Temperatures and ethanol effects on the properties of extruded modified starch

Abstract

Temperature and blowing agent are major factors influencing the properties of extruded foam materials. This study was conducted to determine the influence of temperature and alcohol content on selected properties and molecular weight of acetylated starch foam. Starch acetate, with degree of substitution of three, was prepared from 70% amylose corn starch and extruded with either 16 or 18% (db) ethanol in a single screw extruder at either 120 or 160°C. Unit and solid densities, specific mechanical energy, compressibility, spring index, water absorption and water solubility indices, glass transition temperature, molecular degradation and degree of substitution (DS) of the starch were measured. The samples extruded at 120°C had lower spring indices and water absorption indices (WAI), but higher compressibility and unit density than acetylated starch extruded at 160°C. The samples extruded with 16% ethanol content on a dry basis had lower spring indices and higher WSI than samples extruded with 18% alcohol. The extruded samples had lower solid density, WSI and WAI as compared to non-extruded acetylated starch. A slight decrease in the average molecular weight was recorded as a result of the extrusion processing. The samples extruded at 160°C had high spring indices and low unit densities and thus were more suitable for use as a loose-fill packaging material.