Mechanical performance studies on extruded cornstarch-based plastic manufactures

Twin-screw extrusion of cornstarch produces a strong, yet readily biodegrad able plastic material. Because of the brittleness of these cornstarch plast ics, ASTM standard methods did not apply, and an alternative sample grip wa s developed. A suitable method for the tensile testing of extruded cornstar ch plastics of differing feed composition (amylose content, cross-linking, plasticizer) and processing conditions (temperature) was developed, and qua ntitative values of tensile strength, strain, elastic modulus, and energy w ere obtained. The mean tensile strength of these materials ranged from 667 to 4148 psi, which is in the range of values for low-density polyethylene a nd high-density polyethylene. The high amylose content cornstarch plastics extruded at high temperatures demonstrated greatest strength. Wet/dry studi es of the pure cornstarch materials showed them to degrade readily with ext ended exposure to water, but immersion in water for 1 h in room temperature (17 degrees C) water did not, as measured by standard tensile tests, adver sely affect their strength, but made them more ductile, less stiff and toug her. (C) 1999 John Wiley & Sons, Inc.