Preparation and characterizations of charged poly(vinyl butyral) hollow fiber ultrafiltration membranes with perfluorosulfonic acid as additive

The charged poly(vinyl butyral) (PVB) hollow fiber ultrafiltration membranes were fabricated with perfluorosulfonic acid (PFSA) as additive by wet spinning method. Evolution of the precipitation kinetics, morphologies, permeation performances, electrokinetics and mechanical properties of the as-spun PVB membranes were investigated with the PFSA content and bore fluid. The results illustrate that the PVB/PFSA/N-methyl-2-pyrrolidone (NMP) dopes experience an instantaneous demixing mechanism and the precipitation rate increases with the addition of PFSA. The fibers fabricated with 50 wt% ethanol aqueous solution as bore liquid have an asymmetrical double finger-like structure; nevertheless, the fibers fabricated with 90 wt% NMP aqueous solution as bore liquid form a single finger-like structure. The PVB membranes containing more PFSA content and with 90 wt% NMP aqueous solution as bore fluid have higher hydraulic permeability (Jw) than the fibers containing lower PFSA content and with 50 wt% ethanol aqueous solution as bore fluid. The highest Jw value 78.9 L M−2 H−1 bar−1 is obtained for the PVB membrane with a MWCO of 50.1 kDa. Streaming potential measurements verify that the apparent zeta potential (ζapp) of the PVB membranes fabricated with 50 wt% ethanol aqueous solution as bore liquid ranges from −4.88 mV to −11.28 mV as PFSA content increases from 1 wt% to 3 wt%. The break strain and Young’s modulus values of the resultant fibers increase when the PFSA content increases regardless of the bore fluid.