Textile bleaching is one of the stages in the manufacture of textiles. All raw textile materials, when they are in natural form, are known as 'greige' material (pronounced grey-sh). This greige material will have its natural color, odor and impurities that are not suitable for clothing materials. Not only the natural impurities will remain on the greige material but also the add-ons that were made during its cultivation, growth and manufacture in the form of pesticides, fungicides, worm killers, sizes, lubricants, etc. The removal of these natural coloring matters and add-ons during the previous state of manufacturing is called scouring and bleaching.
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Scouring
Scouring is the first process carried out with or without chemicals, at room temperature or at suitable higher temperatures with the addition of suitable wetting agents, alkali and so on. Scouring removes all the waxes, pectins and makes the textile material hydrophilic or water absorbent. See also scouring wool.
Bleaching
The next process of decolorization of greige material into a suitable material for next processing is called bleaching. Bleaching of textiles can be classified into oxidative bleaching and reductive bleaching.
Oxidative bleaching
Generally oxidative bleachings are carried out using sodium hypochlorite, sodium chlorite or sulfuric acid. Natural fibres like cotton, ramie, jute, wool, bamboo are all generally bleached with oxidative methods.
Reductive bleaching
Reductive bleaching is done with sodium hydrosulphite, a powerful reducing agent. Fibres like polyamides, polyacrylics and polyacetates can be bleached using reductive bleaching technology.
Optical whiteners
After scouring and bleaching, optical brightening agents (OBAs) are applied to make the textile material appear a more brilliant white. These OBAs are available in different tints such as blue, violet and red.