Bleaching of Refiner Mechanical Pulp by a NaOCl·peroxide System and the Characteristic Properties of Bleached Pulp

In order to modify refiner mechanical pulp (RMP), NaOCl·H2O2 and Na0Cl·O3 bleaching of the pulp were carried out under mild conditions. The results obtained were as follows.(1) RMP prepared from mixed soft wood was soaked in NaOCl solutions (available chlorine 1-6%, pH 11) for 10 min at room temperature, and after removing excess NaOCl solution, bleached with H2O2 solutions for 1 hr at 50°C or with O3 at 20°C under gaseous phase for a definite time.The brightness of RMP bleached by the above two methods under optimum conditions increased from 46 to 70% GE. The yield of pulp bleached by a NaOCl·H2O2 system was about 93%. The residual lignin and pentosan contents in the pulp were relatively high. The water retention value and the sheet density of RMP also increased by the bleaching. The tensile strength and tear factor of RMP sheet after bleaching were 3.5 km and 57, respectively.(2) The bleaching of RMP by NaOCl·H2O2 system was clearly a more effective method than NaOCl·O3 system. The brightness and yield of RMP bleached by NaOCl·H2O2 system under optimum conditions were higher than those of NaOCl·O3-bleached RMP. The tensile strength of the NaOCl·H2O2-bleached pulp was lower than that of the NaOCl·O3-bleached pulp, whereas the tear factor was stronger.(3) Comparison of the physical properties and mechanical strengths of RMP and TMP bleached under optimum conditions indicated that NaOCl·H2O2 system is generally a more effective method than NaOCl·O3 bleaching