Polyimide (PI) is a kind of polymer material with high heat resistance developed in the 1950s. It is a new kind of thermosetting engineering plastics. With excellent electrical insulation, wear resistance, high temperature radiation resistance, physical and mechanical properties, it can maintain higher physical and mechanical properties within the range from - 269℃ to 400℃, and also can be long-term used in -240-260 ℃ environment.
In addition, there are a variety of methods of synthetic route, processing and shaping available. Therefore, it can be widely used in the aviation, aerospace, electronics, machinery, chemical industry, microelectronics, instrument, petrochemical industry and has become one of the indispensable materials for rockets, aerospace, and other cutting-edge technology fields. In addition, glass fiber is added PI. The reinforced Graphite and boron fiber can obtain higher hardness and strength, which can replace metal injection engine structural components. PI resin can be used as self-lubricating material after being filled with graphite or polytetrafluoroethylene (PTFE), and can be used to manufacture high-temperature brake pads after being added wear-resistant filler.
Features: PI is widely used because its comprehensive performances of its high temperature resistance, oxidation resistance, radiation resistance, corrosion resistance, heat resistance, high strength, high modulus of dielectric properties.
Application: As a cutting-edge materials with excellent performance, its application in machinery, electronic and electrical industry, instrument, petrochemical industry, and measurement has been growing rapidly, becoming one of the indispensable materials for rockets, aerospace, and other cutting-edge technology fields.
1.According to thermogravimetry, the starting decomposition temperature of full aromatic polyimide is generally about 500℃. Polyimide, synthesized from biphenyl dianhydride and p-phenylenediamine, has a thermal decomposition temperature of 600℃, making it one of the most thermally stable polymers so far.
2.Polyimide is resistant to very low temperatures, fro example, it is not brittle in liquid helium at -269°C.
3.Polyimide has excellent mechanical properties. The tensile strength of unfilled plastic are above 100Mpa, while that of polyimide film (Kapton) is 170Mpa or more, and that of biphenyl type polyimide (Upilex S ) is up to 400Mpa. As engineering plastics, the amount of elastic film is usually 3-4Gpa, while the fiber can reach 200Gpa. According to the theoretical calculation, the tensile strength of composite fiber of pyromellitic anhydride and p-phenylenediamine can reach 500Gpa, second only to carbon fiber.
4.Some varieties of polyimides are insoluble in organic solvents, stable to dilute acid, while generally varieties are not resistant to hydrolysis. This seemingly flawed performance makes polyimide different from the other high performance polymers, namely it can take advantage of the alkaline hydrolysis to recycle material dianhydride and diamine, for example, Kapton film, its recovery rate can reach 80% 90%. Changing structure can also get very hydrolysis resistance varieties, which can be boiled in 120 ℃ for 500 hours.
5.The thermal expansion coefficient of Polyimide is within the range from 2×10-5 to 3×10-5℃, wide thermoplastic polyimide 3×10-5℃, biphenyl 10-6 ℃, and individual species 10 -7°C.
6.Polyimide has high resistance to irradiation, and its film has a 90% strength retention rate after 5 x 109rad electron irradiation.
7.Polyimide has good dielectric properties, and its dielectric constant is about 3.4. When fluorine is introduced, or the air nanometer size is dispersed in polyimide, its dielectric constant can be reduced to about 2.5. The dielectric loss of 10-3, and dielectric strength of 100-300 - kv/mm. Dielectric strength of thermoplastic polyimide is 300 kv/mm, volume resistance is1017 Ω/cm. These properties remain at a high level within a wide range of temperature ranges and frequencies.
8.Polyimide is self-extinguishing polymer with low smoke rate.
9.Polyimide has very little deflation at very high vacuum.
10.Polyimide is non-toxic and can be used to make cutlery and medical utensils, and can withstand thousands of disinfection. Some polyimides also have good biocompatibility, for example, non-hemolytic in blood compatibility experiments, and non-toxic in vitro cytotoxicity experiments.
