Desizing Knowpia

Desizing is the process of removing the size material from warp yarns after a textile fabric is woven.^[1]

Sizing agents edit

Sizing agents are selected on the basis of type of fabric, environmental friendliness, ease of removal, cost considerations, effluent treatment, etc.

Natural sizing agents edit

Natural sizing agents are based on natural substances and their derivatives:

Starch and starch derivatives: native starch, degradation starch, chemically modified starch products
Cellulosic derivatives: carboxymethylcellulose (CMC), methylcellulose, oxyethylcellulose
Protein-based starches: glue, gelatin, albumen

Synthetic sizing agents edit

Desizing processes edit

Desizing, irrespective of what the desizing agent is, involves impregnation of the fabric with the desizing agent, allowing the desizing agent to degrade or solubilise the size material, and finally to wash out the degradation products. The major desizing processes are:

Enzymatic desizing of starches on cotton fabrics
Oxidative desizing
Acid desizing
Removal of water-soluble sizes
Fermentative desizing

Enzymatic desizing edit

Enzymatic desizing is the classical desizing process of degrading starch size on cotton fabrics using enzymes. Enzymes are complex organic, soluble bio-catalysts, formed by living organisms, that catalyze chemical reaction in biological processes. Enzymes are quite specific in their action on a particular substance. A small quantity of enzyme is able to decompose a large quantity of the substance it acts upon. Enzymes are usually named by the kind of substance degraded in the reaction it catalyzes.

Amylases are the enzymes that hydrolyses and reduce the molecular weight of amylose and amylopectin molecules in starch, rendering it water-soluble enough to be washed off the fabric.

Effective enzymatic desizing require strict control of pH, temperature, water hardness, electrolyte addition and choice of surfactant.

Oxidative desizing edit

In oxidative desizing, the risk of damage to the cellulose fiber is very high, and its use for desizing is increasingly rare. Oxidative desizing uses potassium or sodium persulfate or sodium bromite as an oxidizing agent.

Acid desizing edit

Cold solutions of dilute sulphuric or hydrochloric acids are used to hydrolyze the starch, however, this has the disadvantage of also affecting the cellulose fiber in cotton fabrics.

Removal of water-soluble sizes edit

Fabrics containing water-soluble sizes can be desized by washing using hot water, perhaps containing wetting agents (surfactants) and a mild alkali. The water replaces the size on the outer surface of the fiber, and absorbs within the fiber to remove any fabric residue.

Fermentative desizing edit

Fermentative desizing is defined as a fermentation process and involves the Generally Regarded as Safe (GRAS) microorganisms that have a high potential to produce enzymes; it is carried out via impregnation/padding methods, which provide online monitoring and accurate control. The method allows an economical process with low resource consumption and emission compared to the enzymatic method, it is considerably cheaper.^[2]

References edit

^ "Desize". Merriam-Webster. Retrieved 29 July 2018.
^ Chand, Nima (2014). "Fermentative desizing of cotton fabric using an α-amylase-producing Bacillus strain: optimization of simultaneous enzyme production and desizing". Process Biochemistry. 49 (11): 1884–1888. doi:10.1016/j.procbio.2014.07.007.