Introduction
- The loom state cotton fabric contains about 8-12% natural impurities of the total weight of the fibre.
- These impurities mainly consist of waxes, proteins, pectic substances and mineral matters.
- In addition to this, the mechanically held impurities called ‘motes’ are present containing seed-coat fragments, aborted seeds and leave etc. that cling to the fibre.
- Apart from these, the loom-state fabric is also contaminated with adventitious oils such as machine oils, tars, greases etc.
- Scouring is a purifying treatment of textiles.
- The objective of scouring is to reduce the number of impurities sufficiently to obtain level and reproducible results in dyeing and finishing operations.
- Scouring agents can be generally classified into different groups.
- The appropriate type of scouring agent generally depends on the kind of fibre; fabric type i.e. woven or knitted, thick or thin; texturised or non-texturised and the extent of impurities present in the fibre.
Classification of textile scouring agents
- The selection of alkali is most important as free alkali can have a deleterious effect on certain fibres. Alkali neutralises the carboxyl group in cellulose and in pectin.
- The hydroxyl groups on the glucose units in cellulose are also weakly acidic. Owing to this preferential sorption, the concentration of alkali in the fibre is increased and thus attacks the impurities more intensively.
Mechanism of Removal of Impurities
- The action of an alkaline scouring agent is to saponify any residual oils, neutralise carboxylic acids, solubilise any sizing materials and cause dispersion of naturally occurring impurities in natural fibres.
Techniques for Removing Natural Impurities of Cotton during Scouring
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