By: M. Subramanian Senthil Kannan and R. Nithyanandan

ABSTRACT:

The fabric should be free from natural & added impurities before it goes for colouration i.e. dyeing or printing. Some of the chemicals like caustic soda, soda ash, hydrogen peroxide, hydrochloric acid, detergents and auxiliaries that are used at different stages preparatory process to remove such an impurities are found to be harmful to the environment. Caustic soda and soda ash though are safe chemicals; but they cause high TDS in effluent. Detergent and surfactant add phosphorus to the outlet and require special treatment. They are also not easily biodegradable. Auxiliaries like wetting agent contain phenol, which are not removed easily in the course of effluent treatment. Modern wet processing industries are followed the enzymes in the preparatory process instead of using harmful chemical because enzyme are more convenient, effective and environment friendly.

INTRODUCTION:

Enzymes are biocatalyst, and by their mere presence, and without being consumed in the process, enzymes can speed up chemical processes that would otherwise run very slowly. After the reaction is complete, the enzyme is released again, ready to start another reaction. In principle, this could go on forever, but in practically most catalysts have a limited stability, and over a period of time they lose, their activity and are not usable again. Generally, most enzymes are used only once and discarded after; they have done their job.

Enzymes are very specific in comparison to inorganic catalysts such as acids, bases, metals and metal oxides. Enzyme can break down particular compounds. In some cases, their action is limited to specific bonds in the compounds with which, they react. The molecule(s) that an enzyme acts on is known as its substrate(s), which is converted into a product or products. A part of large enzyme molecule will reversibly bind to the substrate(s) and then a specialised part(s) of the enzyme will catalyse the specific change necessary to change the substrate into a product. 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. During industrial process, the specific action of enzymes allows high yields to be obtained with a minimum of unwanted by-products.

Enzymes can work at atmospheric pressure and in mild conditions with respect to temperature and acidity (pH). Most enzymes function optimally at a temperature of 30�C-70�C and at pH values, which are near the neutral point (pH 7). Now-a-days, special enzymes have been developed that work at higher temperatures for specific applications.

Enzyme processes are potentially energy saving and save investing in special equipment resistant to heat, pressure or corrosion. Due to their efficiency, specific action, the mild conditions in which they work and their high biodegradability, enzymes are very well suited for a wide range of industrial applications.

As mentioned earlier, enzymes are present in all biological systems. They come from natural systems, and when they are degraded the amino acids of which they are made can be readily absorbed back into nature.

Enzymes work only on renewable raw materials. Fruit, cereals, milk, fats, meat, cotton, leather and wood are some typical candidates for enzymatic conversion in industry. Both the usable products and the waste of most enzymatic reactions are non-toxic and readily broken down. Finally, industrial enzymes can be produced in an ecologically sound way where the waste sludge is recycled as fertiliser.
Enzymes are used in the textile industry because they Accelerate reactions, Act only on specific substrates, Operate under mild conditions, Are safe and easy to control, Can replace harsh chemicals and enzymes are biologically degradable i.e. biodegradable.


ENZYME APPLICATIONS IN TEXTILE PREPARATORY PROCESS:

Desizing:


Cotton fibres and cotton/synthetic fibre blends are sized, i.e. they are coated with a strengthening, adhesive like material (usually starch or a starch based material) to prevent damage during the weaving process. Size is usually applied to the warp thread, since this is particularly susceptible to mechanical strain during weaving. The material used for sizing is usually starch or a starch derivative. Starch size is most widely used (about 75% of textile industries use starch). The starch is usually obtained from potatoes, from maize and from rice in the.

The size must be removed before a fabric can be bleached and dyed, since it affects the uniformity of wet processing. Various types of desizing methods are available. If the size is water soluble, an alkali wash with detergents may be used. Oxidative chemicals such as persulphate and alkali or bromide and alkali may also be used (may be included in the bleaching process).

Enzymatic Method:

In the textile industry amylases are used to remove starch-based size for improved and uniform wet processing. Amylase is a hydrolytic enzyme which catalyses the breakdown of dietary starch to short chain sugars, dextrin��s and maltose. The advantage of these enzymes is that they are specific for starch, removing it without damaging to the support fabric (e.g. cotton and its blends).
An amylase enzyme can be used for desizing processes at low-temperature. The optimum temperature is 30-60��C, optimum pH is 5.5-6.5.

Scouring:

Scouring is the process of removal of natural and added impurities like fat, wax, sand or dust particles and oils. Conventionally the scouring process carried out by treting the fabric with caustic soda and sodium hydroxide at 70��c to 90��c.

The use of the traditional strongly alkaline process can have a detrimental effect on fabric weight (g/m2) and on the environment. Enzymatic scouring makes it possible to effectively scour fabric without negatively affecting the fabric or the environment. It also minimises health risks since operators are not exposed to aggressive chemicals.

Pectinase enzyme is effective and environmentally friendly for scouring. It breaks down the pectin in the cotton and thus assists in the removal of waxes, oils and other impurities. Novozymes offers an alkaline pectinase for Bio-Scouring that gently but completely removes pectin and other impurities from cotton fibres and that can be used on a range of textile wet-processing machinery.

The optimum Temperature is 50-65��c and PH between 7.5-9.0.

Souring (Bleach Removal):

In conventional method generally, bleaching of cellulose fibres with hydrogen peroxide is optimum at a pH of 10, 5 to 11, at a temperature between 80 and 100 ��C, and for a contact time between 45 minutes and 5-6 hours. After completion of the process the bleached liquor was drained out (The bleaching chemical has to be removed before the dye is applied in order to prevent reaction between the bleach and dye) then the fabric was rinsed with water a number of times to remove the H2O2 from the bleached fabric. Alternatively, a mild reducing agent can be used to neutralize the bleach. In either case, large amounts of water (up to 40 liters per kg of fabric) are required for rinsing resulting in discharge of large volumes of wastewater.

An enzyme can used to replace a chemical agent (such as thiosulfate) in bleach neutralization leading to reduction in water and energy consumption. The enzyme, Terminox Ultra (commercial name of the Novo enzyme) is manufactured and marketed by Novo Nordisk.

A small dose of Catalase is capable of decomposing hydrogen peroxide to water and oxygen. Compared with the traditional clean-up method.


The enzyme specifically breaks down hydrogen peroxide into non-active oxygen and water under mild temperature conditions.

Catalase

2 H2O2 --------------> O2 + 2 H2O

The enzymatic process results in reduced water consumption and reduced energy consumption. The enzyme can be applied directly after the bleaching stage.

The following process recommended for batch processing in e.g. Yarn dyeing equipment, Jet dyers and winches is as follows:

The rinsing step is not required when using the enzyme because the bleaching agent is decomposed and the residues of the enzyme have no effect on textile fibers or dyestuffs.

A catalase used for Bleach Clean-Up in the textile industry. Terminox Ultra ensures complete removal of excess H2O2 without requiring the traditional extra rinsing steps.
The optimum temperature is < 50�C and the optimum pH is 4.0-10.0.

Re-use of catalase treated bleaching bath for reactive dyeing:

That the catalase treated bleaching liquor was reused for dyeing the cotton fabric with reactive dyes i.e. the dyeing in the bleaching bath. Though the hydrogen peroxide was completely destroyed by the enzyme, the bleaching bath formulation and the enzyme caused unacceptable colour changes in the dyed fabric. The unacceptable colour changes in the dyed fabric could be reduced significantly and a good dyeing result can be achieved by varying the parameters of the dyeing process like dye, salt, alkali and enzyme concentrations and bath temperature. However the over all influence of these parameters on the colour difference of the dyed fabric is by the complex action. Selecting the optimum proportion between each of these parameters could be the key for successful dyeing in the catalase treated bleaching bath.

Combined Scouring and Bleaching:

Two enzymes, Amyloglucosidase and Glucose Oxidase can be used for scouring and bleaching process as single bath two step process.

Step 1- Scouring using Amyloglucosidase:

Amyloglucosidase also known as glucoamylase, is also an exo-enzyme which hydrolyses starch. It removes glucose residues in a stepwise manner from the non-reducing end of the starch polymer, hydrolysing a-1,4 and a-1,6 bonds, although at slower rate with the latter bond configuration. The amyloglucosidase enzymes can also catalyse the condensation of glucose residues producing mainly maltose and isomaltose (transglycosylation). Glucoamylases are sensitive to temperature, being inactivated at temperatures above 60 �C. The optimum pH level of these enzymes is 4.0-4.5. Commercial glucoamylases are generally produced from strains of Aspergillus nige

Step 2 � Bleaching using Glucose Oxidase:

The Glucose Oxidase enzyme has to be added in the scoured (Amyloglucosidase) bath. In the presence of molecular oxygen, glucose is oxidised by the enzyme glucose oxidase to gluconic acid and hydrogen peroxide:

D- Gluconic acid is act as a sequestering agent during bleaching. To produce enough amount of hydrogen peroxide in the bleaching bath more amount of Amyloglucosidase has to be added in the scouring bath, there by enough glucose can be produced to obtain atleast 250 mg per litter.

Conclusion:

The awareness among the people regarding environment has made the scientists and technologists to look at textile processing in a different perspective. Of course, biotechnology is not new; traditional products include bread, beer, cheese, wine, and yoghurt. The textile industry was identified as a key sector where opportunities available from adapting biotechnology are high but current awareness of biotechnology is low. In textile processing the enzyme can be successfully used for preparatory process like desizing, Scouring and bleaching. These enzymatic processes are gives the similar results as that of conventional methods. Though this Enzymatic Processes we can reduce the Water consumption, Power energy, Pollution, time, and increasing quality.

REFERENCE:

Gitte Pedersen," Enzymatic treatment of residual bleach in cotton dyeing", draft UNEP Cleaner Production Worldwide publication, 1994.

Annelies den Braber, TME, Institute for Applied Environmental Economics, 2511 BJ The Hague, Netherlands

Skjern Tricotage-Farveri A/S Farverivej 1, DK-6900 Skjern, Denmark

Dr.T.Ramachandran and Dr.A.Venkatachalam, PSG College of technology, Coimbatore. �Improved Energy Conservation in Textile Wet Processing�

Enzyme in Wet Processing, Dr. Nikhil and Dr.Anita Nishkam. The Indian Textile Journal, Feb 2003

Pre Treatments Developments, Dr V A Shenai. The Indian Textile Journal, June 2003.
Novel Trends in Textile Preparatory Process, Dr. Usha Sayed. Colourage, Feb 2002



The Mechanism of Hydrogen Peroxide Bleaching, Josef Dannancher. Textile Chemist & Colourist. Dec 1996, Vol 28 NO.11

Recent Developments in Wet Processing, Pardeshi and Sujita. The Indian Textile Journal, Jan 2003/29.

Enzymes � The Morvellous Molecular Machine, Roshan Paul. The Asian Textile Journal, Jan 2002.

Bleaching using Glucose Oxidase Enzyme, Tetile Research Journal 71(5) 2001 388 � 394.
Catalase Enzyme, Niels P.Jensen. Textile Chemist & Colourist & American Dyestuff Reporter.Vol 32 May 2000.

About the author:

M. Subramanian Senthil Kannan is presently working as a KAM Executive in Consumer Testing Services, SGS India (P) Ltd, Bangalore. He is a Textile Graduate from Bannari Amman Institute of Technology, Tamilnadu. He has obtained his master�s degree in Textile Technology from PSG college of Technology, Coimbatore, Tamilnadu. He is a gold medalist in both of his UG and PG programmes. He has published around 60 articles in various national and international journals. He has also presented many technical papers in various national level symposia and in various national & international conferences. He has won several prizes in paper & poster presentations and quiz competitions in both national and international levels. He has got one and half years of experience in R& D in spinning and weaving and one year in Quality assurance in Spinning.

Email: senthilkannan@gmail.com


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