Correlated Effect of Air Gap and PVP Concentration on the Structure and Performance of PVDF Ultrafiltration Hollow Fiber Membrane

Polyvinylidene fluoride/polyvinylpyrrolidone (PVDF/PVP) hollow fiber membranes were fabricated by dry-jet wet-spinning process. The correlated effects of the air gap length and PVP concentration ((1) the air gap length effect at the low and high PVP concentration in the dope solutions, as well as (2) the effect of the PVP concentration at the same air gap length) on the cross-section structure and membrane performance were investigated. Results indicated that the air gap effect on hollow fiber membranes is more evident for the dope solution with the high PVP concentration than low PVP concentration. In other words, macro-voids grow inwards and mechanical properties decrease and pure water permeability increases as the air gap length decreases. With increasing the PVP concentration in dope solution, large macro-voids/cavities in hollow fiber membranes are suppressed to the finger-like macro-voids. Moreover, the outer separation layer is thickened, and the mechanical properties are increased, as well.