STARCH POLY(VINYL ALCOHOL) FOAMED ARTICLES PREPARED BY A BAKING PROCESS

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.