Bleaching with hypochlorites

Hypochlorites as bleaching agents are still popular despite the anti-chlorine lobby and environmental pressures. Some of these salts which are used for the bleaching of textiles are briefly described. 

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The plant is harvested by hand sickle and, after defoUation, is stripped and scraped by hand or machine decorticated. Because of the high gum (xylan and araban) content of up to 35%, retting is not possible. The fibers are separated chemically by boiling in an alkaline solution in open vats or under pressure, then washed, bleached with hypochlorite, neutralized, oiled to facUitate spinning, and dried. 

The last stages of bleaching (with hypochlorite and chlorine dioxide) have not been found to reduce the resin content significantly. 

Cotton can be bleached with hypochlorite solution at room temperature containing 1 -3 g available chlorine per litre at pH range of 9.5 to 11. The pH is maintained by adding 5 g/1 sodium carbonate in the bleach bath. After bleaching the cloth is treated with dilute hydrochloric acid to neutralise any alkali (souring) present m the cloth. An antichlor treatment with sodium thiosulphate or bisulphite is also recommended to remove any residual chlorine from the cloth. Finally, the cloth is washed with water to rinse out acid from the cloth. 

Bleaching with hypochlorite solution containing 1 g/1 of available chlorine with the addition of 5 g/1 sodium carbonate at pH close to 7 can be done in just 10 min. The system is more reactive in the danger zone and thus bleaching can be done in a shorter time. 

The basic factor to be borne in mind when bleaching with hypochlorites is that the active component can exist in three different states. 

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