IMPROVED OXYGEN DELIGNIFICATION FOR MAGNESIUM-BASED SULFITE PULPS

Addition of a catalytic quantity of sodium borohydride to the magnesiu m-based oxygen delignification of sulfite pulps improves pulp yield, v iscosity, and strength properties. A proposed mechanism to explain thi s behavior assumes that carbonyl groups on the cellulose molecules of sulfite pulps promote cellulose degradation during oxygen delignificat ion. Treatment of pulp with sodium borohydride reduces the carbonyl gr oups to hydroxyl groups, thus stabilizing the cellulose against degrad ation during the oxygen delignification stage. It was found experiment ally that sodium borohydride is reasonably stable under the conditions of a magnesium oxide-based oxygen delignification stage. Therefore, p ulp reduction by sodium borohydride and oxygen delignification can be performed simultaneously in a single stage.