| Bagasse, as one of the richest sources of non-wood raw materials, was significant for paper industry in our country. Combination of oxygen-containing bleaching with soda-oxygen pulping made another step towards achieving the clean pulping of non-wood materials. It is a key point how to improve the selectivity of ozone bleaching of alkali-oxygey pulp greatly, in order to obtain high brightness oxygen-pulp from TCF bleaching.In this paper, self-made high consistency ozone bleaching device was used to study the ozone bleaching of bagasse soda-oxygen pulp. The optimized ozone bleaching were carried out under pulp consistency of 40% with ozone flow of 0.9 kg-min-1/odt for 10min, using compound acids dosage of 1.35% at pH=2.5. The Kappa number of the resulted pulp decreased by 65.49%, brightness increased by 16.0%ISO and viscosity dropped by 55 mL·g-1.The research of TCF bleaching based on ozone bleaching showed that the Kappa number and brightness of bagasse soda-oxygen pulp were sensitive to ozone bleaching time, and 10 min more or less can be thought as a critical point. Supplementary P or Po bleaching stage can reduce yellow reversion, improve the stability of brightness, and their bleaching selectivity were better. Both ZP and Z (Po) give rise to high quality bleached pulp. The physical strength of both ZP and Z(Po) bleached pulp was generally stronger than unbleached pulp, maintaining the level of burst index, tensile index, tear index and folding number were 3.31～3.36 kP·m2·g-1, 54.0～56.9 N·m·g-1,4.92～5.43 mN·m2·g-1 and 142～201 times, respectively.Through the ozone bleaching of pulps from different materials and pulping methods, it is found that the excellent ozone bleaching performance of bagasse soda-oxygen pulp was attributed to the material characteristics itself and the pulping method.The measurement of pentosan content, carboxyl content and crystallinity degree showed that:the unbleached pulp and ozone bleached pulp were in the high content of hemicellulose. Adding additives such as compound acids in ozone bleaching had some protective effects on carbohydrates. Bagasse soda-oxygen pulp contained many carboxyl groups; they would be decreased with ozone bleaching prolonging. The additon of additives can help improve the crystallinity of ozone bleached pulp, and protected the cellulose.The distribution of each component in ozone bleaching waste liquor showed that ozone had a continued effect on pulp and its degradation products. Adding additive can increase delignification, protect carbohydrates, and improve the efficiency and selectivity of ozone bleaching.FTIR,13C-NMR and MS were used in studying the mechanism of delignification and carbohydrate degradation during the ozone bleaching of bagasse soda-oxygen pulp. The results showed that the ozone destroyed the methoxyl, side chain andβ-O-4 etc. in lignin structural units, and then the fragments dissolved from the pulp, however, the carbohydrates were also degraded. Adding additives enhanced the effect of ozone on lignin and its degradation products, and weaken the attack of ozone on carbohydrates, probably owing to getting rid of the oxidation of its C-H and C-OH bonds into ketones greatly, thereby increasing the selectivity of ozone bleaching process. |
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