Relationship among Extrusion Conditions, Cell Morphology, and Properties of Starch-Based Foams—A Review

Environmental impact concern of conventional polymer foams has attracted considerable interest for the development of natural-based polymer foams. Starch is a biopolymer that is gaining acceptability due to its renewability, availability, environmental biodegradation, and low cost. Extrusion is particularly desirable to produce starch-based foams because it can produce a homogeneous mixing, high heat transfer, high pressure, reduction of the residence time, and low production costs. This review explains the transformation of starch during the foam processing and their relationship with extrusion conditions such as water content, barrel temperature, screw configuration and speed, die temperature, and die dimensions and how all these factors impact on the cell morphology, apparent density, expansion ratio, and final properties of starch-based foams. The strategies to reduce water sensitivity are described, as well as the effect of amylose content and the addition of additives to improve the starch-based foams performance as alternative for expanded polystyrene. The extrusion processing conditions can be controlled to obtain the desirable properties for specific applications such as cushioning, packaging, and loose-fill, among others. Also, a brief look at the starch-based foams trends, challenges, and perspectives are also discussed.