Morphology and polymorph study of a polyvinylidene fluoride (PVDF) membrane for protein binding: Effect of the dissolving temperature

A microporous polyvinylidene fluoride (PVDF) membrane was prepared from a PVDF/N-methyl-2-pyrrolidone (NMP) solution using liquid-induced phase separation with 2-propanol as the soft coagulant. In this paper, the effect of the dissolving temperature on the morphology and crystalline structure of PVDF membrane and subsequently on protein binding was studied. Field emission scanning electron microscopy (FESEM) was performed to observe the membrane morphology, and Differential Scanning Calorimeter (DSC) along with Fourier transform infrared (FTIR) spectroscopy was used to investigate the crystallinity and crystalline structure of the membrane respectively. The FESEM and FTIR results show that membrane morphologies and crystalline changed significantly as a result of the dissolving temperature, while no obvious change observed on the crystallinity of the membrane, based on the DSC results. It was found that a critical temperature of 40 °C existed. At lower temperatures, the protein binding ability was governed by the crystalline structure of the membrane, whereas at temperatures greater than 40 °C, the protein binding was primarily governed by the membrane porosity.

Research highlights
► Five different dissolving temperatures in the preparation of PVDF/NMP dope solution were looked into.
► Dissolving temperature greatly affected the final morphology and polymorph structure of the PVDF membrane.
► For protein binding performances, critical temperature at 40 °C existed.
► Protein binding is governed more by the crystalline structure of the PVDF membrane when the temperature is below 40 °C.
► At temperature greater than 40 °C, protein binding is more influenced by the membrane porosity.