23
2017
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03
Carbon fiber for GRP products
Carbon fiber and graphite fiber are both fibers with good mechanical properties. The tensile strength of graphite fiber is about twice that of glass fiber, and the heat resistance is far more than that of glass fiber. The cloth woven with graphite gauze also has good mechanical strength when heated to 25001C. Therefore, fiberglass products can be used as reinforcing materials to produce high temperature and ablation resistant reinforced plastics with comprehensive performance.
As early as the 19th century, carbon fiber was made. The luminous filament of the first electric lamp in the world is carbon fiber. Later, some people carbonized cotton into carbon fiber, but its poor performance did not attract people's attention. It was not until 1958 that it was proposed to carbonize rayon to produce carbon fiber. Two years later, Akio Fujito and other Japanese people made significant improvements in the technology of manufacturing carbon fiber using polypropylene wax fiber as raw material. This method has finally become the main method of industrial production of carbon fiber at present.
The method they proposed is as follows: first, the polypropylene fiber is heated to 200-300 ℃ in the air for pre-oxidation under the condition of stretching. Then, under the protection of inert gas flow, the pre-oxidized fiber is heated to 1000 ℃ for carbonization and decomposition. The hydrogen, nitrogen, oxygen and other components in the fiber turn into gases and leave the molecular chain of the fiber, leaving behind graphitized carbon fibers arranged in a similar graphite structure. The pre-oxidation step in the manufacturing process is called graphitization. Because of graphitization, the arrangement of carbon atoms is closer to that of graphite, and the fracture of carbon atom chain during carbonization can also be reduced. How the molecular chain of synthetic fibers can be transformed into carbon fibers with graphite structure after pre-oxidation and carbonization treatment is not completely understood at present, but the following explanation is based on some grounds:
The originally curly molecular chains of polyacrylonitrile stretch out in the direction of stretching, forming nearly parallel zigzag molecular chains. At high temperature, one or two adjacent molecular chains are connected into a ring, and other atoms other than carbon atoms are removed at the same time to form a fiber composed of hexagonal carbon rings. This process can be represented by chemical symbols on page 95.
Pian fiber is also a new type of reinforcing material with outstanding performance that appeared in the 1960s,. 4 is a nonmetal, usually brown powder or gray shiny crystal. It is also a very hard material, and its hardness is almost the same as diamond. In 1959, American Tari first put forward the proposal of making boron fiber by chemical deposition, which was immediately supported by the United States Air Force Materials Laboratory. After several years of research and development, the flipper fiber has finally developed rapidly into one of the most attractive reinforcing materials with high strength and rigidity.
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