Submitted to: Journal of Environmental Polymer Degradation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/1998
Publication Date: N/A
Interpretive Summary: The use of cornstarch as a raw material for developing biodegradable plastic products had created new and expanded markets for this commodity. Starch alone offers poor physical and water resistance properties but can be used as a filler in other plastics. Because starch is also one of the most abundant and low cost polymer available, it is well suited for blending with other high-cost renewable natural polymers for developing totally biodegradable plastic products at a considerably lower cost. This report describes various formulations for blending cornstarch with polyesters of microbial origin. Blends prepared have excellent mechanical properties and were tested to be mostly biodegradable within 125 days in a natural compost. This report provides knowledge useful for starch-based plastic manufacturers on how to enhance starch compatibility with other natural polymers and to design starch-based materials with controlled biodegradability.
Technical Abstract: Injection molded plastics were prepared by blending poly(hydroxybutyrate-co-valerate) (PHBV) with 30% and 50% cornstarch. These plastics were evaluated for their biodegradability in natural compost by measuring changes in their physical and chemical properties over a period of 125 days. The degradation of plastic material, as evidenced by weight loss and deterioration in tensile properties, correlated with the amount of starch present in the blends (pure PHBV < 30% starch < 50% starch). Specifically, after 125 days exposure, pure PHBV exhibited a total weight loss of 7%. Increasing starch content in blends enhanced PHBV degradation as well. For example, the PHBV blends with 30% starch displayed a total weight loss of 28%, of which 19.3% was due to starch depletion and 8.7% was due to PHBV depletion. PHBV blends with 50% starch had a total weight loss of 55%, of which 34.7% was from starch and 20.3% was from PHBV. GPC analyses revealed a slight decrease in the Mw of residual PHBV. **1H proton NMR integration of branched -CH3 peaks indicated similar rates of degradation for the PHB and PHV moieties of the copolymer.