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1. Nitrile rubber (NBR) is an irregular copolymer synthesized through emulsion polymerization of butadiene and acrylonitrile monomers, with the molecular structure formula: —(CH2-CH=CH)m- (CH2-CH2-CH)n- CN. The development of nitrile rubber began in Germany in 1930; it is a copolymer of butadiene and 25% acrylonitrile. Due to its superior resistance to aging, heat, and wear compared to natural rubber, it has gained significant attention in the rubber industry. During World War II, with the rapid development of weapons and equipment, nitrile rubber, which is heat-resistant and oil-resistant, saw a sharp increase in demand as a material essential for military use. To date, there are over 20 facilities that produce nitrile rubber, with an annual production volume of 560,000 tons, accounting for 4.1% of the world’s total synthetic rubber production. Thanks to its excellent heat resistance, oil resistance, and mechanical properties, it has now become the main type of oil-resistant rubber, accounting for around 80% of the total demand for such rubber. Nitrile rubber saw significant development in the 1950s, and to date there are over 300 different grades of it. Based on the acrylonitrile content, they can be classified as follows: those with an acrylonitrile content of >42% fall into the extremely high-cyanide category; those with 36%～41% acrylonitrile content belong to the high-cyanide category; those with 31%～35% acrylonitrile content are in the medium-high cyanide category; those with 25%～30% acrylonitrile content belong to the medium-cyanide category; and those with less than 24% acrylonitrile content are in the low-cyanide category. The most widely used in industry are the low-cyanide grade Butacrylonitrile-18 (with 17%–20% acrylonitrile content), the medium-cyanide grade Butacrylonitrile-26 (with 27%–30% acrylonitrile content), and the high-cyanide grade Butacrylonitrile-40 (with 36%–40% acrylonitrile content). An increase in the acrylonitrile content can significantly improve the oil and heat resistance of nitrile rubber, but more is not always better, as an increased acrylonitrile content also reduces the rubber’s performance at low temperatures. Nitrile rubber is primarily used to manufacture rubber products that are used in petroleum-based hydraulic oils, lubricants, kerosene, and gasoline, and it can operate at temperatures ranging from -50 to 100 degrees Celsius ； It can be used for short-term operations at 150 degrees, with operating temperatures ranging from -45 to 100 degrees in air and ethanol-glycerin antifreeze. Dicyanide has poor aging resistance; it ages and cracks rapidly in high ozone concentrations, and is not suitable for long-term operation in hot air, nor can it be used in phosphate ester flame-retardant hydraulic oils. General physical properties of nitrile rubber: 1) Nitrile rubber is usually black; the color can be adjusted according to the customer’s requirements, but this will incur additional costs and may affect the performance of the rubber. 2) Nitrile rubber has a slight smell of rotten eggs. 3) Determine whether the material of the seal is NBR based on its oil resistance properties and operating temperature range. 2. Silicone rubber (Si or VMQ) is a linear polymer whose backbone consists of siloxane units (-Si-O-Si), with organic groups serving as side chains. Due to the development of advanced industries such as aviation and aerospace, there is an urgent need for rubber sealing materials that can withstand high and low temperatures. The natural, nitrile, neoprene, and other common rubbers used in early morning applications could no longer meet the needs of industrial development; as a result, in the early 1940s, two companies in the United States began producing dimethylsilicone rubber, which was the earliest form of silicone rubber. Our country also achieved successful research and put it into production in the early 1960s. Over several decades of development, the variety, performance, and production volume of silicone have seen tremendous progress. Main properties of silicone: 1) Heat resistance – Silicone exhibits good thermal stability at high temperatures. It can be used for extended periods at 150°C without any significant change in performance ； It can operate continuously for over 10,000 hours at 200°C, and can even be used for a short period of time at high temperatures of 350°C. 2) Cold resistance: Both low-phenylic silicone rubber and medium-phenylic silicone rubber have a cold resistance coefficient of over 0.65 at -60°C and -70°C, demonstrating good elasticity at low temperatures. The typical operating temperature for silicone is around -50°C. 3) Oil and chemical resistance: Silica has excellent tolerance to polar solvents such as ethanol and propanol, as well as food oils; it causes only minimal swelling, and its mechanical properties remain essentially unchanged ； Silica gel also exhibits good tolerance to low concentrations of acids, bases, and salts; after being placed in a 10% sulfuric acid solution for 7 days, its volume change rate is less than 1%, and its mechanical properties remain essentially unchanged. However, silicone is not resistant to concentrated sulfuric acid, concentrated alkalis, non-polar solvents such as carbon tetrachloride, and toluene. 4) It has strong aging resistance; silicone boasts excellent ozone resistance and radiation resistance, qualities that are beyond those of ordinary rubber. 5) Dielectric properties: Silica has a very high volume resistivity (1014–1016 Ω·cm), and its resistance value remains stable over a wide range. Suitable as an insulating material under high-pressure conditions. 6) Flame-retardant properties: Silicone does not burn immediately when exposed to fire, and it produces fewer toxic gases during combustion; the residues resulting from combustion form insulating ceramic substances. Therefore, silicone is an excellent flame-retardant material. Given these properties, silicone is widely used in seals or rubber components in the home appliance industry, such as those found in electric kettles, ironing boards, and microwave ovens ； Seals or rubber components in the electronics industry, such as phone buttons, shock-absorbing pads inside DVDs, and seals in cable connectors, etc ； Seals on various items that come into contact with the human body, such as water bottles and water dispensers. 3. Fluorocarbon rubber (FKM or Vtion), also known as fluor elastomer, is a polymer in which fluorine atoms are present on the carbon atoms of the main chain and side chains. Since the early 1950s, the United States and the former Soviet Union have been developing fluororubbers. The first products to enter production were VitionA and Kel-F from American companies DuPont and 3M. Over the course of half a century, fluororubbers have made rapid progress in terms of heat resistance, chemical resistance, low-temperature performance, and manufacturing processes, giving rise to a range of product lines. Fluorocarbon rubber possesses excellent heat resistance, ozone resistance, and resistance to various hydraulic fluids. Its operating temperature in air is -40 to 250°C, and its operating temperature in hydraulic oil is -40 to 180°C. Due to the processing of fluororubber, its adhesion and low-temperature performance are inferior to those of conventional rubber, and it is also more expensive; therefore, it is mainly used in high-temperature media where conventional rubber is not suitable, but it is not appropriate for certain phosphate ester solutions. 4. Ethylene propylene diene monomer (EPDM) is a terpolymer of ethylene, propylene, and a small amount of non-conjugated diene olefins. In 1957, Italy achieved industrial production of ethylene-propylene copolymer rubber (EPDM). In 1963, the American company DuPont added a small amount of non-conjugated cyclic dienes as a third monomer to binary EPDM, thereby synthesizing low-unsaturation EPDM with double bonds in its molecular chain. Since the molecular backbone remains saturated, EPDM retains the excellent properties of EPDM while also achieving vulcanization. EPDM exhibits excellent ozone resistance, remaining crack-free for 2430 hours in an environment with an ozone concentration of 1*10-6 ； It has excellent corrosion resistance: it remains stable in the presence of alcohols, acids, strong bases, oxidizing agents, detergents, animal and vegetable oils, as well as certain lipids (however, it swells significantly in petroleum-based fuels and hydraulic fluids, and cannot operate in environments where it is in contact with mineral oils) ； It has excellent heat resistance and can be used for extended periods at temperatures ranging from -60 to 120°C ； It has excellent water resistance and electrical insulation properties. EPDM is naturally beige in color and possesses excellent elasticity. 5. Polyurethane elastomers (PU) are polymers made from polyisocyanates and polyether polyols or polyester polyols and/or small-molecule polyols, polyamines, or chain-extending agents/crosslinking agents such as water. In 1937, Professor Otto Bayer in Germany first discovered that the polyaddition of polyisocyanates with polyol compounds could yield polyurethanes, and this discovery led to their industrial application. Polyurethane elastomers can be used in temperature ranges from -45°C to 110°C. They exhibit high elasticity and strength across a wide range of hardness levels, as well as excellent wear resistance, oil resistance, fatigue resistance, and vibration resistance. In particular, they have good resistance to swelling in both lubricating oils and fuel oils, which is why they are known as \"wear-resistant rubber\". Polyurethane elastomers possess excellent comprehensive properties, and are widely used in various industrial sectors such as metallurgy, petroleum, automotive industry, mineral processing, water management, textiles, printing, healthcare, sports, food processing, and construction. 6. Polytetrafluoroethylene (PTFE): Polytetrafluoroethylene, abbreviated as Teflon in English, is known as the \"king of plastics\"; its common names in Chinese include \"Tiěfúlóng\", \"Tèfúlóng\", \"Teflon\", \"Teifulong\", and \"Taifulong\", among others. It is a polymer compound formed by the polymerization of tetrafluoroethylene, featuring excellent chemical stability and corrosion resistance (it is one of the materials with the best corrosion resistance in the world; it can withstand all other chemicals except molten sodium metal and liquid fluorine, and remains unchanged even when boiled in aqua regia). It also has good sealing properties, high lubricity and non-stick characteristics, electrical insulation, as well as strong resistance to aging. Additionally, it boasts excellent temperature tolerance, allowing it to function over a wide range of temperatures from +250°C to -180°C. Polytetrafluoroethylene itself is not toxic to humans, but one of the raw materials used in its production, ammonium perfluorooctanoate (PFOA), is considered to potentially have carcinogenic effects. Temperature: -20 to 250°C (-4 to +482°F); sudden cooling and heating, or alternating hot and cold operations are allowed. Pressure: -0.1 to 6.4 Mpa (full vacuum to 64 kgf/cm2). Advantages: High temperature resistance – can operate at temperatures up to 250°C. Low-temperature resistance – excellent mechanical toughness ； It can maintain a 5% elongation even when the temperature drops to -196°C. Corrosion resistance – It exhibits inertness toward most chemicals and solvents, and can withstand strong acids, strong bases, water, and various organic solvents. Weather resistance – it has the best aging lifespan among plastics. High lubricity – it has the lowest coefficient of friction among solid materials. Disadvantages: Poor elasticity.