Improved performances of PVDF/PFSA/O-MWNTs hollow fiber membranes and the synergism effects of two additives

The polyvinylidene fluoride/perfluorosulfonic acid/oxidized-multi-walled carbon nanotubes (PVDF/PFSA/O-MWNTs) hollow fiber membranes with 90.0% N-methyl pyrrolidone (NMP) aqueous solution as bore liquid are prepared by the wet spinning method. The membranes with the singly introduced PFSA or O-MWNTs additive are also investigated for comparison. The synergism effects of the two additives of PFSA and O-MWNTs are experimentally verified. The results indicate that the PVDF/PFSA/O-MWNTs hollow fiber membranes show asymmetrical structure. The fingerlike voids in the membranes run through the whole cross-sections. However, the PVDF/O-MWNTs fiber (MC-75) has an evidently different cross-section morphology due to the absence of PFSA. The surface hydrophilicity and permeation flux of PVDF/PFSA/O-MWNTs membranes are evidently improved with the addition of O-MWNTs. The hydraulic permeability J(w), increases from 100.4 LM-2 H-1 bar(-1) to 229.4 LM-2 H-1 bar(-1) as O-MWNTs loading increases from 0.25 wL% to 0.75 wt% for M-25-M-75, and then slightly decreases to 205.3 L M-2 H-1 bar(-1) for M-100. The fibers of M-0 and MC-75 containing a single additive. PFSA or O-MWNTs, only have 80.7 +/- 4.8 LM-2 H-1 bar(-1) and 32.3 +/- 6.1 L M-2 H-1 bar(-1), respectively. The mechanical properties of PVDF/PFSA/O-MWNTs fibers are also improved by adding O-MWNTs up to 0.75 wt%, whereas the fibers only containing a single additive (PFSA or O-MWNTs) present a lower mechanical strength. (C) 2014 Elsevier B.V. All rights reserved,