Engineering flat sheet microporous PVDF films for membrane distillation

A simple phase inversion technique to fabricate hydrophobic microporous films for membrane distillation (MD) is presented. Polyvinylidene fluoride (PVDF) dissolved in triethyl phosphate (TEP) was used as a casting solution with a coagulation bath comprising 2-propanol and water. The effect of processing parameters (PVDF concentration and molecular weight, and composition of coagulation bath) on membrane performance was systematically investigated. Our results demonstrate that an MD membrane with desirable properties can be achieved by carefully controlling the casting parameters. The fabricated membranes exhibited asymmetric structure with a dense top layer and highly porous bottom substrate, and showed markedly different performance (i.e., water vapor flux) depending on the MD membrane orientation. Our results suggest that membrane surface porosity as well as the structure of the membrane are the key factors determining MD membrane performance. (C) 2015 Elsevier B.V. All rights reserved.