Fabrication and characterization of PVDF hollow fiber membranes employing in-situ self-assembly modulation concept

We develop a novel polyvinylidene fluoride (PVDF) hollow fiber membrane utilizing the concept of in-situ self-assembly modulation, which is in terms of in-situ synthesis of amphiphilic copolymers and in-situ solubilization of polyvinylpyrrolidone (PVP). Utilizing the polytetrahydrofuran dimethacrylate ester (PTMGDA) and polyethylene glycol monomethyl ether methyl methacrylate (PEGMA) as reaction monomers, amphiphilic copolymers are in-situ synthesized, denoted as “P(PTMGDA-r-PEGMA)”. Results show that P(PTMGDA-r-PEGMA) and PVP have the synergistic effects on configuration and separation performance of PVDF membrane. P(PTMGDA-r-PEGMA) with high ratio in hydrocarbon chain (75.2%) and PVP not only effectively tunes micro-structure of the dope solutions but also results in the enhancement of the resultant membranes' break strength and their stable permeability. Besides, the supramolecular aggregates of PVDF-P(PTMGDA-r-PEGMA)-PVP (size: 76-157 nm) work as “template” dependence of the macrovoids, which appear in the fibers׳ sponge-like cross-section structure, hence leading to the narrowing pore size distribution. Furthermore, the macrovoids' size enlarges with the increase of content of P(PTMGDA-r-PEGMA) and PVP. It is also found that the permeation flux is controlled by the diffusion of PVP from the interior dope solution and pore-forming of P(PTMGDA-r-PEGMA) during demixing process, which is consistent with the in-situ self-assembly modulation concept. Finally, the newly developed PVDF hollow fiber membranes demonstrate remarkable long-term stable permeability.