Three-layered hollow fiber (HF) membrane and its modification to enhance wetting resistance for membrane distillation (MD)

Abstract

A three-layered hollow fiber (HF) membrane exhibiting enhanced permeability and wet-resistance was fabricated using polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) simultaneously for membrane distillation (MD). The inner, outer, and middle layers of the membrane were prepared using a macrovoid structure of PVDF-CTFE, the finger-like structure of PVDF, and thin spongelike structure, respectively. The size of the macrovoid in the inner layer was enlarged and the permeability was enhanced using the polytetrafluoroethylenes (PTFE) as additive. However, the PTFE did not significantly change the liquid entrance pressure (LEP) of the membrane. The LEP and hydrophobicity of the inner layer of HF was increased by grafting pentafluorostyrene (PFS). The prepared membranes were characterized via several analytical tools, and the performance was evaluated using the vacuum MD (VMD) process. With 10% of PTFE, the size of the internal macrovoid increased, thus improving the flux to 137%. When PFS was grafted on the inner layer, the contact angle (CA) and liquid entry pressure (LEP) values increased to 117 and 154%, respectively, that showed an improvement in the wetting resistance. This study showed that the three-layered structure designed using the PTFE and PFS as an additive and grafting, respectively, were successfully fabricated to improve the wetting resistance and permeability. (C) 2020 Elsevier B.V. All rights reserved.