OXYGEN DELIGNIFICATION OF CHEMICAL WOOD PULPS REINFORCED BY VARIOUS SOURCES OF ALKALI

Abstract

Sodium hydroxide is used in oxygen bleaching because it ionized the phenolic groups of lignin to initiate the bleaching process. However being a strong alkali, it can causes cellulose degradation. Weak alkali such as calcium hydroxide used as substitution for sodium hydroxide to conserve the pulp strength. The impacts of the substitution of sodium hydroxide by calcium hydroxide on softwood and mixed hardwood pulp were characterized by the different pulp properties such as the brightness, kappa number, pentosan content, sugar composition, mechanical properties and pulp viscosity of the pulp. The effect of the substitution of sodium hydroxide by calcium hydroxide was investigated after oxygen stage with alkali substitution and after complete bleaching sequence