Study On Photochemical Bleaching Of Pulp Based On Singlet Oxygen Mechanism

Photochemical bleaching of pulp based on singlet oxygen mechanism is a novel environmentally friendly bleaching method. In the article, photochemical bleaching of pulp based on singlet oxygen mechanism was investigated by using self-assembly device for photochemical bleaching.In the experiments, Tinolux(?) BBS and methylene blue (MB) were used as two different photosensitizers to activate oxygen into singlet oxygen. Photochemical bleaching technology of CTMP was optimized through orthogonal experiments with range and variance analysis, then the influence of primary factors on photochemical bleaching was determined and the probability of photochemical bleaching served as pre-bleaching of hydrogen peroxide bleaching was probed. At the same time the feasibility of photochemical bleaching technology for different pulp species was studied. The conclusions drawn according to experimental data were followed as:1.According to orthogonal experiment of L9(34), the optimum bleaching conditions of BBS as photosensitizer are followed as : temperature 65℃, Tinolux-BBS charge 0.05% (based on oven dry pulp), sodium hydroxide charge 1% (based on oven dry pulp) and time 120 minutes. The optimum bleaching conditions of MB as photosensitizer are the same as those of BBS except for MB charge 0.21% (based on oven dry pulp). The brightness gains of BBS and MB as photosensitizers are 4.81%ISO and 3.63%ISO respectively under the optimum bleaching conditions.2.Through the range and variance analysis of orthogonal experiments, the influencing prominence order of major factors for photochemical bleaching from high to low is photosensitizer charge, temperature, reaction time and pH value when BBS is served as photosensitizer, and the influencing prominence order is temperature, photosensitizer charge, reaction time and pH value when MB is served as photosensitizer. In these factors, photosensitizer charge and temperature are the most prominent for photochemical bleaching.3. When photochemical bleaching was used as the pre-bleaching of hydrogen peroxide bleaching of CTMP, the synergistic effect of photochemical bleaching on hydrogen peroxide bleaching was found. Therefore, photochemical bleaching served as the pre-bleaching of hydrogen peroxide bleaching of CTMP was totally feasible. However, the synergistic effect was not found for KP and deinked pulp from waste book paper.4.Selectivity of photochemical bleaching for KP was inferior to that of hydrogen peroxide bleaching. The brightness gain of CTMP was inferior to those of KP and deinked pulp from waste book paper under photochemical bleaching alone. Those conclusions showed photochemical bleaching maybe not suitable for KP and deinked pulp from waste book paper.The changes of functional groups in pulp before and after photochemical bleaching were also probed by FTIR in order to infer the changes of internal structure of pulp.