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PTFE Introduction

2020-09-02 17:19

Tetrafluoro 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 -. Polytetrafluoroethylene is widely used in various applications that require resistance to acids, alkalis and organic solvents. It is not toxic to humans, but perfluorooctanoate (PFOA), one of the raw materials used in the production process, is considered to have carcinogenic effects.

 

Basic Information

English name

Tetrafluoroethylene (polytetrafluoroethylene)

Proportion

2.15~2.20

Nickname

polytetrafluoroethylene

Melting point

320℃~345℃

English abbreviations

PTFE

Molecular weight

5×10^5~9×10^6

Chemical

(C2F4)n

 

 

 

Chemical properties


Chemical propertiesThe relative molecular mass of PTFE is relatively large, the low is hundreds of thousands, and the high is more than 10 million. Generally, it is a few million of PTFE plate supports (the degree of polymerization is on the order of 10 to the 4th power, while polyethylene only On the order of the 3rd power of 10). Generally, the crystallinity is 90~95%, and the melting temperature is 327~342℃. The CF2 units in the polytetrafluoroethylene 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 in trans, but form a spiral twisted chain, almost covered by the fluorine atom 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 unwound to form a 15/7 helix.

Although the rupture of the carbon-carbon bond and the carbon-fluorine bond in the perfluorocarbon compound needs to absorb energy 346.94 and 484.88kJ/mol, respectively, the depolymerization of polytetrafluoroethylene to produce 1mol of tetrafluoroethylene only requires energy of 171.38kJ. Therefore, during high-temperature cracking, PTFE is mainly depolymerized into tetrafluoroethylene. The weight loss rate (%) of PTFE at 260, 370 and 420℃ is 1×10-4, 4×10-3 and 9×10-2 per hour, respectively. It can be seen that PTFE can be used for a long time at 260°C. As the highly toxic by-products such as fluorophosgene and perfluoroisobutylene are produced during high-temperature cracking, special attention must be paid to safety protection and to prevent PTFE from contacting open flames.

 

Mechanical properties


PTFE IntroductionIts friction coefficient is extremely small, only 1/5 of polyethylene, which is an important feature of perfluorocarbon surface. In addition, because the fluorine-carbon chain intermolecular forces are extremely low, PTFE is non-sticky.

PTFE maintains excellent mechanical properties in a wide temperature range of -196~260℃. One of the characteristics of perfluorocarbon polymers is that they are not brittle at low temperatures.

Chemical corrosion and weather resistance

Except for molten alkali metals, PTFE is hardly corroded by any chemical agents. For example, in concentrated sulfuric acid, PTFE-coated gasket, nitric acid, hydrochloric acid, or even boiled in aqua regia, its weight and performance have no change, and it is almost insoluble in all solvents. It is only slightly soluble in all alkane above 300℃ (about 0.1g/100g). PTFE does not absorb moisture, is non-flammable, and is extremely stable to oxygen and ultraviolet rays, so it has excellent weather resistance.

 

Electrical properties

PTFE has low dielectric constant and dielectric loss in a wide frequency range, and has high breakdown voltage, volume resistivity and arc resistance.

Physical properties

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

Radiation resistance

Polytetrafluoroethylene has poor radiation resistance (104 rad), and it degrades after being exposed to high-energy radiation, and the electrical and mechanical properties of the polymer are significantly reduced.

aggregation

Polytetrafluoroethylene is produced by radical polymerization of tetrafluoroethylene. Industrial polymerization is carried out under stirring in the presence of a large amount of water to disperse the heat of reaction and facilitate temperature control. The polymerization is generally carried out at 40~80℃ and 3~26 kgf/cm2 pressure. Inorganic persulfate and organic peroxide can be used as initiators, or a redox initiation system can be used. 171.38kJ of heat is released during polymerization of tetrafluoroethylene per mole. Dispersion polymerization must add perfluorinated surfactants, such as perfluorooctanoic acid or its salts.

 

Application

Polytetrafluoroethylene can be formed by compression or extrusion processing; it can also be made into water dispersion for coating, impregnation or making fibers. Polytetrafluoroethylene is widely used as high and low temperature resistant, corrosion resistant materials, insulating materials, anti-stick coatings, etc. in nuclear energy, aerospace, electronics, electrical, chemical, machinery, instruments, meters, construction, textiles, food and other industries.

 

Chemical nature


PTFE IntroductionInsulation: Not affected by the environment and frequency, the volume resistance can reach 1018 ohm·cm, the dielectric loss is small, and the breakdown voltage of the PTFE Pall ring is high.

High and low temperature resistance: The temperature has little effect on the change, the temperature range is wide, and the usable temperature is -190~260℃.

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

Surface non-stickiness: No known solid material can adhere to the surface, it is a solid material with the smallest surface energy.

Atmospheric aging resistance, radiation resistance and low permeability: long-term exposure to the atmosphere, the surface and performance remain unchanged.

Non-flammability: The oxygen limit index is below 90.

2017 Copper Clad Laminate Industry Summit Forum was grandly held
The 2018 Copper Clad Laminate Industry Summit Forum was grandly held
Nitrogen introduction [ 2020-09-02 ]
The chemical formula is N2, which is usually a colorless and odorless gas, and nitrogen is generally less dense than air. Nitrogen accounts for 78.08% (volume fraction) of the total atmosphere and is the main component of air. Under standard atmospheric pressure, when cooled to -195.8°C, it becomes a colorless liquid, and when cooled to -209.8°C, liquid nitrogen becomes a snow-like solid. Nitrogen is chemically inactive and difficult to react with other substances at room temperature, so it is often used to make preservatives. However, it can undergo chemical changes with certain substances under high temperature and high energy conditions to produce new substances useful to humans.
PTFE Introduction [ 2020-09-02 ]
Tetrafluoro 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 -. Polytetrafluoroethylene is widely used in various applications that require resistance to acids, alkalis and organic solvents. It is not toxic to humans, but perfluorooctanoate (PFOA), one of the raw materials used in the production process, is considered to have carcinogenic effects.
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