Factors effecting hypochlorite bleaching operations

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. 

Hypochlorite ionises differently under different pH conditions and active component can be effective in three different states (Fig. 6-2). In the region of pH 7, 

The commercial solution of sodium hypochlorite contains 14-15% available chlorine, compared to 35-36% in bleaching powder. The concentration of hypochlorite in the bleaching bath generally varies from 1 to 3 g/1 available chlorine. The optimum bleaching conditions, however, depend on the degree of discolouration of the cloth and thus the temperature and time of reaction should be adjusted according to the requirement. The concentration of hypochlorite solution is normally estimated by means of standard thiosulphate or arsenite titration. 

The addition of salt in the hypochlorite bleaching bath increases the activity in the initial period due to the production of nascent chlorine. The addition of chloride moves the equilibrium to the left-hand side, but after, say 15 min, when the 

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