Having strong mechanical strength and high thermal, chemical, and fouling resistances is a crucial requirement for a membrane to apply for industrial and municipal water and wastewater treatment. Poly -ethylene-chlorotrifluoroethylene- -ECTFE- offers unique chemical resistance, high temperature resistance, excellent mechanical properties and durability. These outstanding properties make ECTFE as a promising polymer for membrane applications. In this study, a porous ECTFE hollow fiber membranes with a bicontinuous structure were prepared, for the first time, using HALAR® ECTFE 901 -Solvay specialty polymers Co.- and DEP and GTA solvents via the TIPS method. The thermodynamic phase diagrams for both polymeric systems -ECTFE/DEP and ECTFE/GTA- showed a liquid–liquid -L-L- phase separation region, prior to solid– liquid -S-L- phase separation -polymer crystallization-. The morphologies of hollow fiber membranes were observed by scanning electron microscopy -SEM- and it was observed that a bicontinuous structure was formed through L-L phase separation. The investigation into the spherulite growth rate showed that the rate of 4.0×10−2 μm/sec with DEP reduced to 1.5×10−2 μm/sec for GTA, while the crystallinity increased from 25 to 30%. Therefore, in the GTA system, the spherulite number was higher and the size was smaller than in the DEP system. Thus, the solvent type affected spherulite morphology and crystallinity. Uniform bicontinuous membrane structures were obtained when the ECTFE concentration was 20–30 wt% due to L-L phase separation. When the ECTFE concentration increased from 20 to 30 wt%, the water permeability sharply decreased from 1112 to 5 Lm-2h-1atm-1 and from 1250 to 1.0 Lm-2h-1atm-1 for DEP and GTA, respectively. Although the mechanical properties of the hollow fiber membrane prepared using both solvents -DEP and GTA- decreased with decreasing polymer concentration, the tensile strength and elongation of the membrane prepared with an ECTFE concentration of 20 wt% were about 1.9 MPa and 60%, respectively, which are still acceptable values. The hollow fiber membranes prepared in this study showed superior performance in comparison with the ECTFE membranes reported in previous studies about either flat sheet or hollow fiber membranes.

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