Teflon rod manufacturers take you to learn about Teflon, also known as polytetrafluoroethylene. Polytetrafluoroethylene is a polymer of tetrafluoroethylene. The English abbreviation is PTFE. The basic structure of polytetrafluoroethylene is - CF2- CF2- CF2- CF2- CF2- CF2- CF2- CF2- CF2- CF2- CF2- CF2- CF2- CF2-. Polytetrafluoroethylene is widely used in various materials that require resistance to acid, alkali, and organic solvents. It is not toxic to humans, but one of the raw materials used in the production process, perfluorooctanoic acid ammonium (PFOA), is considered to have carcinogenic effects.
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.
Although the fracture of carbon carbon bonds and carbon fluorine bonds in perfluorocarbons requires energy absorption of 346.94 and 484.88 kJ/mol, respectively, the depolymerization of polytetrafluoroethylene to produce 1 mol of tetrafluoroethylene only requires energy of 171.38 kJ. 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.
Mechanical properties, its friction coefficient is extremely small, only 1/5 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.
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 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.
Electrical performance: Polytetrafluoroethylene has low dielectric constant and loss over a wide frequency range, and has high breakdown voltage, volume resistivity, and arc resistance.