Novel hydrophobic PVDF membranes prepared by nonsolvent induced phase separation for membrane distillation

Polyvinylidene fluoride (PVDF) was used for membrane preparation using the nonsolvent induced phase separation (NIPS). In this paper, the effect of the polymer concentration in the dope solution and the nonsolvent bath composition is widely investigated. In particular, the effect of increasing concentrations of ethanol in the coagulation bath on the morphology and characteristics of the membranes, as well as on their performance in membrane distillation of pure water and a brine was evaluated. FESEM analysis, coupled with contact angle determination highlighted different coagulation paths that allowed to obtain superhydrophobic membranes at higher ethanol concentrations. Moreover, the polymer concentration had major effects on the overall porosity and pore size of the membrane. By tuning the membrane preparation conditions, it was possible to obtain membranes that showed great distillate flux as well as a complete salt rejection during the vacuum membrane distillation tests.