PREPARATION AND CHARACTERIZATION OF MICROCELLULAR POLYSTYRENE FOAMS PROCESSED IN SUPERCRITICAL CARBON-DIOXIDE

The foaming of polystyrene using supercritical (SC) CO2 has been studi ed to better understand the microcellular foaming process, as we plan future studies that involve the creation of composite microcellular fo ams. Rapid decompression of SC CO2-saturated polystyrene at sufficient ly high temperatures (above the depressed T-g) yields expanded microce llular foams. The resulting foam structures can be controlled by manip ulating processing conditions. Experiments varying the foaming tempera ture while holding other variables constant show that higher temperatu res produce larger cells and reduced densities. Structures range from isotropic cells in samples retaining their initial geometry to highly expanded foams recovered in the shape of the foaming vessel and having oriented, anisotropic cells and limited density reduction. Higher sat uration pressures lead to higher nucleation densities and hence smalle r cells. Decreasing the rate of depressurization permits a longer peri od of cell growth and therefore larger cell sizes. Foams having a bimo dal distribution of cell sizes can be created by reducing the pressure in two stages.