Comparison of Cationic and Unmodified Starches in Reactive Extrusion of Starch–Polyacrylamide Graft Copolymers

Graft copolymers of starch and polyacrylamide (PAAm) were prepared using reactive extrusion in a corotating 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. Cationic starch graft copolymers generally had lower molecular 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 modification may therefore be a way to tailor the properties of starch–PAAm graft copolymers.