Preparation and properties of swelling-resistant polyperfluoroethylene propylene/polytetrafluoroethylene composite film

Nanofiltration membranes with polytetrafluoroethylene (PTFE) fiber membranes as the support layer are commonly used for non-polar organic solvent filtration, but PTFE fibers are prone to swelling phenomenon in solvents, which leads to the deterioration of membrane filtration efficiency. This paper proposes a strategy to improve the swelling resistance of the PTFE fiber membrane by impregnating the coating with polyperfluoroethylene propylene (FEP) emulsion as the finishing agent. The principle of improving the swelling resistance of PTFE fiber membrane after FEP finishing was analyzed, the effects of FEP mass fraction and sintering temperature on the swelling performance of FEP/PTFE composite film was investigated, and the bonding fastness between FEP and PTFE fiber film and the separation performance of FEP/PTFE composite film were examined. The results show that FEP is applied to the PTFE fiber film, and the sintering treatment makes FEP melt to realize the wrapping of PTFE micro primary fibers, thus enhancing the dimensional stability of PTFE fibers. The changes in the apparent morphology, mechanical properties, and solvent flux of FEP/PTFE composite membranes after 7 d n-hexane immersion experiments are better than those of PTFE-based membranes, and with the increase of the mass fraction of FEP and the drying temperature, the greater the area of FEP attached to PTFE fiber membrane, the more obvious the stability improvement. The mass loss rate of the FEP/PTFE composite membrane after ultrasonic cleaning for 6 h is ±0.27%, with good interfacial compatibility and excellent bonding fastness. After FEP finishing, the rejection rate of 300nm SiO₂ pollutants in FEP/PTFE composite membrane is as high as 99% before and after soaking in n-hexane solvent for 7 days, and the rejection rate is basically unchanged after soaking in four typical non-polar organic solvent environmental systems for 7 days. The results provide strategic support for popularizing and applying PTFE-based organic solvent-resistant separation membranes.