POST-EXTRUSION STEAMING OF STARCH ACETATE FOAMS

摘要

Post-extrusion steaming was applied to extruded foam blends of starch acetate and cellulose or polylactic acid (PLA). Extrudates were obtained by twin-screw extrusion at 160°C barrel temperature and 225 rpm screw speed for starch acetate-cellulose blends and 150 rpm screw speed for starch acetate-PLA blends. Extrudates were steamed at atmospheric pressure for six different steaming times and time intervals (steamed once for 1, 2, and 4 min and steamed twice for 1, 2, and 4 min with 1 min between cycles.) One sample was steamed at 960.3 kPa. Extrudates without post-extrusion steaming were used for comparison. Radial expansion ratio, unit and bulk densities, unit and bulk spring indices, and thermal conductivity of the steamed and unsteamed samples were measured. Scanning electron micrographs were taken to observe foam cell structures. The highest radial expansion ratio of starch acetate-cellulose extrudates was obtained after steaming twice for 2 min with a 1 min interval between cycles. Thermal conductivity of the foams decreased slightly as the steaming time was increased. Functional properties of the post-extrusion steamed starch acetate foams were strongly dependent on the formation of inter-molecular linkages between cooked starch acetate and melted cellulose or PLA