Dual-layer PVDF/PTFE composite hollow fibers with a thin macrovoid-free selective layer for water production via membrane distillation

Abstract

In this study, the polyvinylidene fluoride (PVDF)/polytetrafluoroethylene (PTFE) composite is used to fabricate hollow fiber membranes for seawater desalination via direct contact membrane distillation (DCMD) application. The incorporation of PTFE particles in the formulated dope solution can efficiently suppress the formation of macrovoids and enhance the outer surface hydrophobicity. Dual-layer hollow fibers with a desirable macrovoid-free morphology and a relatively thin (13±2μm) outer-layer can be obtained via blending 30wt% of PTFE particles in the outer-layer dope. The resultant dual-layer hollow fiber (DL-30) displays a moderately high contact angle of 114.5° and porosity of 81.5%. Compared to the single-layer hollow fiber with 30wt% (SL-30) PFTE particles, the DL-30 fiber exhibits a flux enhancement of approximately 24% that is contributed to the reduction in inner-layer mass transfer resistance. Dual layer membrane configuration with a lower wall thickness as well as larger outer and inner diameters provides even higher water vapor transport is potentially suitable for desalination. Both single- and dual-layer PVDF/PTFE hollow fiber membranes reveal good long-term stability of up to 100h of continuous testing. By utilizing the state-of-the-art dual-layer spinning technology, hollow fiber membranes with better performance (i.e. enhanced flux) and morphology (i.e. macrovoid-free) can be tailored.