Morphological Studies of Potato Starch Modified by Grafting Using Mn³⁺ as Initiator and by Saponification

Abstract

A series of starch‐g‐polyacrylonitrile copolymers of starch granules and starch gel were synthesized with the Mn3+ initiating system. The samples were examined and photographed in a scanning electron microscope before and after homopolymer extraction in N, N‐dimethylformamide., The grafted starch was hydrolyzed in aqueous acid solution to remove the starch moiety. The graft copolymers were also saponified with aqueous sodium hydroxide to convert nitrile groups to carboxamide and sodium carboxylate groups. The micrographs show that polyacrylonitrile is grafted both on the surface and in the interior of the granule. At higher grafting ratios the products contain increasing amounts of grafts inside the granule, but the centre of the granule is always hollow. The saponified graft copolymer retains its granular structure, in spite of the swelling and the high temperature during the hydrolysis, although the surface of the granules becomes smoother.