Hypochlorite Bleaching Of Straw Chemical Pulp At High Temperature And Its Mechanism

The straw is the significant material for pulping and paper making .Almost paper mills are always bleaching the non-wood pulp by H\HP. In this article the non-wood pulp including the reed-AP,wheat straw-AP and wheat straw SFP were bleached by hypochlorite and HTP. The effects of effective chlorine charge, bleaching temperature and time on pulp brightness, viscosity, as well as kappa number were investigated. Vanillin and 3,4-Dimethoxybenzaldehyde were used as phenolic and non-phenolic lignin model compounds. they reacted with hypochlorite at a high temperature, then the varieties of their structures were investigated. The sufficient conclusions are drawn as follows:1. Through bleaching at high temperature (HT), the reed-AP reached a lower kappa number and higher brightness than through bleaching at normal conditions (HC). And in high temperature, lignin is activated, so that in the following P sequence, delignification react more easily。After HTP good viscosity can be achieved。2. The optimum bleaching conditions for reed-AP are, temperature 70℃, time 15min, effective chlorine charge 5%。3. COD of the waste water after HT bleaching of reed-AP increases with bleaching temperature increasing, COD HT at 70℃is 19% higher than HC4. The effection of bleaching by HT is more excellent for wheat straw-AP than SFP.5. Kappa number of bleached wheat straw-AP and wheat straw SFP drops in accordance with the increase of effective chlorine and bleaching temperature, and a lower kappa number of H bleached pulp can be obtained at 75℃. However, it goes up a bit while bleaching temperature is 90℃. Pulp goes up rapidly with the increase of effective chlorine charge and bleaching temperature。a highest brightness of H bleached pulp can be obtained at 75℃. The effect of bleaching time on pulp kappa number and brightness is not evidently.6. The optimum bleaching conditions for wheat straw-AP and wheat straw SFP are, temperature 70℃, time 10min, effective chlorine charge 5%.7. The effection of HTP is infected by the conditions of HT.8. Phenolic lignin model is able to react with hypochlorite, however the non-pHenolic is not.9. The reaction of vanillin and hypochlorite is affected by temperature, but not the time. At a high temperature, the benzene ring is damaged more seriously, and more oxidation generated.10. At a high temperature, more oxidation reactions occurred between ClO- and carbohydrates, so that genetated more organic acid.