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Basic knowledge of polytetrafluoroethylene (PTFE)

Source: Time:2018-06-05 13:51:18 frequency:

Among fluoroplastics, PTFE is the most expensive and widely used, and it is an important variety in fluoroplastics. The chemical structure of polytetrafluoroethylene is formed by replacing all hydrogen atoms in the polyethylene with fluorine atoms.

Product Name: PTFE

English name: Polytetrafluoroethylene

Alias: PTFE; Teflon; Teflon; teflon; Teflon; F4; King of Plastics; テフロン (Japanese) [English abbreviation for PTFE, trade name Teflon & reg;, Chinese translation varies from place to place: mainland translation for Teflon ®, Hong Kong translated to Teflon ®, Taiwan translated as Teflon ®

Molecular formula: [CF2CF2]n

Production method: polytetrafluoroethylene is formed by radical polymerization of tetrafluoroethylene. The industrial polymerization is carried out by stirring in the presence of a large amount of water to disperse the heat of reaction and to facilitate temperature control. The polymerization is generally carried out at 40 to 80 ° C under a pressure of 3 to 26 kgf/cm 2 , and an inorganic persulfate or an organic peroxide may be used as an initiator, or a redox initiation system may also be used. An exotherm of 171.38 kJ per mole of tetrafluoroethylene was polymerized. The dispersion polymerization requires the addition of a perfluoro type surfactant such as perfluorooctanoic acid or a salt thereof.

Uses: Can be made into rods, plates, tubes, films and various special-shaped products for aerospace, chemical, electronics, machinery, medicine and other fields.

Remarks:

Polytetrafluoroethylene [PTFE, F4] is one of the best materials for corrosion resistance in the world today, so it has the reputation of "plastic king". It can be used for a long time in any kind of chemical medium, and its production solves many problems in the fields of chemical industry, petroleum, pharmaceuticals and so on. PTFE seals, gaskets, gaskets. PTFE seals, gaskets, and gaskets are molded by suspension polymerization of polytetrafluoroethylene resin. Teflon has excellent chemical resistance and temperature resistance compared to other plastics, and it has been widely used as a sealing material and a filling material.

High chemical stability and excellent chemical resistance, such as strong acid resistance, strong alkali, strong oxidant, etc., outstanding heat resistance, cold resistance and abrasion resistance, long-term use temperature range of -200-+250 ° C, Excellent electrical insulation and independent of temperature and frequency. In addition, it has the characteristics of no stain, no water absorption, no burning. The suspension resin is generally formed by molding and sintering, and the obtained rods, plates or other profiles can be further processed by machining methods such as planing, drilling and milling. The bar can be made into an oriented film by turning and drawing.

Polytetrafluoroethylene (PTFE) characteristics:

1. Strength (high strength - weight ratio)

2. Chemically inert

3. Biocompatibility

4. High thermal resistance

5. High chemical impedance in harsh environments

6. Low flammability

7. Low coefficient of friction

8. Low dielectric constant

9. Low water absorption

10. Good weathering properties

Detailed introduction:

Polytetrafluoroethylene is a polymer of tetrafluoroethylene. The English abbreviation is PTFE. The trade name is "teflon" (teflon). Known as the "king of plastic". The basic structure of polytetrafluoroethylene is - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 -. Polytetrafluoroethylene is widely used in various applications requiring acid and alkali resistance and organic solvents. It is not toxic to humans, but one of the raw materials used in the production process, perfluorooctanoic acid (PFOA), is considered to be likely to be carcinogenic.

The relative molecular mass of PTFE is relatively large, low in the hundreds of thousands, high in more than 10 million, generally in the millions (degree of polymerization in the order of 104, and polyethylene in only 103). The crystallinity is generally 90 to 95%, and the melting temperature is 327 to 342 °C. The CF2 units in the PTFE molecule are arranged in a zigzag shape. Since the radius of the fluorine atom is slightly larger than that of hydrogen, the adjacent CF2 units cannot be completely cross-oriented, but form a helical twisted chain, and the fluorine atoms are almost covered. The surface of the entire polymer chain. This molecular structure explains the various properties of polytetrafluoroethylene. When the temperature is lower than 19 ° C, a 13/6 helix is formed; at 19 ° C, a phase change occurs, and the molecules are slightly untwisted to form a 15/7 helix.

Chemical properties:

The chemical structure of polytetrafluoroethylene is formed by replacing all hydrogen atoms in the polyethylene with fluorine atoms. Its molecular formula is:

The F atom in the PTFE molecule covers the C-C bond and the C-F bond is particularly stable, and it is not attacked by any chemicals other than the alkali metal and elemental fluorine.
The F atom in the PTFE molecule is symmetric, and the two elements in the C-F are covalently combined. There is no free electron in the molecule, and the whole molecule is neutral. The PTFE has excellent dielectric properties, and since the PTFE molecular structure has no gram bond, its crystallinity is high. Due to P

The TFE molecule has an inert fluorine-containing outer shell that gives it outstanding non-stick properties and a low coefficient of friction.

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.

High and low temperature resistance: The influence on temperature is not changed much, and the temperature range is wide. The temperature can be used from -190 to 260 °C.

Self-lubricating: It has the smallest coefficient of friction in plastic and is an ideal oil-free lubricating material.

Non-sticky surface: Known solid materials do not adhere to the surface and are a solid material with minimal surface energy.

Resistance to atmospheric aging, radiation resistance and low permeability: long-term exposure to the atmosphere, surface and properties remain unchanged.

Non-combustible: The oxygen limit is below 90.

Chemical resistance and weather resistance: In addition to molten alkali metal, polytetrafluoroethylene is hardly corroded by any chemical agents. For example, in concentrated sulfuric acid, nitric acid, hydrochloric acid, or even boiling in aqua regia, there is no change in weight and properties, and it is almost insoluble in all solvents, and is slightly soluble in per-alkanes (about 0.1 g/100 g) only above 300 °C. Teflon does not absorb moisture, is non-combustible, and is extremely stable to oxygen and ultraviolet rays, so it has excellent weather resistance.

Although the cleavage 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 requires only 171.38 kJ of energy. Therefore, at the time of pyrolysis, the polytetrafluoroethylene is mainly depolymerized into tetrafluoroethylene. The weight loss rate (%) of polytetrafluoroethylene at 260, 370 and 420 ° C was 1 × 10 -4 , 4 × 10 - 3 and 9 × 10 - 2 , respectively. It can be seen that polytetrafluoroethylene can be used at 260 ° C for a long time. Due to the highly toxic by-products such as fluorophosgene and perfluoroisobutylene, it is necessary to pay special attention to safety protection and prevent PTFE from contacting open flames.

It does not melt at a temperature of 250 ° C and does not become brittle at an ultra-low temperature of -260 ° C. Teflon is smooth and abnormal, even ice is better than it; its insulation performance is particularly good, and the thick film of the newspaper is enough to withstand the high voltage of 1500V.

Physical properties:

The mechanical properties of polytetrafluoroethylene are relatively soft. Has a very low surface energy.

Polytetrafluoroethylene (F4, PTFE) has a series of excellent performance: high temperature resistance - long-term use temperature of 200 ~ 260 degrees, low temperature resistance - still soft at -100 degrees; corrosion resistance - resistant to aqua regia and all organic solvents; Weather resistance - the best aging life in plastics; high lubrication - has the smallest friction coefficient (0.04) in plastics; non-sticky - has the smallest surface tension in solid materials without adhering to any substance; non-toxic - physiologically inert; Excellent electrical properties, ideal for Class C insulation. PTFE materials are widely used in important departments such as defense industry, atomic energy, petroleum, radio, electric machinery, and chemical industry.

Products: Teflon rods, tubes, plates, turning plates. Polytetrafluoroethylene is a polymer of tetrafluoroethylene. The English abbreviation is PTFE. The structural formula is . It was discovered in the late 1930s and was put into industrial production in the 1940s. Properties Polytetrafluoroethylene has a relatively high molecular weight, low in the hundreds of thousands, and high in the range of more than 10 million, generally in the millions (degree of polymerization in the order of 104, and polyethylene in only 103). The crystallinity is generally 90 to 95%, and the melting temperature is 327 to 342 °C. The CF2 units in the PTFE molecule are arranged in a zigzag shape. Since the radius of the fluorine atom is slightly larger than that of hydrogen, the adjacent CF2 units cannot be completely cross-oriented, but form a helical twisted chain, and the fluorine atoms are almost covered. The surface of the entire polymer chain. This molecular structure explains the various properties of polytetrafluoroethylene. When the temperature is lower than 19 ° C, a 13/6 helix is formed; at 19 ° C, a phase change occurs, and the molecules are slightly untwisted to form a 15/7 helix.

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