Preparation of polypropylene microfiltration membranes via thermally induced (solid-liquid or liquid-liquid) phase separation method

Polypropylene (PP) hollow fiber microfiltration membranes with excellent performance were successfully prepared from the PP-binary diluent system via thermally induced liquid-liquid (L-L) phase separation method. The binary diluent consisted of myristic acid and diphenyl carbonate. The effects of the binary diluent on phase separation and membrane structure were systematically investigated. With the decrease in the weight ratio of myristic acid to diphenyl carbonate, the Flory-Huggins interaction parameter between PP and the binary diluent became more positive, and the mechanism of phase separation changed from solid-liquid (S-L) to L-L. This resulted in the membrane structure changing from spherulitic to bicontinuous. Moreover, as the weight ratio of myristic acid to diphenyl carbonate decreased from 11/9 to 2/3, the L-L phase separation region kept enlarging while the viscosity of the whole system became higher. The pore size of the cross-section increased due to the longer coarsening time while the surface pore size decreased due to the higher viscosity of the system. The bulk porosity of resultant PP membranes was mostly higher than 70% and pure water flux were generally larger than 650 L m(-2) h(-1). In addition, the PP hollow fiber microfiltration membrane possessed excellent mechanical properties (tensile strength of 3.47 MPa and elongation of 118%) and good separation performance (rejection to PEO (M-w = 1000 kDa) of 94.6%) when the weight ratio of myristic acid to diphenyl carbonate was 2/3. (C) 2015 Wiley Periodicals, Inc.