2, polyimide classification and application
(6). Polyimide adhesive
PI (polyimide) adhesive is a class of organic heterocyclic adhesives containing imide ring structure in the main chain, with excellent high-temperature mechanical properties, dielectric properties and radiation resistance, the disadvantage is that easy to hydrolyze under alkaline conditions, has been widely used in aerospace, precision electronic machinery and other high-tech fields, and solved the problem of lower heat-resistant temperature of the upper limit of other organic adhesives.
From the 1970s, the National Aeronautics and Space Administration (NASA) Langley Research Center, DuPont and Hughes Aircraft Co. have developed a series of high-temperature resistant PI adhesives code-named LARC-TPI, NR-150R2PI-S02 and LARC-13, etc., and has been widely used in a variety of aircraft. 1990s. In the 1990s, Amoco and Cytec of the United States, Japan's Mitsui East Pressure Chemical Company have become the world's most famous production of Pl adhesive companies.
(7). polyimide film
In the early morning of December 8, 2018, the Chang'e-4 probe was launched from the Xichang Satellite Launch Center, marking China's first soft landing on the back of the moon, lunar patrol exploration and survival on lunar night and other aspects of a major breakthrough. Chang'e-4 successfully brought the national flag to the back of the moon, marking space with a "Chinese logo".
It is reported that the national flag of the probe is not made of common textiles such as chemical fiber fabrics, silk and cotton. As we all know the space environment is very special, the lunar surface does not exist in the atmosphere, is a vacuum state to receive sunlight, the lunar surface in the daytime maximum temperature of up to 123 ℃. At night, outside the lunar module, the temperature on the moon will plummet to minus 233 ℃.
Such a temperature difference is difficult for ordinary materials to tolerate. Moreover, the ultraviolet rays produced by the sun are very strong, and there are also cosmic rays and high-energy particles with radiation effects, which have a strong destructive effect on the materials.
The flag material entrusted with this important task is precisely the polyimide organic polymer film, which is completely different from the common flag on the ground, and it can withstand the harsh lunar surface environment without fading or deformation.
Polyimide film in addition to the spacecraft as a "coat", as well as in the military applications, in microelectronics, nano, liquid crystal, separation membrane, laser, new energy fields and other fields can see its figure. For example, transparent polyimide film can be used as a soft solar cell substrate; PI can be used as the next generation of lithium-ion battery diaphragm materials and so on.
In recent years, with the development of the electronics industry, high-performance polyimide film has become a key material for microelectronics manufacturing and packaging, and is widely used in the manufacture of ultra-large-scale integrated circuits, automatic splicing carrier tape, flexible packaging substrates, flexible connecting tape lines and so on.
Polyimide film, source: Yung Da Electric
In addition, polyimide is an ideal material for high-temperature resistant gas separation membranes because of its high heat resistance and good all-around performance. At present, a very small number of polyimide varieties are applied to high-temperature-resistant gas separation membrane materials for the separation of various gas pairs (e.g., hydrogen/nitrogen, nitrogen/oxygen, carbon dioxide/nitrogen, carbon dioxide/methane, etc.), for the removal of water from air, hydrocarbon feed gases, and alcohols, and also for use as permeation evaporation membranes and ultrafiltration membranes. However, conventional polyimide resins are difficult to dissolve and melt, thus limiting the possibility of their widespread industrial application.
(8).Polyimide Aerogel
Polyimide aerogel (PIA) is a three-dimensional porous material consisting of polymer molecular chains cross-linked with each other, combining the excellent performance of polyimide and aerogel, which not only has the excellent characteristics of polyimide, but also has the aerogel's lightweight, ultra-low density, high specific surface area, low thermal conductivity, low acoustic impedance, environmental durability, and low dielectric constant, and other outstanding characteristics, these special properties allow polyimide aerogel to be used as a permeable evaporation membrane and ultrafiltration membrane. These special properties make polyimide aerogel materials have excellent application prospects in the fields of thermology, electricity, mechanics and acoustics.
Polyimide Aerogel, Source: polymer.com
In order to realize the manned Mars landing program in the development of heavy payload transportation technology, NASA research centers apply polyimide aerogel materials in the research of supersonic inflatable aerodynamic decelerator (HIAD), which provides a solution for the research of spacecraft braking payload and volume efficiency, and due to the durability of polyimide aerogel materials, it also has a wide range of applications in the fields of propellant tanks, rover ultralight and multifunctional materials, and space residence. multifunctional materials, and space habitats.
In addition to the aerospace field, polyimide aerogel materials have good application prospects in the fields of electronic communications, heat-insulating and flame-retardant materials, adsorption and cleaning, sound insulation and acoustic absorption, catalytic carriers, and wire/cable insulation.
(9).Polyimide-based composites
Fiber-reinforced composites are a new generation of lightweight materials after magnesium-aluminum alloys, and the composites with polyimide as the resin base have excellent high-temperature resistance and tensile properties, and are widely used. Polyimide resin-based composites with polyimide high heat resistance, excellent mechanical properties, dielectric properties, solvent resistance, etc., is currently the highest temperature of the resin-based composites, in the aviation (especially aviation engines), aerospace and other fields have been widely used.
After nearly 40 years of development, polyimide high-temperature resin-based composites have developed four generations of composites, the use of temperature has been improved, the most advanced fourth-generation polyimide resin-based composites can be used for a long time at 450 ℃.
At present, China's polyimide composites application and research and development is still catching up, AVIC composite materials companies and other enterprises have been able to produce third-generation resin products.
In addition, with the gradual maturation of the carbon fiber industry, carbon fiber reinforced composites demand growth is obvious, polyimide + carbon fiber combination as one of the most excellent composite material combinations, to seize the high-end market advantage is obvious.
3, the conclusion
polyimide almost all kinds of polymer materials, including high-performance films, engineering plastics, foams, chemical fibers, adhesives, resin matrix, insulating materials, functional materials, composites and so on.
The performance of polyimide is strongly dependent on its chemical structure, and different structures of polyimide can be selected or synthesized according to the application, and can also be modified by copolymerization, blending, filling, and reinforcement. The development of new polyimide is inseparable from the development of new monomers, special structure of diamine and dianhydride monomers is the development of new varieties of polyimide is necessary to ensure that the reduction of monomer cost is the key to reduce polyimide.
As polyimide-related materials in aerospace, military, high-end electronics and other sensitive areas have an irreplaceable role, most of the foreign polyimide raw materials, technologies and products in China to implement a strict blockade. Although domestic enterprises have been trying to catch up, but our localization and mass production of high-end products and foreign advanced level is still not a small gap. Therefore, the development of polyimide-related products is very urgent and has a long way to go!
Source "China Composites Industry Association official website".