Effect of H2O2 bleaching with ultrasonication on the properties of thermomechanical pulp and unbleached kraft pulp

The best bleaching efficiency of pulp was obtained using H2O2 with ultrasonication (at 20 kHz) of the pulp mixture at 45 °C for 30 min. The ISO brightness of the bleached pulp increased up to 1.9%, although the bleached pulp yield was slightly reduced to 1.5%. Magnesium sulfate was used as a bleaching stabilizer to increase the bleached pulp yield and viscosity. As a result, the bleached pulp yield and viscosity increased by 2.1% and 10%, compared with fully bleached pulp at the end of the process, respectively, despite a decrease in ISO brightness.