| INTRODUCTION | | | | A lot of dynamism is thus going to be apparent in the |
| Textile industry is a mother industry upon which | | | | coming years with efforts to improve market |
| millions of people are dependent. Out of the various | | | | shares.Mercerisation improves lustre, enhances |
| sectors of textile's production, the processing segment | | | | dyeability, and improves the strength and also the soft |
| is one of the weak sectors although weaving and | | | | feel. For the cotton fabrics 50 to 54oTw (22.5%) |
| garmenting also fall in the same category. Share of | | | | sodium hydroxide solution is used at room temperature |
| Indian textiles and clothing production is 3.3% of the | | | | for 45 to 60 seconds in which case caustic pick up |
| world production and the world textile export has been | | | | varies from 25 to 40%. Normally 10% of the caustic is |
| growing at the rate of 5.58% per annum and clothing | | | | consumed in the operation on the weight of the fabric |
| export 6.44% per annum. The overall textile and | | | | and 75% of the caustic is recovered. For the viscose |
| clothing export growth rate is around 6% per annum. | | | | rayon 8 - 10% caustic soda is to be used the |
| We can say, the finished products are being more | | | | parameters of mercerisation followed by scouring and |
| welcomed than the unfinished textiles.From the | | | | washing should be so adjusted that the final fabric |
| business strategy point of view too, the maximum | | | | should be almost neutral. Wet on Wet mercerisation |
| value addition is possible when we go for supplying | | | | and hot mercerisation are the additional two |
| finished material as RMG fabric or the Garments. Due | | | | processes. In the latter 60oC temperature is used |
| to the increase in the demand for clothing, the | | | | causing the even effect on the skin and core of the |
| processed goods are now in large demand.CHANGE | | | | fabric and the better dyeability can thus be obtained. |
| IN TRENDS | | | | Hot mercerisation can make use of shorter machine. |
| There are lots of factors which are responsible for | | | | The efficiency of such mercerisation operation can |
| the present day change in scenario of the wet | | | | reflect in barium activity number or deconvolution count, |
| processing of textiles. Good quality at competitive | | | | the former method is however preferred to |
| prices is becoming the key factor with trade | | | | latter.DYEINGThe proper selection of dyes and |
| globalisation. Hence, the wet processing sequence is | | | | machines as well as the dyeing aids are the key |
| accordingly being changed, keeping in mind the end | | | | factors to get right first time products. The shade |
| objective of obtaining high quality goods at the most | | | | matching, the production of solid shades and defect |
| competitive prices.To get the best quality fabric of | | | | free dyeing are the day to day challenges faced by |
| international standards, one needs to have the best of | | | | the dyers.Once the fabric undergoes controlled |
| spinning and weaving technologies employed, before | | | | pretreatments and brought in a ready to dye stage, |
| subjecting the fabric to various operations of wet | | | | the dyeing becomes the next challenge to get uniform |
| processing. However, for a textile wet processor, it | | | | and consistent shades right at the first attempt (RFT). |
| becomes the most challenging task to get the right | | | | The proper selection of dyes and machine depends |
| shades at first time and also at competitive cost with | | | | upon number of factors. The first and the topmost is |
| the best quality. The high performance standards | | | | the nature of the fibre, the variety and the quantity of |
| expected by the consumer are to be met with, in | | | | fabric being processed as well as quality standards |
| addition to the adherence to the norms of eco-friendly | | | | required. Number of challenges faced by the dyer |
| processing, which is the need today. All these | | | | includes shade matching, production of solid shade and |
| characteristics lead the direction of research in textile | | | | defect free dyeing. With the general knowledge of the |
| wet processing and the various operations actually | | | | nature of the dyestuff and performance properties as |
| carried out in the processing industry. Many a times, it | | | | well as their applicability on various fibres, the selection |
| has been observed that there is a huge difference in | | | | of a given class of dye is not a big problem. However, |
| the process sequence to be ideally followed vis-a-vis | | | | depending upon structure of individual dyes, its |
| the one actually practiced at the shopfloor. Otherwise, | | | | chormophores and auxochromes, hues and |
| e.g., how do you explain high twisting of microdenier | | | | substantivity differ. e.g. as a class, reactive dyes react |
| yarn and weight reducing the fabric made out of it with | | | | with the cellulosic fibres and thus said to be giving vary |
| causticisation process? There are many other | | | | good performance properties. But they suffer many a |
| examples.Wet processing can be broadly divided into | | | | times with poor extent of fixation, problem of |
| pretreatment, dyeing, printing and finishing. Irrespective | | | | hydrolysis, sensitivity to metal ions, poor chlorine bleach |
| of the various stages of operations falling under the | | | | fastness etc.The use of salt in reactive dyeing further |
| above mentioned classification, every single method | | | | adds TDS to the effluents. The advancement in this |
| followed finds its basis and objective of the following:. | | | | class of dyes are thus aimed at improving their |
| Maintenance of high quality | | | | exhaustion and fixation by improving the reactivity and |
| . Cost effectiveness | | | | decreasing their sensitivity to temperature and pH |
| . Better performance | | | | variations. HE and ME dyes showing high exhaustion |
| . Lower effluents and minimum input cost | | | | are thus recommended for dyeing of Knit goods, |
| . Minimum use of chemicals | | | | which is carried out on winches where a lot of |
| . Environment friendly process | | | | variation in temperature and pH occur. While the |
| . Application of latest machinery which can guarantee | | | | former is homo bi-reactive system, the latter one is |
| the reproducibility of the product once | | | | hetero bi-reactive system and their fixation claimed to |
| approved.PRETREATMENTDegumming | | | | be as high as 85%. The reactive dyes of LS type |
| DesizingAlthough, acid desizing, rot steeping and | | | | which make use of low salt and some based on |
| enzymatic desizing are quite well accepted methods | | | | fluorine are increasingly recommended. While dyeing |
| of desizing the fabric containing starch based sizes, | | | | the compound shades, the rate of dyeing as well as |
| different types of amylase base enzymes are | | | | compatibility of dyes have to be taken into |
| available in the market and as its consumption as well | | | | consideration so that the shades do not go off the |
| as production is increasing day by day, the cost of | | | | tone.The vat dyes are the costliest class of dyes, |
| enzymes is coming down and the processors thus | | | | although they offer best of performance properties |
| been able to make use of such enzymes, which are | | | | and many a times in polyester/cotton blends, disperse- |
| quite specific in action with respect to concentration, | | | | reactive and disperse-vat are recommended. In such |
| pH, temperature and do not pose any danger of fiber | | | | blends selection of disperse dyes is also equally |
| degradation.In pretreatment, either the yarn or the | | | | important which are stable to alkali so that, once the |
| fabric requires to be treated with such chemicals that | | | | polyester component is dyed, the vat pigment |
| subsequently are turned to be receptive to the dyes | | | | mechanically deposited is reduced in alkaline blank vat |
| and chemicals as well as finishes. In case of silk, most | | | | solution. While the vat dye thus gets fixed on the |
| of the quality goods manufacturers degum the silk in | | | | cotton component the additional reduction clearing |
| the hank form before subjecting it for bleaching and | | | | treatment is totally eliminated in this case. The recent |
| then dyeing. Since, they intend to use these yarns for | | | | trend is also to cationise cotton or the cellulosic |
| woven designs; the treatment in the hank form as well | | | | material and apply the reactive dyes in acidic |
| as its colouration becomes handy. Besides the age-old | | | | conditions so that the protonated or cationised cotton |
| method of degumming of silk using Marsellies soap or | | | | adsorbs the reactive dye anions at the enhanced rate |
| sometimes 501 soap, nowadays enzyme like | | | | and subsequent fixation in alkaline medium gives very |
| Degummase is used to remove the sericin, the | | | | high shade build up. Number of quaternary amines and |
| cementing agent of the silk fibroin. Many also prefer to | | | | cationising agents are used towards this purpose and |
| remove the sericin to a limited extent, so that the | | | | in many cases reactive dye systems can eliminate the |
| strength of silk yarn is kept intact. Companies | | | | use of salt. This not only reduces, the TDS of the |
| like Himatsingka exporting almost 100 per cent of their | | | | effluent, but also drastically reduces unfixed dye being |
| products - upholstery and curtain materials, have found | | | | drained out in the effluent. Polyester fibre dominating |
| an enviable position in this business. The Central Silk | | | | the apparel scene, it is but natural that one chooses |
| Board as well as the ministry of textiles are working | | | | Disperse dyes. While they are being selected, one |
| on improving the quality of silk and training silk reelers | | | | needs to take into consideration their energy class, |
| so that India can not only increase the silk yield but also | | | | diffusion number, migration rating etc. The dyeing is |
| improve its share in the silk trade.Enzymes such as | | | | based on diffusion-controlled mechanism and thus for |
| proteases are also used in wool processing. Not only | | | | the compound shades, it is highly necessary that these |
| are the scales removed, imparting anti-felting property, | | | | dyes are selected from the same subclass so that in |
| but the wool fibre is found to give improved dye | | | | general the performance properties and shade build up |
| uptake. Cotton fabric is normally subjected to desizing | | | | are not drastically affected. Serilene brand of VX dyes |
| and a number of research methods talk about desizing | | | | of Yorkshire chemicals, UK offers most compatible |
| with hydrolytic and oxidative desizing agents, plasma | | | | range of disperse dyes in which case shade prediction |
| treatment, etc. The rot steeping, acid desizing and | | | | and matching become relatively easy and their edge in |
| enzymatic desizing are the conventional hydrolytic | | | | performance can be apparent from pale to dark |
| desizing techniques which are widely followed. | | | | shades. Now a days, trend is to shorten dyeing cycles |
| However, the recent trend is to use the size paste | | | | and many a times one bath dyeing of the binary and |
| based on acrylic and PVA formulations which are | | | | ternary blends is attempted. Disperse dyes applicable |
| easily washable and the quantity of starch in the size | | | | in alkaline conditions are also offered by some of the |
| paste is greatly reduced so that BOD in the effluent is | | | | manufacturers which are most suitable in polyester |
| accordingly diminished.Different types of enzymes | | | | cotton blends where the cotton component requires |
| mainly "amylase based" are in the market, which being | | | | alkalinity for application of reactive, vat or sulphur dyes. |
| concentration specific, pH specific and temperature | | | | One of the methods developed makes use of |
| specific, are most satisfactorily used. Some of the | | | | simultaneous disperse-acid dyeing and finishing of |
| enzymes require sodium and potassium chloride to | | | | polyester/cotton bland .Initially the method was |
| increase their activities, whereas the heavy metal ions | | | | developed for one bath acid dyeing -resin finishing of |
| such as mercury, copper, zinc, iron are strong inhibitors | | | | cotton/cellulosic material.The selection of acid dye |
| for the action of enzymes of amylase type. Although | | | | however is quite critical and it should have |
| the enzymes - pancreatic, bacterial and malt type | | | | abstractable-H in its amino group substituent .Finishing |
| work in the range of 6-7, 5-7 and 4.6 - 5.2 pH range | | | | agent like DMDHEU gets attracted to cotton to one |
| and the temperature 40-55ø, 60-70ø and | | | | end while anchoring or holding acid dye molecules on |
| 40-50øC respectively, special desizing agent such | | | | the other end. Dyeing was quite fast and so called non |
| as Finogene DH 250 N, (Korean company) works in | | | | substantive acid dyes can be applied on cotton |
| the range of pH 5-9 and the advantage of such | | | | simultaneously resulting in improvement in crease |
| enzyme is that the cotton waxes get partially | | | | recovery angles. When the same system is extended |
| emulsified due to the alkalinity, which can be removed | | | | to polyester/cotton blend for disperse-acid-dyeing-cum |
| in subsequent operations. Thermozyme, an enzyme | | | | resin finishing from single bath by pad - thermosol |
| stable at high temperature is known to bring about | | | | technique, it was found that polyester and cotton |
| desizing almost instantly at higher temperature.Oxidising | | | | component can be dyed with respective dyes, and |
| type of desizing agents are energy saving, acting on all | | | | heat-setting as well as finishing take place almost |
| the sizes and offer shortening of the process | | | | simultaneously. Washing- off problem in reactive dyes |
| sequence. Sodium bromite and potassium persulphate | | | | is always a challenging task which impairs the fastness |
| are quite important oxidative agents.ScouringAlthough | | | | properties of the dyes if hydrolysed dye is not fully |
| soda boil is so far the best method of scouring, the | | | | washed out. Though non-ionic detergent is |
| efforts are on to make use of pectinase and lipase | | | | recommended for the same, the recently introduced |
| together as one shot chemical in which case, it is | | | | Bio rinsing making use of Bylase RP / Assist RP, the |
| understood that while pectinase will loosen the | | | | enzyme which decolorises selectively the hydrolysed |
| hydrophobic waxes due to the hydrolysis of pectins | | | | dyestuff from the fabric and also the unfixed reactive |
| and the lipase can bring about the hydrolysis of | | | | dyestuff in unexhausted bath provides a great |
| waxes.The persulphate could be incorporated in the | | | | promise. This reduces the consumption of water, |
| scouring process, eliminating separate desizing stages. | | | | energy and time as it is claimed to be quite efficient |
| Simultaneous desizing and scouring can be carried out | | | | washing- off process. The use of cationic dye-fixing |
| by padding the cloth in 2-3 gpl potassium persulphate | | | | agent is quite common in the case of direct dyed |
| and 40-50 gpl NaOH and subsequently steaming in J | | | | material which is obvious as they have very high |
| box. While desizing can be achieved in 1-3 mins, | | | | solubility in water imparting poor wash fastness |
| scouring takes 90 to 120 mins, in J box or 2-10 minutes | | | | properties. However, due to the presence of unfixed |
| in vapour locks machines. Of all these methods, acid | | | | hydrolysed dye on the fabric as a result of incomplete |
| steeping, enzyme and bromite desizing and | | | | washing-off, it becomes essential even in case of the |
| simultaneous scouring and desizing with persulphate | | | | reactive dyed material, to subject it for the treatment |
| are the cheapest as far as cost considerations are | | | | of cationic dye fixing agent. The hydrolysed dye acting |
| concerned. As far as scouring operation is concerned, | | | | as a direct dye being held on the fabric by hydrogen |
| although a number of attempts have been made at | | | | bonding, complexes with cationic dye fixing agent and |
| scouring the fabric using Lipase type of enzymes to | | | | brings about fixation of dye, improving its wet rubbing |
| hydrolyse the triglycerides which are hydrophobic in | | | | fastness at least by half a grade.In case of garment |
| nature, there has been no substitute really worth | | | | dyeing, in case of the post finishing process, reactive |
| mentioning to the soda boil, which can give expected | | | | dyes can be used provided the garments so finished |
| absorbency.The pectinase enzyme is used to | | | | are already subjected during finishing with certain |
| hydrolyse the pectins and remove the same from | | | | nitrogen containing additives. These additives used |
| cotton causing loosening of the hydrophobic waxes | | | | during finishing render the dyeability to the finished |
| which are easier to get rid of in subsequent washing. | | | | garment and upto about 85% dyeability can be |
| The action of lipase subsequently brings about | | | | regained even after finishing the garment at the |
| hydrolysis of such hydrophobic waxes and thus | | | | intermediate level, which otherwise is known for |
| nowadays, the pectinase and lipase are getting | | | | displaying only 15-20% dyeability. This phenomenon of |
| increasing importance in the process of scouring. One | | | | additives improving the finished goods dyeability works |
| research study indicates the pretreatment of the fabric | | | | similar to process of Cationisation and requires almost |
| with chloroform followed by pectinase treatment. But | | | | similar conditions as used in dyeing of cationised |
| one can understand the limitation of application as | | | | cotton.From the environment point of view the general |
| chloroform is used here to dissolve non-cellulosic | | | | trend is to make use of non-dusting powders of the |
| impurities.Solvent assisted scouring makes use of five | | | | dye and thus granules are preferred to dusting |
| per cent solvent, which is emulsified and also can be | | | | powders. Higher concentrates of dyes are also used |
| coupled with bleaching and desizing. In this case the | | | | to decrease the volume being handled. As the |
| hydrogen peroxide not only acts as bleaching agent | | | | automation is increasingly accepted and high quality |
| but also as an oxidative desizing agent. In other words, | | | | standards become pivotal part of the business, the |
| alkaline scouring till today remains the most suitable | | | | most modern machines with auto dispensing systems |
| way of scouring. Solvent scouring is of theoretical | | | | are coming in use .To cater to such modern machine |
| importance so far as cotton is concerned. However, in | | | | with colour kitchen and auto dispensing systems, liquid |
| case of silk and wool, solvent such as | | | | dyes become an important and essential formulation. |
| perchloroethylene is used, provided sophisticated | | | | Presently the Dispersol and Procion T dyes are |
| machinery is available for total recycling of the solvent. | | | | supplied in liquid formulation and so also some of the |
| The carbonisation of wool after solvent treatment is | | | | soluble sulphur dyes. However, very soon most of the |
| done with H2SO4.Kier and J boxes are used for | | | | dyestuffs would be required to be supplied in liquid |
| scouring of cotton fabric with soda boil at 4-5 per cent | | | | formulation, so that most modern automatic and |
| on the weight of the fabric with wetting agent upto 3 | | | | microprocessor based systems of dyeing can be |
| gpl. Sodium sulphite (about 1%) brings down the | | | | made use of, especially in which case the shade |
| scouring time in the pressure boil which otherwise | | | | reproducibility is of utmost importance. The Procion T |
| requires 8-12 hours at 30 PSI (1.5-2 Kgs/Cm2). Open | | | | dyes are acid fixable liquid reactive dyes based on |
| width scouring though initially was carried out on the | | | | phosphoric acid condensation products and they also |
| jiggers, now pad roll process can also be used. The | | | | carry the potential of making the fabric flame retardant |
| recently introduced continuous bleaching range of | | | | while being the integral part of the fabric.To continoue |
| Benninger is becoming popular although capital | | | | to read more articles on Textile, Fashion, Apparel, |
| investment is high. The small processing units can | | | | Technology, Retail and General please visit If you wish |
| make use of modern jiggers for scouring, bleaching | | | | to download/republish the above article to your |
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| 1,400 kg (3,000 mts bottom weight) can be | | | | Source". Also, you have to make it hyperlinked to our |
| processed.Key pointsIncreasing environment | | | | site.Copyright © 2006Fibre2fashion has emerged |
| consciousness leading to eco-friendly textile processing | | | | as a distinctive B2B platform for global Textile, Apparel, |
| has driven our R&D efforts in search of safe | | | | Fashion and Retail and allied industries. offers business |
| substitutes for the dyes and finishes. | | | | solutions, news, articles and information that help to |
| The specific needs of the customers such as | | | | survive and sustain in the most hostile and competitive |
| flame-retardancy or anti-bacterial properties have | | | | business environment. |
| further created challenges in this field. | | | | |