Scouring Process for Cotton:

It is a process to remove all undesirable impurities especially natural origin like fats, wax, vegetable matter such as seed coat fragments, pectins, protein etc. Scouring process also removes some added impurities (which are not naturally present) such as oil stains, residual sizing material. Scouring process improves absorbency of cotton material. With the improved absorbency, water can transport dyes and chemical within the cotton fibres. Proper scouring is must for uniform dyeing and printing. The main objective of scouring is to  make textile material highly hydrophilic or improve water absorbency.

Mechanism of scouring: Following are main points related to mechanism of scouring:

i) Saponification: The vegetable oil, which is immiscible with water, is glyceride of fatty acids. When such oil are heated with a solution of sodium hydroxide (Caustic soda) in water, the oil splits up into its constituents fatty acid and glycerine. Glycerine is miscible with water easily and the fatty acids reacts with sodium hydroxide present in the solution forming its sodium salt i.e soap which is also soluble in water. Thus oil is removed.

Saponification process

ii) Emulsification: Wax and non saponifiable oils (Non polar) are removed by emulsification as they are immiscible in water (Polar). Normal washing soap  is used as a emulsifying agent which make emulsion of them. Soap generated from the saponification process also act as a emulsifying agent.

The scouring process brings following changes in cotton fibres:

i) Oils and fatty acids are converted into soaps.
ii) Pectins and pectose are converted into soluble salts of pectic acid.
iii) Mineral matters are mostly dissolved or settle down.
iv) Non saponifiable oils are emulsified by the soluble soaps generated from the saponificable oils.
v) Additive dirt's are removed.
vi) Residual sizing materials are broken down into soluble products.