Synergy of supercritical CO2 and superheated H2O for enhanced processability of polyethersulfone towards open cell foams

Processing of a high glass transition (T_g) polymer such as polyethersulfone (PES; T_g = 225°C) poses a challenge as it requires high processing temperatures or sometimes toxic solvents. In this work, we report of a facile process using superheated water (shH₂O) and supercritical carbon dioxide (scCO₂) co‐media. PES solids were foamed in the scCO₂/shH₂O co‐media or scCO₂ alone in a batch process at different temperatures. The scCO₂/shH₂O produced a synergistic effect and achieved PES foams even at processing temperatures as low as 85°C below the nominal T_g; whereas, scCO₂ alone required higher processing temperatures. Moreover, the scCO₂/shH₂O co‐media produced highly porous PES foams that were at least 23% higher in porosity than what was obtained using scCO₂ alone. In addition, the scCO₂/shH₂O produced open cell foams at some processing conditions; whereas, scCO₂ produced closed cell morphologies. Since both CO₂ and H₂O are innocuous, this approach has potential for use in the preparation of ultrafiltration membranes, which currently require the use of toxic solvents for their fabrication by way of the phase inversion process. Moreover, the use of scCO₂/shH₂O is a cost‐effective approach for the processing of high T_g polymers at significantly lower temperatures. POLYM. ENG. SCI., 58:1108–1114, 2018. © 2017 Society of Plastics Engineers