Preparation And Application Of The GPAM As Paper Stiffening Agent

Bending stiffness is of great importance for paper and paperboard. Secondary fiber is used in a large scale as the shortage of wood raw material in domestic, and this leads to the decreasing of paper stiffness properties. Paper mills have attached great importance on the paper stiffness and the improvement of bending stiffness of paper and paperboard has a very important significance. In this paper, the synthesis techniques and application of a novel stiffener were studied in detail, further the reinforcing mechanism of the stiffener on paper was discussed as well. Concrete work and major achievements included were as follows:1 The glyoxal-polyacrylamide resin (GPAM) was synthesized by two-step polymerization. In the first step, CPAM was prepared by radical polymerization with cationic monomer. In the second step, graft copolymerization occured between glyoxal and the backbone-CPAM, and then we got the finished product GPAM. The effects of the reaction conditions on the properties of the product and stiffness of handsheets were discussed, and the optimum reaction conditions were: dosage of initiating agents, dosage of DMC, reaction temperature, concentration of the monomers, pH of the reaction medium and reaction time of the first step were 0.3%, 25%, 45℃, 25%, 5.0～6.0 and 2h respectively; pH of the reaction medium, dosage of glyoxal, reaction temperature, concentration, and time of the second step were 5.0, 25%, 60℃, 10%, 90min respectively.2 GPAM was applied in handsheets as wet end additives, cellulose modifier and surface sizing agent to discuss how it affected the stiffness and RCT of paper.①As wet end additives. Factors such as other additives were discussed to see their effects on the stiffness and RCT of handsheets. The optimum conditions of GPAM applied in the white corrugated medium were: dosage of aluminum sulfate, dosage of cationic dispersed rosin, pH of slurry, beating degree, contact time with slurry were 2.0 %, 0.5%, 5～6, 40～45°SR, 5min respectively. The bending stiffness was with an increase of approximate 28% and RCT was with an increase of 17.5% when the dosage of GPAM was 0.75%. In addition, it could improve the retention of fiber to a certain extend.②As fiber modifier. Bending stiffness of OCC can be improved by modifying cellulose fibers of stock. Orthogonal experiments based on chemical dosage, reaction temperature and time were performed. Experimental results were shown as follows: the proper process applied with PAE were 1.0%, 80℃and 30min respectively; the proper process applied with GPAM were 0.5%, 90min and 30min respectively.③Surface sizing. GPAM, PAE, OST, and sodium silicate were used to discuss their stiffening effects on the white paper and corrugated medium. The results showed that surface sizing can improve the bending stiffness and RCT of paper. Tensile strength, folding endurance, tearing strength of sized paper can also been improved without decreasing whiteness.3 Mechanism of reinforcing the bending stiffness of paper was discussed.