Micelle-like macrovoids in mixed matrix PVDF-PTFE hollow fiber membranes

Unique 'micelle-like' macrovoids have been observed for the first time in the polyvinylidene fluoride-polytetrafluoroethylene (PVDF-PTFE) hollow fiber membranes. FESEM results show that the incorporation of 30 and 40wt% PTFE particles (<1 mu m) reduces the number of finger-like macrovoids in the membrane matrix, while micelle-like marrovoids (about 10 mu m in size) are formed when PTFE loading is increased to 50wt% or higher. 50wt% PTFE is the critical particle concentration for micelle-like macrovoid formation. The origins of micelle formation may be attributed to the adhesion and cohesion forces between air bubbles and particles in the supersaturated PTFE solution. A more rigorous degassing of the PVDF-T50 polymer dope solution may enhance the suspension homogeneity and eliminate the micelle-like macrovoid formation. It is therefore concluded that the micelle-like macrovoid formation arises from the agglomeration of gas bubbles upon PTFE particles with the aid of water diffusion and convection during the phase inversion of membrane formation. (C) 2009 Elsevier B.V. All rights reserved.