ORIGINAL PAPER Comparison of Cationic and Unmodified Starches in Reactive Extrusion of Starch–Polyacrylamide Graft Copolymers J. L. Willett V. L. Finkenstadt Ó US Department of Agriculture 2009 Abstract Graft copolymers of starch and polyacrylamide (PAAm) were prepared using reactive extrusion in a cor- otating twin screw extruder. The effect of cationic starch modification was examined using unmodified and cationic dent starch (&23% amylose) and waxy maize starch (&2% amylose). For a fixed acrylamide/starch feed ratio, conversion, graft content, and grafting efficiency were essentially unaffected by starch type or modification. Cat- ionic starch graft copolymers generally had lower molec- ular weight PAAm grafts compared to the unmodified starch, whereas amylose content had little or no significant effect. In addition, the frequency of grafting was higher with cationic starch. These results indicate that cationic modification of starch enhances formation of grafting sites, resulting in graft copolymers with more grafts of lower molecular compared to unmodified starch. Cationic modi- fication may therefore be a way to tailor the properties of starch–PAAm graft copolymers. Keywords Starch Á Graft copolymers Á Reactive extrusion Introduction Starch graft copolymers offer opportunities to combine the hydrophilic, biodegradable, and environmental properties of starch with functional properties of synthetic polymers [1]. A wide variety of starch graft copolymers have been reported and described. We have reported the preparation of starch–polyacrylamide (PAAm) copolymers using reactive extrusion [2, 3]. In a recent report, we noted some differences in grafting properties between cationically modified starches and unmodified starches [4]. In particular, the molecular weights of grafted PAAm were lower with cationic star- ches, while the graft frequency was increased. Cationic starches therefore gave graft copolymers with more grafts of lower molecular weight PAAm compared to unmodified starches. In this report, we explore this effect further by expanding the acrylamide/starch feed ratios and the initi- ator concentrations. Materials and Methods The commercially available starches were provided by Tate and Lyle North America. Two unmodified starches (Pure Food Powder and Waxy 7350) and corresponding cationic modified starches (Stalok 300 and Stalok 180, respectively) were used as received. The average degree of substitution of the modified starches was approximately 0.03, corresponding to one cationic group per 30 anhy- droglucose units (AGU). PFP and Stalok 300 are referred to as normal corn starch (NCS) with approximately 25% amylose, whereas Waxy 7350 and Stalok 180 are waxy maize starches (WMS) with amylose contents of less than 2%. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. J. L. Willett (&) Á V. L. Finkenstadt Plant Polymer Research Unit, USDA-ARS National Center for Agricultural Utilization Research, Peoria, IL 616104, USA e-mail: jl.willett@ars.usda.gov 123 J Polym Environ DOI 10.1007/s10924-009-0145-8