Reactive Extrusion of Starch–Polyacrylamide Graft Copolymers Using Various Starches

Graft copolymers of polyacrylamide and various substrates were prepared by reactive extrusion in a twin screw extruder using ammonium persulfate as initiator. Substrates included unmodified starches (corn, waxy maize, wheat, and potato), cationic starches, dextrin, dextran, and polyvinyl alcohol (PVOH). The feed ratio of substrate to monomer was 2:1. Average conversion of monomer to polymer was 88.9% (±5.1%). Graft contents for the starch substrates were approximately 25% with grafting efficiencies of about 70%. Polyacrylamide graft molecular weights ranged from 317,000 to 769,000. Absorbencies at pH 7 for saponified graft copolymers prepared with unmodified starches were approximately 200 g/g and approximately 150 g/g for the cationic starches, dextran, and PVOH. In electrolyte solution (0.9% NaCl), absorbencies were in the range of 26–59 g/g, depending on substrate type. Saponified dextrin copolymers were essentially soluble with absorbencies of 6 g/g in water and 12 g/g in 0.9% NaCl.