Starch poly(vinyl alcohol) foamed articles prepared by a baking process

Composite foam plates were prepared by baking a mixture of granular starch and aqueous poly(vinyl alcohol) (PVOH) solution inside a hot mold. Foam strength, flexibility, and water resistance were markedly improved by addition of 10-30% PVOH to starch batters. The improvement in strength at low humidity was greater for partially (88%) hydrolyzed PVOH while strength at higher humidities improved most with fully (98%) hydrolyzed PVOH. Foam flexibility increased with higher PVOH molecular weight. Scanning electron micrographs of the surface of the foams revealed a phase-separated morphology in which swollen starch granules were 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 starch-PVOH foams biodegraded relatively rapidly (weeks) while the PVOH component degraded more slowly (months). Baked foams prepared from starch and PVOH have mechanical properties that are adequate for use as packaging containers over a nide range of humidity. (C) 1998 John Wiley & Sons, Inc.