Fluorinated ethylene propylene (FEP) is a fluoropolymer that is made of tetrafluoroethylene and hexafluoropropylene. Compared to PTFE and PFA, FEP is the most inexpensive of the three fluoropolymers. FEP exhibits similar properties to the others but is most easily formable of the group. Fluoron’s product, Fluoroclear is an FEP based cover that allows for application to systems in the aerospace industry. Fluoron’s fluoropolymer based solutions are custom made and are guaranteed to deliver the best performance.
Temperature and Thermal Properties
Since Fluoroclear is a FEP based material, it has a lower melting point and lower operating temperature relative to Fluoron’s PFA based Fluoroflex and PTFE based Fluorostat products. The melting point of FEP is 260°C and the maximum operating temperature before breakdown is 204°C. The melt flow rate of FEP is over one million times lower than that of PTFE. This means that it can be custom thermoformed and molded based on the application, while retaining its desired physical properties. On the opposite end of the temperature spectrum, FEP can also be serviced at temperatures as low as -250°C without becoming brittle or cracking. Thus, making Fluoroclear a highly desirable product for environments with dynamic temperature range.
The thermal properties of FEP that make the material a match for volatile environments are its thermal conductivity constant and thermal expansion constant. The thermal conductivity constant of 0.209 W/(m*K) means that FEP is a preferred insulator and able to keep heat within localized parts of a system. As such, Fluoroclear’s low thermal conductivity stops extraneous heat from propagating to other subsystems and causing thermal fatigue and deformation. The thermal expansion coefficient of 12 x 10-5 K-1 conveys that the material undergoes negligible physical expansion and contraction between the temperatures of 20°C and 100°C. This conveys that Fluoroclear can be deployed in space constrained environments without risk of changing physical size.
Chemical Inertness and Reactivity
The chemical resistance of FEP is similar to other fluoropolymers in that its strength is derived from the fluorocarbon bonds of its molecular structure. As such, FEP is able to withstand exposure to a wide range of acidic and basic fluids without reacting or corroding. Common fluids that come in contact with FEP include but are not limited to acids – like hydrochloric and sulfuric acid, alkalis – like sodium hydroxide and ammonia, and hydrocarbons – which are typically fuels, like gasoline or ethanol.
In terms of permeability, the respective permeability constants of FEP for CO2, O2 and N2 are 273 Ng*cm/m2s, 637Ng*cm/m2s, and 91 Ng*cm/m2s .These low permeation constants of the material disallow interaction between fluids of systems within a space constrained system – a concept known as outgassing. This is ideal for guaranteeing purity for respective life sustaining lines and fuel lines in aerospace applications. This permeation quality also guarantees that they do not affect each other’s performance.
Mechanical Properties
In terms of mechanical properties, FEP is a highly durable, transparent and UV resistant material. It also exhibits objectively high tensile strength and non-wetting capabilities. In-line with being formable and processable in a dynamic range of temperature conditions, FEP is more flexible than PTFE. However, this comes with the tradeoff of it having a lower tensile strength relative of 14.5 to 21 MPa, compared to the 27 MPa rating of PTFE. The non wetting characteristics exhibited by FEP are a water absorption rate of less than 0.1%, meaning that Fluoroclear is hydrophobic and uniquely positioned to keep water and condensation buildup away from sensitive components of systems, such as electronics.
Electrical Properties
Like PTFE and PFA, FEP has a low dielectric constant of approximately 2.1 and a relatively lower dielectric strength. These qualities, coupled with its surface resistivity of 1016 Ohm/sq makes FEP an electrically stable fluoropolymer. In the presence of electricity, FEP does not discharge it along its surface, making it a prime candidate in systems that are constrained by space and infrequent maintenance.. As such, Floroclear is a versatile solution for insulating electrical and electronic systems – device subsystems, cabling and wiring.
Applications in Aerospace Subsystems
For aerospace applications, Fluoroclear is best applied in scenarios where it is used as a custom cover or custom jacket or wrap to hold systems in place. Fluoron offers the ability to custom manufacture the covers or jackets needed. In these scenarios, it would be thermoformed to meet the specific requirements at hand – whether that be jacketing for a bundle of safety critical wire or acting as a base cover for a vehicle nozzle.The innate qualities of FEP prove superior to legacy aerospace materials as it is able to withstand the harsh chemical, mechanical, and electrical strain present within the industry. Fluoroclear leverages these qualities by being deployable in caustic environments without corroding, handling the mechanical strain that is present during thermal cycling, and keeping systems sufficiently sealed away to guarantee purity at the parts per million scale.