Study Of Pvdf-fe₃o₄ Hybrid Ultrafiltration Membranes

Polyvinylidene fluoride (PVDF) with excellent chemical stability and appropriate temeperature tolerance is one of materials applied to prepare ultrafiltration (UF) membranes, but its hydrophobic property limits the application of PVDF UF membrane due to serious membrane fouling. In order to improve hydropholic property, some inorganic filler can be added into the casting solution to prepare organic-inorganic hybrid PVDF ultrafiltration membranes. Fe3O4 is a kind of hydrophilic filler with magnetic property. An external magnetic field may change the arrangement of Fe3O4 particles in the membranes and influence the structures and the properties of membranes. However, PVDF-Fe3O4 UF hybrid membranes were not reported in the literatures.PVDF-Fe3O4 hybrid membranes with different Fe3O4 content and PVDF concentration were prepared by a wet phase inversion process. The membranes were investigated by ultrafiltration experiments for water flux, rejection, anti-fouling ability and anti-pressure strength. The cross-sectional structures were examined by a scanning electron microscopy (SEM). PVDF-Fe3O4 hybrid membranes with different Fe3O4 content and PVDF concentration were also prepared in an external magnetic field by a wet phase inversion process. In addition, a comparison between membranes prepared in no external magnetic field and membranes prepared in an external magnetic field was given by some further experimental data from contact angle, FTIR and DMA.The results shows that the water fluxes of membranes prepared in no external magnetic field slowly increase with Fe3O4 content (less than 65wt%), and then abruptly increase with Fe3O4 content (changed from 65wt% to 80wt%); The rejection of membranes slowly first rises with Fe3O4 content, and then keep stable when Fe3O4 content reaches 65wt%. Membranes with 70wt%～75wt% Fe3O4 filler have better intensity. The membrane with 70wt% Fe3O4 and 14.6wt% PVDF has a best composite performance.The performances of membranes prepared in an external magnetic field have the same change trends as those of membranes prepared in no external magnetic field. However, the obvious change of micro-structures from the cross sections can be observed in the those membranes with 60wt% Fe3O4 above the macro pores in the sublayer become parellel to the membrane surface along the external magnetic field. The membrane with 70wt% Fe3O4 and 14.6wt% PVDF has also a best composite performance.An external magnetic field can improve the water flux and the hydrophilic property of membranes, but has no obvious effect on the rejection of membranes.