New Bleaching Method for KP with Permanganate (I).

New pulp bleaching method with permanganate was examined using hardwood KP and OKP. Permanganate is a strong oxidant and converted to manganate via manganese dioxide by reaction with reductants such as pulps under acidic conditions. In this study, kraft pulps are treated with permanganate under mild acidic condition at 70°C. After the treatment, pulps were washed with water two times. Degradation products from lignin and manganese compounds deposited on the surface of pulps were dissolved successfully by washing with water.The K value of hardwood kraft pulps were easily decreased by the permanganate treatment. The selectivity in permanganate delignification seemed to be better than in ozone delignification. A combination of an oxygen stage and a permanganate stage with a small charge of permanganate was preferable. Physical properties of treated pulps were not changed by the permanganate treatment as far as optimum condition were used. Permanganate treatment followed by hydrogen peroxide bleaching yielded high brightness pulps, indicating the possibility of TCF bleaching sequence using permanganate stage.