Raw material belt, commonly known as: raw tape.
A kind of auxiliary product commonly used in plumbing installations, used for pipe joints, to enhance the tightness of pipe joints.
The chemical name of the raw material is PTFE. At present, ordinary white Teflon tape is used for HVAC and water supply and drainage, and the natural gas pipeline also has a special PTFE tape. In fact, the main raw material is PTFE. , but some processes are not the same.
PTFE is a tetrafluoroethylene polymer. English abbreviation is PTFE. The basic structure of PTFE is: - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - PTFE is widely used in various needs of anti-acid and organic solvents, it It is not toxic to humans itself, but one of the raw materials used in the production process, PFOA, is considered to be possibly carcinogenic.
The relative molecular mass of PTFE is relatively large, with a low number of several hundred thousand, and a high number of more than 10 million, generally several million (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. The fluorine atoms are almost covered. 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 420C 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 flame.
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. 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.
Its mechanical properties have a very small coefficient of friction, only one-fifth that of polyethylene. This is an important feature of the perfluorocarbon surface. Because of the extremely low intermolecular forces between fluorine-carbon chains, PTFE has no stickiness.
PTFE maintains its excellent mechanical properties over a wide temperature range from -196 to 260°C. One of the characteristics of perfluorocarbon polymers is that they are not brittle at low temperatures.
Chemical Resistance and Weather Resistance In addition to molten alkali metals, PTFE is hardly corroded by any chemical agents. For example, in concentrated sulfuric acid, nitric acid, hydrochloric acid and even boiling in aqua regia, there is no change in weight and performance, and it is almost insoluble in all solvents. It is only slightly soluble in perlane (about 0.1 g/100 g) at 300C or above. PTFE does not absorb moisture, is not flammable, and is extremely stable against oxygen and ultraviolet rays, so it has excellent weather resistance.
Electrical properties Teflon has low dielectric constant and dielectric loss over a wide frequency range, and has high breakdown voltage, volume resistivity, and arc resistance.
Radiation resistance PTFE radiation resistance is poor (104 rad), caused by high-energy radiation degradation, polymer electrical and mechanical properties were significantly reduced.
Polymeric polytetrafluoroethylene is produced by free radical polymerization of tetrafluoroethylene. The industrial polymerization reaction is carried out by stirring in the presence of a large amount of water to disperse the heat of reaction and facilitate the control of temperature. The polymerization is generally carried out at 40-80° C. and 3-26 kgf/cm 2 pressure. Inorganic persulfates and organic peroxides may be used as initiators, and redox initiation systems may also be used. An exotherm of 171.38 kJ per mole of tetrafluoroethylene polymerized. Dispersion polymerization requires the addition of perfluorinated surfactants such as perfluorooctanoic acid or its salts.
Applications Polytetrafluoroethylene can be molded by compression or extrusion; it can also be made into an aqueous dispersion for coating, impregnation, or making fibers. PTFE is widely used in high-temperature, low-temperature and corrosion-resistant materials, insulating materials, and anti-stick coatings in the atomic energy, aerospace, electronics, electrical, chemical, mechanical, instrumentation, construction, textile, and food industries.
Chemical properties
Insulation: It is not affected by the environment and frequency, the volume resistance can reach 1018 ohm·cm, the dielectric loss is small, and the breakdown voltage is high.
Resistance to high and low temperature: little effect on temperature, a wide range of temperature range, the use of temperature -190 ~ 260 °C.
Self-lubricity: With the smallest friction coefficient in plastic, it is an ideal oil-free lubricant.
Non-stick surface: No known solid material can adhere to the surface. It is a solid material with minimal surface energy.
Resistance to atmospheric aging, radiation resistance and low permeability: long-term exposure to the atmosphere, surface and performance remain unchanged.
Incombustible: The oxygen limiting index is below 90.
Physical properties
The mechanical properties of PTFE are soft. Has a very low surface energy.
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