Polyacrylonitrile (also called PAN) carbon fiber is the second successful carbon fiber developed after the viscose based carbon fiber. It is a carbon fiber with the highest yield, the largest variety, the fastest development and the most mature technology in various carbon fibers.
Polyacrylonitrile fiber, in chemical fiber, the name of the commodity is acrylic. It is a synthetic fiber formed by polymerization of acrylonitrile monomer. The CN base is very active and is heated to form a trapezoidal structure, which is more stable than the original structure, so it is not easy to melt. If the polyacrylonitrile fiber is heated, the non carbon atoms are discharged in the form of NH3. The yield of carbon fiber can reach 57% higher than that of viscose fiber, so it is an ideal precursor for the production of carbon fiber.
The breakthrough of the two key technologies for the preparation of PAN based carbon fiber is to directly heat the polyacrylonitrile fiber and transform it at a temperature of 80 degrees. After that, the fiber contracts and the polymer chain begins to bend and twist. In the original spinning process, the polypropylene molecular chain formed by stretching was disoriented along the fiber axis, so carbon fibers could not be obtained after carbonization.
In early twentieth Century of sixty, Jin Teng Nan, a Japanese Industrial Technology Research Institute in Osaka, found that PAN fibers were slowly heated in air. However, after carbonization, a tensile modulus of 165GPa and a yield of 50% were obtained. It has made a breakthrough in the technology of making carbon fibers from polyacrylonitrile.
When PAN fibers are heated to 220 degrees in air and keep enough time, oxygen in air will form oxygen bonds between fibers and link two fiber molecular chains together. Because the CN bonds of each fiber molecule are in different angles in the space, it is only a number of fibers (not all) that produce an oxygen bridge reaction. The PAN level of pre calculation theory after the maximum oxygen content of more than 15%, generally 8-10%. Because of the bridging effect of oxygen chains, the polyacrylonitrile fibers pre oxidized become solid cross-linked structures. The stable structure of black carbon can keep the original fiber form when carbonized.
Although Shinto Akio used oxygen bonds to crosslink molecular chains, the fibers were protected from the original fiber shape and made of carbon fibers. However, PAN fibers were highly oriented polymer molecules formed during high tension during spinning. The degree of orientation of fiber molecules is still decreasing during pre oxidation. Therefore, the strength of carbon fibers made at that time is higher than that of viscose based carbon fibers at that time, but in general it is not very good.
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