Membrane distillation with hydrophobic macrovoid-free PVDF–PTFE hollow fiber membranes

Hydrophobic polyvinylidene fluoride–polytetrafluoroethylene (PVDF–PTFEPVDF–PTFE) hollow fiber membranes for desalination via direct contact membrane distillation (DCMD) are successfully fabricated. The incorporation of PTFE particles (<1 μm) into the polymeric matrix enhances the hydrophobicity of the membranes, yielding a resultant water contact angle of 103°. FESEM analysis confirms the formation of macrovoid-free hollow fiber membranes with uniform particle distribution at 50 wt.% PTFE loading. All the fabricated membranes exhibit narrow pore size distributions and have relatively small mean pore diameters between 0.116 and 0.308 μm. Hollow fiber membranes spun at higher air gaps result in above 6% improvement in permeate flux because of the reduction in membrane wall thickness and greater surface porosity. The fabricated membranes demonstrate high thermal efficiency (EE) of above 80% when subjected to a hot feed solution of 80 °C. PVDF–PTFE membranes spun at an air gap of 4 cm and with 50 wt.% particle loading demonstrate an optimal separation performance of 40.4 kg/m2 h permeation flux as well as ∼99.8% salt rejection at 80 °C. This performance is comparable or even higher than the commercial hydrophobic membranes for DCMD studies.