Suppression of cell creation through control of volume expansion

This study was carried out to investigate the morphological changes of polymers when the volume expansion of polymer-gas mixtures is suppressed. The polycarbonate-CO₂ mixture specimens used in the experiments were prepared using a pressure vessel used in the batch foaming process. The foaming was carried out in an oil bath, which does not inhibit volume expansion, and in constant volume foaming equipment, which is specially designed to suppress volume expansion. Experiment results confirmed that the foaming temperature increased when the volume expansion of the specimens was suppressed. As the volume expansion of the specimens decreased, their foaming rate also declined relative to the oil bath. These phenomena can be explained by the fact that the volume expansion of the specimens during foaming was suppressed by the cavity of the constant volume foaming equipment. Moreover, external pressure was applied to the specimens, and pressure gradient was observed in the polymer.