Wide liquid-liquid phase separation region enhancing tensile strength of poly(vinylidene fluoride) membranes via TIPS method with a new diluent

Poly(vinylidene fluoride) (PVDF) membrane is widely used in water purification and wastewater treatment. In present paper, thermally induced phase separation (TIPS) was employed, and maleic acid dibutyl ester (DBM), a new diluent, was introduced for PVDF membrane preparation. Phase diagram and the effects of polymer concentration and quenching temperature on the structure, morphologies, properties, and performances of PVDF membranes were investigated. During the quenching process of PVDF/DBM system, liquid-liquid phase separation happened, and PVDF membranes with a bi-continuous structure were fabricated. What is interesting is that the liquid-liquid phase separation region was much wider than other PVDF/diluent systems. Thus, it is possible to fabricate PVDF membrane with a bi-continuous structure at high polymer concentrations, without stretching or additives. With the increase in polymer concentration and quenching temperature, mean pore size and pure water flux of the PVDF membrane decreased. Tensile stress of the prepared PVDF membranes reached to 6.18 MPa, because the wide liquid-liquid phase separation region induced a bi-continuous structure when the concentration of the PVDF membrane was at around 30%.