Study On Bleaching And AKD Sizing Technology Of Waste Newspaper Deinked Pulp

With the development and progress of the society, the demand of paper was constantly growing and the quality requirement of paper was higher and higher. So far the proportion of straw which accounted for papermaking raw materials decreased year by year, but the amount of waste paper significantly increased and newsprint production exceeded demand. In order to expand the use of waste newspaper deinked pulp, bleached waste newspaper deinked pulp was mixed in other fibers to make common culture paper. Because the brightness of waste newspaper deinked pulp was low, and there were fewer surface sizing devices in newsprint paper machine in China, it was necessary to work on bleaching and the inner sizing technology of waste newspaper deinked pulp.Waste newspaper deinked pulp was mainly composed of mechanical pulp and chemi-mechanical pulp. So, bleaching agent and bleaching method which were suitable for mechanical pulp were used in bleaching waste newspaper deinked pulp. The technology of hydrogen peroxide (P) and formamidine sulphinic acid (F) single stage bleaching and hydrogen peroxide-hydrogen peroxide (PP) and hydrogen peroxid-formamidine sulphinic acid(PF) two stages bleaching of waste newspaper deinked pulp was emphatically investigated. The results showed that the brightness of waste newspaper deinked pulp could reach to 64%(ISO) for adopting hydrogen peroxide single stage bleaching. However, it was up to 59%(ISO) in formamidine sulphinic acid single stage bleaching which showed worse bleaching ability than hydrogen peroxide. For the two-stage bleaching of the waste newspaper deinked pulp, 4%H2O2-4%H2O2 two stages bleaching with 20.1%(ISO) brightness gain was better than 4%H2O2-1.6%FAS two stages bleaching.Referring to the main quality index of culture paper, the culture paper which was made of 70% of bleached waste newspaper deinked pulp mixed with 10% of softwood pulp and 20% of hardwood pulp could reach to national standard. Comparing with CS (Cationic Starch)/Silica sol retention system, CPAM(Cationic Polyacrylamide)/Bentonite retention system would be better for the pulp system which contains more deinked pulp. Additionally, the best addition order was CS - AKD - PCC (Precipitated Calcium Carbonate) - CPAM - Bentonite. In this sizing system, the effect of sizing was enhanced by adding CS to neutralize the anionic trash in the pulp before adding AKD. But if PCC (Precipitation Calcium Carbonate) was added before sizing agent, it will do great harm to the retention of AKD (Alkyl Ketene Dimer) and the sizing performance.In addition, orthogonal test was designed to optimize AKD sizing process. And the optimal conditions were as follows:AKD dosage 0.4%, CS dosage 0.6%, PCC dosage 5% and CPAM dosage 0.03%. As the addition amount of AKD increased, Zeta potential value also decreased. The variation tendency of sizing performance was essentially consistent with the Zeta potential value and cationic demand of furnish. Meanwhile, the results showed that the Zeta potential value and cationic demand of furnish system were obviously influential in the AKD sizing performance. The Zeta potential value and cationic demand decreased with the addition of CS increasing, and the effects of CS on the Zeta potential value of pulp were stronger than AKD on the Zeta potential value of pulp.