Study On Dissolved And Colloidal Substances Released During The Recycling Of ONP

The recycled fibers have become important raw materials for pulp and papermaking, but a lot of contaminants such as pressure-sensitive adhesive, hot melt adhesive, coating adhesive and ink dispersed in the pulp suspension during waste paper recycling. The contaminants could deposit on the forming wire, press section and dryers or the surface of paper sheets, which was harmful to the production efficiency and the product quality.The dissolved and colloidal substances released during the recycling of American 8# old newspaper were investigated in this thesis. First, the DCS released during the pulping of ONP and bleaching of the de-inking pulp was studied, and the qualitative analysis of the resin and fatty acids were performed by GC-MS. Then the release dynamics of the resin and fatty acids were studied, and the quantitative analysis of them was carried out by GC. Finally, the interactions between cationic polymers and DCS were researched.The physical permances of DCS releasing during pulping of ONP were determined, and the results showed that the dissolved substances contribute largely to the conductivity of the DCS, while the colloidal substances are responsible for the turbidity. The cationic demand comes from both the dissolved and colloidal substances. In the process of pulping, with the increase of NaOH dosage, H2O2 dosage and the time of pulping, the cationic demand and conductivity of DCS are both improved, and the absorbance at 280 nm was also increased.The qualitative and quantitative analysis of the DCS released during the pulping was determined by GC-MS and GC, and the results showed that the amount of fatty acids was higher than that of the resin acids. The fatty acids were rich in palmitic acid and hexadecanoic acid, while the resin acids were rich in isopimaric acid and dehydroabietic acid. The resin and fatty acids were easily transformed to water-solubility soap because of the existence of NaOH, and their contents increased with the increase of NaOH dosage. The time of pulping also accelerated the release of the resin and fatty acids.The alkaline hydrogen peroxide bleaching further promotes the release of DCS. The increase of NaOH, H2O2 dosage and temperature would result in the increase of cationic demand, conductivity and absorbance at 280 nm during the bleaching of deinked pulp. The resin and fatty acids during bleaching process were analyzed by GC. It was shown that the released resin and fatty acids increased significantly with the increasing of NaOH and H2O2, the bleaching temperature also promoted the releasing of them. The components of resin and fatty acids releasing in bleaching process were same as those in pulping process.In this work, the interactions of the cationic polymers including poly (diallydimethylammonium chloride)(PDADMAC), CPAM and DCS were studied. The residual turbidity and cationic demand of DCS water showed the flocculation efficiency of cationic polymers. The results showed that different amount of PDADMAC and CPAM were needed to destabilize DCS completely for their different cationic charge density and different flocculation mechanisms for DCS. The flocculation mechanism of PDADMAC was mainly the charge mosaic mechanism for its high cationic charge density and the flocculation mechanism of CPAM was mainly the bridge flocculation due to its low cationic charge density and its molecular conformation.