Study on the structure and vacuum membrane distillation performance of PVDF composite membranes: I. Influence of blending

In this study membranes were fabricated from the blend of high (H) and low (L) molecular weights poly(vinylidene fluoride) by the phase inversion process. The membranes so fabricated were characterized by scanning electron microscopy, gas permeation tests, contact angle (CA) and liquid entry pressure of water (LEPw) measurement, and further subjected to vacuum membrane distillation (VMD) in a scenario that was applicable for cooling processes, where the feed water temperature was maintained at 27 degrees C. It was found that the H:L mixing ratio did not affect the membrane surface hydrophobicity (as reflected by the CA) significantly. The water vapor flux of VMD was found to be the highest at the intermediate range of H:L ratio, i.e., 4:6, at which the thickness of the sponge-like layer showed a minimum, the pore size showed a maximum, the finger-like macro-voids formed a more orderly single-layer structure, and the LEPw showed a minimum. (C) 2014 Elsevier B.V. All rights reserved.