Enzyme in textile processing
by M. Aslam Khan, Textile Consultant.

Classification and Nomenclature:

Enzymes are large high molecular weight protein structures with highly specific active sites with the molecule that performs the catalytic reactions. They are produced by living cells that catalyze specific chemicals or biochemical reactions.

Enzyme range from individual protein with a collative molecular mass (RMM) of around 13000 catalyzing a single reaction, to multi-enzyme complexes of RMM of several million catalyzing, many distinct reactions.

The enzyme is principally classified according to the chemical reaction they catalyze, as this is a specific property that distinguishes one enzyme from others.

  • A systematic name is given to an enzyme until a chemical reaction is known.
  • An enzyme name is assigned to a group of proteins with the same catalytic properties.
  • Enzymes from different sources, such as animals, plants, and organisms.
  • The direction of the reaction is chosen.

There are six classes of an enzyme that are distinguished by the first digit of the EC code, the second and third digit describe the type of reaction catalyzed.

These six classes are identified as follow:

  1. Oxidoreductases: Enzyme that catalyzes oxidoreductase reactions. 2nd EC digit indicates group in the hydrogen donor e.g CHOH, aldehyde, and ketone, 3rd EC digits indicate the type of acceptor involved.  e.g alcohol dehydrogenase.
  2. Transferases: Enzyme transferring a group e.g methyl, glucosyl, phosphate, e.g glucokinase.
  3. Hydrolases: Enzyme that catalyzes the cleavage of C-O, C-N-C, and some other bonds, e.g carboxypeptidase.
  4. Lyases: Enzyme that cleaves C-C. C-N, C-O, and other bonds by elimination leaving double bond or rings, or add groups to double bonds, such as decarboxylase, dehydratase.
  5. Isomerases: Enzymes that catalyze geometric or structural changes within one molecule.  e.g Isomerase.
  6. Ligases: Enzyme catalyzing the joining of two molecules coupled with the hydrolysis of diphosphate bond in ATP.or similar triphosphates. 2nd EC digit indicates the bond formed,e.g C-O, C-S, C-N. 3rd EC digit is only used in C-N ligases. e.g pyruvate carboxylase.

Structure of Enzyme:

Enzymes consist of one or more polypeptides and each polypeptide is a chain of amino acids linked together by peptide bonds. Polypeptide chains fold up when synthesized to form a unique three-dimensional shape, determined by their amino acid sequences. Multiple weak interactions stabilize the conformation of polypeptides and factors such as pH, heat, and chemicals that disrupt these interactions distort the polypeptide conformation. Enzyme loses their functional activity when their three-dimensional conformation is distorted in this manner, through enzyme denaturation.

There are two main types of proteins: Fibrous and Globular.

Fibrous:

Proteins normally have a structural role in biological systems. They are insoluble in water and are physically durable. The three-dimensional structure is relatively simple and usually elongated.

  • Alpha- keratin: main protein of hair, nail, wool, horns, and feathers.
  • Beta – Keratin: Main component of silk and spider web.
  • Collagen: A measure protein of cartilage, tendons, skin, and bones.
  • Elastin: Protein found in ligaments in the walls of arteries.

Globular:

Proteins are generally soluble in water and can often be crystallized from solutions. They have a complex three-dimensional structure and tend to adopt an approximately spherical shape in which the amino acid chain is tightly folded. All enzymes belong to this type in which globular proteins have a functional role in biological systems.

The vast majority of enzymes are oligomeric enzymes with a molecular weight of more than 35000. Enzymes that lacks a quaternary structure are known as monomeric enzymes comprising a single polypeptide chain.

Monomeric enzymes typically have 100-300 amino acid residues and have a molecular weight in the range of 13000-35000. Many proteolytic (Proteases) are monomeric enzymes, they catalyze the hydrolysis of peptide bonds in other proteins.

Enzymes commonly use in textile processing are:

  • Desizer – alpha-amylase.
  • Bio scour – pectinase.
  • Bio polish -  cellulase.
  • Bleaching- lyccase.

The use of enzyme in textile wet processing is encouraged by the following properties they have:

  • Specific nature of the reaction, without any side effects.
  • Low energy, mild conditions, Noncorrosive.
  • Biodegradable.
  • Unfavorable conditions of pH and temperature reduce the activity of enzymes.
  • Improved fabric quality.
  • Favorable for ETP.
  • Less damage to the fabric.
  • Less water, energy, and chemicals required.
  • Accelerate the reaction.
  • Easy to control.
  • Eco friendly.

Uses of the enzyme in Textile wet processing:

Amylase: These are mainly used for desizing and convert starch into water-soluble shorter chain sugars dextrin and maltose. Amylases act on the starch molecule and hydrolyze to give dextrin and small polymer of glucose, alpha-amylases being produced from filamentous fungi and bacteria are mostly used in industries.

It is applicable at low temperatures ranging from 30c to 60 c and pH 5.5 – 6.5.

Pectinase: are used to replace the very harsh and strong chemicals i.e the caustic soda in scouring of textile but having many advantages over the caustic treatment. The pectinase is used in combination with cellulase. The pectinase destroys the cotton cuticle by digesting the pectin and removing the connection between the cuticle and body of the fiber whereas cellulase can destroy the primary wall of cellulose immediately under the cuticle of cotton.

BOD and COD of enzymatic scouring is 20 – 50% as compared to caustic scouring which is 100 %.

Cellulase:

Mainly use in denim fabric to upgrade the quality of the fabric, to remove the protruding fiber, and modifying the surface structure of the fiber.

  • It gives the fabric a soft and smooth handle.
  • It can replace the singeing process.
  • In singeing, chances are there that the fiber comes back after repeated wash and causes piling.
  • In bio polishing effect is permanent.
  • Improve drape ability.
  • Slight improvement in absorbency.
  • The product becomes more attractive and value-added.
  • Anti-shrink treatment of wool.

Cellulases are the hydrolytic enzymes that catalyze the breakdown of cellulose to smaller oligosaccharides and finally to glucose. It shows optimal activity in the temperature range of 30 – 60 c and pH is 5.5- 6.5. The major use of this enzyme is in denim processing. The market share is 14 % of the global industrial enzyme market.

Pectinase:

Pectinase is used to replace the very harsh and strong chemicals i.e the caustic soda in scouring of textiles but having many advantages over the caustic treatment. The pectinase is used in combination with cellulase. The pectinase destroys the cotton cuticle by digesting the pectin and removing the connection between the cuticle and body of the fiber whereas cellulase can destroy the primary wall of cellulose immediately under the cuticle of cotton.

BOD and COD of enzymatic scouring is 20 – 50% as compared to caustic scouring which is 100 %.

Alkaline pectinase is produced by genetically modified bacillus strain. The bio scouring process in batch and continuous process (Lange & Handerson, 2000) has been performed successfully.

The enzyme will degrade pectin, thereby destabilizing the structure in the outer layer. These are removed easily by the subsequent wash process. The pectinase offers the following advantages over conventional caustic scouring.

  • Textile becomes soft.
  • The low temperature required.
  • Low water consumption.
  • No neutralization chemicals required.
  • Low water pollutants.
  • Presence of Ca ion advantageous.

Disadvantages:

  • High chemical cost.
  • The degree of whiteness is less as compared to caustic scouring.
  • Less removal of seed coat and motes.

Laccase:

Laccase in combination with other enzymes is used in denim processing for the bleaching of indigo. Laccase can be used as a pretreatment step for subsequent peroxide bleaching to achieve a high level of whiteness. Research is going on to replace peroxide with enzymes to achieve the requirement of bleaching standards.

Catalases:

They are used in textile processing for the removal of residual peroxide after bleaching catalases convert hydrogen peroxide into water and oxygen.

References:

  • Arthur Cavaco, Paulo university of Minho Portugal. (Textile Processing with enzyme). Edited by Cavaco Paulo and G. M, Gubitz.
  • George Gubitz. Granz university. Austria. (Catalysis and processing).
  • V.A. Nierstrasz and Warmoeskerken. University of Twenk. (Process engineering and industrial enzyme applications).
  • S.M.Hossen uzzal. Bangladesh. (Enzyme and it's applications in Textile Processing.
  • Dr. Kiro Moisov, (Enzyme applications in Textile preparatory Process).

 

 
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