Submitted to: Macromolecular Chemistry and Physics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 7, 2005
Publication Date: July 26, 2005
Citation: Finkenstadt, V.L., Willett, J.L. 2005. Reactive extrusion of starch-polyacrylamide graft copolymers: effects of monomer/starch ratio and moisture content. Macromolecular Chemistry and Physics. v.206:1648-1652. Interpretive Summary: It is often necessary to chemically modify starch to provide specific properties desired for end-use applications. Starch modification often requires large quantities of water and can generate significant amounts of undesired by-products. We have demonstrated the potential of a rapid, continuous process known as reactive extrusion to modify starch and other agricultural materials while using much less water than conventional processes. Two important variables in reactive extrusion of starch are the amount of water (moisture content) and the concentration of modifying agent. We have found that these variables significantly impact the efficiency of the reaction as well as the properties of the modified starch. These results demonstrate the potential of producing starch-based materials with specific properties through control of processing and composition variables. This process may lead to new materials based on starch, with reduced environmental impact of processing.
Technical Abstract: The effects of monomer/starch feed ratios and moisture content during reactive extrusion of starch-polyacrylamide graft copolymers were investigated. Acrylamide/starch ratios ranged from 0.20 to 1.87 at 50% moisture content, while moisture content was increased from 45% to 75% with an acrylamide/starch ratio of 0.33. Conversion of monomer to polymer was essentially independent of monomer content and ranged from approximately 85% to approximately 95%. Molecular weight of grafted polyacrylamide increased as the acrylamide/starch ratio increased. Graft efficiency was constant at approximately 75% for monomer/starch ratios of 0.77 or less, and decreased to 52.3% as the monomer/starch ratio increased to 1.87. Higher acrylamide/starch ratios gave more frequent grafts of higher molecular weight. As moisture content decreased from 75% to 45%, conversion and graft content increased from 78% and 14% to 97% and 23%, respectively. Lower moisture content gave fewer grafts of higher molecular weight. Ungrafted polyacrylamide homopolymer increased with monomer/starch ratio and moisture content. These results indicate that graft copolymer properties can be controlled through the monomer/starch ratio and moisture content during reactive extrusion.