Physical properties of starch-based foams as affected by extrusion temperature and moisture content

Although considerable effort has been made to improve the physical and mechanical properties of starch-based foams, they still do not compare favorably with traditional plastic foams. The properties of the foams depend largely on the starch moisture content and extrusion conditions. The purpose of this study was to evaluate the effects of extrusion temperature and moisture content of starch-based foams on selected physical properties. Blends composed of 49% wheat and corn starch (dry solid basis), 33% synthetic polymers, 10.5% total water, 7% blowing agents, and 0.5% nucleating agent were extruded at 100-160 degreesC extruder barrel temperatures and 100 rpm screw speed using a single-screw C. W. Brabender laboratory-scale extruder. Starch-based foams were equilibrated at different relative humidities (10-90%). Moisture adsorption isotherms, bulk densities, and expansion ratios of the starch-based foams were studied. The moisture adsorption isotherms of starch-based foams were rising sigmoidal curves similar to those of grains and grain products. The bulk density of the starch-based foams decreased as the extrusion temperature increased. The highest expansion occurred when the blends containing normal wheat starch were extruded at 140 degreesC. The starch-based foams were four to eight times more dense than polystyrene foam. (C) 2001 Elsevier Science B.V. All rights reserved.