Nylon, with the chemical name polyamide (abbreviated as PA), is a general term for thermoplastic resins containing repetitive amide groups —(NHCO)— on the molecular main chain. It was the first synthetic fiber developed by the outstanding American scientist Carothers and his research team. Its emergence was a major breakthrough in the synthetic fiber industry and an important milestone in polymer chemistry. The raw materials of nylon are usually coal, water and air. It is generally formed by synthesizing the two basic chemical substances hexamethylenediamine and adipic acid, and then polymerizing them by mixing them together. Common types of nylon include nylon 6, nylon 66, nylon 610, etc. Nylon has the following characteristics: - **Excellent mechanical properties**: Good tensile strength, impact strength and rigidity, excellent wear resistance, and the comprehensive mechanical properties are better than those of general plastics. - **Good self-lubricating property**: Low friction coefficient, and the addition of fillers such as molybdenum disulfide and graphite can further improve the wear resistance. - **Better electrical insulation**: However, the resistance value will decrease with the increase of temperature and water absorption rate, and the dielectric constant and dielectric loss will increase. - **Excellent chemical corrosion resistance**: It can withstand hydrocarbons, oils and general solvents; but water and alcohols and their similar compounds can cause it to swell and it can be dissolved in polar phenolic compounds and methanol solutions of calcium chloride at room temperature. - **In terms of thermal properties**: The melting temperature range is narrow, the heat distortion temperature is not high, and the distortion temperature can be increased after being reinforced with glass fibers; the thermal conductivity is very low, and the coefficient of linear expansion is large. - **Environmental resistance**: The performance is stable under indoor room temperature environment and remains unchanged for a long time, but when exposed outdoors, especially when the temperature exceeds 60°C, the performance will gradually decline. There are many varieties of nylon. According to the classification of the polymerization mechanism, it can be divided into nylon l prepared by ring-opening polymerization of lactams (l represents the number of carbon atoms in the repetitive lactam), and nylon mp prepared by condensation polymerization of diamines and diacids (m and p are the number of carbon atoms in the repetitive diamines and diacids, respectively). Common types of nylon are as follows: - **Nylon 6**: It is formed by ring-opening polymerization of lactam under the action of high temperature and initiator. It is a milky white or slightly yellow crystalline polymer with a melting point of 215-225°C, a glass transition temperature of 48°C, a long-term heat resistance temperature of 105°C, and a continuous use temperature of 65°C. It has self-extinguishing property, high water absorption rate, excellent wear resistance and self-lubricating property, and strong solubility to hydrocarbon organic solvents. - **Nylon 66**: It is prepared by melt polycondensation of equimolar hexanediamine and adipic acid at 270-275°C. It is a semi-transparent or opaque milky white crystalline polymer with a melting point of 260-265°C, a glass transition temperature of 65°C, a heat distortion temperature of 70°C, and can jump to 250°C after adding 30% glass fiber. It has good insulation performance, but the electrical performance will decrease with the increase of temperature and water absorption rate. It also has high strength, hardness, rigidity and creep resistance, excellent fatigue resistance, and good tolerance to most solvents at high temperatures, but it is vulnerable to the corrosion of inorganic acids, chlorinated solvents and heavy metal salts. - **Nylon 1010**: First, decanediamine and sebacic acid are synthesized into polyamide 1010 salt, and then heated and melted to be prepared by dehydration polycondensation reaction. It is a white or light yellow solid, non-toxic and odorless, with a density of 1.03-1.05g/cm3 and a melting point of 195-210°C. It has low hygroscopicity, good cold resistance, high rigidity, excellent wear resistance and self-lubricating property, is elastic, has good impact resistance, good dielectric performance, good solvent resistance, and can be dissolved in concentrated sulfuric acid, phenols and formic acid, etc., but insoluble in hydrocarbons, lipids, lower alcohols and general organic solvents. Nylon can be processed by methods such as injection molding, extrusion molding, and monomer casting, and is widely used in many fields such as automobiles, electronic and electrical, machinery, daily necessities, and sports goods. For example, in the automotive industry, nylon can be used to manufacture engine parts, electrical parts, vehicle body parts and automotive pipes, etc.; in the electronic and electrical industry, it can be used to manufacture rice cookers, electric vacuum cleaners, high-frequency electronic food heaters, air conditioner pipes, terminals, switches and resistors, etc.; in the mechanical industry, it can be used to manufacture gears, turbines, bolts, nuts, housings and other large mechanical parts; in terms of daily necessities, nylon films can be used for food packaging; in sports, it can be used to make ski boards, racket frames, ice skates, fishing rods, fishing lines, etc. However, nylon also has some disadvantages, such as high water absorption, poor dimensional stability; poor heat resistance and light resistance, and poor retention. But these deficiencies can be improved through modification to expand its application range. Modification methods include glass fiber reinforced modification, flame retardant modification, transparent modification, weather resistance modification, etc., to meet the specific requirements for the performance of nylon under different usage conditions or environments. Nylon has the advantages of being non-toxic, lightweight, having excellent mechanical strength, wear resistance and good corrosion resistance. With the development of technology and in-depth modification research, its application fields are still expanding.