The deformation of brittle starch foams

Abstract

There exists a theoretical model to describe the deformation of solid foams which relates the mechanical properties to the foam density and the cell-wall properties. Previous work has assumed that the wall properties are constant for a wide range of different density foams and can be characterized by the properties of the unfoamed material. In this paper we show that, when considering extruded starch foams, variation of the extrusion parameters in order to produce different bulk density foams has an effect on the cell-wall material: notably upon the crystallinity,T _g and wall density. Therefore, both the bulk foam and cell-wall mechanical properties were measured in order to test the full theory. For the relative fracture stress, excellent agreement was found between the predicted power law behaviour and the experimental results. However, the power law for the relative modulus is larger than the predicted value.