Preparation of PVDF membrane based on “In-situ Template-TIPS” technology and the investigation on membrane formation mechanism, microstructure regulation and permeability

Abstract

In this work, poly(vinylidene fluoride) (PVDF) flat membrane was prepared via “In-situ template-TIPS” technology using poly(vinylpyrrolidone) (PVP) as template. The membrane formation mechanism and microstructure evolution of this method were expounded for the first time. The effect of PVP content on the crystallization behavior of the dope, the microstructure, the crystallization behavior and the permeability of the membrane was investigated in detail. Interestingly, the solidification of PVP from the diluent via air-cooling at room temperature not only hindered the PVDF crystallization, but also the growth of PVP led to the formation of porous surface and eliminated the thick and dense skin layer, and thus formed the inter-connected structure and higher porosity (The maximum porosity is 88.9%). The maximum pure water flux reached as high as 3420 L m−2 h−1. The membrane also indicated an excellent performance in rejection of bacteria and separation of “petroleum ether/water” emulsion (nearly 100%). The α crystal phase was formed for the membrane by air-cooling at room temperature. The non-isothermal crystallization kinetics revealed that PVP can act as a heterogeneous nucleating agent for PVDF crystallization and hindered the growth of PVDF crystal in three-dimension. The research presented a novel and simple idea for tailoring the microstructure of membrane via TIPS process.