Cross-Linked Dual-Layer Poly(vinylidene Fluoride) Hollow Fiber Membranes for Organic Solvent Nanofiltration

A dual-layer (DL) PVDF loose nanofiltration (NF) hollow fiber membrane (HFM) was designed via optimized phase inversion process using a continuous online-coating device. Subsequently, the loose DL PVDF HFM was cross-linked through a one-pot amine-based reaction to improve the solvent stability. Changes in chemical structure were characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscope (XPS). The solvent stability in DMF of the membranes with different cross-linking time was investigated through measuring swelling ratio of the membranes. In addition, thermogravimetric analysis (TGA) and mechanical property were also conducted to study physico-chemical changes of the cross-linked DL PVDF hollow fiber membranes. The results showed that this cross-linking process significantly improved the stability in polar solvent, accompanied by a decrease in thermal stability and mechanical properties. A cross-linking time of 8 h was found to produce DL PVDF HFMs with most balanced properties. The performance of cross-linked membranes was evaluated via filtering various solutes in ethanol solution and typical solvents containing Rose bengal (RB). The cross-linked DL HFMs showed rejection of RB more than 99% in solvent with methanol, ethanol, isopropanol, and acetone and permeance of 9.3, 7.6, 5.2, and 8.7 L/(m 2 ·h·bar), respectively. Besides, the prepared membranes also presented exceptional performance stability for treatment of RB/ethanol solution. Thus, they have great potential for real organic solvent nanofiltration applications.