TENSILE TOUGHNESS OF MICROCELLULAR FOAMS OF POLYSTYRENE, STYRENE-ACRYLONITRILE COPOLYMER, AND POLYCARBONATE, AND THE EFFECT OF DISSOLVED-GAS ON THE TENSILE TOUGHNESS OF THE SAME POLYMER MATRICES AND MICROCELLULAR FOAMS

This paper reports on the tensile properties of microcellular foams of three different thermoplastics, since there have been several reports in the literature, but with indefinite conclusions so far, that micro bubbles act in a manner similar to rubber particles in toughening ther moplastics. Polystyrene (PS), styrene-acrylonitrile copolymer (SAN), a nd polycarbonate (PC), were selected based on their different intrinsi c ductilities. The gas supersaturation technique was used to generate samples with microbubbles. The effect of the presence of microbubbles inside the polymer matrix was separated from the effects of the pressu re and thermal history experienced by the samples. Nitrogen gas dissol ved into PS, and to a lesser extent into SAN, caused an increase of th e tensile toughness, but this increase decayed with time as nitrogen g as diffused out of the samples. Furthermore, microcellularly foamed PS samples showed some limited improvement in terms of tensile toughness after all the nitrogen gas diffused out. SAN and PC showed deteriorat ion of the tensile toughness in the presence of microbubbles.