RELATIONSHIPS BETWEEN MICROSTRUCTURE AND MECHANICAL PROPERTIES OF CELLULAR CORNSTARCH EXTRUDATES

Abstract

ABSTRACT 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 (R2 = 0.72) with the Gibson–Ashby model for brittle foams, while crushing stress did not fit as well (R2 = 0.41). Cellular characteristics had moderate to high correlation (|r| = 0.48–0.81) with mechanical properties, and provided significant insight into the deformation mechanism of the foams.PRACTICAL APPLICATIONSMechanical properties of extruded biopolymeric foams are largely determined by their microstructure, but the relationships involved have not been properly understood. This study used mechanical testing in combination withnoninvasive x‐ray microtomography to investigate these relationships. Results from this study furthered understanding of the deformation mechanism of brittle foams, and represent an important step toward the ability to better design crisp and crunchy food products with desired textures.