BEHAVIOUR OF BIOPOLISHING ON DYEABILITY AND CERTAIN PROPERTIES OF COTTON FABRICS

Conventional chemical processes are generally severe and fi bre damage may occur. Enzymes are characterized by their ability to operate under mild conditions and as a result processes can be carried out without further damaging the fi bers. Enzymes are also readily biodegradable and therefore potentially harmless and environmentally friendly. Biopolishing enzymes used in biopolishing, off ers a number of benefi ts such as improvement in pill resistance, superior colour brightness, softness and cooler feel. Biopolishing treatment, given to the cotton fabrics using cellulases, often infl uences dyebility and certain physical properties of the fabrics after treatments. This work represents a review of behavior of cellulase treatment on dyeability and various properties of cotton fabrics.


INTRODUCTION
Biotechnology is defi ned as application of biological organisms, systems and processes to manufacturing and processing industries.This is refl ected in ability of enzymes to recognize other biological systems and to catalyse a vast range of specifi c chemical reactions under moderate and much more economic conditions [1].Recent advances in biofi nishing of cellulosic fabrics have led to multiple improvements of surface properties.The main objective of biofi nishing is to upgrade the fabric by removing the protruding fi bers.The conventional methods are temporary, potentially toxic, and fi bers return to the surface after a few washings and form fuzz.The fuzz on the surface of the fabrics constitutes the major reason for customer dissatisfaction.However, by using enzymes in the fi nishing process, the protruding fi bers can be permanently removed from the fabric thus eliminating the fuzz.The enzyme treatment not only keeps the fabric looking new after repeated washings, but enhances Review paper UDC: 677.21.027.615.1 DOI: 10.5937/tekstind1901020M feel, color, softness and drapeability which translates into a higher quality textile or apparel product [2,3].
Enzymes are biological catalysts.A catalyst is any substance which makes a chemical reaction go faster, without itself being changed.All enzymes are made of protein and because they are sensitive to heat, pH and heavy metal ions.
Hydrolytic treatment of cellulosic fabrics and garments with cellulases has become a common treatment step in textile processing [4].Cellulase preparations consist of several diff erent cellulolytic enzymes which act synergistically in hydrolysing cellulose to glucose.
Cotton fabric has several impurities such as fats and waxes, pectinous substances, proteinous matter, ash etc.In order to remove these impurities, scouring of cotton fabric is normally carried out with strong alkali at high temperature and for longer duration.Although, this treatment gives very good results, one of the problems is high loss in weight of cellulosic material.On the other hand, bleaching removes any unwanted colour from the fi bres.In the enzymatic treatment, producers of textile enzymes recommend dosages of approximately 0.05 to 6% of cellulase preparation on garment weight [5].
Biopolishing is an important fi nishing treatment carried out on cellulosic fabrics using acid cellulases to achieve improvement in gloss, luminosity of colours and resistance to pilling, cooler feel and clear surface [6].
Biopolishing of cotton fabrics carried out, either before or after the dyeing process, has an infl uential role on dyeability of the fabrics.Bulky dye molecules used in cotton fabrics react only in the accessible regions of fi bres, which are, also major parts of the substrates for enzyme hydrolysis during biopolishing.Extent of cellulase attack on dyed fabrics depends on molecular size of dyesand aggregation of dye molecules, besides the process conditions [7].
Cellulase pretreatment enhances penetration of alkali during scouring and increases the alkaline degradation of seed fragments in the subsequent process [8].Presence of various components in the total cellulases plays a dominating role in altering surface morphology of the fi bres [9].
Cellulases are inducible enzymes synthesized by a large diversity of microorganisms including both fungi and bacteria during their growth on cellulosic materials.These microorganisms can be aerobic, anaerobic, mesophilic or thermophilic.Among them, the genera of Clostridium, Cellulomonas, Thermomonospora, Trichoderma, and Aspergillus are the most extensively studied cellulase producer [10].

COTTON FIBRE AND HIS STRUCTURE
Cotton, the seed hair of plants of the genus Gossypium, is the purest form of cellulose readily available in nature.It has many desirable fi bre properties making it an important fi bre for textile applications.Cotton is the most important of the raw materials for the textile industry.The cotton fi bre is a single biological cell with a multilayer structure.The layers in the cell structure are, from the outside of the fi ber to the inside, cuticle, primary wall, secondary wall, and lumen.These layers are diff erent structurally and chemically [11].
The primary and secondary walls have diff erent degrees of crystallinity, as well as diff erent molecular chain orientations.The cuticle, composed of wax, proteins, and pectins, is 2.5% of the fi ber weight and is amorphous.The primary wall is 2.5% of the fi ber weight, has a crystallinity index of 30%, and is composed of cellulose.The secondary wall is 91.5% of the fi ber weight, has a crystallinity index of 70%, and is composed of cellulose.The lumen is composed of protoplasmic residues [12].
Cotton cellulose consists of crystalline fi brils varying in complexity and length and connected by less organized amorphous regions with an average ratio of about two-thirds crystalline and one-third non-crystalline material, depending on the method of determination [13].The chemical composition of cellulose is simple, consisting of anhydroglucose units joined by β-1,4-glucosidic bonds to form linear polymeric chains.

CELLULOSE AND CELLULASES
Cellulose is considered as one of the most important sources of carbon on this planet.Agriculture wastes contain a high proportion of cellulosic matter which is easily decomposed by a combination of physical, chemical and biological processes.The major components of these are cellulose and hemicellulose (75-80%) while lignin constitutes only 14%.These wastes have been insuffi ciently disposed leading to environmental pollution.Recycling of agricultural residue can be achieved naturally and artifi cially by microorganisms.Aerobic organisms such as fungi, bacteria, and some anaerobic organisms have been shown to be able to degrade some constituents of these residues.
Cellulases are hydrolytic enzymes that catalyse the breakdown of cellulose to smaller oligosaccharides and fi nally glucose.Cellulases are enzymes which hydrolyze the β-1,4-glycosidic linkage of cellulose and synthesized by microorganisms during their growth on cellulosic materials [14].
The commercially available cellulases are a mixture of enzymes: endogluconases, exogluconases and cellobiases.The application of cellulases in textile processing started in the late 1980s with denim fi nishing.Currently, in addition to biostoning, cellulases are also used to process cotton and other cellulose-based fi bres.Cellulases are usually classifi ed by the pH range in which they are more eff ective and, accordingly, acid cellulase, neutral cellulase and alkaline cellulase.Cellulases are inducible enzymes which are synthesized by microorganisms during their growth on cellulosic materials.
Cellulases were introduced in textile and laundry only a decade ago, they have now become the third largest group of enzymes used in these applications.Microbial cellulases fi nd applications in textile industries as biostoning of jeans, biopolishing of textile fi bers, improved fabrics quality, improved absorbance property of fi bers, softening of garments, improved stability of cellulosic fabrics, of excess dye from fabrics etc. [1,15].Bio-stoning and biopolishing are the best-known current textile applications of cellulases.Denim stonewash enzymes or denim enzymatic treatments has replaced traditionally used pumice stones since it is more environmentally friendly and reduces overall damage to the denim while still producing the "stone washed" which is still very popular today.The advantages in the replacement of pumice stones by a cellulose-based treatment include less damage of fi bers, increased productivity of the machines, and less work-intensive and environment benign [19].
In Table 1 are given the applications of cellulases in the textile industry.

Function Application Reference
Cellulase, preferably neutral and endoglucanase rich Removal of excess dye from denim fabrics; soften the cotton fabrics without damaging the fi bre Bio-stoning of denim fabrics; production of high quality and environmentally friendly washing powders Galante et al., 1998 [16]; Godfrey, 1996 [17] Cellulase, preferably acid and endoglucanase rich

Restoration of softness and colour brightness of cotton fabrics
Production of high quality fabrics Galante et al., 1998 [16]; Godfrey, 1996 [17]; Kumar et al., 1994 [18] 4. BIOPOLISING AND DYEABILITY Biopolishing (de-pilling enzymes) is a biological process in which the cellulose acts on the surface of the fabric.The enzyme molecule is more than a thousand times larger than a water molecule and is therefore too large to penetrate the interior of a cotton fi ber.
The objective of the process is elimination of micro fi brils of cotton through the action of cellulase enzyme.The acidic cellulases, when used in biopolishing, off ers a number of benefi ts such as improve softness and water absorbance property of fi bres, strongly reduce the tendency for pill formation, and provide a cleaner surface structure with less fuzz [20].
In the case of fabrics dyed with direct dyes, the effi ciency of biopolishing is highly infl uenced by size, substantivity, molecular weight and concentration of dyes in the fabrics [21].Fabrics dyed with reactive dyes of diff erent reactive groups exhibit surface roughness after processing with crude cellulases, purifi ed EG and CBH, due to poor biopolishing eff ects compared to the undyed fabrics [21,22].Presence of vat dyes does not infl uence the weight loss during cellulase treatment in many cases [7,23].In denim washing, acid cellulases are used in stonewashing, stoneless washing processes to impart various eff ects to the fabrics in terms of contrast, shade and smoothness [24].

PROPERTIES OF BIOPOLISHED COTTON FABRICS
Presence of various components in the total cellulases plays a dominating role in altering surface morphology of the fi bres [9].Adsorption of cellulases on the surface of substrates takes place immediately after the introduction and remains even after washing [25].Cellulase treatments remove the corrugated spiral structures, causing erosion and longitudinal fi ssures [27].
Water absorbency and water retention properties of fabrics are modifi ed after biopolishing [27].Cellulase treated fabrics show higher energy dissipation under wet condition.Wettability of the fabrics after biopolishing improves by 35-85% depending upon construction of the fabrics [28].Enzyme treatment of cotton fabrics increases transverse swelling of fi bres by 14%.Water retention capacity of cotton fabrics increases by 24-28%, due to splitting of microfi brils [29].
Changes in the degree of polymerization, degree of crystallinity and weight loss of fabrics signifi cantly infl uence tensile properties in terms of tensile elongation, tensile and compressive resilience, shear rigidity, hysteresis and surface friction [30].Strength of dyed fabrics appears to be better (less strength loss) than that of fabrics treated with enzymes and then dyed, though the diff erences are not signifi cant [31].
A linear relationship exists between depilling and weight losses for total cellulase and endo-rich cellulase [28].Slow kinetics of enzymatic degradation of crystalline cotton celluloses allows handle of the fabrics to be improved without excessively damaging the fabrics [32].Harshness produced by the alkaline mercerization can be counteracted by cellulase treatment, while soft handle of liquid ammonia treated samples can further be enhanced by the cellulase treatment.Cellulase treatment lowers the tensile and compressional energy, which essentially means improved handle [32].

CONCLUSIONS
The progress in biotechnology of cellulases and related enzymes is truly remarkable and attracting worldwide attention.New enzymes with high specifi c activity, increased reaction speed, and tolerance to more extreme temperatures and pH could result in development of continuous processes.The textile industry can greatly benefi t from the expanded use of these enzymes as non-toxic, environmentally friendly compounds.Textile processing industry is characterized by high consumption of energy and resources and time consuming processes.
Biopolishing of cotton fabrics off ers unmatched results that can otherwise be achieved using chemical fi nishes.Eff ective enzyme treatment, which depended on fi ber content and treatment level, resulted in progressive weight loss.Biopolishing employs ba-sically the same cellulose action to remove fi ne surface fuzz and fi brils from cotton and viscose fabrics.The polishing action thus achieved helps to eliminate pilling and provides better print defi nition, colour brightness, surface texture, drapeability, and softness without any loss of absorbency.