Microcellular thermoplastics are novel materials containing a large number of closed cells, typically 106/cm3 or more, of order 10 microns in diameter. Such a microstructure allows a significant reduction in density without compromising the essential mechanical properties. Recently remarkable new materials have been produced from polycarbonate and from polyethylene terephthalate (PET), using carbon dioxide as the nucleating gas. In PET, high concentrations of carbon dioxide have been found to crystallize PET, enabling creation of cellular composites with an integral, crystalline skin. In polycarbonate, bubble densities of 5 billion/cm3 or more have been achieved, allowing for creation of microcellular foams with a wide range of properties. In this research a detailed characterization of the CO-2 polycarbonate and CO2-PET material systems will be carried out. The CO2-induced crystallization in PET, molecular orientation in cell walls, and the cell morphology will be studies. Bubble nucleation phenomena in both PET and polycarbonate will be experimentally characterized. Also the mechanical behavior of microcellular composites will be measured and related to the microstructure via a theoretical model.
