Mordanting and peroxide bleaching

The best chance for an efficient bleaching of highly pigmented wool with minimum fibre damage is provided by the use of metal catalysts in a mordanting step preceeding peroxide bleaching. 

Mordanting is done in presence of hypophosphorous acid and it is an excellent stabiliser for iron (II) ions under mordanting conditions (Table 6.2). More impor- 

In the second stage, bleaching is carried out in alkaline condition of hydrogen peroxide. Iron that settles on the surface and inside the fibre acts as a catalyser and brings about enhanced bleaching action by extremely reactive radicals (HO  

HO2 ) that are produced from oxidising agent. The bleaching conditions are summerised in Table 6.3. Tetrasodium pyrophosphate (diphosphate) (10 g/1) is a TABLE 6.3 

Fibre type Hp (35%) (ml/1) pH (adjusted with amm. hydroxide) Temp. (°C) Time (min) 

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