Fabrication of PVDF hollow fiber membranes via integrated phase separation for membrane distillation

In this study, polyvinylidene fluoride (PVDF) hollow fibers with interpenetrating network morphologies were fabricated via complex thermally induced phase separation (c-TIPS) by integration of non-solvent induced phase separation (NIPS) and thermally induced phase separation (TIPS) at 80 °C and then tested in membrane distillation (MD). The effects of solvents, additive and bore fluid on the membrane morphology, pore structure and MD performance were investigated. Direct-contact membrane distillation (DCMD) for desalination was carried out to evaluate membrane permeability and salt rejection. Using a weak solvent like triethylphosphate (TEP) and weak bore fluid like polyethylene glycol (PEG-200) in the c-TIPS favors the formation of an interpenetrating network morphology. In addition, PEG-200 increased the roughness and water contact angle of the inner skin. The hollow fibers fabricated via the c-TIPS at low temperature presented high permeability, mechanical strength and long-term stability. In desalination of formulated seawater, a distillate flux of 61.6 kg/m2h with NaCl rejection of 99.99% was achieved at feed temperature of 71 °C.