Chlorine-free Bleaching of Eucalyptus Kraft Pulp Using a Mixture of Peroxymonosulfuric Acid and a Trace of Chlorine Dioxide

This study proposed eco-friendly chlorine-free bleaching as a method of pulp production for papermaking. As a wood species with excellent cooking ability, 12-year-old Eucalyptus globulus wood chips were kraft-cooked and oxygen (O)-bleached in a laboratory, and then the bleaching response was evaluated. In addition, these were compared with an O-bleached kraft mill pulp (LOKP), which was produced in a mill from mixed wood chips of E. globulus and Acacia spp. A five-stage bleaching sequence (O-P-sa-E-p-P-sa-E-d) using O-bleaching, peroxymonosulfuric acid (P-sa) treatment and alkaline hydrogen peroxide (Er) treatment was adopted. Produced E. globulus kraft pulp (yield : 50.1%, kappa number : 16.0. brightness : 33.3% ISO, viscosity 72.2 mPa.s) provided a bleached pulp with brightness of 88.6% ISO and viscosity of 10.8 mPa-s. Using a modified bleaching process by adding a small amount of CIO2 to the P-sa stages in a sequence of O-(P-sa+CIO2)-E-p-(P-sa+CIO2)-E-p, viscosity of the bleached pulp was increased to 12.3 mPa.s with no significant change in brightness. The LOKP resulted in brightness of 90.1% ISO and viscosity of 8.7 mPa.s in the 0-13.-Ep-P.-E, sequence, and the viscosity was improved to 9.4 mPa.s in the O-(P-sa+CIO2)-E-p-(P-sa-+-CIO2)-E-p sequence.