Biodegradable foams based on extracted fractions from sorghum by-products

Abstract

Agricultural by-products comprise abundant, renewable sources of value-added compounds for the food and packaging industries. The production of biodegradable foams can be focused on replacement of polystyrene-foam with biodegradable materials, which are regarded as environmentally friendly. In this study, biodegradable food trays were developed via thermopressing, using modified and unmodified corn starches with additional extracted fractions (celluloses, hemicelluloses, and lignin) from sorghum stalk and bran. The effect of several formulations of extracted fractions from sorghum by-products on bio-foam properties was studied. All trays presented thicknesses between 3 and 4.17 mm, density between 0.16 and 0.64 g cm−3, and moisture content between 5 and 12% (dry basis). The foam trays made from chemically modified starch had lower densities, higher tensile strength and elongation at break than unmodified starch. The increment of cellulose fraction from 2% to 5% and hemicellulose fraction from 1% to 10% had significant effect on the trays’ physical and mechanical properties. All trays exhibited no color and structural changes during storage at 25 °C and 4 °C. The formulation presenting the best properties contained 2% of cellulose and 1% of hemicellulose, had a maximal resistance of 0.77 MPa and 9.46 mJ of total work, attributes which corresponded to a compact, homogenous, and dense microstructure.