Preparation of ethylene chlorotrifluoroethylene co-polymer membranes via thermally induced phase separation

Microporous ethylene chlorotrifluoroethylene co-polymer(ECTFE) membrane was prepared via thermally induced phase separation(TIPS) method. By an analysis of interaction parameter, compatibility of ECTFE/diluent systems and the membrane cross-section morphologies, the liquid-liquid phase separation was found during the TIPS process when diethyl phthalate(DEP) was chosen as a diluent. The thermodynamic phase diagram confirms that a large liquid-liquid phase separation region for the ECTFE/DEP system was observed. The monotectic point of this system appeared at a high polymer concentration which was approximately up to 55%. Moreover, the effects of the cooling temperature and coarsening time on membrane structure, porosity, and tensile strength were also investigated. The results showed that a faster cooling rate and shorter coarsening time at 458 K led to membranes with smaller pore size.