Improving cellulose viscosity protection and delignification in ozone bleaching of low-consistency pulp with water-soluble chitosan

Abstract The effect of water-soluble chitosan (WSC) with molecular weights (Mw) from 1.0×104 to 1.0×106 on cellulose viscosity protection was explored during the treatment of low-consistency pulp with the ozone bleaching process (OBP). Through determination of the change in crystallinity, carboxyl content, and physical strength of ozone-bleached refined dissolving pulp, WSC was shown to effectively protect cellulose viscosity by scavenging free radicals and forming a protective film deposited on the fiber surface to prevent the destruction of cellulose by oxidants. During the OBP of sulfate hardwood pulp (SHP), application of a 0.5 % dose of WSC with a Mw of 1.0×105 increased not only the cellulose viscosity but also the selectivity of ozone delignification. The brightness, viscosity, and delignification selectivity of the bleached SHP were enhanced by 3.88±0.05 %, 13.0±0.10 %, and 76.6±0.50 %, respectively. Accordingly, the indexes of tensile strength, burst strength and tear strength of the resulting SHP hand sheet were increased by 38.6±1.0 %, 74.8±1.5 %, and 117.3±2.5 %, respectively. WSC had the best performance among the reported additives of equal weights for protection of cellulose viscosity in improving the pulp qualities after the OBP.