- Hydrolytic Method
- Oxidative Method
Desizing is a process that involves the removal of sizing materials that were used in weaving processes. Desizing increases the absorbency power of the fabric. Sizing materials refer to starch, wax, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC).
Objectives of Desizing
- Removal of starch materials.
- To increase the affinity to dry chemicals.
- Increasing the absorbency power of fabric.
- To increase the luster of the fabric dyeing and printing.
- To make the fabric ready for the immediate next process.
Types of Desizing
1. Hydrolytic Method
a. Rot Steeping: In this method, the fabric is passed through padding that contains warm water (40-60C) and then the fabric is stored for 12 hours (for 60C water) or 24 hours (for 40C water). In the meantime, the pectin and organisms that exist in water liquefying enzymes remove the starch.
b. Acid Steeping: Cold diluted hydrochloric or sulphuric acid is used to hydrolyze the starch. Though acid method can affect the cellulosic structure of cotton fibres, hence it’s not suitable for cotton.
c. Alkali Steeping: Sizing materials are removed by the alkaline hydrolysis. The fabric is treated with 0.4-0.6% NaOH at 60-70C and stocked for 8-10 hours.
d. Enzymatic Steeping: In Enzymatic desizing is the starch is removed by using enzymes on fabric. Amylase enzyme hydrolyzes and reduces the molecular weight of amylose and amylopectin molecules in starch. Then starch can be removed by washing-off the fabric. Some of the common Enzymes are Rapidase, Biolase, Bactolase, Ferment D, Fermosol, Novofermosol etc.
2. Oxidative Method
a. Bromide Desizing
b. Chlorite Desinzing
c. (NH4)2S2O8 Desizing