Influence of ethanol content and temperature in coagulation bath on the microstructure and performance of polyvinylidene fluoride ultrafiltration membranes

In this article, polyvinylidene fluoride (PVDF) ultrafiltration membranes were prepared via phase inversion method. The influence of different ethanol content and temperature in coagulation bath on the microstructure of PVDF membranes was discussed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) measurements. Rejection experiment was conducted with the bovine serum albumin (BSA) solution. The FTIR and XRD analysis showed the higher ethanol content and temperature of coagulation bath promoted the α crystal form of PVDF membranes. The increase of ethanol content in coagulation bath led to a decrease in the mean pore size and porosity and the increase of BSA rejection rate and break strength of PVDF membranes. This was because of the increase of ethanol content in coagulation bath that resulted in the formation of the more sponge-like structures and the fewer finger-like structures, which enhanced the compactness of the membranes. The PVDF membrane prepared in ethanol/pure water (60/40) coagulation bath at 20 °C showed a greater BSA rejection rate of 91.87% and break strength of 1.89 MPa with a mean pore size of 29.26 nm. Meanwhile, the increase in temperature of coagulation bath had a positive effect on the mean pore size, porosity, and hydrophilicity of PVDF membranes to a certain extent.