EFFECTS OF POLY(ETHYLENE GLYCOL) ON THE PHYSICAL-PROPERTIES OF BLENDED MOLECULES OF STARCH AND POLY(ETHYLENE-CO-ACRYLATE, AMMONIUM SALT)

A mixture of starch (36%) poly(ethylene-co-acrylate, ammonium salt) (4 1%), water (12.5%), urea (8.4%), and poly(ethylene glycol) (M(n) 4600) (2.1%) were converted to plastic test pieces by extruding (130 degree s C), drying and grinding (25 degrees C), and hot pressing (175 degree s C). After equilibration at similar to 50% relative humidity and 25 d egrees C, the test pieces contained 3.5-4.6% moisture and 2.3% poly(et hylene glycol) (PEG). Among wheat, corn, potato, and rice starches, th e wheat starch (WS) blend showed the highest Young's modulus (181.3 MP a), whereas the corn starch (CS) blend had a modulus and elongation th at almost matched those of low-density polyethylene. When PEG was elim inated from the WS formulation, tensile strength remained constant, bu t Young's modulus doubled. The modulus decreased continually as test p ieces absorbed water up to 27% moisture, but elongation and argon lase r light transmittance were optimum at similar to 12% moisture. Differe ntial scanning calorimetry indicated that PEG formed a solid inclusion complex with amylose upon drying at 60 degrees C, but no complex was detected in dilute alkali by optical rotation.