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

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 Jw increases from 100.4 L M−2 H−1 bar−1 to 229.4 L M−2 H−1 bar−1 as O-MWNTs loading increases from 0.25 wt% 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 L M−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.