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Role of Enzymes in Textile Wet-Processing

Enzymes are proteins formed by long linear chains of amino acids linked by peptide bonds. They are present in all living cells which carry out vital functions in the metabolic process, of growth and cellular reproduction, transforming and conserving energy. They are biological catalysts capable of notably accelerating the chemical reactions which occur in living organisms. They are produced by cells, but they are not viruses or bacteria and they cannot reproduce autonomously; they are therefore “alive” even though not biologically active, in determined conditions of pH, temperature, liquor composition and so on.

From the beginning of nineties till today, the biggest development of modern enzymology is made in the textile segment with the introduction of :

cellulase for bio-finishing cellulosic fabrics and garments,
catalase for elimination of hydrogen peroxide after bleaching,
amylase for desizing processes,
pectinase for bioscouring of raw cotton,
protease for the treatment of wool and silk and
laccase for oxidation of dyes such as indigo.

ENZYMATIC DESIZING : Enzymes are bio-chemicals which a specific action on only one type of compound and which bring about a chemical change in it. They are contained within all living system and carry out many functions. For e.g. their role in digestion, the modern agencies used for desizing into three groups. The only amylase family of enzyme have an action on starch (Amylose and Amylopectin). These amylase convert the starch mixture very rapidly to soluble dextrin and then more slowly convert this to reducing substances and sugar, such as maltose.

stepsEnzymes suffer from one disadvantage, that if the condition of temperature and pH are not favorable, their desizing activity is destroyed. After passing fabric from desizing solution fabric is batched for 8-12 hours. During this time starch is converted from insoluble starch to soluble alpha-glucose. This water soluble product could be easily washed out in actual practice. Most of the companies offer 2-3 types of desizing enzymes that can be used for different temperature and pH ranges. At Matex, we have developed a universal kind of desizing enzyme, Matzyme BIO-DS, that can be used at varied pH and temperature range.

ENZYMATIC BIO-SCOURING : The bio-scouring of raw cotton as an alternative to alkaline scouring has been studied in depth over recent years. The basic idea is simply that of hydrolyzing those non-cellulosic components responsible for water repellency of cotton, using enzymes . This is done by using a specific degradation process in delicate pH and temperature conditions and then removing them with a successive hot rinse.

The pectinase destroys the structure of the cuticle, hydrolyzing the pectins and removing the links with wax and protein, as well as between these and the remaining fibre structure. The pectin links the wax to the cellulose of the primary wall, but it is not necessary to eliminate all the pectin for providing hydrophilic properties. Even when 30% of the residual pectin remains on the fabric, a wash at 80-90°C after a dwelling stage eliminates the solubilized waxes.

Advantages of the Bio-scouring :

– Saving of water and energy.
– Lower environmental impact and easier to treat wastewater.
– Better compatibility with other processes, machinery and materials.
– Lesser attacks on the fibre structure, loss of weight and resistance, with improved quality of the article.
– Better and more uniform affinity for dyes.
– In the case of woven fabrics, the possibility to combine the desizing and bio-scouring steps in just one;
– In the case of knitted fabrics, combining bio-scouring with bio-polishing using cellulase, with a jet or overflow machine.
– Possibility of scouring cotton even when blended with more delicate fibres.

ENZYMATIC BIO-FINISHING : The uses of cellulase in textiles permits the development of a new range of finishing and “fashion effect” industrial processes for fabrics and garments, with an absolutely environment-friendly approach. Bio-polishing or Bio-finishing with cellulase is carried out both on pieces as well as made up garments and it can be carried out before dyeing or after dyeing also to give a sort of stone-wash effect. Matzyme BIO-F is a cellulase enzyme that eliminates the dead/immature cotton whereas Matzyme DS is effective in de-pilling as well as surface hair removal.

clip_image004Bio-polishing treatments permit:
– Elimination of dead or immature cotton, of neps and surface hairiness.
– “Natural” softening with an improvement of hand and drapability.
– Permanent prevention of reiterated fibrillation and pilling.
– Increase in hydrophilic properties, particularly in the case of terry fabrics.
– Better cleanliness and brightness, as well as uniformity of dye.
– Better overall quality of the material.
– The possibility of creating finishing to suit new and original fashion effects.
– Use of an entirely environmentally friendly process.

ENZYMATIC BIO-WASHING/BIO-STONING :

There are two types of enzyme washes for denim :

  • Stone-wash : This is done to achieve stone-wash effect to denims. Cellulase enzymes are natural proteins which are used in denim garment processing to get stone wash look on to the denim garments without using stones or by reducing the use of pumice stone. There are many limitations and drawbacks associated with stone washing process, which can be overcome by using new enzyme based washing technology. Cellulase attacks primarily on the surface of the cellulose fibre, leaving the interior of the fibre as it is, by removing the indigo present in the surface layer of fibre. Matzyme BIO-W is one such type of cellulase enzyme that give excellent stone-wash effects.
  • Cellulase-wash : This is done to achieve a wash down appearance on denim garments. This enzymes are selective only to the cellulose and will not degrade starch. Under certain conditions, their ability to react with cellulose will result in surface fibre removal (weight loss). This will give garments a washed appearance and soft hand. Matzyme BIO-G is especially designed for this cellulase washing of denim garments with low back-staining that offers improved lustre.

clip_image006Advantages of enzyme washing

– Soft handle and attractive clean appearance is obtained.
– No severe damage to the surface of yarn.
– Simple process handling and minimum effluent problem.
– Better feel to touch and increased gloss or luster.
– Prevents tendency of pilling after relatively short period of wear.
– Can be applied on cellulose and its blend.
– Due to mild condition of treatment process is less corrosive.
– More reproducible effect can be obtained.
– It allows more loading of the garment into machines.
– Environmental friendly treatment.
– Less damage to seam edges and badges.
– Wear and tear of equipment is minimum due to absence of stone.
– Use of softener can be avoided or minimized.
– Easy handling of floor and severs as messy sludge of stones does not interfere.
– Due to absence of stone, labour operation of stone removal is not required.
– Homogenous abrasion of the garments.

ENZYMATIC PEROXIDE KILLING :

Matzyme VHK is a catalase enzyme derived from the submerged fermentation of a genetically modified strain of Aspergillus niger. It has been proven to be highly effective in catalyzing the decomposition of hydrogen peroxide into oxygen and water.

2H2O2                           VHK                                                  O2 + 2H2O

                                  

In textile wet-processing, this is often the most preferable method of hydrogen peroxide removal after bleaching step as the enzyme and the breakdown products are totally inert to reactive dyestuffs.

In treating natural fibres composed of proteins, like silk and wool, protease can be used. On wool, with some protease base enzymatic preparations, interesting effects can be achieved which have some commercial importance, such as:
– Softening and modification of hand characteristics.
– Anti-pilling and surface cleaning.
– Better drapability.
– “Aged” look for garments of clothing.
– Improved comfort.

In the case of anti-pilling treatment for wool woven and knitted fabrics, a protease has been launched on the market which can be used solely on pre-chlorinated wool. Unfortunately, treatments using only protease do not confer anti-felting properties on wool.

Table. 1 shows the possible uses of protease enzymes in wool.

Table :1

1) Limit the typical tendency of wool to “shrink and felt”
2) Solve dimensional stability problems
3) Provide “machine wash” characteristics for the fabric
4) Eliminate the negative properties emerging in fabric care processes (e.g. hygroscopic expansion)
5) Enhance the fabric colouring
6) Prevent the pilling effect after some finishing processes
7) Eliminate motes (in alternative to the conventional carbonising methods)
8) Bio-scouring and Bleaching of wool
9) Possibility of enhancing the original fineness and softness characteristics of wool
10) Enhance the evenness of wool fabric fibres subjected to pre-dyeing treatments
11) Obtain stone-wash effects on yarn dyed fabrics, but above all on piece-dyed wool fabrics

ENZYMATIC DEGUMMING : Enzymatic degumming of silk using protease permits the sericin to become hydrolyzed and at the same time other protein residues deposited by the silkworm. Through this enzymatic treatment, special effects are sought for softening and for the hand (e.g. peach-skin, draping, suede-like effects etc) demanded by fashion or the market. It should, however, be noted that, while protease on silk can certainly give interesting and commercially valid results, they are still difficult treatments to carry out correctly in order to avoid irreversible damage.

Recently a new oxido-reducing (laccase) enzyme was also proposed for breaking the irreversible oxidative breaking of indigo which gives denim garments a “cleaned” effect on back-staining (using low quantities) or bleaching (using higher quantities).

Enzymology is however finding increasingly large space in the practice of preparing and finishing of textiles.

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