Chemical properties Resistance to atmospheric aging: re […]
Resistance to atmospheric aging: resistance to radiation and low permeability: long-term exposure to the atmosphere, the surface and properties remain unchanged.
Incombustible: The oxygen limiting index is below 90.
Acid and alkali resistance: insoluble in strong acids, strong bases, and organic solvents (including argentic acid, ie, fluorinated sulfonic acid).
Antioxidant: Resistant to strong oxidants.
Density: 2.1–2.3 g/cm3;
The mechanical properties of PTFE are soft. Has a very low surface energy.
Polytetrafluoroethylene (F4, PTFE) has a series of excellent performance: high temperature - long-term use temperature of 200 ~ 260 degrees, low temperature - still soft at -100 degrees; corrosion resistance - able to resist aqua regia and all organic solvents; Weather resistance - the best aging life in plastics; high lubrication - with the smallest coefficient of friction in plastics (0.04); non-stick - with minimal surface tension in solid materials without adhesion to any substances; non-toxic - with physiological inertia; Excellent electrical performance is ideal for Class C insulation. A thick layer of newspaper can block the high voltage of 1500V; it is smoother than ice. PTFE materials are widely used in the defense industry, nuclear power, petroleum, radio, electric machinery, and chemical industries. Products: PTFE-tetra-ethylene rods, tubes, plates, turned plates. PTFE is a tetrafluoroethylene polymer. English abbreviation is PTFE. The structural formula is: CF3(CF2CF2)nCF3. Found in the late 1930s and put into industrial production in the 1940s. Properties The relative molecular mass of PTFE is relatively large, with a low number of hundreds of thousands, and a high number of more than 10 million, generally in the millions (degree of polymerization is on the order of 104, while polyethylene is only on 103). The general crystallinity is 90-95% and the melting temperature is 327-342°C. The CF2 units in the polytetrafluoroethylene molecule are arranged in a zigzag shape. Since the fluorine atom radius is slightly larger than hydrogen, the adjacent CF2 units cannot be completely trans-oriented, but form a helical twisted chain, almost covering the fluorine atoms. The surface of the entire polymer chain. This molecular structure explains the various properties of PTFE. When the temperature is lower than 19°C, a 13/6 helix is formed; at 19°C, the phase change occurs and the molecule is slightly unraveled to form a 15/7 helix.
Although in the perfluorocarbons, the carbon-carbon bonds and the carbon-fluorine bonds require energy absorption of 346.94 and 484.88 kJ/mol, respectively, the depolymerization of PTFE to 1 mole of tetrafluoroethylene requires only 171.38 kJ of energy. Therefore, in the pyrolysis, PTFE is mainly depolymerized into tetrafluoroethylene. The weight loss rate (%) of PTFE at 260, 370, and 420°C was 1 × 10 - 4.4 × 10 -3 and 9 × 10 - 2 per hour, respectively. It can be seen that PTFE can be used at 260°C for a long time. Since high-temperature pyrolysis also produces highly toxic by-products such as phosgene and perfluoroisobutene, special attention must be given to safety and protection against PTFE exposure to open flames.