Enzyme and Its Applications in Textile Processing

Enzyme: 

Enzymes are protein catalysts produced by living cells that catalyze specific chemical or biochemical reactions. The use of enzymes in textile processes has gained increased interest due to the advantages of enzymes being non-toxic, biodegradable, and environmentally friendly. Enzymes can be safely used in textile wet processing like desizing, scouring, bleaching, dyeing, and finishing, while traditional chemicals can cause many problems including pollution of effluents when disposed into the environment. Advances in enzyme technology use in the textile industry have made it possible to explore the potential of single enzymes or enzyme mixtures for specific applications. Hydrolases (e.g., amylases, cellulases, pectinases, proteases) and oxidoreductases have been employed for fabric preparation and finishing.

Enzymes are large high-molecular weight protein structures with highly specific active sites within the molecule that perform the catalytic reaction. Replacing enzymes with simpler compounds that mimic the behavior of these biocatalysts could significantly increase the reaction rate, facilitate the enzymatic process and decrease costs.

Introduction to Enzymes: Enzymes are a Greek word ‘Enzymos’ meaning ‘in the cell’ or ‘from the cell’. They are the protein substances made up of more than 250 amino acids. Based on specificity they are grouped. The concept of treating fabrics with enzymes to improve their surface properties was first developed in Japan in 1989. The treatment has assumed more important due present concern of clean and eco-friendly environment under the following group: 

1. Oxidoreductases- oxidation, reduction reaction
2. Transference- transfer of functional group
3. Hydrolases- hydrolysis reaction
4. Lyases- addition to double bond or its reverse
5. Isomerses- isomerisation
6. Ligases- formation of bonds with ATP clevags

Enzymes have bright future in wet processing of textile industry. Enzymes do not produce toxic effluent as they can easily deactivated disposal off. Enzymes are high-molecular weight proteins that consist of intertwined chains of amino acids. Enzymes act as catalysts for chemical or biological reactions. Compared with common chemical catalysts, enzymes are more efficient and increase the reactionrate by 107 – 1013. Compared to general chemical catalysts, enzymes have the added advantage to make a reaction occur under mild conditions such as fairly low temperature, normal pressure, and in neutral aqueous solution. They also have the advantage of being non-toxic, bio-degradable, and environmentally-friendly. Enzymes are highly substratespecific.

They react with their substrates at a region within the protein molecule which is called active site. The active site of the enzyme must have the necessary structure characteristics to recognize the right substrate and the proper chemical environment to make the reaction happen.

The enzymes most commonly involved in textile applications are hydrolases and oxidoreductases. They can be safely used in the textile industry in fabric preparation and finishing processes.

The silent features of enzymes application in textile processing:

1. Extremely specific nature of reaction involved, with practically no side effect.
2. Low energy requirement, mild condition of use safe to handle, non-corrosive in their applications.
3. On account of lesser quantities of chemical used in process as well as ease of biodegradability of enzymes result in reduced loads on ETP plants.
4. Enzymes under unfavorable condition of pH or temperature, chemically remain in same form but their physical configuration may get altered i.e. they get “denature” and lose their activity, for this reason live steam must never be injected in a bath containing enzyme bath must done in pre-diluted form.
5. Compatibility with ionic surfactant is limited and must be checked before use. Nonionic wetting agents with appropriate cloud point must be selected for high working efficiency as well as for uniformity of end result.
6. High sensitivity to pH, heavy metal contamination and also to effective temperature rang. Intense cautions are required in use.

Advantages of Enzymes Used in Textiles: 

• Lower discharge of chemicals and wastewater and decreased handling of hazardous chemicals for textile workers.
• Improved fabrics quality.
• More fashion choices longer garment life/wear due to lower damage of original fabric.
• Reduced chemical load, reduced water consumption, lower energy consumption.
• Enzyme is more eco-friendly.

Properties of Enzymes Used in Textiles: 1. Enzyme accelerates the reaction:

• An enzyme accelerates the rate of particular reaction by lowering the activation energy of reaction
• The enzyme remains intact at the end of reaction by acting as catalyst

2. Enzymes operate under milder condition:

• Each enzyme have optimum temperature and optimum pH i.e. activity of enzyme at that pH and temperature is on the peak
• For most of the enzyme activity degrades on the both sides of optimum condition

3. Alternative for polluting chemicals: 

• Enzymes can be used as best alternative to toxic, hazardous, pollution making chemicals
• Also some pollutant chemicals are even carcinogenic. When we use enzymes there is no pollution

4. Enzyme acts only on specific substrate: 

• Most enzymes have high degree of specificity and will catalyse the reaction with one or few substrates
• One particular enzyme will only catalyse a specific type of reaction. Enzymes used in desizing do not affect cellulose hence there is no loss of strength of cotton

5. Enzyme is easy to control: 

• Enzymes are easy to control because their activity depends upon optimum condition

6. Enzymes are biodegradable: 

• At the end of reaction in which enzymes used we can simly drain the remaining solution because enzymes are biodegradable and do not produce toxic waste on degradation hence there is no pollution

Mechanism of Enzyme Action: 
Lock & Key Theory Enzymes have active centers, which are the points where substrate molecule can join. Just as a particular key fits into a lock, a particular substrate molecule fits into the active site of the enzyme. The substrate forms a complex with the enzyme. Later the substrate molecule is converted into the product and the enzyme itself is regenerated (Fig.1). 

Fig. 1 Lock & Key model of enzyme specificity

The process continues until the enzyme is poisoned by a chemical bogie (Fig.2) or inactivated by extremes of temperature, pH or by other negative conditions in the processing environment. 

Fig. 2 Active site of enzyme blocked by poison molecule

Enzyme Treatments of Textiles Textile Use and Effects:

Types of Enzyme	Textile Use and Effects
Cellulases	Biofinishing, biopolishing, anti-pilling, softness, smoothness, lustreimprovement and stone-washed Effects on denim
Amylases	Standard procedure for the removal of starch warp size
Proteases	In household washing agents better removal of protein containing soil orstains. Anti-felting of wool, accompanied by high loss of weight, tearstrength and of the typical handle, degumming of silk with the problem ofsilk fibroin damage
Lipases	In detergents for the hydrolysis of lipids
Pectinases	Hydrolysis of pectins, for example in cotton 'preparation' and retting offlax and hemp
Catalases	Catalyse the decomposition of hydrogen peroxide, important beforereactive dyeing of printing of peroxide bleaching fabrics and yarn
Peroxidases	Used as an enzymatic rinse process after reactive dyeing, oxidativesplitting of hydrolysed reactive dyes on the fibre and in the liquor,providing better wet fastness, decolourised waste water and potentiallytoxic decomposition compounds (aromatic nitro-compounds)
Ligninases	Removal of burrs and other plant compounds from raw wool
Collagenases	Removal of residual skin parts in wool
Esterases	In development: polyester finish, removal of 01 igomers
Nitrilases	In development: polyacrylonitrile preparation for better coloration

Various Enzymes Used in Textile Processing: Amylases: Which convert amylose or amylopectin polymers , commonly referred to as starch in to water soluble shorter chain sugars (Starch desizing)

Pectinases: Which hydrolyse pectins consisting of linear polymers of galacturonic acid (bio-scouring replacing caustic)

Lipases: Which hydrolyse fats and oils into alcohol and organic acids.

Proteases: Which catalyse splitting protein molecules, and in the extreme may break the protein into the component amino acids.

Catalases or Peroxidases: Which catalyse the decomposition of peroxide, also known as peroxide killer.

Cellulases: Which catalyse the hydrolysis of cellulosic materials (bio-singeing or bio-polishing).

Enzyme Applications in Textile Preparatory Process: Enzymatic Desizing : 
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 and maltose. 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.

Enzymatic Scouring (Bio-scouring):Scouring is removal of non-cellulosic material present on the surface of the cotton. In generally cellulase and pectinase are combined and used for Bioscouring. In this 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 can destroy 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%). Handle is very soft in enzymatic scouring compared to harsh feel in alkaline scouring process. Enzymatic scouring makes it possible to effectively scour fabric without negatively affecting the fabric or the environment. It also minimizes health risks hence operators are not exposed to aggressive chemicals.

Enzymatic Bleaching: 
The purpose of cotton bleaching is to decolourise natural pigments and to confer a pure white appearance to the fibres. The most common industrial bleaching agent is hydrogen peroxide.

Conventional preparation of cotton requires high amounts of alkaline chemicals and consequently, huge quantities of rinse water are generated. However, radical reactions of bleaching agents with the fibre can lead to a decrease in the degree of polymerisation and, thus, to severe damage. Therefore, replacement of hydrogen peroxide by an enzymatic bleaching system would not only lead to better product quality due to less fibre damage but also to substantial savings on washing water needed for the removal of hydrogen peroxide. An alternative to this process is to use a combination of suitable enzyme systems. Amyloglucosidases, pectinases, and glucose oxidases are selected that are compatible concerning their active pH and temperature range. Tzanov et al. (2003) reported for the first time the enhancement of the bleaching effect achieved on cotton fabrics using laccases in low concentrations. In addition, the short time of the enzymatic pre-treatment sufficient to enhance fabric whiteness makes this bio-process suitable for continuous operations. Also, Pereira et al. (2005) showed that a laccase from a newly isolated strain of T. hirsuta was responsible for whiteness improvement of cotton most likely due to oxidation of flavonoids. More recently, Basto et al. (2006) proposed a combined ultrasound-laccase treatment for cotton bleaching. They found that the supply of low ultrasound energy(7W) enhanced the bleaching efficiency of laccase on cotton fabrics. Natural fabrics such as cotton are normally bleached with hydrogen peroxide before dyeing. Catalase enzyme is used to break down hydrogen peroxide bleaching liquor into water molecules and less reactive gaseous oxygen. Compared with the traditional clean-up methods, the enzymatic process results in cleaner waste water or reduced water consumption, a reduction of energy and time.

Bio-polishing: 
Bio-polishing, a technique first adopted by the Danish Firm Novo Nordisk for the finishing treatment of cellulosic fabrics with cellulase enzymes. The main objectives of the bio-polishing is to upgrade the quality of the fabric by removing the protruded fibres from the surface and modification of the surface structure of the fibre, thereby making it soft and smooth. In conventional process protruded fibres are removed by singing process and smoothness imparted by chemical treatment. The conventional methods are temporary, fibres return on the surface of the fabric and chemicals are removed after few washing and fuzz is formed. The fuzz on the surface spoils the fabric appearance and generates customer’s dissatisfaction whereas biopolishing is permanent and it not only keeps the fabric in good condition after repeated washing but also enhances feel, colour, drapeability etc consequently products become more attractive to the customer and fetch better prices. The bio-polishing treatment offers the following advantages: 

• Improved pilling resistance.
• A clearer, lint and fuzz-free surface structure.
• Improved drapeability and softness.
• The effects are durable
• Slight improvement in absorbency
• Fashionable effects on fabric like distressed look of denim

Enzymatic Treatment to Denim: 
Denim is heavy grade cotton. In this dye is mainly adsorbed on the surface of the fibre. That is why fading can be achieved without considerable loss of strength. In traditional process sodium hypochlorite or potassium permanganate was used called as pumice stones(Pedersen and Schneider, 1998).

Disadvantage of These Method are as Follows: 

• Pumice stones cause large amount of back-staining.
• Pumice stones are required in very large amount.
• They cause considerable wear and tear of machine.

These disadvantages lead to give rise the process of use of enzymes. Cellulase enzyme is used in denim washing. Cellulase works by loosening the indigo dye on the denim in a process know as “Bio-Stonewashing”. A small dose of enzyme can replace several kilograms of pumice stones. The use of less pumice stones results in less damage to garment, machine and less pumice dust in the laundry environment.

Anti-shrink Treatment for Wool:
 A process conventionally used for wool shrink-proofing is chlorination. This process degrades the exo-cuticle of the wool, forming cysteic acid residues and protein losses.

This process has been replaced by proteinases treatment due to their high specificity and much lower environmental impact. However, proteinase treatment leads to protein degradation, resulting in deterioration of fiber strength and limited shrink resistance. A patent application about the use of laccase from T. versicolor plus a mediator to increase the shrink resistance of wool was published (Yoon 1998). Also, Lantto et al. (2004) found that wool fibers can be activated with laccase if a suitable mediator is present. Therefore, the use of laccase for anti-shrink treatment of wool seems very attractive.

Conclusions: 
Enzymes can be used in order to develop environmentally friendly alternatives to chemical processes in almost all steps of textile fibre processing. There are already some commercially successful applications, such as amylases for desizing, cellulases and laccases for denim finishing, and proteases incorporated in detergent formulations. Further research is required for the implementation of commercial enzyme based processes for the biomodification of synthetic and natural fibers. There is still considerable potential for new and improved enzyme applications in future textile processing.

As with all chemicals and products, enzymes too have their own merits and limitations. They show specific action without undesirable effects on other components and normally operate under mild temperature and pressure conditions, but at the same time are sensitive to temperature, pH, humidity and contaminants. They often shorten the process cycle reducing time, water consumption and wastewater generation. The main hindrance in using enzymes is their high cost. 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.

Enzymes are emerging in a big way in the field of textile wet processing.If their cost can be managed, enzymes can be put to use in a much bigger way for textile processing applications.

References: 

1. Impact of bio- technology on the textile industry; Rakesh Doshi;Asian Textile journal, Jan 2002
2. Role of enzymes in textile processing industry; O L Shanmugasundaram & S Kumaravel; Asian Dyer;NOV-DEC2005
3. Enzymes in wet processing; Dr.Nikhil Verma& Dr. Anita Nishkam; The Indian Textile JournalFeb2003/37
4. Application of biotechnology in textile; M Muthu manickem and J Ganesh Prasad; Asian Dyer,oct2006/67
5. Recent research on biotechnology in textile ; Dr.Danny E Akin &Ian R Hardin; colourage, Annual2004/55