Polysulfone foam with high expansion ratio prepared by supercritical carbon dioxide assisted molding foaming method

Polysulfone (PSU) is considered as an important candidate for the fabrication of high-performance microcellular polymers, but the preparation of PSU foam with a high expansion ratio still remains a big challenge worldwide. In this study, high expansion ratio PSU foam was successfully prepared by a supercritical carbon dioxide (CO₂) assisted molding foaming method. The foaming behavior of PSU under supercritical CO₂ was systematically studied in various process conditions and different microcellular structures were created in PSU foams. The results showed that foaming temperature and CO₂ concentration were the key factors to obtain microcellular foams with tailored microstructures. The cellular structure and expansion ratio of PSU foam obviously changed with different foaming temperatures. The expansion ratio and average cell size firstly increased and then decreased as foaming temperature increased. However, the cell density decreased and then remained stable as foaming temperature increased. The maximum expansion ratio of 11.0 was reached at the optimum foaming temperature of 200 °C. Cellular structure and morphologies of the foam changed obviously at CO₂ concentrations below 5% and remained stable at CO₂ concentrations above 5%. Finally, the prepared PSU foams exhibit excellent mechanical strength, good thermal conductivity, and superb heat retardancy, thus may have great potential application as a kind of substitute material in the electrical wire and cable industry, railway and steamer transportation, oil and gas platforms, military use and in other fields.