Preparation and characterization of PVDF–PFSA blend hollow fiber UF membrane

Polyvinylidene fluoride (PVDF)–perfluorosulfonic acid (PFSA) blend hollow fiber ultrafiltration (UF) membranes were prepared by wet-spinning method using pure water as an external coagulation solution. Coagulation kinetics of PVDF–PFSA–DMAc system was measured by light transmittance experiment. Using PEG10000 (Mw = 10,000), lysozyme (Mw = 14,400), PEG20000 (Mw = 20,000) and BSA (Mw = 67,000), the separation performances of PVDF–PFSA blend hollow fiber UF membranes were obtained. Based on the experimental results, the delayed demixing process was observed for the dope solution M-1 without PFSA-H while the instantaneous demixing process was observed for the others with PFSA-H in the dope solutions M-2 to M-6. The precipitation rate increased with the increment of the PFSA-H concentration in PVDF–PFSA dope solution. The bore fluid solution with 95:5 DMAc:H2O resulted in single finger-like voids for PVDF–PFSA-H UF membrane. The pure water permeation flux of PVDF–PFSA-H UF membranes firstly increased from <0.1 × 10−5 to 119.1 × 10−5 L m−2 h−1 Pa−1 (<0.1 to 119.1 L m−2 h−1 bar−1) for M-1 to M-4(1) and 137 × 10−5 L m−2 h−1 Pa−1 (137 L m−2 h−1 bar−1) for M-4(2), and decreased from 119.1 × 10−5 to 79 × 10−5 L m−2 h−1 Pa−1 (119.1 to 79 L m−2 h−1 bar−1) for M-4(1), M-5 and M-6 as the PFSA-H concentration changed from 0% to 5% and total PVDF–PFSA-H concentration was 20 wt.%. The molecular weight cut-off (MWCO) of PVDF–PFSA blend hollow fiber UF membranes spun from 20 wt.% PVDF–PFSA-H concentration with 3–5 wt.% PFSA-H was about 20,000 while that spun from 22 wt.% PVDF–PFSA-H or PVDF–PFSA-Na concentration with 5 wt.% PFSA-H or PFSA-Na was about 10,000. As the WPFSA-H/WPVDF increases from 2/18 to 5/15 for M-3–M-6, JBSA/Jw increases from 0.53 to 0.79. The anti-fouling property of PVDF–PFSA-H blend UF membrane is superior to PVDF–PFSA-Na blend membrane. Based on FTIR spectra, PFSA-H existed in PVDF–PFSA blend hollow fiber UF membranes. There is no obvious variation of the intensity of the characteristic peak at 983 cm−1 assigned to C–O–C group of PFSA-H molecules. This also illustrated that PVDF–PFSA-H blend hollow fiber UF membranes were stable.