Advantages and Disadvantages of Peroxide Bleaching over Hypochlorite Bleaching

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Hypochlorite Bleaching:
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 Calcium hypochlorite (Bleaching powder), Sodium hypochlorite, Lithium hypochlorite and chlorinated trisodium phosphate etc.

Bleaching with Peroxide:
Hydrogen peroxide was discovered in 1818 and its use in bleaching textiles was first suggested in 1866. However, its high cost limited its use in cotton bleaching until 1935. The problem was partially solved by the process using barium peroxide and phosphoric acid. In 1926 hydrogen peroxide was manufactured by an electrolytic process based on the decomposition of persulphuric acid (H2SOs).

Advantages and Disadvantages of Peroxide over Hypochlorite Bleaching

Advantages :
1. Peroxide is an universal bleaching agent and can be employed for wool, silk as well as cotton. It is specially suited to the bleaching of union fabrics containing both cotton and wool or silk.
2. Hydrogen peroxide is a milder reagent than hypochlorite and the degrading effect of peroxide bleaching on cellulose is less influenced than is the case with hypochlorite.
3. Peroxide is capable of continuing the scouring action simultaneously with the bleaching action, thus a single stage combined scour and bleach or a continuous method is possible using hydrogen peroxide.
4. Peroxide bleaching is in general less liable to have adverse effect on dyed threads. The white effect is good and permanent and there is less risk of yellowing at a later stage.
5. Thorough rinsing followed by scouring or antichlor treatment is required with hypochlorite bleaching, whereas with peroxide a comparatively short rinsing suffices.
6. With hydrogen peroxide, there is no danger of equipment corrosion, no unpleasent odours and no limitations as to processing techniques.
6. Increasing strict control over the discharge of AOX from chlorine bleaching liquors has led to a greater advantage of peroxide processes for bleaching cellulosic fibres.

Disadvantages:
1. Bleaching with peroxide is costlier than that of hypochlorite or bleaching powder.
2. Hydrogen peroxide bleaching requires stabilization usually with silicates which brings the risk of forming resist stains in subsequent dyeing, and causes a build-up of hard crystalline deposits on plant and machinery causing abrasion damage to the fabric during passage..
3. 'Catalytic damage' occurs during hydrogen peroxide bleaching of cotton fabrics and results in small spots of unevenly dyed fabric or even, in severe cases, the formation of small holes.
4. There is limitation in white obtained on acrylic fibres. It also causes deleterious effect on skin when used in a concentrated form..

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