Starch - g - Polyacrylamide based Hydrogels, Graft Copolymerization initiated by NO2

摘要

The graft copolymerization of acrylamide and starch was carried out in an aqueous solution of NO2 in the presence of N,N' - bisacrylamide crosslinker at 50°C. The effects of concentrations of acrylamide, starch, initiator and crosslinker on the polymer yields were investigated. The yield increased with acrylamide concentration in the feed ratio whereas it showed an increase and then started to decrease with starch concentration in the feed ratio. The degree of swelling of the hydrolyzed graft copolymer was determined in deionised water and found to be about 400 which is comparatively lower than that of polyacrylamide. The degree of swelling of unhydrolyzed graft copolymer was significantly low. The hydrolyzed polymers contain both amide and carboxyl groups in their chains which are highly polar. Thus the swelling increases due to an increase of ionized groups. The water absorbency of the graft copolymers increased with the increase of the concentration of acrylamide in the feed ratio, whereas it also increased with the increasing concentration of starch in the feed ratio but after certain level of starch concentration increased, it began to decrease. It was observed that the increase of degree of crosslinking caused the decrease in the degree of water swelling. The hydrogels, so obtained, is capable of undergoing sevral swelling and deswelling cycles indicating its reversible character.