Aging and moisture effects on the tensile properties of starch/poly(hydroxyester ether) composites

The effects of starch and aging on the mechanical properties of starch/poly(hydroxyester ether) (PHEE) composite materials were characterized. Native or modified cornstarches were extruded with PHEE. Composites were aged for up to 20 months at either 23°C and 50% relative humidity (RH) or over calcium sulfate to keep the composites dry. The tensile strength (TS) of the composites was affected by the type of starch filler that they contained. Composites containing native or crosslinked starch had significantly greater TS than composites containing octenylsuccinated starch. It was thought that the octenylsuccinate modification of the starch granule affected the adhesion between the starch and PHEE. Aging the composites at 50% RH had a significant effect on the mechanical properties of the composites, with TS and Young's modulus (YM) significantly decreasing and the elongation to break significantly increasing after 20 months of storage. Composites stored at 50% RH absorbed water, which caused changes in the mechanical properties by plasticizing PHEE. Composites containing poly(lactic acid) and PHEE did not experience large reduction in TS and YM when aged at 50% RH, even though they also absorbed water.