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    Performance and Application Status of PTFE Yarn
     Jan 13, 2021|View:723

    Polytetrafluoroethylene (PTFE) is abbreviated as "TEFLON". In 1938, Dr. R. S. Plunkett of DuPont research laboratory in New Jersey first invented polytetrafluoroethylene, which was commercialized in 1946. PTFE is a highly crystalline polymer of tetrafluoroethylene (TFE) monomer, which is white, non-toxic, and tasteless. Its polymer molecule is repeatedly connected by one (cf2-cf2-1) structural unit, which is the latest engineering plastics used in various industries.

    The composition and structure of polytetrafluoroethylene determine its following properties

    1. High chemical stability

    PTFE yarn can bear all kinds of a strong acid, strong base, strong oxidant, and reducing agent except molten alkali metal, fluorine element, strong fluorination medium and sodium hydroxide above 300 ℃. Its chemical corrosion resistance exceed that of precious metals, glass, ceramics, enamels, and alloys. Even uranium fluoride, a strong corrosive agent in the atomic energy industry, does not corrode it.

    2. Wide range of temperature

    PTFE yarn can be used in a wide range from - 250 ℃ to 260 ℃, and it can still maintain certain flexibility even at an ultra-low temperature of - 260 ℃. At 260 ℃, its breaking strength is still about 5MPa (about 1 / 5 of room temperature), and its bending strength is up to 1.4mpa.

    3. Outstanding stickiness

    PTFE yarn is a kind of solid material with the lowest surface energy at present. Its surface tension is only 0.019 n / m. almost all solid materials can not adhere to its surface. Only liquid with surface tension below 0.02 n / M can completely infiltrate its surface.

    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, which is the lowest self-lubricating material found at present.

    5. Excellent electrical insulation performance

    PTFE yarn is a highly nonpolar material with excellent dielectric properties and excellent arc resistance. When discharging at high voltage, it only releases some cracked non-conductive gas and will not cause a short circuit due to carbonization.

    6. Excellent aging resistance and radiation resistance

    There is no photosensitive group in the PTFE molecule, so it is not only stable in size at low temperature and high temperature but also has the same performance in harsh environments. It is not invaded by microorganisms in a humid state and has high protection ability against various kinds of radiation.

    7. Minimal water absorption

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

    Application of PTFE yarn

    PTFE yarn has excellent high and low-temperature performance and chemical stability, good electrical insulation, non-adhesion, weather resistance, non-flammability, and good lubricity. It has been widely used in the aerospace field and a wide range of daily commodities and has become an indispensable material in modern science and technology, military industry, and civil engineering to solve many key technical problems. The following mainly introduces the application of PTFE in anti-corrosion, anti-wear, sealing, anti-corrosion, anti-sticking, electrical, architectural, and medical.

    1. Application of PTFE yarn in anti-corrosion and anti-wear

    According to the relevant statistics of developed countries, in today's industrialized countries, the economic loss caused by corrosion accounts for about 4% of the total national economic output value every year. A considerable number of accidents in chemical production are caused by chemical reactions caused by equipment corrosion and medium leakage. It can be seen that the loss caused by corrosion is good, the harm is serious, and has aroused people's extensive attention. PTFE material overcomes the common plastics, metals, graphite, ceramics, and other corrosion resistance, poor flexibility, and other shortcomings. With its excellent high and low-temperature resistance and corrosion resistance, it can be used under 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 conveying pipe and exhaust pipe for corrosive gas, liquid, steam, or chemicals. The push pipe formed by PTFE dispersion resin is lined into the steel pipe to form a lining, or the glass fiber is wrapped outside the PTFE push pipe for reinforcement, or the steel wire is braided and wrapped outside the PTFE push pipe for reinforcement, which can transfer the liquid medium under high pressure. As an indispensable part of hydraulic transmission, it can greatly improve the fracture strength at high temperature and has good bending fatigue.

    Because the friction coefficient of PTFE material is the lowest among the known solid materials, it makes filled PTFE material the most ideal material for oil-free lubrication of mechanical equipment parts. For example, lubricating oil is easy to pollute the equipment in papermaking, textile, food, and other industrial fields, so filling PTFE material can solve this problem. In addition, experiments show that adding a certain amount of solid additives in engine oil can effectively save about 5% of engine fuel oil.

    1. Corrosion-resistant sealing material of PTFE yarn

    Another major application of PTFE in the chemical industry is sealing material. Due to its good comprehensive performance, polytetrafluoroethylene is incomparable to any kind of sealing material. It can be used in various harsh occasions, especially for high temperature and high corrosion resistance.

    PTFE yarn has long fiber, high strength, large plasticity, and good calenderability. It can be completely sealed with less pressing force. It is easy to operate and apply. It is more efficient when used on uneven or precise surfaces. It has good sealing performance and can improve anti-corrosion ability and expand its application range.

    PTFE packing is used in the sealing of sliding parts, which can obtain good corrosion resistance and stability. Moreover, it has certain compressibility, resilience, and low sliding resistance. Filled PTFE sealing material is widely used in a wide range of temperatures. It is the main substitute of traditional asbestos gasket material at present. It has the properties of high modulus, high strength, creep resistance, fatigue resistance, high thermal conductivity, low coefficient of thermal expansion, and friction coefficient. Adding different filters can expand the application range.

    2. Application of PTFE anti-adhesion

    PTFE yarn has the minimum surface tension of solid materials, does not adhere to any substances, but also has the excellent characteristics of high and low-temperature resistance, non-toxic, so PTFE as a coating is often used as the anti-stick lining of tableware, mainly used for nonstick pot and microwave oven liner.

    In the textile industry, a large number of chemical sizing agents are used for sizing, especially when using styrene-butadiene latex, acid methylcellulose, polyvinyl acetate, and other highly viscous sizing agents, serious roll sticking phenomenon will occur. At this time, it is necessary to remove the sticking package before continuous production, which not only increases the amount of labor, low production efficiency, but also affects the product quality It can also be used in all kinds of plastic packaging sealing machine.

    3. Electrical application

    The inherent low loss and dielectric constant of PTFE make it an ideal insulating material for wires and cables. The reasons for using PTFE as wire coating layer: it has excellent electrical properties, its volume resistivity can reach 1017 Ω, surface resistivity is greater than 1016 Ω, and remains unchanged at 100% relative humidity; its dielectric constant is as low as 2.0, and its dielectric loss tangent is about 2 × 10-4, which is independent of temperature and frequency; it has good heat resistance, long-term use at 260 , good insulation, and can reach class H or above; it has strong electrical properties Toughness and flexibility, even as low as - 90 , are not affected; aging resistance, excellent weather resistance, high chemical stability; non-combustible and low smoke. The printed circuit board made of PTFE has been widely used in the aerospace field, so PTFE products are especially suitable for telecommunications, computers, testing and measurement, national defense, and many other high-performance, high challenge fields.

    4. Application in construction

    With the development of the economy at home and abroad, many cultural and entertainment facilities use it as the roof material in construction, which has been widely used abroad. The first building using this material was built in California in the 1970s. In recent two years, it has also been used in China, such as the 80000 stadia in Shanghai, the top of the Hongkou Stadium, the Oriental Pearl Tower, the Beijing Olympic Bird's nest, and so on. PTFE, as a membrane material for building, has a durability of more than 20 years (the current common acrylic polyurethane coatings, acrylic silicone coatings, and silicone coatings with high decorative and weather resistance generally have a durability of 5-10 years, and the silicone polyester coatings have maximum durability of 10-15 years); moreover, it has good self-cleaning performance, does not absorb dust and dirt, and rainwater can wash away the attachments on the surface, It can reduce the cleaning cost, so it is suitable for the occasions with high cleanliness requirements.

    5. Medical and health applications

    A variety of polymer products were widely used in modern medical treatment, which greatly excluded and replaced the application of metal and other materials in the medical field. These products are not only used in the human body and contact with human tissues but also used in various medical devices. In recent years, polymer PTFE has good flexibility and biocompatibility and is gradually becoming an important part of biological functional materials.

    PTFE has low surface tension, non-hydrophilic, and good biocompatibility, so it can be used in artificial blood vessels. The increase of potential energy on the inner surface of the artificial blood vessel wall will promote the sedimentation and coagulation of endothelial cells, which is the result of the obvious biological reaction of the surrounding tissue caused by the change of surface energy of microporous PTFE products. The use of this property can prevent the thrombosis process in the graft space. The tube of gastroscope forceps is made up of expanded PTFE and rubber plastic film. Because it can bend and deform at will and has no foreign body reaction in contact with the human body, it can be used to sample the human stomach immediately, take the foreign body, and remove polyps. It can operate freely and avoid unnecessary pain for patients.

    In addition, PTFE can be made into the artificial cruciate ligament, joint, esophagus, trachea, urethra, and bile duct in medicine. It can also be used for plastic surgery, bone tissue replacement, promoting fracture healing, skin or organ transplantation, periodontal tissue regeneration, etc.

    6. Other applications

    PTFE yarn also has many applications, such as the use of its porous membrane, as filter material can selectively pass through gas or liquid, used for gas-liquid separation, gas-gas separation, and liquid-liquid separation of the filter membrane; adding conductive carbon black pressure can also make the heating body, such as the middle heating layer of electric heating blanket.

    With the continuous development of material application technology, the application research of PTFE and its modified materials abroad in recent years has made it a very mature material. Although there has been some development in China, there is still a big gap between China and foreign countries in modification research and processing technology. PTFE yarn has an excellent performance in many aspects, which is incomparable with other materials, and its application field is very broad.

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