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Abstract
A mixture of starch (36%) poly(ethylene-co-acrylate, ammonium salt) (41%), water (12.5%), urea (8.4%), and poly(ethylene glycol) (M n 4600) (2.1%) were converted to plastic test pieces by extruding (130°C), drying and grinding (25°C), and hot pressing (175°C). After equilibration at −50% relative humidity and 25°C, the test pieces contained 3.5–4.6% moisture and 2.3% poly(ethylene glycol) (PEG). Among wheat, corn, potato, and rice starches, the wheat starch (WS) blend showed the highest Young's modulus (181.3 MPa), whereas the corn starch (CS) blend had a modulus and elongation that almost matched those of lowdensity polyethylene. When PEG was eliminated from the WS formulation, tensile strength remained constant, but Young's modulus doubled. The modulus decreased continually as test pieces absorbed water up to 27% moisture, but elongation and argon laser light transmittance were optimum at −12% moisture. Differential scanning calorimetry indicated that PEG formed a solid inclusion complex with amylose upon drying at 60°C, but no complex was detected in dilute alkali by optical rotation.