HIGH TEMPERATURE PEROXIDE BLEACHING-AN ALTERNATIVE METHOD TO OBTAIN HIGH BRIGHTNESS FOR CHINA FIR CTMP PULP

摘要

The CTMP pulping properties of China fir by pressurized refining with various sodium sulfite dosages in chemical pretreatment stage were investigated. The alkali dosage and temperature during hydrogen peroxide bleaching are very important for improving the brightness of China fir CTMP. The research results show that, CTMP pulps of China fir have excellent bulk properties, and are suitable to be used as furnishes of board products. There is a light-color for CTMP pulp produced by atmospheric refining comparing with pressurized refining. The bleachability of the pulp produced by atmospheric refining is good. The better bleachability can be obtained when the sodium sulfite was applied in the pretreatment stage with the dosage as 25kg/t. oven dry pulp. For the one-stage hydrogen peroxide bleaching of China fir chemimechanical pulps, the suitable dosage of NaOH is about 45 kg/t. oven dry pulp at the usage level of 60 kg/t oven dry pulp of H2O2 to obtain a maximum brightness up to 80% ISO. High temperature bleaching (more than 85°C) is more effective and suitable for China fir CTMP pulps to bleach to a high brightness in short time (less than three hours) compared with conventional bleaching conditions as: temperatures, 70°C and 55°C.