Acetylated starch-polylactic acid loose-fill packaging materials

Abstract

Different genetic and botanical sources of starches are available for use in hydrophobic starch-based packaging materials. The objectives of this study were to evaluate the effects of the type of acetylated starch and the presence of polylactic acid (PLA) and ethanol on the functional properties of extruded foams, and to compare the specific mechanical energy requirements for preparing these foams. Acetylated starches prepared from potato and native (25% amylose) and high amylose (70%) corn starches were extruded with 0, 7.5, or 15% PLA and 8, 13, or 18% ethanol using a twin-screw extruder with a 160 °C barrel temperature and 180 rpm screw speed. Response surface methodology was employed to study the acetylated starch, PLA, and ethanol effects on radial expansion ratio, bulk density and compressibility of the extruded foams and the specific mechanical energy required to extrude the acetylated starch–PLA blends. The acetylated potato and native and high amylose corn starches had degrees of substitution (DS) of 1.09, 2.05, and 2.65, respectively. Acetylated 70% amylose cornstarch agglomerates had the highest hardness whereas acetylated potato starch had the lowest. Higher DS acetylated starch had higher radial expansion ratio, compressibility, specific mechanical energy requirement, and lower bulk density than acetylated starch–PLA foam. Ethanol functioned as a blowing agent to expand the foams and as a solubilizing agent to depolymerize the PLA and starch to form a homogeneous dough. Foam expansion increased with addition of PLA.