Strengthening blends of poly(lactic acid) and starch with methylenediphenyl diisocyanate

Poly(lactic acid) (PLA) is a biodegradable polymer, but its applications are limited by its high cost. Blending granular starch with PLA reduces the cost, but the blend has poor strength properties. In this study, a 55/45 (w/w) mixture of PLA (weight‐average molecular weight = 120,000 Da) and dried wheat starch was blended thermally in an intensive mixer with or without a low level of methylenediphenyl diisocyanate (MDI). Blends with MDI had enhanced mechanical properties that could be explained by the in situ formation of a block copolymer acting as a compatibilizer. Scanning electron micrographs showed reduced interfacial tension between the two phases. The presence of MDI also enhanced the mechanical properties of the blend at temperatures above the glass‐transition temperature. Water uptakes by the PLA/starch blends with and without MDI did not differ.