Rl. Shogren et al., STARCH POLY(VINYL ALCOHOL) FOAMED ARTICLES PREPARED BY A BAKING PROCESS, Journal of applied polymer science, 68(13), 1998, pp. 2129-2140
Composite foam plates were prepared by baking a mixture of granular st
arch and aqueous poly(vinyl alcohol) (PVOH) solution inside a hot mold
. Foam strength, flexibility, and water resistance were markedly impro
ved by addition of 10-30% PVOH to starch batters. The improvement in s
trength at low humidity was greater for partially (88%) hydrolyzed PVO
H while strength at higher humidities improved most with fully (98%) h
ydrolyzed PVOH. Foam flexibility increased with higher PVOH molecular
weight. Scanning electron micrographs of the surface of the foams reve
aled a phase-separated morphology in which swollen starch granules wer
e embedded in a matrix of PVOH. The starch component was gelatinized (
melted) during baking while the PVOH component crystallized to a high
degree during baking. Crosslinking agents such as Ca and Zr salts were
added to starch batters to give further increases in water resistance
. Respirometry studies in soil showed that the starch component of sta
rch-PVOH foams biodegraded relatively rapidly (weeks) while the PVOH c
omponent degraded more slowly (months). Baked foams prepared from star
ch and PVOH have mechanical properties that are adequate for use as pa
ckaging containers over a nide range of humidity. (C) 1998 John Wiley
& Sons, Inc.