Updated: Mar 13, 2021
Desizing is carried out to remove the sized (added) impurities from the woven cotton material.
The given cotton material is weighted accurately and run through the bath boiling water for 10 minutes. The fabric is taken out, squeezed and steeped into the acid or enzyme bath for one to two hours at the respective temperature (50o c for acid bath and 60o c to 80o c for enzyme bath). After desizing the fabric is washed first with hot water and then with cold water thoroughly to remove the impurities and the residual chemicals (acid or enzyme).The fabric is then dried in air oven and weighed accurately to calculate the weight difference.
Mechanism of Desizing:
Acid steeping (Hydrolytic): In acid steeping, mineral acids such as hydrochloric acid, sulphuric acid and nitric acid are preferred. Since, nitric acid is yellow color in nature & if it is used, then the cotton fabric will be colored Hence, the application of nitric acid is not recommended. The fabric is steeped in dilute acid solution (HCl /H2SO4) for one hour at 50°C with material to liquor ratio (MLR) 1:20. The starch present in the cloth is liquefied and solubilised starch is removed by washing. Since, acids can attack cellulose; precaution has to be taken to avoid tendering of cotton fabric. It is essential to neutralize the fabric to avoid hydrolytic damage. The fabric should be washed first with hot water after desizing, since cold water reduces the solubility of de- graded products present in the fabric.
Enzyme desizing: Enzymes are categorized into different types such as; vegetable, animal and bacteria. Malt extract based enzyme (amylase) is usually preferred for enzymatic desizing of cotton fabric under neutral pH. They are activated in a wide range of temperature and pH levels based on the type of enzyme. The main advantage of enzyme desizing is that when the temperature increases beyond the optimum level (i.e., 75- 80°C), fabric damage is avoided since the enzyme itself gets deactivated. The fabric is immersed in enzyme solution for 1 to 2 hours at 60° C - 80°C thoroughly washing with hot water and then with normal water.
The given grey woven cotton fabric is desizing used acid steeping method and percentage of weight loss after desizing was calculated.