A Study Of Totally-Chlorine-Free Bleaching Of Masson Pine Kraft Pulp For High Brightness

The following aspects had carefully been studied in this thesis. The first was one-stage as well as two-stage oxygen delignification process of masson pine kraft pulp. The second was activating pretreatment before oxygen delignification. The third was stabilization of pulp viscosity during the course of oxygen delignification. The fourth was subsequent hygrogen peroxide bleaching and its pretreatment.Finally,based on the former studies, a total chlorine free(TCF) bleaching sequence for masson pine kraft pulp had been put forward. Meanwhile,the mechanism of activating pretreatment before oxygen delignification and hydrogen peroxide bleaching had also been investigated in this thesis.The study on two-stage oxygen delignification of masson pine kraft pulp showed that the relatively suitable condition were as follow, the first stage: 4.0%NaOH, 0.5%MgSO₄, 50min at 80 ℃, 12%consistency and 0.6Mpa oxygen partial pressure. In the second, all the conditions were the same as the first stage except the temperature, which was 90 ℃ instead of 80 ℃. By means of the two-stage oxygen delignification,the pulp with Kappa number 8.06; intrinsic viscosity 687cm3/g and brightness 45.0%(SBD) could be achieved.Acidified hydrogen peroxide, Sodium nitrite, Chlorine, Caro's acid and an activating agent(named as X) were used to treat the pulp before its oxygen delignification to improve its delignifying selectivity. The results showed that chlorine and the activating agent were the best among these agents,a high level of delignification (about 60%) was achieved while maintaining acceptable pulp viscosity. Especially, when...