Comparative study on the prebleaching of bamboo and hardwood pulps produced in Kharnaphuli Paper Mills

In order to lower bleaching costs, various prebleaching methods have been investigated. In the current work 3 prebleaching methods, peroxyformic acid, oxygen, and xylanase, were investigated in bamboo and hardwood kraft pulp produced by Kharnaphuli Paper Mills. Among these 3 methods, peroxyformic acid showed the most promising results. Peroxyformic acid prebleaching reduced kappa numbers by 38% and 30% and increased brightness by 12.2% and 8.6% in hardwood and bamboo pulp, respectively. Using 30 kg ClO2 t^–1 of pulp, hardwood pulp attained 77.2% brightness, while peroxyformic-acid–prebleached pulp attained 86% brightness without a reduction in viscosity in D0EpD1 bleaching sequences. To achieve 80% brightness, peroxyformic acid prebleaching saved 33% ClO2, while oxygen prebleaching saved 17% ClO2. Xylanase prebleaching was not an efficient method for these pulps. Bamboo pulp showed lower bleachability than hardwood pulp. The papermaking properties of the bleached pulps did not show significant variation after prebleaching, with the exception of tear index in peroxyformic-acid–prebleached pulp. When considering bleachability and papermaking properties, peroxyformic acid was the best prebleaching option for reducing ClO2 consumption.