THERMOPLASTIC STARCH BLENDS WITH A POLY(ETHYLENE-CO-VINYL ALCOHOL) - PROCESSABILITY AND PHYSICAL-PROPERTIES

We investigated the effect of poly(ethylene-co-vinyl alcohol) (EVOH) c oncentration on the processability and physical properties of thermopl astic starch plasticized with glycerine and water. Waxy maize starch ( Amioca), native com starch (Melogel), and a treated high amylose com s tarch (Hylon VII) were employed to explore the effect of starch type o n blend properties. All the starches exhibited similar changes in prop erties with increasing EVOH content. The minimum injection pressure re quired for filling a standard test specimen (a measure of processabili ty) decreased with increasing EVOH concentration and provided an indic ation of improved processability. Blends with high amylose com exhibit ed higher injection pressures than the corresponding waxy maize or nat ive com starch blends. The ductility of all the thermoplastic starches was significantly increased upon the addition of EVOH. The waxy maize blends were stiffer and the high amylose com blends exhibited higher elongation at low EVOH concentrations, but all the starch/EVOH blends exhibited similar physical properties when the EVOH concentration was greater-than-or-equal-to 50 wt%. An investigation of physical properti es of this blend series after long term aging from 10% to 90% relative humidity is in progress. Future studies include rheology, electron mi croscopy, and thermal analysis to more fully elucidate phase behavior in these binary blends.