| Abstract: | Graft polymerization of acrylamide onto rice starch was investigated under different conditions using potassium persulphate, benzoyl peroxide or potassium permanganate as initiator. This has led to establishment of the most appropriate grafting conditions for each of these initiators. Under these conditions grafting was characterized by two rates regardless of the initiator used. The first rate occurred during the initial stages of polymerization while the second during the later stages. The first rates of grafting for the three initiators were very close indicating the insignificant effect of the nature of the initiator on grafting during the initial stages of the reaction. On the other hand, the second rates of grafting exhibited the order: potassium persulphate < benzoyl peroxide < potassium permanganate, reflecting the role played by the nature of initiator during the later stages of the reaction. Substantial differences in solubility were observed between polyacrylamide-starch graft copolymers and unmodified starch as well as among copolymers prepared using the three initiators. Although the copolymers acquired higher solubility percent than the unmodified starch, yet nature of initiator, graft yield, structural changes in the copolymer occuring during grafting and the temperature of solubility measurement determined the solubility percent. Copolymers prepared using benzoyl peroxide or potassium persulphate showed lower viscosity than the unmodified starch. The opposite was the case with respect to copolymer prepared using potassium permanganate. |
