FEP is the abbreviation of fluorinated ethylene propylene copolymer, commonly known as F46. FEP has a completely fluorinated structure similar to PTFE, except that part of the fluorine atoms in the main chain of PTFE are replaced by trifluoromethyl groups as follow.
Because FEP is a branched polymer, FEP has lower crystallinity than PTFE, lower melting point and better processing performance.
- Chemical resistance
FEP resin has excellent chemical resistance. Except for reacting with fluorine element, molten alkali metal and chlorine trifluoride at high temperature, it will not be corroded when it comes in contact with other chemicals.
- Insulation performance
The dielectric coefficient of FEP resin remains basically unchanged in a wide temperature (-80 ~ 200°C) and frequency range (50 ~ 10^10 Hz). The volume resistivity of FEP resin is very high, and it changes little with temperature, and it is not affected by water and moisture. The breakdown field strength of FEP resin increases as the thickness decreases.
- Mechanical properties
The hardness, tensile strength and friction coefficient of FEP resin are slightly higher than that of PTFE. FEP is prone to creep, which must be taken into consideration when designing components to be used under continuous stress. The surface energy of FEP resin is very low, so it is difficult to wet.
- FEP can be used to modify PTFE/glass fiber (GF) composite materials to improve the performance. PTFE/GF composite material has the advantages of low dielectric constant and low dielectric loss, but the composite material has the typical disadvantage of high porosity. Because the viscosity of FEP is lower than that of PTFE, partial replacement of PTFE with FEP can greatly reduce the porosity of PTFE/GF composites. The properties such as porosity, dielectric properties and water absorption of the FEP modified PTFE/GF composite material have been improved, which has the potential in microwave circuit application.
Figure 2. The influence of FEP content on porosity and water absorption 
- FEP is considered to be a material with excellent chemical resistance to phosphoric acid and electrolyte, and it has good mechanical properties and thermal stability. At the same time, combined with graphite's excellent electrical and mechanical properties and corrosion resistance, the two can be used to manufacture conductive fluorinated ethylene-propylene composite materials for high-temperature bipolar plates. When the graphite particles are well dispersed, a structure-optimized FEP/graphite composite bipolar plate can be prepared, which provides a robust and scalable strategy for achieving high performance and large area bipolar plates.
Figure 3. Schematic of mechanical ball-milling of FEP powder on graphite surface 
- Combining the acid resistance, alkali resistance and corrosion resistance of FEP, FEP powder can be thermoformed on a polydimethylsiloxane (PDMS) template to prepare a super-hydrophobic surface with a lotus leaf-like structure of FEP. Clean containers, etc. 
- Ying Yuan, Jing Yang, Bingliang Tan, Bin Tang, Enzhu Li, Shuren Zhang, J Mater Sci: Mater Electron 28 (2017) 6015-6021.
- Moon Hee Lee, Ho Young Kim, Seong Moon Oh, Byung Choon Kim, Daesuk Bang, Joong Tark Han, Jong Seok Woo, International Journal of Hydrogen Energy 48 (2018) 21918-21927.
- Chuan-Sheng Liu, Wen-Qu Jiang, Zi-Sheng Guan, Chemical Journal of Chinese Universities 5 (2011).
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