Effect of Fine Cell Size on Improvement of Bending Fracture Strength of Foams

Advent of foamed plastics, that allow materials to be reduced and also the mechanical properties to be maintained or even improved, would substantially extend the fields of applications as a resource saving material. In this paper, on an assumption that the mechanical properties of foams are determined by the molecular orientations of cell walls associated with foaming, the study was made on how to enhance the strength of foams, which has revealed the following results. With very fine cell sizes, PS foams attain strengths that are higher than those estimated from the stress concentration and the foam magnification. This was assumed to be due to increase in the surface area of cell walls caused by foaming, as well as enhancement of molecular orientation of cell walls associated with foaming.