Synyhesis of graft copolymers of cassava starch and styrene by free-radical polymerization

Abstract

Graft copolymers of cassava starch and styrene monomer were synthesized by free radical polymerization using benzoyl peroxide as initiator in aqueous medium. The influence of the ratio of starch and styrene monomer, the amount and purity of benzoyl peroxide, the mixing method, the reaction temperature and time were studied. In this experiment, each 5.0 g of starch and styrene monomer with 0.5 g of benzoyl peroxide, mixed and synthesized at 80℃ for 2 hours, provided 35.84 percent add-on, 95.64 percent conversion, 46.09 percent homopolystyrene formed, 53.91 percent grafting efficiency, 51.26 percent grafting ratio, and 88.08 percent yield, FT-IR was used to characterize the chemical structure of graft copolymers whereas DSC and TGA were employed to investigate the thermal properties. GPC revealed that the propagation rates of both homopolystyrene and grafted polystyrene were the same in terms of molecular weight and molecular weight distribution. Homopolystyrene beads were formed in this system via suspension polymerization and they were removed after Soxhlet extraction as presented in morphological analysis. This graft copolymer showed higher tendency to be soluble in solvents which can solubilize starch than in solvents which can solubilize polystyrene. Its percent moisture absorption was in between those ungrafted starch and polystyrene.