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Concept
Desizing
Summary
Desizing is the process of removing the size material from warp yarns after a textile fabric is woven.
Sizing agents are selected on the basis of type of fabric, environmental friendliness, ease of removal, cost considerations, effluent treatment, etc.
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
Polyacrylates
Modified polyesters
Polyvinyl alcohols (PVA)
Styrene/maleic acid copolymers
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 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.
In oxidative desizing, the risk of damage to the cellulose fiber is very high, and its use for desizing is increasingly rare.
Official source
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