Compressive behavior of microcellular polystyrene foams processed in supercritical carbon dioxide

Microcellular polystyrene foams have been prepared using supercritical carb on dioxide as the foaming agent. The cellular structures resulting from thi s process have been shown to have a significant effect on the corresponding mechanical properties of the foams. Compression tests were performed on hi ghly expanded foams having oriented, anisotropic cells. For these materials an anisotropic foam model can be used to predict the effect of cell size a nd shape on the compressive yield stress. Beyond yield, the foams deformed heterogeneously under a constant stress. Microstructural investigations of the heterogeneous deformation indicate that the dominant mechanisms are pro gressive microcellular collapse followed by foam densification. The phenome non is compared to the development of a stable neck commonly observed in po lymers subjected to uniaxial tension, and a model that describes the densif ication process is formulated from simple energy balance considerations.