Water solubility, thermal characteristics and biodegradability of extruded starch acetate foams

Starch based foams have been studied as replacements for non-degradable expanded polystyrene (EPS) as loose-fill packaging material because of starch's total degradation and low cost. However, starch's hydrophilicity, poor mechanical properties and dimensional stability limited their applications. Acetylated starch with a high degree of substitution (DS) is an alternative. Starch acetates with DS 1.11, 1.68, and 2.23 were extruded with either water or ethanol as solvents. The effects of DS and type of solvent on the starch acetate foam's water absorption index (WAI), water solubility index (WSI), thermal behavior (glass transition temperature [T_g], melting temperature [T_m], and thermal decomposition temperature), and biodegradability were investigated. There was a significant interaction (P < 0.05) between solvent type and DS on WAI and WSI of the foams. As DS increased from 1.11 to 2.23, WAI and WSI increased when ethanol was used as solvent and decreased when water was used as solvent. The T_g values of starch decreased with acetylation and with increasing DS, but increased with extrusion. Acetylation and extrusion increased the thermal stability of the foams. The rate of biodegradation of the foams decreased with increasing DS. The foams, extruded with ethanol, had higher degradation rates than those with water.