Effect of polymer loading on superhydrophobic PVDF/TiO₂ supported membrane for membrane distillation

Membrane distillation (MD) is an attractive separation process since it can be used to recover water with nearly 100 % non-volatile rejection. MD is also considered to be environmentally friendly since the waste heat at low temperature or the solar energy heat can be used for the separation. Despite of having these great features, MD has not been widely used for commercial purpose up to date. The hindrance factors include the lack of commercially available membrane that tailored for MD, the low permeation flux as well as operational issues especially membrane wetting and fouling. In this work, polyvinylidene fluoride (PVDF) membranes incorporated with TiO2 nanoparticles were modified using hydrophobic silane to enhance the permeate flux and to reduce membrane wetting. The polymer loading was varied in the range of 13 - 16 wt% to form thin membranes on woven support via dual bath coagulation. This coagulation technique produced membranes with spongy structure and rough surface. The dry membrane was modified by using low surface energy silane, tridecafluro-1,1,2,2-tetrahydrooctyl triethoxysilane. TiO2 nanoparticles embedded on membranes provided the active site for silane modification process. All the membranes possess superhydrophobic surface with water contact angle beyond 160 °. The increment of polymer loading reduced the average pore size from 0.41±0.01 μm (13 wt%) to 0.34 ± 0.04 μm (16 wt%). Aside from that, the membrane porosity was reduced while membrane thickness was increased with the increasing polymer loading in dope solution. After 8 h of MD operation, the modified PVDF/TiO2 membrane with 13 wt% polymer loading in dope solution showed the highest permeation flux. The membrane with large pore size, high porosity, low thickness and great hydrophobicity is preferable in MD.