The main purpose of bleaching
The main purpose of bleaching is to destroy the pigment molecules in textile fibers, thus giving textile products a white appearance. Bleaching usually takes place after refining and is often the last step in the pre-treatment. After refining, most of the impurities have been removed, the water absorption has been greatly improved, with good conditions for subsequent processing, but the pigment has not been touched, so the varieties with high whiteness must be bleached. Bleaching varies according to the object of processing, such as fiber bleaching, yarn bleaching and fabric bleaching. The bleaching methods and equipment vary according to the situation, but the basic principles of bleaching are the same.
It has been shown that bleaching can also play a positive role in removing impurities from textiles. The high temperature, alkaline condition and oxidation of bleaching agent are helpful to remove the symbiotic impurity in cotton fiber, so it has the refining effect. The effect of bleaching is different according to the properties of bleaching agent and the process conditions used. Because of the high content of natural impurities in cotton and the different properties and distribution of these impurities, it is almost impossible to remove them completely in refining, so bleaching has the task of continuing to remove impurities.