Compressive elastic modulus and its relationship to the structure of a hydrated starch foam

The elastic modulus of a hydrated starch foam was evaluated from indentation and compression tests. After using an appropriate correction factor, based on specimen aspect ratio and Poisson’s ratio, the indentation elastic moduli were found to be identical to the compressive ones. Image analysis showed that the foam possessed a non-periodic but self-similar texture, with a fractional dimension (FD) of 1.89±0.07 for cell numbers and 2.41±0.16 for areal mass of cell wall solids. The relative modulus exhibited a power law dependence on relative density. This dependence was corroborated from microstructural considerations of the scaling behaviour of the elastic properties according to a weak-link regime theory. The theory was deemed apt for starch foam, since the underlying microstructure of the cell walls of the foam is comprised of swollen starch spherulites sintered by a linear polymer (amylose) that is exuded from the spherulites during processing.