Pulping and bleaching of plantation fast-growing acacias (Part 2) - Comparison of conventional and modified kraft cookings

When the conventional kraft pulping was applied for Acacia auriculiformis, the transition from the initial to the bulk delignification phase occurred at about 22% delignification and at a temperature 130 to 140°C. Yield and viscosity loss became significant when the kappa number of the pulp was lower than 18. Based on these observation, two modified kraft cooking processes were applied in this study, pretreatment of wood chips with a sodium sulphide solution and with a high sulphidity white liquor, to obtain low kappa number pulp from Acacia auriculiformis. Although it was confirmed that pretreatment by these two methods followed by kraft cooking resulted in 3 to 4 kappa number reduction, this reduction were not as large as expected when the viscosity loss was minimized. Because a pulp of kappa number 18 can be easily obtained from this wood by the conventional process in an acceptable yield and viscosity, it does not seem to be beneficial to apply modified cookings to the pulping of this wood.