Soda-AQ pulping of softwood, the influence of cooking parameters on fiber properties and bleachability

The effects of cooking parameters on both delignification rate and on carbohydrate degradation in soda-AQ pulping of softwood were examined. In addition, the fiber properties as well as the bleachability of the soda-AQ pulps were studied. The cooks were performed in a flow-through reactor in which the chemical concentrations were constant throughout the cook, the reaction times were adjusted so that all pulps reached a target kappa of 26. A possible synergistic effect on cooking time decrease was found when both [OH(-)] and [AQ] were increased in the soda-AQ cook. Both pulp yield and viscosity at kappa number 26 went through a maximum with respect to the [OH(-)] in the cooking liquor. A viscosity gain at a given kappa number was obtained when [AQ] was increased at a given [OH(-)]. Results indicate that through optimization of [OH-(]) and [AQ] in the cook, soda-AQ pulps with Fiber strength, determined as zero-span tensile index, equal to that of kraft pulp can be produced. Increasing the [OH(-)] during cooking decreases the hydrogen peroxide consumption in order to reach a certain brightness during bleaching according to O(OP*)DQ(PO*). However, when the [AQ] was increased the hydrogen peroxide consumption in order to reach a certain brightness increased.