KhushbooShrimali, Ph.D. Scholar, ShrimatiNathibaiDamodarjiThackersaey University, Mumbai
Guide Name: Prof. ElaDedhia, NirmalaNiketan College of Home Science, Mumbai
Enzymes are generally globular proteins consisting of long linear chains of amino acids that fold to produce a three-dimensional product. Each unique amino acid sequence produces a specific structure possessing unique properties. Enzymes are extremely efficient and highly specific biocatalysts. The primary sources of enzymes for commercial use are animal tissue, plants and microbes.
Enzymes are naturally occurring substances and are often not readily available in sufficient quantities for industrial use. Although to facilitate industrial use, desired enzyme can be produced by isolating microbial strains and optimizing the conditions for growth. There is a large number of microorganisms which produce a variety of enzymes (Boyer, 1971; Fersht, 2007).
The rise in the level of various kinds of pollutions has created a major awareness among the consumers for using eco-friendly products. Governments of many countries have also imposed limitations on release of pollutants. This in turn has resulted in a rise in demand for green and clean processes. One of the sectors of industry that holds a major share in the global pollution is textile industry. Therefore use of enzymes on textiles play a key role as an alternative process for textile processing and have become an integral part of the textile processing industry.
The process of use of enzymes is energy saving and does not require any special equipment for heat resistance, pressure or corrosion. Their efficiency, high biodegradability and the mild conditions of working mark their use in a wide range of industrial applications. Enzymes work only on renewable raw materials. Fruit, cereals, milk, fats, cotton, leather and wood are some typical candidates for enzymatic conversion in industry (Uhlig, 1991; Ruttloff, 1994). Out of the 7000 enzymes known, only about 75 are used in the textile industry (Quandt&Kuhl 2001).
Enzymes are biocatalyst and can speed up the chemical process without even being consumed in the process. Usually most enzymes are not reusable after a reaction but some enzymes can be released again and mark their use in another reaction also. For each type of reaction in a cell there is a different enzyme and they are classified into six broad categories namely hydrolytic, oxidising and reducing, synthesising, transferring, lytic and isomerising.
The specificity of enzymes is more when compared to other inorganic catalysts such as acids, bases, metals and metal oxides. The molecule that an enzyme acts on is known as its substrate, which is converted into a product or products. Originally, enzymes were classified on the basis of functions they perform. But later, in 1956 an International Commission on Enzymes (EC) was established by the International Union of Biochemistry (IUB), in consultation with the International Union of Pure and Applied Chemistry (IUPAC), to classify hundreds of enzymes that had been discovered by that point. A standardized terminology was also formed to name the newly discovered enzymes systematically.
The commission divided the enzymes into six categories depending on their basic function (Uhlig, 1991; Ruttloff, 1994):
- EC1 Oxidoreductases: catalyze oxidation/reduction reactions.
- EC2 Transferases: transfer a functional group.
- EC3 Hydrolases: catalyze the hydrolysis of various bonds.
- EC4 Lyases: cleave various bonds by means other than hydrolysis and oxidation.
- EC5 Isomerases: catalyze isomerization changes within a single molecule.
- EC6 Ligases: join two molecules with covalent bonds.
Enzymes used in Textiles
Mainly two types of enzymes are used in textile processing industry. The desizing process includes the use of Amylases and in the finishing area cellulases are used for softening, bio-stoning and reducing of pilling propensity for cotton goods. The other enzymes used in the processing of textiles are pectinases, lipases, proteases, catalases, xylanases etc.
Application of enzymes on textiles
In textile industry, there is a wide use of enzymes because of their beneficial nature(Uhlig, 1991; Ruttloff, 1994):
- They accelerate reactions,
- Act only on specific substrates,
- Operate under mild conditions,
- Safe and easy to control,
- Can replace harsh chemicals
- Are biologically degradable i.e. biodegradable
The various applications of enzymes in textile area includes the effect of fading of denim and non-denim, bio-scouring, bio-polishing, wool finishing, peroxide removal, decolourization of dyestuff, etc. (Cavaco-Paulo and Gubitz, 2003; Chelikani et al., 2004; Barrett et al., 2003; Sharma, 1993; Nalankilli, 1998; Shenai, 1990).
Enzymes in various textile processes
A wide variety of enzymes have been used on textiles since ages. The current application of enzymatic processing in the textile industry revolves mainly around hydrolases and now to some extentoxidoreductase. The enzymatic desizing of cotton with α-amylases is state-of-the-art since many decades (Marcher et al., 1993). The other cotton pre-treatment and finishing process includes the use of cellulases, pectinases, hemicellulases, lipases and catalases (Meyer-Stork, 2002). The enzymatic degumming of silk is done withsericinases (Gulrajani, 1992), the felt-free-finishing of wool with proteases (Fornelli, 1994) and the softening of jute with cellulases and xylanases (Kundu et al., 1991).
When compared with the conventional processing, the enzymatic processing has been proved advantageous like its use in catalytic concentrations at low temperatures and at pH-values near to neutral (Uhlig, 1991; Ruttloff, 1994).
Amylase is a hydrolytic enzyme which catalyses the breakdown of dietary starch to short chain sugars, dextrin and maltose which gives uniform wet processing. The advantage of these enzymes is that they are specific for starch, removing it without damaging to the support fabric. An amylase enzyme can be used for desizing processes at low-temperature (30-60ºC) and optimum pH is 5,5-6,5 (Cavaco-Paulo and Gübitz, 2003).
Enzymatic Scouring (Bioscouring)
Scouring means the removal of non-cellulosic material present on the surface of the cotton. Enzymescellulase and pectinase are combined and used for Bioscouring. Pectinase destroy the cotton cuticle structure by digesting the pectin and removing the connection between the cuticle and the body of cotton fibre whereas Cellulase destroys the cuticle structure by digesting the primary wall cellulose immediately under the cuticle of cotton. Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) of enzymatic scouring process are 20-45 % as compared to alkaline scouring (100 %). Total Dissolved Solid (TDS) of enzymatic scouring process is 20-50% as compared to alkaline scouring (100%). Enzymatic scouring results in very soft handle compared to harsh feel in alkaline scouring process. It also minimizes health risks hence operators are not exposed to aggressive chemicals (Pawar et al., 2002).
Cotton bleaching is done to decolourise natural pigments and give a pure white appearance to the fibres. Mainly flavonoids are responsible for the colour of cotton (Hedin et al., 1992; Ardon et al., 1996). The traditional processing of cotton requires high amounts of alkaline chemicals and generate huge quantities of rinse water. Therefore, the conventional bleaching agent hydrogen peroxide can be replaced by an enzymatic bleaching system which would result in a better product quality due to less fibre damage and savings on washing water needed for the removal of hydrogen peroxide.
For this procedure, Amyloglucosidases, pectinases, and glucose oxidases are used as they are compatible concerning their active pH and temperature range.
A finishing process to improve fabric quality and reduce fuzziness and pilling property of the cellulosic fibre is called Bio polishing. This process involves the action of cellulose enzyme in order to discard micro fibrils of cotton (Stewart, 2005; Cavaco-Paulo, 1998; Cavaco-Paulo et al., 1996; Lenting and Warmoeskerken, 2001).
Bio polishing is a finishing process to obtain a cooler, cleaner, lustrous, soft fabric.
Enzymatic treatment to denim
A fading effect is given to the denim in its finishing process. The conventional method of giving this finish was done using sodium hypochlorite or potassium permanganate was used called as pumice stones (Pedersen and Schneider, 1998). Denim is heavy grade cotton and the dye is mainly adsorbed on the surface of the fibre due to which fading can be achieved without considerable loss of strength.
The use of pumice stone carries some disadvantages with it like:
Pumice stones cause large amount of back-staining.
Pumice stones are required in very large amount.
They cause considerable wear and tear of machine.
The enzymatic finishing of denim fabric is done with cellulase enzyme as it loosens the indigo dye on the surface of denim. This process is known as “Bio-Stonewashing”. A small dose of enzyme can replace several kilograms of pumice stones. This process results in less damage to garment, machine and less pumice dust in the laundry environment.
More recently, some authors showed that laccase was an effective agent for stone-washing effects of denim fabric with and without using a mediator (Campos et al., 2001; Pazarloglu et al., 2005).
Use of enzymes not only provides us with eco-friendly environment but also saves a lot of money by reducing water and energy consumption thus reducing the cost of production. Enzyme producing companies are also coming up with more new technologies and products in this area.
The major limitation in the use of enzyme processing is the high cost of enzymes. This technology can still become a widely and extensively used technology if its cost could be managed. In textile processing the enzyme can be successfully used for preparatory and finishing process like desizing, scouring and bleaching and is appropriate to create a cleaner and greener environment and product too.
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