Synthesis and Application of Chitosan-Starch Graft Copolymers as Paper Strengthening Agent

摘要

A series of chitosan samples with different degree of deacetylation(DD)and different relative molecular weights were respectively used as dry-strengthening agents for handsheets made of wheat straw pulps.Then one kind ofchitosan that had most distinct dry-strengthening effect on pulp was selected to be used as the raw material for chitosan-starch graft copolymerization.Then a series of graft copolymers of chitosan with cation starch were synthesized and their strengthening effect on handsheets was experimented subsequently.It was found that the strengthening effect of the copolymer was better than that of unmodified chitosan.The strengthening experimental results showed that the optimum graft copolymerizing conditions was as follows: reaction time at 90°C was 2h,mchitosan:mstarch=1:4,the concentration of grafting agent(formaldehyde)was 0.8%(v/v).The breaking length and tearing index of handsheets made of wheat straw pulp were respectively increased by 25.6% and 16.9% with 1.0% dosage of the graft copolymer.In addition,mchitosn:mstarch was equal to 1:4 when the copolymer was synthesized ,which means that the dosage of chitosan in application as paper strengthening agent was effectively reduced by this modified method,so it is an efficient method to modify chitosan and apply it in paper pulp as dry-strengthening agent.