(368g) Novel Dynamic Microcellular Polystyrene Processing in Supercritical CO2

Supercritical carbon dioxide (ScCO2) for its unique properties can enhances the diffusivity and solubility in polymer matrix in microcellular plastic processing. The effect of thermodynamic state of CO2 on microcellular processing was investigated with a novel dynamic microcellular processing setup developed previously. This setup can form a steady shear flow and an oscillatory shear flow superimposed perpendicular to the steady shear flow. The basic working principle of this setup is to form a single-phase polyemr/ScCO2 solution with the shear mixing of the rotor (steady shear or combined shear), and then cell nucleation under thermal instability by rapid pressure release. Material used in this paper is pure polystyrene pellet, and the blowing agent is environmental friendly supercritical CO2 (ScCO2). The effects of saturation pressure and shear flow on polystyrene cell morphology are investigated with this setup. The cell morphology was analyzed with a scanning electron microscope. The results show that the sample foamed with gaseous CO2 has a small cell density, large cell size and none uniform cell distribution. While, foamed with supercritical CO2 the cell density is increased and cell size is decreased significantly. And the cell density is increased and cell size decreased further with the increased of supercritical CO2 pressure. The shear flow has a significant influence on the aggregated state of polymer. When processed under simple steady shear flow the final cell structure show an oval shape. The cell was elongated seriously along the direction of shear flow. While processed under combine shear, a cell structure of larger cell density and more uniform cell distribution is obtained, and the cell shape is nearly spherical. This indicates that the aggregated state of polymer is changed by the superimposed oscillatory shear. The changed aggregated state is helpful to get a fine cell structure, and thus can improve final product properties.