Production of engineering plastics foams by supercritical CO2

The foams of poly(ethylene terephthalate) (PET) and polycarbonate (PC) are prepared by rapid depressurization of CO2-saturated molten resin. It is fou nd that the foamable temperature and pressure for PET and PC are nearly ide ntical, and the attainable expansion ratio of the produced foam is generall y less than 10. The effect of saturation temperature on the nucleation is m ainly a result of the competition between the viscosity effect and the solu bility effect. However, the effect of saturation pressure on the nucleation is twofold: the degree of supersaturation and the rate of depressurization . The effect of lowering the depressurization rate and changing the depress urization pattern on the polymeric foams is also investigated in this work. By careful observation of the microstructure, it is concluded that the foa ming process is dominated by the nucleation kinetics. This study provides s everal alternative techniques for controlling the microstructure and the ex pansion ratio of PET and PC foams.