Biodegradable starch-PLA polymers

Researchers at the US Department of Agriculture (USDa) lab at Peoria, IL, prepared a number of compositions from granules of poly(hydroxy ester ether) adipic, granules of cornstarch, and pellets of polylactic acid (PLA). Starch was first dried to a moisture content of 1% wt. moisture. Dried starch was mixed by hand with the other components and compounded in a Brabender PL2000 torque rheometer using a mixing screw with a fluted dispersive mixing section and a notched distributive section. Strands of the composition from the rheometer were air cooled and palletized. Some of the compositions tested had starch/PLA/adipic ratios of: 60/36/4; 60/20/20; and 60/4/36. The pellets were refitted into the rheometer, now fitted with a slit die to form thin sheets, which were stamped to form tensile bars for physical testing. The first sheet did not provide a smooth sheet and could not be tested whereas the second had a tensile strength of 17.6 megapascals (MPa). The third sheet had a tensile strength of 30.4 MPa.