The effect of blending ratio on the compatibility, morphology, thermal behavior and pure water permeation of asymmetric CAP/PVDF membranes

An asymmetric cellulose acetate propionate/polyvinylidine fluoride (CAP/PVDF) blend membrane was fabricated using the phase inversion method-induced by immersion precipitation-and the effect of blending these two semi-crystalline polymers was studied. Morphological and thermal studies were conducted using field-emission scanning electron microscopy (FE-SEM) and thermogravimetric analysis/differential scanning calorimetry (TGA/DSC). The contact angle and pure water flux (PWF) were also studied to evaluate the membrane performance. The results indicate that blending PVDF can alter the thermal properties of the resulting membranes, particularly the thermal stability. At lower ratios of PVDF to CAP, the precipitation process is governed by a liquid-liquid demixing phase separation, which leads to an increase in the amount of macrovoids and the pure water flux. However, at higher ratios of PVDF to CAP, crystallization dominates, and the membrane structure is replete with packed and interlocked crystalline particles, resulting in a reduction in the porosity and pure water flux. (C) 2011 Elsevier B.V. All rights reserved.