A graft copolymer was synthesized by copolymerization of gelatin with methylacryloxyethyl-trimethylammoniuM chloride (DMC), acrylamide (AM) and 2-acrylamido-2methyl propane sulfonic acid (AMPS). The copolymerization was conducted in aqueous solutions initiated by redox initiator. The product was a kind of amphoteric graft copolymer. The effect of reaction conditions, e.g., the concentration of monomers and initiator, the reaction time, the temperature, the pH as well as the total solid content on graft copolymerization, were discussed. The optimuM conditions were that the temperature was 50°C, the reaction time was 6h, the pH value was 7, the total solid content was 12%, the concentration of the initiator was 1.25%, the weight ratio of AM and DMc was 4: 1, the ratio of cationic monomer to anionic monomer was 1: 1.5, and the cationic monomers should be added into the system earlier than the anionic monomers. The existence of the amphoteric gelatin could be proved by the IR analysis of the graft copolymer. When the graft copolymer was used as a dry strength agent for bleached wheat straw pulp, the breaking length and burst index of the handsheets were remarkably improved.
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