid, more economical and less environment-damaging bleach ing. Re incke l8

described acid quick bleac hing with hydrogen perox ide in conti nuous and d iscontinuous application as we ll as opt imised red uctive bleaching with hydrosulphite. New develop ments B lankit AN and AR have been presented .

Cegarra el al. 19 investiga ted environmental properties of d ifferent stabili zers fo r wool bleac hing with hydrogen perox ide. Al ka line phosphates are not be ing used in modern textil e scouring and bleac hing operati ons because of their adverse e nvironmental effec ts. They used three di f ferent stabili ze rs ,name ly sodium nitrilotriaceta te, sod ium diethylene tri aminopentamethyl phosphonate and a mi xture of sodium pyrophosphate + ammoniu m oxalate . The last one is usuall y recommended fo r perox ide bleaching of wool. The P content of the mixed stabili zer was found to dec rease to 57% of the initial quantity in the effluent, whi ch is concentrated one. Al so, the eutrophicati on va l ues were within the range. Thus, the mixed stabili zer was found to be more useful , at the same time be ing e nvironment fri endl y.

T he whiteness obtained in wool bleaching was fo und to enhance by the presence of protease, with both peroxide bleaching and when sodium dithi onate or bi sulphite was used2o

. However, the increased whiteness is accompanied by the loss in both weight and stre ngth .

The effec t of enzyme treatment on whi teness, dyeability and other properti es of wool tops and wool fabrics have been inves tigated by Schumacher el al.21

•

ft is shown that protea~e treatment improves the

120 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 200 1

whiteness as well as dyeability with Lanasol Reactive Dyes.

3.2 Dyeing of Wool

Seventy per cent of dyes used for wool either contain heavy metals like chromium or require chromium for their applications. About 30% of this total utilizes traditional afterchrome method using dichromate anions added to exhausted dye bath or separately in fresh bath.

Afterchrome dyes are widely used for wool dye ing si nce they are economically attractive, have outstanding wet fastness and provide full shades. The main disadvantage is the le ft out chromium in the e ffluent. Generally, it should be Img/L remaining in the exhausted dye bath. Chroming is usually carried out by aftertreating the chelatable dye with dichromate. Optimum pH conditions under wh ich divalent dichromate anion exhausts on wool are essential to determine, since these will reduce residual chromium in the dye bath.

According to Thomas et al. 22, after the reduction of

chromi urn-VI to chromium-III, 1: 1 and 1:2 complexes are formed in fi bre. In the exhausted bath, both chromi urn-VI and chromi um-III ex i st. Chromi urn-III takes part in gl ucose metabolism of human organ ism and therefore essential. Chromium-VI is most toxic , toxicity being related to its oxidation potential. It eas ily penetrates cell membranes and oxid ises cell components. It is also absorbed by skin and respiratory tract. Two mg/L total chromium and O.Smg/L of chromium-VI are permitted at individual process stage, but not in the completely diluted effl uent. Complex ing agents and salts inhibit extraction of chromi um and , therefore, need to be eliminated from the bath.

Maximum exhaustion of dichromate occurs below pH 3.S due to its high affinity to protonated NH4 of wool. Reduction of chromium-VI to chromium-III occurs fairly rapidly within the fibre and it is accompanied by oxidation of cystine disulphide linkages. Under strong acidic conditions, chromium­III will be repelled by protonated amino groups and if pH is low, then chromium-Ill will even be desorbed.

Houlton23 has reviewed the methods which are being applied to wool dyeing to reduce chromium levels in the effluent. In metal complex dyes, heavy metal is precomplexed with a dye chromophore by the man ufacturer. It is mostLY chromium, but coba lt

a lso is used to form 1: 1 or 1:2 metal complex dyes. The 1: 1 metal complex dyes are fi rst deve loped and these are applied from strongly acidic bath. These are mainly used for dye ing of piece goods where good migration properties are essentia l for level dyeing. The 1: 2 metal complex dyes give greater wet fastness and are applied under less acidic conditions. These are mainly used for dyeing of tops, loose wool and yarn.

The level s for chromium In effluent from traditional chromium dyeing are 20-1S0 mgfL. Optimised conditions for dyeing can reduce the m substantia ll y. Thus, for 1: 1 and 1:2 metal complex dyes , the chromium levels can be reduced to 3-13 mg/L and < 7mg/L respectively. Modified dyei ng processes help in this regard .

There are several parameter in chrome dyeing which, when optimized, can reduce chromium residues24

.

The add ition of dichromate must be minimised in ' accordance with the dyestuff manufacturers recommendations, since reduced chromium additions will lead to lower residuallevels.

If the dye bath exhaustion is incomplete before chroming, then residual dye in the liquor will be chromed and remain in the liquor to add to the discharged chromium. Optimum results are obtained by chroming in a fresh bath or by increasing dye bath exhaustion.

There is an optimum pH region (3.S - 3.8) to be attained with formic acid for ensuring maximum efficiency of chroming and ,therefore, minimum res idual chromium levels. Other acids may reduce the efficiency of chroming.

It is also essential, for maximum chroming efficiency, to eliminate chemicals from the chroming bath wbch will inhibit the chromium-dye interaction, such as sequestering agents . Sulphate ions also inhibit the exhaustion of the dichromate anion and should also be omitted from chrome dye baths.

A range of optimised chroming methods are avai lable to minimise the chromium residues in dyehouse effluent from chrome dyeing. Techniques have been developed by IWS, Bayer, Ciba - Gei gy and Sandoz.

The Bayer technique as well as Sandoz method uses minimum dichromate levels, calculated from their own published chrome factors for each dyes tuff, and the addition of sod ium sulphate or Lyocol CR

SHUKLA: ENVIRONMENT -FRIENDLY PROCESSING OF PROTEIN FIBRES 12 1

respecti vely to the chroming bath to a id level chroming when using the minimum dichromate levels.

The IWS low-temperature (90°C) chrome dyeing method uses sodium thiosulphate in chroming, and offers the advantages of reduced fibre damage and energy savings as well as reduced levels of chromium in the effl uent. In application of 1: 1 meta l complex, high ac idity (8% H2S0 4) is used to promote migration and , therefore, levelness. Increasing migration reduces exhausti on of chromium and, therefore, hi gh levels of res idual chromium in the bath . Ciba has developed modified 1: 1 complexes (Neolan P) which are applied at pH 3.5-4 but along wi th spec ific auxiliary which promotes dye bath exhaustion, reduces fibre damage and increases shade reproducibility. Another way is us ing su lphamic ac id in place of H2S04 (BASF). This slowly decomposes in hot dye bath and increases pH to reduce ac idity. The initial pH 2.0-2.5 in combination with a specific auxiliary ensures good migration whilst the increase to pH 3.0-3.5 as the dye bath temperature increases, gives good exhaustion.

Xing and Pailthorpe25.26 controlled the pH of dye

bath at < 3.5 for 2 min before dichromate was added and then at > 3.5 after most reduction of dichromate had taken pl ace. Sulphamic acid was used for this purpose. It can react with primary amino groups of wool and also, it hydrol yses at boil , thereby increasing the dye bath pH grad uall y and significantl y in chroming stage. The chromium-VI and chromium­III res idues can be reduced either separately or simultaneously without damagi ng wool. They further found that the rare earth cations can complex with the chrome dyes to form coordination compounds. The coordination compounds formed in this way are not stable and the rare earth cations are replaced by trivalent chromium ions in the afterchroming stage. This ion exchange process allows time for chromium ions to migrate on wool substrate and hence leve l chroming is achieved in spite of low level of dichromate addition. The reduction in exhausted bath was sign ificant without any adverse effects to wool or colour.

In an art icle on improvements in wool dyeing, Bide27 stated that the environmenta l pressures on the mordant dyeing led to the development of a number of methods of low- chromium dyeing. All these method s involve close control of the leve l of

chromium applied, and of pH during dye ing and chroming. In various ways, the methods ensure that most of the chromium is converted from chromium­VI to chromium-III and thi s is complexed by wool rather than di scharged with dye bath.

Acid dosing systems for 1:2 metal complex dyes also reduce fibre damage and speed up dyeing process . Removal of chromium from the bath gives problem of chromium containing sludge. Ciba has developed a new reac tive bl ack for wool, which does not contain any metal and has very high fastness equi va lent to chrome dyes.

Sokolowska et al?8.29 synthesized 1:2 iron complexed azo dyes and compared the ir properties with 1:2 chromium and 1:2 cobalt commercial analogs. They found that the new black dyes are very good for wool and nylon from the light and rubbing fastness point of view, at the sa me time they are ecofriendly.

Julia et al. 3D made use of a luminium as an alternative to chromium and optimised the dyeing conditions to obta in maximum fastness levels for the chrome dyes on wool.

Schuh and Wolf 31 deve loped an environ ment­friendly method for dyeing wool in black shades and hence to avoid afterchroming. It was fou nd that the use of porphyrazi nes enables this to be done.

Rao et al. 32 are of the opinion that it is desirable to replace chrome mordanting in application in anticipation of a total ban on chromium in industrial effl uents and a viable alternative method of mordanting has to be thought of. In the decentralised sector of Indi an industry, natural dyeing has scope for exploitation.

Ahmed et al. 33 carried out the dyeing of the natural dyes kamala, indi go, turmeric and henna on mulberry silk. It was found that the general appearance, lustre and texture of kamala dyed si lk fabric was better than that of other dyed samples .

Most natural dyes are less stable to light when compared to the best synthetic dyes. Gupta34 has tabulated the light fastness ratings of several common Indian natural dyes on wool.

The use of dyes derived from vegetable and animal raw matelials has been discussed in a review35

. The benefi ts of lI si ng natural dye with respect to energy usage, water consumption, biodegradability and allergenic e ffects arc presented together wi th

122 I DIAN 1. FIBRE TEXT. RES., MARCH-JUNE 200 1

information on their CUITent ava ilability, performance with respect to colour yield , fastness properties and technical problems that need to be overcome.

3.3 Finishing of Wool

In textile sector, the manufacture of non-shrinkable wool is the most important process si nce this type of wool a llows hand and machine wash ing, without the garments being damaged by fe lting shrinkage. Numerous procedures are followed for making wool non-shrinkable . Some of these procedures may present problems from an ecologica l point of view.

T he ava il ability of an anti-fe lting treatment compatible with ecology is nowadays a most desirable objecive. Wool treatment with enzymes could be one of these systems. The enzymatic application on wool to make it non-shrinkable has been studied fo r a long time and yet the practical results have not been industrially successful.

The ma in proble m with thi s enzymatic process is that a distinct change in wool handle occurs due to intensive action of the proteases needed to break down the layer of sca les chiefly responsible for wool fe lting. Moreover, the process also causes a loss in strength of the wool since enzyme act ion within the fibres also takes place during this intens ive action.

The achievement of different variations in handle through changes in the surface of wool fabrics by enzymatic processes has now become a rea lity. In thi s way, cashmere like handle can be produced on a relatively smooth and flat woven wool fabric by enzyme treatment. Such enzyme treatments are also suitab le for finishing cheap wool qualities.

Riva et al. 36 worked on shrinkproofing of wool usi ng a proteolytic enzyme, derived from the bacterium Streptomyces Fradiae Protease(SFP), capable of attacking natural keratin and hydrol ys ing some peptide linkages. They found that the shrinkage reduced even at low enzyme concentration and the effect increased wi th increasing concentration and time.

Details are given of an enzymatic method for the anti-fe lting finishing of wooI 3

? Anti-felting finishing of wool can be carried out on current machines in the tex tile finishing industry and the method is environment friendly as no chlorine is involved . The natural charac teri stics of wool are re tained and

whiteness, pilling behaviour and dyeability are improved .

McDeritt and Winkler38 descri bed a method for treating wool with a proteolytic enzyme and a transglutaminase. The method results in improved shrink resistance, handle, appearance, wettability, reduction of fe lting tendency, increased whiteness, reduction of pilling, improved softness , etc. Further, the method also results in reduced weight loss , reduced fibre damage and improved strength.

Au lbach39 described an e nzyme process for anti­fe lting trea tment of wool tops .

Nolte et al.40 studied the enzymatic (proteolytic and lipo lytic) treatments on wool (untreated and shrink-res ist treated) materi al from easy care po int of view and found that such treatments have hi gh potential in substituting norma l processes in order to save environmental hazards of process ing and that the treatments are useful in providing a rage of benefits to wool such as reduced fe lting and pi lling propensity, improved softness and low-temperature dyeability.

3.4 Plasma Treatment of Wool

Ecological and economic restnctlons, which are increasingly imposed on the textile industry, require the development of environment-friendly and economic processes. Effluents originating from wool process ing get polluted with a variety of substances ,e.g. chloro -organic compounds from antifelt fi nishing and dyeing processes or heavy metals from dyeing.

In wool finishing processes such as printing , dyeing and anti-felt finishing, surface morphology plays an impOltant role. The required surface modification is mainly accomplished by wet chemical processes. An appropriate alternative to the conventional techniques is given by the aftertreatment of wool with low­temperature glow discharges.

A number of investigations on the effect of plasma treatment on wool have shown that it leads to improvement in the mechanical propelties of the fibre and also improves the dyeability with acid dyes and reduces the felting tendency. This is due to a surface -specific modification of wool by the plasma pretreatment. On treating wool fibres with di fferent plasma gases, the extent of hydrophilic groups increases and part of cystine in the surface layer is converted to cysteic acid. The density of crosslinks in the surface layer of wool decreases by the reactive species in the plasma gas and this increases the dye uptake.Also, the

SHUKLA : ENVIRONMENT -FRIENDLY PROCESSING OF PROTEIN FIBRES 123

endocuticle and the interscale cell membrane complex are modified to facilitate the diffusion of the dye.

The internal lipids of the cell membrane complex are modified to a certain extent. These changes in the fibre interior are caused by short range ultraviolet radiation which is produced by the low-temperature glow discharge plasma apart from the chemical active species such as electrons, radicals, etc.

Hocker et al. 4 1 observed improved acid, chrome and reactive dye uptake at shorter boiling times with excellent fastness levels on dyeing of glow discharge­treated wool for only 20 min. Also, the method was found useful to enhance chromium uptake, thereby reducing the levels of chromium discharged in the effluent.The plasma treatment leads to a higher degree of reactive dye fixation. Thus, the quality of the effluent from reactive dyeing can be improved by pretrating wool with gas discharges. No AOX was detected in the effluent of the ammonia aftertreatment bath .

3.5 Wool Effluent- Reuse and Recycle

Waste water from wool processing in carpet manufacture is treated for recycling after screening, sand filtration, microfiltration, coagulation with Ah(S04)3, adsorption on coal, second coagulation and heating to 60-80°C for COD, surfactant, suspended solids, and turbidity removal with efficiency >90% (ref. 42).

The key to wool scouring waste water disposal is the recovery of the wool grease to the greatest extent. A new technique, centrifugal extraction, used for grease recovery has been introduced by Liu and Li43. Centrifugal extractor was used as the main separator and hexane was used as the extractor solvent. It is claimed that the technique is especially suitable for scouring the lower grease content effluent.

The system for dyeing of wool called Sirolan Low Temperature Dyeing offers energy savings and reduces the quantity of unused dyestuffs and chemicals discharged44

• The wool scour waste treatment system Sirolan- CF removes 95 % of wool wax and 99% of soil from waste water.

The Environ Proof System from Petric Group Ltd 4 5 is designed to minimise effluent contamination in moth-proofing carpet yarn . It reduces manual handling of the chemical , uses automated liquor preparation and computer monitor application .

Keratinic polypeptides were prepared from wool lint waste by treatment with acids or alkalis at

elevated pressure and temperature in the presence of catalysts46

. These were reacted with fatty acids , acrylic acid or butadiene derivatives and used as protective coatings for wool in dyeing, washing, bleaching and fixing. The quality of wool was improved.

Proteins and protein hydrolyzates as well as modified proteins could be used as textile finishing agents, thus providing a new field of application for protein waste products. These were applied to wool top and fabrics under bleaching and dyeing conditions and their effect on the sorption of the wool fibres as well as their effectiveness as fibre protective agents was studied by Schaefer47 .

Dextran-immobilized Proteinase K was found more active than Proteinase K at pH 8 and 50°C. By limiting the enzyme reaction to the wool fibre surface, the immobilization of the enzyme made it possible to recycle it after an initial period on the wool and offered technical as well as ecological and economical advantages in the processing of wool

48 top .

4 Remarks The ways and means are available at the disposal

of a chemical processor to evolve an ecofriendl y wool/silk product, even with desired value addition . However, certain processes like ultrasound and plasma treatment need to be explored at the bulk processing level.

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