Preparation and characterization of starch/poly(L-lactic acid) hybrid foams

Starch/poly(L-lactic acid) (PLA) hybrid foams were prepared by baking a mixture of starch, PLA, and other ingredients in a hot mold. The effects of relative humidity, storage time, PLA content, and type and content of added plasticizer (e.g. glycerol, urea, or ammonium chloride) on moisture and water absorption, mechanical properties, and enzymatic degradability of the as-prepared foams were investigated. In all of the conditions investigated, the ultimate tensile strength was shown to exhibit a maximum when the relative humidity was 42% RH (for a fixed storage time of 7 days) and when the storage time was 2 days (for a fixed relative humidity of 42% RH). Addition of PLA helped improve the ultimate tensile strength and the percentage of elongation at break of the hybrid foams. Resistance to water absorption of the starch/PLA hybrid foams was superior to that of pure starch foams. Lastly, enzymatic degradation tests in an a-amylase solution showed that addition of PLA improved the resistance to enzymatic degradability of the hybrid foams. (C) 2004 Elsevier Ltd. All rights reserved.