Polytetrafluoroethylene (Polytetrafluoro ethylene) is abbreviated as PTFE, and the trade name is "Teflon" (Teflon), commonly known as "Plastic King". 1938, DuPont Research Laboratory, New Jersey, USA

 

Dr. R.S. Plunkett first invented polytetrafluoroethylene, which was commercialized in 1946. PTFE is a highly crystalline polymer of tetrafluoroethylene (TFE) monomer, white, non-toxic, and odorless. its polymer molecules

 

Is composed of a (CF2 a CF2 one) a structural unit repeated connection, is currently the application of the latest type of engineering plastics in various industries.

 

1. Structure and characteristics of PTFE

 

(1) In PTFE, fluorine atoms replace hydrogen atoms in polyethylene. Since the larger radius of fluorine atoms is (0.064nm), which is larger than the radius of hydrogen atoms (0.028nm), and the fluorine atoms of adjacent macromolecules

 

Negative charges repel each other, causing the C- C chain to gradually twist from the planar, fully extended tortuous conformation of polyethylene to the helical conformation of PTFE, and form a tight complete "fluoro" protection.

 

layer, which gives it a chemical stability unmatched by other materials and a low cohesive energy density.

 

(2) The bond energy of the C- C bond is 372kJ/mol, and the bond energy of the C- F bond is 347kJ/mol, which is the stronger of the known bond energies, so the intramolecular bond is firm, the heat resistance is high, and the long-term use temperature is-

 

250 ℃ ~ 260 ℃, while the bond length of C- C bond is 1.54 × 1010m, and the bond length of C- F bond is 1.41 × 1010m, which is shorter among common single bonds, so the chemical properties are stable and difficult to be compared with other substances.

 

chemical reaction, showing excellent weather resistance, stain resistance and chemical resistance.

 

(3) There is no branched chain on the main chain of the macromolecule, and cross-chains are formed inside the whole, so its molecular profile is smooth. In addition, TFE monomer has perfect symmetry, which makes the attraction and surface energy between PTFE molecules low.

 

PTFE has a very low surface friction coefficient, and it is easy to transfer to the dual surface during the sliding process to form a thin transfer film.

 

 

Figure 1: PTFE tube Source: Dankai

 

2. The composition and structure of PTFE determine its performance as follows

 

2.1 high chemical stability

 

PTFE can withstand all strong acids, strong bases, strong oxidants, reducing agents, etc. except for molten alkali metals, fluorine elements, and strong fluorinated media, as well as sodium hydroxide above 300°C. Its resistance to chemical decay

 

The corrosion performance exceeds that of precious metals, glass, ceramics, enamel and alloys, etc., even if the uranium fluoride on the strong corrosive agent in the atomic energy industry does not corrode it.

 

2.2 widely used temperature range

 

PTFE can be used in a wide area of -250~260 ℃, and can still maintain certain flexibility even at ultra-low temperature of -260 ℃; At 260 ℃, its breaking strength still remains about 5MPa (about

 

For 1/5 of room temperature), the yield resistance is 1.4MPa.

 

2.3 outstanding non-tackiness

 

PTFE is currently the smallest surface energy of a solid material, surface tension of only 0.019N/m, almost all solid materials can not adhere to its surface, only the surface tension of 0.02N/m

 

The liquid can completely wet its surface.

 

2.4 abnormal lubricity

 

Because the mutual attraction between PTFE macromolecules is small, and the surface attraction to other molecules is also very small, so its friction coefficient is very small, and it is the self-lubricating material with the lowest friction coefficient found at present.

 

2.5 excellent electrical insulation properties

 

PTFE is a highly non-polar material, has very good dielectric properties; arc resistance is excellent, in high-voltage discharge, only some of the cracking of the non-conductive gas and will not cause a short circuit carbonization.

 

2.6 excellent aging resistance and radiation resistance

 

There is no photosensitive group in PTFE molecule, so it is not only stable in size at low temperature and high temperature, but also unchanged in performance under harsh environment. It is not attacked by microorganisms in wet state, and it is not affected by various ray radiation devices.

 

It has very high protection capability.

 

2.7 minimal water absorption

 

The water absorption rate of PTFE is generally about 0.001~0.005%, and its permeability is also low.

 

3. Application of PTFE

PTFE has excellent high and low temperature performance and chemical stability, good electrical insulation, non-adhesion, weather resistance, non-flammability and good lubricity, and is used in a wide range of daily commodities from the aerospace field,

 

It has become an indispensable material for solving many key technologies in modern science and technology, military and civilian use. The following mainly introduces PTFE in anti-corrosion wear reduction, sealing, corrosion resistance, anti-sticking, electrical, construction and medical

on the application.

 

Application of 3.1 PTFE in Anti-corrosion and Anti-wear

 

According to the relevant statistics of developed countries, in today's industrialized countries, the annual economic loss caused by corrosion accounts for about 4% of the total national economic output value. A considerable number of accidents in chemical production are due to equipment decay.

 

Corrosion, caused by a chemical reaction caused by leakage of the medium. It can be seen that the damage caused by corrosion is serious and has attracted widespread attention. PTFE material overcomes the common plastic,

 

Metal, graphite, ceramics and other corrosion resistance, poor flexibility and other shortcomings, with its excellent high and low temperature resistance and corrosion resistance, can be used in harsh conditions of temperature, pressure and medium,

 

It has become the main corrosion-resistant material in petroleum, chemical, textile and other industries.

 

PTFE pipe is mainly used as a corrosive gas, liquid, steam or chemical delivery pipe, exhaust pipe. The push pipe molded by PTFE dispersion resin is lined into the steel pipe to form a lining, or in the PTFE push pipe

 

The tube is wound with glass fiber reinforcement, or the PTFE push tube is braided and wound with steel wire to transfer the liquid medium under high pressure. As an indispensable part of hydraulic transmission, it can be greatly improved

 

The rupture strength at high temperatures is at the same time good bending fatigue.

 

Since the PTFE material has the lowest coefficient of friction of the known solid materials, this makes the filled PTFE material the most desirable material for oil-free lubrication of mechanical equipment parts. such as paper, textile, food

 

Equipment in industrial fields such as lubricating oil is easy to pollute the product, so filling PTFE material solves this problem. In addition, experiments have shown that adding a certain amount of solid additives to the oil can be

 

Effectively save about 5% of engine fuel oil.

 

PTFE -3.2 corrosion-resistant sealing material

 

Another major application of PTFE in the chemical industry is sealing materials. Due to the good comprehensive performance of PTFE, it is unmatched by any kind of sealing material. It can be used for sealing in various harsh occasions, especially

 

This is when high temperature and corrosion resistance are required.

 

PTFE raw material with long fiber, high strength, and plastic, good ductility, applied a small pressing force can be completely sealed, easy operation and application, used in uneven or structural precision surface

 

It is more efficient, has good sealing performance and can improve corrosion resistance, expand its scope of use.

 

The sealing of the sliding part uses PTFE packing, which can obtain good corrosion resistance and stability, and it has a certain compression resilience and low sliding resistance. Filled PTFE sealing material service temperature range

 

Widely, is the main substitute for traditional asbestos gasket materials, but also has high modulus, high strength, creep resistance, fatigue resistance, and high thermal conductivity, thermal expansion coefficient and friction coefficient of small performance, plus.

 

Different fillers can be used to expand the scope of application.

 

Application of 3.3 PTFE anti-sticking property

 

PTFE material has the smallest surface tension in solid materials, does not adhere to any substance, but also has the excellent characteristics of high and low temperature resistance, non-toxic, so PTFE is often used as a coating for tableware

 

Lining, mainly used for non-stick pans and microwave ovens.

 

In the textile industry, a large number of chemical slurries are used for yarn sizing, especially when using styrene-butadiene latex, acid methyl cellulose, polyvinyl acetate and other very viscous slurries, serious sticking will occur.

 

At this time, it is necessary to remove the sticky bag in order to continue production, which not only increases the labor volume, low production efficiency, and affects the quality of the product.

 

Similarly, it can also be applied to various plastic packaging and sealing machinery.

 

3.4 electrical applications

 

PTFE's inherent low loss and dielectric constant make it an ideal insulation for wire and cable. The reason why PTFE is used as a wire coating: it has excellent electrical properties, and its volume resistivity can reach

 

1017 Ω, surface resistivity greater than 1016 Ω, also unchanged at 100% relative humidity; dielectric constant as low as 2.0, dielectric loss tangent of about 2 × 10-4 and all independent of temperature frequency; heat resistance

 

Good, long-term use at 260 ℃, good insulation, can reach H level or above; It has strong toughness and flexibility, even if it is as low as -90 ℃, the toughness is still not affected. Aging resistance, excellent weather resistance,

 

High chemical stability; non-flammable and low smoke. The printed circuit board made of PTFE has been widely used in the field of aerospace, so PTFE products are particularly suitable for telecommunications, computers, measurement and testing.

 

test and measurement, defense and many other high-performance, challenging areas.

 

Application of 3.5 Architecture

 

With the development of domestic and foreign economy, many cultural and entertainment facilities in the construction of it as a canopy material, which has been widely used abroad, the use of this material in the first building built in the 70 s

 

in California, USA. In the past two years, it has also been used in China, such as: Shanghai 80,000 Stadium, Hongkou Stadium's canopy, Oriental Pearl Tower, Beijing Olympic Bird's Nest, etc. PTFE for construction

 

The number of years of durability of the film material is more than 20 years (the current common high decorative, high weather resistance acrylic polyurethane coatings, acrylic silicone coatings and silicone coatings, the number of years of durability is generally 5~10

 

year, silicone polyester coating is only 10 to 15 years); and its self-cleaning is good, does not absorb dust and dirt, rain can wash away the surface attachments, can reduce the cost of coating cleaning, so suitable.

 

In the case of high cleanliness requirements.

 

3.6 medical and health applications

 

In modern medicine, a wide variety of polymer products are widely used, which greatly excludes and replaces the application of metal and other materials in the medical field. These products are not only used in the human body and with the human body tissue phase

 

contacts, also used in various devices in the medical field. In recent years, polymer PTFE has good flexibility and biocompatibility, and is gradually becoming an important part of biological functional materials.

 

PTFE surface tension is small, non-hydrophilic, good biocompatibility, can be used for artificial blood vessels, the increase of the potential energy of the inner surface of the artificial blood vessel wall will promote the settlement and coagulation of endothelial cells, which is microporous PTFE.

 

The modification of the surface energy of the article results in a significant biological reaction of the surrounding tissue, and this property can be used to prevent the thrombotic process in the graft space. Using expanded PTFE and rubber plastic film composition

 

Gastroscope clamp catheter, because it can be bent and deformed at will, no foreign body reaction in contact with the human body, used for instant sampling of the human stomach, taking foreign bodies, polyp removal, etc., can be operated freely, so that patients can avoid

Unnecessary suffering.

 

In addition, polyPTFE can be made into artificial cruciate ligament, joint, esophagus and trachea, urethra, bile tube and so on. Can also be used for plastic surgery, bone tissue replacement, promote fracture healing, skin or organ migration

implant, periodontal tissue regeneration, etc.

 

3.7 Other Applications

 

PTFE also has many applications, such as the use of its membrane with porous, as a filter material can be selectively through the gas or liquid, for gas-liquid separation, gas-gas separation and liquid-liquid separation of filtration

 

Film; adding conductive carbon black pressure to it can also make a heating element, such as the intermediate heating layer of an electric blanket.

 

4. Conclusion

 

With the continuous development of material application technology, in recent years, foreign research on the application of PTFE and its modified materials has made it a very mature material.

 

There is still a big gap between research and processing molding technology and foreign countries. PTFE has excellent performance in many aspects, is unmatched by other materials, the application field is very broad.

 

This article is originally created by Teflon's little sister. Welcome to pay attention and take you to grow knowledge together!