Difference between revisions of "Textile bleaching"
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Latest revision as of 10:16, 20 September 2010
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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. This greige material will be with its natural color, odour 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 in to a suitable material for next processing is called bleaching. Bleaching of textiles can be classified in to oxidative bleaching and reductive bleaching.
Oxidative bleaching
Generally oxidative bleachings are carried out using sodium hypochlorite, sodium chlorite or hydrogen peroxide. Natural fibres like cotton, ramie, jute, wool, bamboo are all generally bleached with oxidative methods.
Reductive bleaching
Reductive method of bleaching is done with Sodium hydrosulphite, a powerful reducing agent. Fibres like Polyamide, Polyacrylics and Polyacetates can be bleached using reductive bleaching technology.
Optical whiteners
After scouring and bleaching, Optical Brightening Agents (OBA), are applied to make the textile material to appear more brilliant whites. These OBA are available in different tints such as blue, violet and red.
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