Ultra-low density epoxy/polystyrene foam composite with high specific strength and pseudo-plastic behavior

Hierarchical co-continuous composites were prepared by impregnation of a deformed bed of expanded polystyrene granules with epoxy resin. The composite structure comprises a highly-porous open-cell epoxy foam skeleton in which the cells were filled with expanded polystyrene. The density of the composites varied within 0.22-0.32 g/cm(3) and could be controlled by the compression ratio of the expanded polystyrene granule bed. The peak stress to fracture under quasi-static compression was 2-6 MPa, depending on density, which resulted in high specific strength of 10-18 MPa/(g/cm(3)). The peak stress in the expanded polystyrene/epoxy foam composites was about 50% higher than that of epoxy foams with unfilled cells, suggesting a synergetic response by the constituents of the composite. Even more interestingly, in contrast to the brittle and catastrophic fragmentation of the unfilled epoxy foam at the peak stress, a "pseudo-yield" plateau behavior was observed in the composites.