However, below pH 3.5 the chlorite decomposes too rapidly for efficient bleaching. This practice conserves bleach because only the bleach in contact with the plant material is activated to decompose. Hydrogen peroxide IS available commercially as a 50 per cent solution. Typically peroxide will remove about half the lignin before cellulose fibres are damaged, hence it is an ideal first bleach in a multi-step process. On the other hand, a light peroxide bleach is often used after chlorite bleaching to increase resistance to yellowing.
Peroxides are extremely sensitive to trace metal contamination, which causes rapid decomposition.
Peroxide bleaches best at pH 10.5. Above this point it becomes unstable and decomposes too rapidly, whereas a lower pH results in a slow rate of bleaching. Hydrosulphite is widely used for paper bleaching. Hydrosulphite has maximum bleaching power at pH 5.5 to 6.0. It is stable in alkaline solution.