Property Of FEP Resin
The structural characteristics of fep
F46 resin, like polytetrafluoroethylene, has a completely fluorinated structure. The difference is that part of the fluorine atom in F46 main chain is replaced by trifluoromethyl (- CF3).
It can be seen that F46 resin and polytetrafluoroethylene are both composed of carbon and fluorine elements, and the carbon chain is completely surrounded by fluorine atoms, but there are branches and side chains on the main chain of F46 macromolecules. The difference in structure has no great influence on the upper limit of temperature range of materials under long-term stress. The upper limit temperature of F46 is 200 ℃, while the highest use temperature of polytetrafluoroethylene is 260 ℃. However, due to the difference in structure, F46 resin has a fairly definite melting point and can be processed by general thermoplastic processing method, which greatly simplifies the processing technology. This is not what polytetrafluoroethylene has. This is the main purpose of modifying polytetrafluoroethylene with hexafluoropropylene.
2. Properties of FEP
The content of hexafluoropropylene in F46 has a certain effect on the properties of copolymers. At present, the content of hexafluoropropylene in F46 resin is about 14% ~ 15% (mass fraction).
2.1. Physical properties
At present, there is no feasible method to determine the molecular weight of F46 resin. However, its melting viscosity at 380 ℃ is lower than that of polytetrafluoroethylene (103-104pa. S). It can be seen that the molecular weight of F46 is much lower than that of polytetrafluoroethylene.
The melting point of F46 varies with the composition of the copolymers. The melting point of F46 decreases with the increase of hexafluoropropylene content. According to the results of DTA, the melting point of F46 resin made in China is mostly between 250 ~ 270 ℃, which is lower than that of polytetrafluoroethylene.
F46 resin is a kind of crystalline polymer, the crystallinity is lower than that of polytetrafluoroethylene. When F46 melt cools slowly to the temperature below the crystal melting point, the macromolecule recrystallizes, the crystallinity is between 50% and 60%; when the melt cools rapidly by quenching, the crystallinity is between 40% and 50%. The crystal structure of F46 is spherulite, which varies with resin, processing temperature and heat treatment.
2.2. Electrical insulation performance
The electrical insulation performance of F46 is very similar to that of PTFE. Its dielectric coefficient is almost constant in the wide range of UHF from 50Hz to 1010hz, and it is very low, only about 2.1. The dielectric loss tangent varies with frequency, but not with temperature
The volume resistivity of F46 resin is very high, generally larger than 1015 Ω. M, and it changes little with temperature, and is not affected by water and moisture. Arc resistance is greater than 165S.
The breakdown field of F46 increases with the decrease of thickness. When the thickness is more than 1mm, the breakdown field strength is more than 30KV / mm, but does not change with the change of temperature.
2.3. Thermal performance
F46 resin is next to polytetrafluoroethylene in heat resistance and can be used continuously in the temperature range of - 85 ~ + 200 ℃. Even in the limit case of - 200 ℃ and + 260 ℃, its performance does not deteriorate, and it can be used for a short time.
The thermal decomposition temperature of F46 resin is higher than the melting point temperature, and significant thermal decomposition occurs above 400 ℃. The decomposition products are mainly tetrafluoroethylene and hexafluoropropylene. Because the isoterminal group of F46 macromolecule usually decomposes at the temperature above the melting point, it is necessary to pay attention to proper ventilation when processing at the temperature above 300 ℃. F46 is quite stable below the melting point temperature, but its mechanical strength loses a lot at 200 ℃. The decrease of melt viscosity and the thermal decomposition of copolymers can be analyzed by the increase of melt index.
F46 is not completely hard and brittle at - 250 ℃, and it also has a small elongation and certain flexibility, which is even better than PTFE, which is inferior to all other kinds of plastics.
2.4. Chemical resistance
The chemical resistance of F46 is similar to that of Teflon and has excellent chemical resistance. In addition to the reaction with fluorine element, molten alkali metal and chlorine trifluoride at high temperature, they are not corroded in contact with other chemicals.
2.5. Mechanical properties
Compared with polytetrafluoroethylene, F46 has a slightly higher hardness and tensile strength, and a slightly larger friction coefficient. At room temperature, F46 has better creep resistance, but when the temperature is higher than 100 ℃, the creep resistance is lower than that of PTFE.
2.6. Other performance
F46 resin has very good oxidation resistance and high atmospheric stability. The radiation resistance of F46 is better than that of polytetrafluoroethylene, which is slightly inferior to that of polyethylene. In the air and room temperature, the minimum absorption dose of F46 that begins to change performance is 105-106rad (103-104gy), so it can be used as radiation resistant material.