Preparation and properties of swelling-resistant polyperfluoroethylene propylene/polytetrafluoroethylene composite film
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摘要: 以聚四氟乙烯(PTFE)纤维膜为支撑层的纳滤膜常用于非极性有机溶剂过滤，但PTFE纤维在溶剂中易产生溶胀现象，导致膜过滤效能变差。本文提出以聚全氟乙丙烯(FEP)乳液为后整理剂，经浸渍涂层处理提升PTFE纤维膜耐溶胀性能的策略。分析FEP后整理提升PTFE纤维膜耐溶胀性的原理，探究FEP质量分数和烘燥温度对FEP/PTFE复合膜溶胀性能的影响规律，考察FEP与PTFE纤维膜间的结合牢度及FEP/PTFE复合膜的分离性能。结果表明：将FEP施加于PTFE纤维膜上，烘燥处理可使FEP熔融，进而实现对PTFE微原纤的包裹，从而提升PTFE纤维的尺寸稳定性。FEP/PTFE复合膜在正己烷中浸泡7 d后的表观形貌、力学性能、溶剂通量衰减变化情况均优于纯PTFE纤维膜，且随着FEP质量分数和烘燥温度的增加，FEP在PTFE纤维膜上的附着面积也越大，稳定性改善程度越明显。FEP/PTFE复合膜经超声清洗6 h后质量损失率为±0.27%，表明FEP与PTFE纤维间的界面相容性好、结合强度较高。在正己烷溶剂中浸泡7 d前后的FEP/PTFE复合膜对300 nm SiO2污染物的截留率均高达99%以上，在四种典型非极性有机溶剂环境体系浸泡7 d后截留率也基本保持不变，表现出了优异的过滤性能。本文的研究结果可为PTFE基耐有机溶剂分离膜的推广和应用提供策略支持。Abstract: 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.
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图 1 PTFE纤维膜FE-SEM图像： (a) 浸泡前；(b) 浸泡后
Figure 1. FE-SEM images of PTFE fiber membrane：(a) before soaking (b) after soaking
图 3 不同质量分数FEP分散液制备的复合膜的FE-SEM图像：(a-d)：(1wt%-4wt%) FEP/PTFE；(e-h)：(1wt%-4wt%) FEP/PTFE-7 d
Figure 3. FE-SEM images of composite membranes prepared with different mass fractions of FEP dispersions: (a-d): (1wt%-4wt%) FEP/PTFE; (e-h):(1wt%-4wt%) FEP/PTFE-7 d
图 4 不同FEP质量分数膜样品的机械性能分析
Figure 4. Mechanical properties analysis of membrane samples with different FEP mass fractions
图 5 不同FEP质量分数膜样品的性能分析
Figure 5. Performance analysis of membrane samples with different FEP mass fractions
图 6 不同烘燥温度下复合膜的FE-SEM图像：(a-d)：3wt%FEP/PTFE-(25℃-360℃)；(e-h)：3wt%FEP/PTFE-(25℃-360℃)-7 d
Figure 6. FE-SEM images of composite membranes at different sintering temperatures: (a-d)：3wt%FEP/PTFE-(25℃-360℃)；(e-h)：3wt%FEP/PTFE-(25℃-360℃)-7 d
图 7 不同烘燥温度下膜样品的机械性能分析
Figure 7. Mechanical properties analysis of membrane samples at different sintering temperatures
图 8 不同烘燥温度下膜样品的性能分析
Figure 8. Performance analysis of membrane samples at different sintering temperatures
图 9 FEP/PTFE复合膜的结合牢度测试：(a)原膜的FE-SEM图像，(b)超声6 h后膜的FE-SEM图像，(a1、b1)膜截面的FE-SEM图像(c)红外光谱图
Figure 9. Binding fastness test of FEP/PTFE composite membranes before and after ultrasonic testing (a) FE-SEM images of the primary membrane, (b) FE-SEM images of the membrane after 6 h of ultrasound, (a1、b1) FE-SEM images of Membrane cross-section,(c)Infrared spectrograms
图 10 FEP/PTFE复合膜的分离性能
Figure 10. Separation performance of FEP/PTFE composite membrane
表 1 不同聚全氟乙丙烯(FEP)/聚四氟乙烯(PTFE)复合膜的制备参数
Table 1. Preparation parameters of different polyperfluoroethylene propylene (FEP)/ polytetrafluoroethylene (PTFE) composite films
Membrane samples (before soaking) Mass fraction of FEP/wt% Sintering temperature /℃ Membrane samples
(after soaking)PTFE 0 300 PTFE-7 d 1wt%FEP/PTFE 1 300 1wt%FEP/PTFE-7 d 2wt%FEP/PTFE 2 300 2wt%FEP/PTFE-7 d 3wt%FEP/PTFE 3 300 3wt%FEP/PTFE-7 d 4wt%FEP/PTFE 4 300 4wt%FEP/PTFE-7 d 3wt%FEP/PTFE-25℃ 3 25 3wt%FEP/PTFE-25℃-7 d 3wt%FEP/PTFE-280℃ 3 280 3wt%FEP/PTFE-280℃-7 d 3wt%FEP/PTFE-320℃ 3 320 3wt%FEP/PTFE-320℃-7 d 3wt%FEP/PTFE-360℃ 3 360 3wt%FEP/PTFE-360℃-7 d 
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表 2 PTFE纤维膜在非极性溶剂浸泡7 d后溶胀比
Table 2. Swelling ratio of PTFE fiber film soaked in non-polar solvent for 7 d
Non-polar solvent Swelling ratio of PTFE fiber film/% N-hexane 1.99 Tetrahydrofuran 1.01 Trichloromethane 1.03
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