Wet dispersion of graphene assisted constructing multiple interface pores of PVDF hollow fiber membranes via melt-spinning and stretching

In this work, in order to further improve the permeability of poly(vinylidene fluoride) (PVDF) hollow fiber microfiltration membranes through melt-spinning and stretching (MS-S), we doped graphene (GE) in the forming membrane system of the previous work via wet dispersion and successfully prepared PVDF hollow fiber microfiltration membranes with multiple interface pores. GE could be uniformly dispersed and embedded in the PVDF matrix through the wet dispersion, which could obviously improve the interface layer between the matrix phase (PVDF) and the dispersed phase (GE) due to their poor compatibility of organic/inorganic phases. In addition, the stress concentration would be generated at the interface between GE and PVDF, which resulted in PVDF forking to many tiny fibers. Thus, the multiple interface pores between organic/organic (PVDF/polysulfone(PSf)) and organic/inorganic (PVDF/GE) phases could occur and be controlled precisely through the further stretching. The results showed that GE could improve the pore size and porosity of the prepared membranes obviously. In addition, the pore size of the prepared membranes could be controlled from 0.258 to 1.066 µm by changing the stretching ratios. Accordingly, pure water flux increased from 174.5 to 2782.9 L m-2 h-1. Applied to filter the active sludge suspension, the prepared PVDF microfiltration membranes exhibited a high rejection (>99.5%), and the turbidity decreased obviously (˂0.5 NTU). In particular, there were not any hazardous solvents used in the preparation process, which could achieve green preparation of PVDF membranes.