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 40 wt% PTFE particles (<1 μm) reduces the number of finger-like macrovoids in the membrane matrix, while micelle-like marcovoids (about 10 μm in size) are formed when PTFE loading is increased to 50 wt% or higher. 50 wt% 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.