Technology for total chlorine-free bleaching of kraft pulp

Abstract

Acid treatment was developed for non-chlorine bleaching of an oxygen-delignified hardwood kraft pulp. About 70% hexenuronic acid in the kraft pulp was removed after the acid treatment at pH 3 for 1 hour at 105°C. After full bleaching with the acid treatment (A) followed by the ozone (Z) and the hydrogen peroxide (P), the final brightness of the pulp reached approximately 85% ISO, keeping the viscosity over 15.0 cP. Little hexenuronic acid existed in the kraft pulp after this bleaching (A-Z-E-P). Furthermore, the brightness stability of this pulp was much better than that of chlorine dioxide bleached pulps.