An investigation on the microcellular structure of polystyrene/LCP blends prepared by using supercritical carbon dioxide

Foamed PS/LCP blends with cell diameter less than 7 μm are prepared by using supercritical CO2, 25 MPa, and 80°C for 6 h. Characterization of the microcellular structure of these blends is conducted to reveal the influence of LCP addition, LCP ratio and compatibilizer used on the microcellular blends. Due to poor adsorption of supercritical CO2 by LCP under the experimental conditions, the microvoids only exist in the polystyrene phase of the blends. Where in the LCP phase, the microfibrils and spheres retain their original morphology and a skin-core structure exist as in the unfoamed PS/LCP blends. The LCP ratio and the compatibilizer, zinc neutralized lightly sulfonated polystyrene ionomer (ZnSPS), influence the cell size of the microcellular blends. A significant decrease of cell diameter in low LCP composition is observed, and then the change is much less and levels off in higher LCP composition. An increase of cell size is found from skin to core, which is resulted from the effect of the skin-core structure of the PS/LCP blends and the effect of competition between gas diffusing in the cells and diffusing out of the skin. The microcellular blends with ZnSPS has larger cell size than those without ZnSPS, which is the consequence of the improvement of interfacial adhesion, where CO2 could easily diffuse out through the gap between poor adhesion interface of blends without ZnSPS. It is also found that the cell density in the microcellular blends is slightly larger than that in the microcellular polystyrene. This implies an additional heterogeneous nucleation of LCP to the homogeneous nucleation of polystyrene.