Submitted to: Polymers and the Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/30/2005
Publication Date: 3/18/2006
Citation: Willett, J.L., Finkenstadt, V.L. 2006. Reactive extrusion of starch-polyacrylamide graft copolymers using various starches. Polymers and the Environment. 14:125-129. Interpretive Summary: Starch, a renewable product from crops such as corn, wheat, and potatoes, is a low-cost raw material that offers opportunities for the development of functional polymers. One approach to improving starch functionality is the formation of starch graft copolymers (SGPs), which combine the properties of starch with synthetic polymers. Using a continuous process called reactive extrusion, we have prepared SGPs and evaluated their use as superabsorbents which are capable of holding more than 100 times their weight in water. We have found that the water absorbent properties depend on the type of starch used to make the SGP, and that native unmodified starches give higher absorbencies than modified starches. These results demonstrate the potential of producing starch-based superabsorbents using a continuous extrusion process, which has benefits compared to the conventional batch process. These starch-based superabsorbents offer new market opportunities for starch, and improve the economic competitiveness of U.S. agriculture.
Technical Abstract: 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 g/g to 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.