Investigation on Optical and Mechanical Properties of MOW Deinked Pulp by Neutral Deinking

Literature and purpose: conventional alkaline deinking has some limitations such as yellowing mechanical fibers in alkali environment (alkaline darkening), low yield due to the dissolution of most of the material in the presence of chemicals, increasing costs and water effluent result from chemicals such as sodium hydroxide and sodium silicate. These limitations caused trends to reduce the pH of repulping to a neutral level, which is known as neutral deinking. This study was done to investigate the possibility of using neutral deinking as an alternative for alkaline conventional deinking of mixed office waste papers, to reduce the problems like alkaline darkening and waste waters pollution load.
Materials and methods: Mixed office waste papers was treated using sodium sulfite at three levels of 1, 2 and 3 percent (base on oven dry weight of pulp) at treatment times of 15, 30 and 45 min. The physical, mechanical and optical properties of deinked pulp were measured according to standard TAPPI test methods.
Results: The results of the Scoring equation shown that treatments A, B, C, D, E, F, G, H and I, have scores of 5095/1, 4517/1, 4735/1, 407/1, 4875/1, 4843/1, 5416/1, 5266/1 and 4963/1 respectively, And blank treatment with 5821/1score among all treatments was rated higher. But among neutral deinking treatments, G and H are the highest ratings. Which has 3% sodium sulfite and time are 15 and 30 minutes respectively. So, the use of 3% sodium sulfite as the optimal value for the chemical treatment that can replace for chemicals in conventional methods, such as sodium hydroxide, hydrogen peroxide, sodium, etc. Times 15 and 30 had a better condition than 45 minutes; it can be used as chemical treatment time in the re-pulping stage.
Conclusion: The results showed that treatment with 3% sodium sulfite for 15 and 30 min had better results than other treatments. Also scoring method indicated that treatment by 3% sodium sulfite for 30 min which used for deinking of MOW pulp had higher score compared with other treatments and also conventional alkaline deinking treatment. In other words, it has the best results in both optical and mechanical properties. The results of optical and mechanical investigations of this treatment were close to the conventional alkali treatment and can be suitable alternative for conventional method.
Conclusion: The results showed that treatment with 3% sodium sulfite for 15 and 30 min had better results than other treatments. Also scoring method indicated that treatment by 3% sodium sulfite for 30 min which used for deinking of MOW pulp had higher score compared with other treatments and also conventional alkaline deinking treatment. In other words, it has the best results in both optical and mechanical properties. The results of optical and mechanical investigations of this treatment were close to the conventional alkali treatment and can be suitable alternative for conventional method.