STRUCTURE AND PROPERTIES OF STARCH POLY(ETHYLENE-CO-VINYL ALCOHOL) BLOWN FILMS/

Blends of native corn starch and poly(ethylene-co-vinyl alcohol) (EVOH ), with starch : EVOH ratios of 1 : 1 (SE-50) and 2 : 1 (SE-67A, SE-67 B), were processed into blown films. SE-67A had a higher glycerol and water content and was processed at 5 degrees C higher than was SE-67B. The films were conditioned to various moisture contents by equilibrat ing at a constant relative humidity and by oven drying at 41 degrees C . Equilibrium moisture content, which ranged from 2 to 11%, increased with increasing starch content at a given relative humidity. Mechanica l properties depended strongly on starch and moisture content as well as on processing history. The extension to break of SE-50 was only abo ut one-third that of EVOH, while that of the 2 : 1 blends was even low er. SE-67A exhibited a higher extension to break, lower tensile streng th and modulus, and greater moisture sensitivity than those of SE-67B. Differential scanning calorimetry and dynamic mechanical analysis rev ealed evidence of interactions between starch and EVOH, probably indic ative of extensive intermixing but not necessarily miscibility. Scanni ng electron micrographs of fracture surfaces revealed extensive differ ences in texture with microcracking in SE-50 and SE-67A. The combinati on of the analytical results provide a basis for explaining many aspec ts of the mechanical behavior including the marked difference in prope rties between SE-67A and SE-67B. (C) 1997 John Wiley & Sons, Inc.