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This post was last edited by Green Lotus on 2018-10-19 at 10:31. Teflon possesses unique and excellent properties, which enable its wide use in various fields. However, it has certain shortcomings in terms of wear resistance, hardness, creep resistance, etc. To improve its overall mechanical properties, we usually add filling materials to polytetrafluoroethylene in order to meet various requirements. Therefore, it is very important to choose the right filling materials that suit our needs. Based on the performance requirements of the composite material, we can choose to use a single material or multiple materials together for filling. The filling material serves to reinforce the structure of the PTFE mixture, without undergoing any chemical reaction with PTFE. Below are the advantages and disadvantages of the properties modified by various PTFE filling materials. Glass fiber-modified Teflon. Glass fiber is a commonly used inorganic material, which is obtained by cutting and grinding glass fiber filaments followed by screening. The main role of glass fiber powder in PTFE composites is to provide reinforcement, thereby increasing the material’s compressive strength, hardness, and wear resistance, as well as reducing shrinkage and thus improving the dimensional stability of PTFE. Glass fiber powder is required to have a certain length-to-diameter ratio, so that it can act as a structural component within the PTFE resin. It is necessary that the whiteness of this powder be high; contaminated waste fibers should not be used in its production. Typically, PTFE filler is added in the form of alkali-free or low-alkali glass fiber powder. This type of fiber powder is brittle, inexpensive, resistant to high temperatures, and has good corrosion resistance; it is only susceptible to corrosion by strong alkalis, hydrofluoric acid, and concentrated phosphoric acid. Carbon fiber-modified Teflon. Carbon fiber is a high-performance inorganic filler material with high strength and modulus, low density, no creep, resistance to extremely high temperatures in non-oxidizing environments, good fatigue resistance, low thermal expansion coefficient, excellent corrosion resistance, as well as good electrical and thermal conductivity. However, as the carbon fiber content increases, the tensile strength and elongation of the composite material decrease, while its compressive strength and hardness increase. Relatively speaking, the addition of carbon fiber provides a better reinforcing effect than graphite or glass fiber. Through comprehensive analysis, carbon fiber, as a PTFE filling material, can enhance the creep resistance, pressure resistance, wear resistance, and temperature resistance of composite materials; it particularly performs well in water circulation lubrication and pneumatic sealing applications. Graphite-modified PTFE: Graphite is an allotrope of elemental carbon that exists in the form of crystalline carbon. The graphite powder commonly used as a PTFE filler is blackish-gray in color, has a greasy texture, and is soft; it is one of the minerals with extremely high heat resistance. Graphite possesses excellent high-lubricity, high-conductivity, high-absorption, and catalytic properties, as well as very high plasticity. Graphite is often used as a filler or performance enhancer in rubber, plastics, and various composite materials to improve their wear resistance, compressive strength, or conductivity. Graphite-filled PTFE exhibits excellent chemical resistance, compressive strength, creep resistance, and good thermal conductivity, but its wear resistance is inferior to that of glass fiber-filled PTFE. Molybdenum disulfide-modified Teflon. Molybdenum disulfide is a blackish-gray solid powder with a metallic luster. Chemical formula MoS2, melting point 1185°C, density 4.80 g/cm3 (14°C). The molybdenum disulfide commonly used is synthetically produced. Molybdenum disulfide is insoluble in water, dilute acids, and concentrated sulfuric acid, as well as in other acids, bases, and organic solvents; however, it is soluble in aqua regia and boiling concentrated sulfuric acid. It has a slight irritant effect. Molybdenum disulfide powder is a conductive material that feels slippery to the touch. The product features good dispersibility and non-sticking properties, making it suitable for lubrication in mechanical applications involving high temperatures, high pressures, high speeds, and heavy loads. As a filler for polytetrafluoroethylene, it can improve the hardness, wear resistance, and lubricity of composite materials; it is a neutral inorganic filler. Tin-brass powder-modified PTFE, copper powder-modified PTFE – Tin-brass powder is often used as a filling material for PTFE; generally, spherical or irregularly shaped granular copper powder produced by atomization can be used. They possess good strength, thermal conductivity, wear resistance, and color luster, and are available in 200 to 250 mesh. Bronze powder is easy to process, has good plasticity, and excellent wettability. The product appears as a greenish-yellow powder with a high loose density. It is greenish-yellow in color during molding; after sintering, it gradually changes from bright to darker in color, even turning black due to oxidation. Adding copper powder to PTFE materials improves their thermal conductivity, compressive strength, wear resistance, and heat resistance. Once the copper powder is evenly distributed, care should be taken to avoid excessive shaking, so as to prevent it from settling at the bottom of the PTFE resin and affecting its performance. Bronze powder is a type of metal powder that corrodes in the presence of acids and bases, and oxidizes and changes color when exposed to water. Polyimide-modified Teflon: Polyimide is one of the organic polymer materials with the best overall properties; it can withstand temperatures of over 400°C. It does not become brittle even at extremely low temperatures. Polyimide appears as a light yellow powder, is lightweight, non-toxic, resistant to creep, wear-resistant, self-lubricating, provides good electrical insulation, and is also corrosion-resistant. Its tensile strength is ≥100 MPa, and its elongation rate is >120%; it is a self-extinguishing polymer with a low smoke emission rate and significant fire-resistant properties. Polyimide, when used as a filler in PTFE, can effectively address the issues related to the wear resistance and dimensional stability of PTFE materials, as well as its excellent resistance to extreme temperatures and its dielectric properties. It is an excellent soft organic filler that does not damage the mating parts. It can be used for mechanical components such as compressor vanes, piston rings, and seals for special pumps. Polyphenylene modified Teflon: Polyphenylene modified Teflon appears as a crystalline powder or granules in a light yellow to brownish-yellow color. It is a commonly used high-quality organic Teflon filler. It has a low density, around 1.24 g/cm3, exhibits high mechanical stiffness, strong compressive resistance, excellent creep resistance, is easy to machine, and possesses high load-bearing capacity as well as good self-lubricating properties. Polyphenyl ester possesses high thermal stability, the highest thermal conductivity among plastics, good electrical insulation properties, and excellent chemical resistance. Filling polyphenylene with PTFE increases the hardness of the composite material, and improves its properties in terms of heat resistance, lubricity, insulation, radiation resistance, and solvent resistance. It can be used as high-temperature resistant oil-free lubrication bearings, sliders, piston rings, heat-resistant fixtures, washers, fillers, thrust rings, and electronic and electrical components. In recent years, polyphenylene-filled PTFE materials have been developed for use in the aerospace industry. Stainless steel powder-modified Teflon: Stainless steel powder-modified Teflon – stainless steel is a type of steel that is resistant to corrosion and oxidation, as well as possessing high chemical stability. Stainless steel powder is made by grinding and sieving stainless steel material. Stainless steel powder boasts advantages such as corrosion resistance, heat resistance, thermal conductivity, and wear resistance. When filled with Teflon and molded followed by sintering, the resulting product exhibits a silver-gray natural metallic luster. The addition of stainless steel powder can increase the hardness, compressive strength, wear resistance, and thermal conductivity of the composite material.