PTFE rod manufacturers analyze the characteristics of PTFE, and PTFE has a series of excellent performance: high temperature resistance - long-term use temperature of 200~260 degrees Celsius, low temperature resistance - still soft at -100 degrees Celsius; Corrosion resistance - resistant to aqua regia and all organic solvents; Climate resistance - the best aging life in plastics; High lubrication - with the smallest friction coefficient in plastic (0.04); Non adhesive - having the minimum surface tension in a solid material without adhering to any substance; Non toxic - with physiological inertness; Excellent electrical performance, making it an ideal C-grade insulation material. PTFE materials are widely used in important sectors such as national defense and military industry, atomic energy, petroleum, radio, power machinery, chemical industry, etc.
Products: PTFE rods, tubes, plates, and turning plates. Polytetrafluoroethylene is a polymer of tetrafluoroethylene. The English abbreviation is PTFE. The structural formula is. In the late 1930s, it was discovered that it was put into industrial production in the 1940s. The relative molecular weight of polytetrafluoroethylene is relatively large, ranging from hundreds of thousands to over 10 million, usually in the millions (polymerization degree is in the order of 104, while polyethylene is only in 103). The general crystallinity is 90-95%, and the melting temperature is 327-342 ℃. CF2 units in polytetrafluoroethylene molecule are arranged in zigzag shape. Since the fluorine atomic radius is slightly larger than that of hydrogen, the adjacent CF2 units cannot be completely trans cross oriented, but form a helical twisted chain, and the fluorine atoms almost cover the surface of the entire polymer chain. This molecular structure explains the various properties of PTFE. When the temperature is below 19 ℃, a 13/6 helix is formed; At 19 ℃, a phase transition occurs, and the molecules slightly unravel, forming a 15/7 helix.
Mechanical properties: Its friction coefficient is extremely small, only 1/5 of that of polyethylene, which is an important feature of perfluorocarbon surfaces. Due to the extremely low intermolecular force between fluorine carbon chains, polytetrafluoroethylene is non viscous. Electrical performance: Polytetrafluoroethylene has low dielectric constant and loss over a wide frequency range, and has high breakdown voltage, volume resistivity, and arc resistance.
Radiation resistance: The radiation resistance of polytetrafluoroethylene is poor (104 rads), and it causes degradation after being subjected to high-energy radiation, resulting in a significant decrease in the electrical and mechanical properties of the polymer.
Polymerization: Polytetrafluoroethylene is formed by free radical polymerization of tetrafluoroethylene. Industrial polymerization reactions are carried out by stirring in the presence of a large amount of water to disperse the reaction heat and facilitate temperature control. Polymerization is generally carried out at 40~80 ℃ and 3~26 kilogram-force/cm2 pressure. Inorganic persulfate and organic peroxide can be used as initiators, or redox initiation system can be used. 171.38 kJ of heat is released during the polymerization of tetrafluoroethylene per mole. Dispersion polymerization requires the addition of perfluorinated surfactants, such as perfluorooctanoic acid or its salts.
Expansion coefficient (25-250 ℃) 10-12 × 10-5/℃.
Polytetrafluoroethylene maintains excellent mechanical properties over a wide temperature range of -196-260 ℃, and one of the characteristics of perfluorocarbon polymers is that they remain brittle at low temperatures.
Chemical properties: The chemical structure of polytetrafluoroethylene is formed by replacing all hydrogen atoms in polyethylene with fluorine atoms. Its molecular formula is: the F atom in PTFE molecule covers the C-C bond, and the C-F bond energy is high and particularly stable. Except for alkali metals and elemental fluorine, it is not corroded by any chemicals. The F atom in PTFE molecule is symmetrical, and the two elements in C-F are covalently bound. There are no free electrons in the molecule, and the entire molecule is neutral. It makes PTFE have excellent dielectric properties. Because there is no gram bond in the molecular structure of PTFE, its crystallinity is very high. Due to the inert fluorine containing shell outside the PTFE molecule, it has outstanding non stick performance and low friction coefficient. Insulation: Not affected by environment and frequency, with a volume resistance of up to 1018 ohms • cm, low dielectric loss, and high breakdown voltage.
High and low temperature resistance: The impact on temperature is not significant, and the temperature range is wide. It can be used at temperatures of -190~260 ℃.
Self lubrication: With the smallest friction coefficient among plastics, it is an ideal oil-free lubricating material.
Surface non adhesion: Known solid materials cannot adhere to the surface and are the solid materials with the smallest surface energy.
Atmospheric aging resistance, radiation resistance, and low permeability: Long term exposure to the atmosphere, the surface and properties remain unchanged. Non combustible: Oxygen limiting index below 90.
Chemical corrosion resistance and weather resistance: Except for molten alkali metals, polytetrafluoroethylene is hardly corroded by any chemical reagents. For example, when boiled in concentrated sulfuric acid, nitric acid, hydrochloric acid, or even aqua regia, its weight and properties remain unchanged, and it is almost insoluble in all solvents. It is only slightly soluble in total alkanes (about 0.1g/100g) above 300 ℃. Polytetrafluoroethylene does not absorb moisture, is non flammable, and is extremely stable to oxygen and ultraviolet rays, so it has excellent weather resistance.
Although the breaking of carbon carbon bonds and carbon fluorine bonds in perfluorocarbons requires energy absorption of 346.94 and 484.88kJ/mol, the depolymerization of polytetrafluoroethylene to produce 1mol of tetrafluoroethylene only requires energy of 171.38kJ. So during high-temperature cracking, polytetrafluoroethylene mainly depolymerizes to tetrafluoroethylene. The weight loss rates (%) of polytetrafluoroethylene at 260, 370, and 420 ℃ are 1% per hour, respectively × 10-4, 4 × 10-3 and 9 × 10-2. It can be seen that polytetrafluoroethylene can be used for a long time at 260 ℃. Due to the production of highly toxic by-products such as fluorophosgene and perfluoroisobutylene during high-temperature cracking, special attention should be paid to safety protection and prevent polytetrafluoroethylene from coming into contact with open flames. It does not melt at a temperature of 250 ℃ and does not become brittle at ultra-low temperatures of -260 ℃. Polytetrafluoroethylene is exceptionally smooth, even ice cannot compare to it; It has excellent insulation performance, and a thick film of newspaper is enough to withstand high voltage of 1500V.