Relationships between microstructure and mechanical properties of cellular cornstarch extrudates

Relationships between mechanical properties and microstructure of brittle biopolymer foams were investigated using noninvasive imaging as a tool. Cornstarch was processed in a twin-screw extruder to produce brittle foams with varying microstructure. X-ray microtomography was used to measure microstructure features of the foams, including average cell diameter (2.07-6.32 mm), cell wall thickness (0.13-0.25 mm) and cell number density (18-146 cm(-3)). Mechanical properties, including compression modulus (2.2-7.8 MPa), crushing stress (42-240 kPa), number of spatial ruptures (2.6-3.6 mm(-1)), average crushing force (22-67 N) and crispness work (6.4-22 N.mm), were determined instrumentally. Compression modulus had a reasonably good fit (R-2 = 0.72) with the Gibson-Ashby model for brittle foams, while crushing stress did not fit as well (R-2 = 0.41). Cellular characteristics had moderate to high correlation (vertical bar r vertical bar = 0.48-0.81) with mechanical properties, and provided significant insight into the deformation mechanism of the foams.