Graft polymerization of cationic methacrylate, acrylamide, and acrylonitrile monomers onto starch by reactive extrusion

Abstract

Starch graft copolymers were prepared from cationic methacrylate (CM), acrylamide (AAm), and acrylonitrile (AN) monomers by continuosu twin-screw extrusion processing. The monomers were reacted separately with cornstarch under various conditions in the extruder with ceric ammonium nitrate (CAN) as the initiator. The purpose of the study was to determine the feasibility of grafting substantial levels of monomer onto the starch within brief reaction periods of 3-7 min. Effects of temperature, monomer-starch weight ratio, starch concentration, CAN addition level, screw speed, and other variables in the extrusion process were studied. For comparison, starch graft copolymers from these monomers were prepared by typical 2-hr batch processes at relatively low mineral concentration, temperature, and shear stress conditions. In extrusion processing, starch graft polyacrylonitrile (St-g-PAN) copolymer products with high conversion of monomer to polymer (74-78%) and high synthetic polymer add-on (42-44% of product weight) were achieved within a reaction period of 7 min. Under similar extrusion conditions, add-on was 16-19% and conversion was 19-23% for AAm. Maximum add-on was only 6.7% for the CM monomer. AAm also was reacted with waxy maize to give 18-23% add-on. The waxy maize copolymers were more water soluble than the cornstarch copolymers. Results suggest that the continuous extrustion process could be particularly promising as a viable means of rapidly and efficiently producing St-g-PAN copolymers that are useful after saponification as commerical water-absorbent materials.