Polypropylene hollow fiber membrane prepared with green binary diluents via TIPS: Effects of spinning process parameters and VMD desalination performance

Environmental-friendly castor oil (CO) and soybean oil (SO) were used as mixed diluents to spin polypropylene (PP) hollow fiber microporous membrane (HFMM) via thermally induced phase separation. With the addition of castor oil, the cloud point temperature gradually increases, and the region of liquid-liquid phase separation becomes larger. The membrane pore structure changes from a spherulitic form to a continuous sponge-like pore structure. Particularly, the effects of spinning process parameters (spinning speed, spinneret temperature and bore liquid temperature) on HFMM properties (e.g., mechanical properties, water contact angle, pore size and pore size distribution) and desalination performance of vacuum membrane distillation (VMD) were further studied. A higher spinning speed and smaller temperature difference between dope and spinneret/bore fluid increase pore size and reduce membrane porosity. The PP HFMM produced under the spinneret temperature of 160 °C, the bore fluid temperature of 113 °C, and spinning speed of 16.1 m/min reached relatively high VMD desalination performance both feeding 10 g/L NaCl solution (water flux 18.4 kg/m²·h and salt rejection 99.99 %) and petrochemical saline wastewater (water flux 14.0 kg/m²·h and salt rejection 99.5 %). This paper has important guiding significance for the mass production of PP HFMMs.