Location: Plant Polymer Research
Title: Properties of extruded starch-poly(methyl acrylate) graft copolymers prepared from spherulites formed from amylose-oleic acid inclusion complexes Authors
Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 30, 2013
Publication Date: N/A
Interpretive Summary: Soft, flexible plastic materials can be chemically bonded to starch granules by procedures that were developed earlier at NCAUR. Chemically combining soft plastics with hard, rigid particles of starch produces tough plastic materials that can be molded or extruded to form biodegradable consumer articles such as planting containers. Since these products contain about 50 % starch, they will biodegrade in the soil and will therefore not contaminate the environment. The current study has shown that the properties of these composite plastics depend upon the size of the starch particles used to prepare them. Small particles of crystalline starch, that can be economically prepared by cooking starch with fatty acids derived from vegetable oils, yield composite plastics with properties that are superior to those obtained from ordinary granules of corn starch that have particle sizes about 10-20 times larger. This research will be beneficial to a CRADA partner, and also to other companies interested in manufacturing biodegradable plastics.
Technical Abstract: Mixtures of high amylose corn starch and oleic acid were processed by steam jet-cooking, and the dispersions were rapidly cooled to yield amylose-oleic acid inclusion complexes as sub-micron spherulites and spherulite aggregates. Dispersions of these spherulite particles were then graft polymerized with methyl acrylate, both before and after removal of un-complexed amylopectin by water-washing. For comparison, granular, un-cooked high amylose corn starch was also graft polymerized in a similar manner. Graft copolymers with similar percentages of grafted and un-grafted PMA were obtained from these polymerizations. The graft copolymers were then processed by extrusion, and the tensile properties of the extruded ribbons were determined. Although extruded ribbons with similar tensile strengths were obtained from the three starch-PMA graft copolymers, much higher values for % elongation were obtained from the spherulite-containing systems. Also, the tensile properties were not significantly affected by removal of soluble, un-complexed amylopectin by water-washing prior to graft polymerization. These results are consistent with the observation that these PMA-grafted starch particles did not melt during extrusion, and that continuous plastic ribbons were formed by the fusing together of these particles in the presence of small amounts of thermoplastic PMA matrix.