Effects of polyvinyl alcohol content and hydrolysis degree on the structure and properties of extruded starch-based foams

Growing global awareness of environmental issues has led to increased research interest in starch-based foams as a biodegradable packaging material. However, limitations such as low foaming ratio and poor water resistance hinder their development and industrial application. This study aimed to address these challenges by investigating the effect of the polyvinyl alcohol (PVA) content and hydrolysis degree on foam properties, providing insight into the intricate interplay between melt viscoelasticity and foam characteristics. The results demonstrated that the foaming behaviors, viscoelastic properties, thermal stabilities and mechanical performances of the foams were significantly improved with increasing hydrolysis degrees of PVA. These enhancements were attributed to hydrogen bonding interactions and intermolecular entanglements between starch and PVA chains. Additionally, the incorporation of PVA resulted in a remarkable reduction in the water absorption capacity (WAC) of the foams. Specifically, the foam containing 20% PVA with a hydrolysis degree of 98% exhibited the lowest WAC of 7.46% at 75% RH, the lowest bulk density of 12.42 kg/m3, the highest foaming ratio of 54.66, and the highest porosity of 99.39%. These properties were equivalent to those of commercially available expanded polystyrene (EPS). Furthermore, the addition of 20% PVA yielded the highest compressive strength of 110.58 MPa and the highest recovery of 92.75%, indicating great potential for diverse cushioning applications. Overall, this work highlights the significant potential for wider application of starch-based foams in large-scale industrial settings.