Parameters in peroxide bleaching operations

It is very difficult to specify strict guidelines for optimum bleaching conditions for hydrogen peroxide as the operation is normally affected by the nature and quality of the goods to be bleached, the amount of bleaching required and on the equipment available. However, the following general variables are considered to be important  

In practice cotton bleaching with hydrogen peroxide is carried out at 90-100°C, but the temperature may be increased to 120°C in the case of pressurised equipment with a corresponding reduction in process time. The rate of bleaching increases with the increase in temperature, but at the same time solution becomes unstable and degradation of cotton increases. Below 80 C, the evolution of perhydroxyl ion is very slow so also the rate of bleaching. 

The optimum concentration of hydrogen peroxide depends on number of factors namely liquor ratio, temperature and class of fibre. In the batch process using kiers about 2-4% (o.w.f.) hydrogen peroxide is sufficient for cotton fabrics with a liquor ratio of 10 1 to 20 1. In the continuous process, the cotton fabrics are saturated with bleach bath containing 1 -2% (o.w.f) hydrogen peroxide. Very high concentration may damage the fibre. 

The time required to bleach with hydrogen peroxide depends on temperature, class of fibre and equipment used for bleaching. In general, the time of bleaching is inversely proportional to the temperature of the bleaching bath. Cotton may be bleached in open kiers by circulating heated hydrogen peroxide solution (88-95 C) for 6 to 10 hours. 

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