Aspen fiber addition improves the mechanical properties of baked cornstarch foams

Abstract

Recently, there have been efforts to manufacture single-use articles, such as fast food packaging and containers, from biodegradable materials. Starch-based foams have been developed to replace the expanded polystyrene foam packaging currently in use. Starch-based foams are water sensitive, and thus, their mechanical properties are susceptible to changes in relative humidity. In this report, aspen fiber was added to baked cornstarch foams to improve its mechanical properties. Foam trays were made with fiber content of the batter ranging from 2.5 to 45%. The starch–fiber composite foam trays were formed by heating a starch-based batter inside a closed mold. The trays were stored at different relative humidities (5, 20, 50, 81, and 93%) for 1 week prior to mechanical testing. Aspen fiber increased the baking time needed to make a complete tray. Batters containing greater than 15% fiber needed to be added in higher amounts to the mold to make complete trays. The strength of the foam trays increased as fiber content of the trays increased, until fiber content reached about 15%. Trays containing between 15 and 30% fibers had no significant difference in tray strength. Trays containing more than 30% fiber had lower tray strength. The lower tray strength was thought to be due to the lack of uniform fiber distribution at high fiber content. Displacement of the trays at break was also affected by fiber content. The effect of fiber on displacement at break was greatest at extreme relative humidities. At low humidity (5%), displacement at break went from 2.2 to 5.4 mm as fiber content increased from 2.5 to 40%. Displacement at break increased from 9 to 20 mm as the fiber content increased from 2.5 to 40% for trays stored at 93% relative humidity. Fiber content did not effect displacement at break for trays stored at moderate relative humidities. Fiber content of 15% was adequate to increase the tray strength. Greater amounts of fiber (up to 30%) can be added without detrimental affects to strength, but increasing fiber above 15% increased baking time and increased the amount of batter needed to make a complete tray.