Influences of the structure parameters of multi-walled carbon nanotubes(MWNTs) on PVDF/PFSA/O-MWNTs hollow fiber ultrafiltration membranes

Oxidized-multi-walled carbon nanotubes(O-MWNTs) with different structure parameters were employed to prepare polyvinylidene fluoride(PVDF)/perfluorosulfonic acid(PFSA)/O-MWNTs hollow fiber ultrafiltration membranes by wet spinning method with 90.0% N-methyl pyrrolidone(NMP) aqueous solution as bore liquid. The results demonstrate that the structure parameters of O-MWNTs slightly influence the morphologies and surface hydrophilicity of the resultant hollow fiber membranes. However, they evidently affect the hydraulic permeability of PVDF/PFSA/O-MWNTs membranes, which increases from 142.3 L M−2 H−1 bar−1 to 181.2 L M−2 H−1 bar−1 with the increasing diameter of MWNTs from 10–20 nm to 20–40 nm by adding 0.5 wt% O-MWNTs in dopes. This phenomenon can be attributed to the expanding mass transfer area of O-MWNTs with the increasing diameter. However, the hydraulic permeability decreases to 154.3 L M−2 H−1 bar−1 with the further increasing the diameter to 40–60 nm because much more PVDF dope severely immerses into the relatively wider channels of O-MWNTs. The PVDF/PFSA/O-MWNTs membranes spun from the dopes containing 0.75 wt% O-MWNTs have the similar tendency in permeability. The variations of pore size and MWCO with the structure parameters of O-MWNTs are in accordance with that of permeability. The mechanical properties of PVDF/PFSA/O-MWNTs hollow fiber membranes evidently decrease in the three indicators of tensile strength, breaking elongation and Young modulus as the O-MWNTs diameter increases from 10–20, 20–40 and 40–60 nm.