Preparation and properties of starch/poly(vinyl alcohol) composite foams

Starch/poly(vinyl alcohol) (PVA) composite foams were prepared by baking a mixture of starch, PVA, and other ingredients in a hot mold. The effects of relative humidity, storage period, PVA content, and type and content of plasticizer (e.g. glycerol, urea, or ammonium chloride) on moisture content, water absorption, mechanical properties, and biodegradability of the as-prepared foams were investigated. In all of the testing conditions investigated, the ultimate tensile strength was shown to be a maximum when the relative humidity was 42%RH (for a fixed storage period of 7 days) and when the storage period was 2 days (for a fixed relative humidity of 42%RH). Addition of PVA improved the ultimate strength and the elongation at break of the composite foams. An increase in the amount of added plasticizer was responsible in an increase in the percentage of elongation at break at the expense of the tensile strength of the composite foams. Resistance to water absorption of starch/PVA composites foams was found to be superior to that of pure starch foams. Lastly, enzymatic degradation tests with alpha-amylase showed that addition of PVA affected a little to the enzymatic degradability of the composite foams.