High Strength Bio-Foams of Cassava Starch/Wheat Gluten Blends by Microwave Processing

Environmental issues have a high impact on the selection of materials for packaging. Advanced research in biodegradable materials has shown that starch-based foams could be an effective replacement for petroleum-based polystyrene foam. However, pure starch (ST) foam has some disadvantages, including low water resistance and poor mechanical properties. In this study, wheat gluten (WG) protein was added to starch-based foams, and the foam structure was formed using microwave processing to improve those properties. This was the first report on a novel bio-foam made from ST/WG blend utilizing a rapid and energy-efficient microwave foaming process that resulted in improved foam structure and high strength. The effect of foam blending ratios (ST100, ST95/WG5, ST90/WG10, ST80/WG20, and ST70/WG30 by weight) were studied. It was found that due to WG's nucleating effect, the cellular microstructure of the ST/WG blend foams was denser with smaller cell size and thicker cell walls than the pure ST foam. Mechanical properties of the foams compared by the flexural strength and modulus have shown that increasing the amount of WG significantly enhanced the foam's properties. Based on the findings of this study, ST90/WG10 exhibited a notably high flexural strength and modulus of 9.5 MPa and 412.8 MPa, respectively, which were more than 9 times stronger than expanded polystyrene foam. Furthermore, the addition of WG protein improved the water resistance of the blend foams. This study demonstrates that the new bio-foam based on ST and WG (as a blending component), which can be quickly produced by microwave heating, is a very promising alternative for high strength, good water resistance, and eco-friendly foam packaging applications.