Carbon fibers are the state of the art when it comes to high strength, high modulus fibers. Carbon fibers are manufactured by spinning a suitable polymer precursor and thermally treating the resultant fiber to optimize its mechanical and chemical properties. Precursors are chosen to be materials that metamorphose into graphite-like structures.
Spinning is designed to orient the graphite-like molecular structure of the fiber parallel with the fiber axis. This results in the orientation of strong covalent molecular bonds along the axis of the fiber where stress is applied. In general, the degree of heat treatment applied to a given fiber affects its mechanical properties by promoting the development of the fibers inherent graphite-like structure, which has significant mechanical strength. A. Graphite has both PAN (polyacrylonitrile) and Pitch based fibers available in chopped and milled form. Various types of sizing are also available to provide the right fiber surface configuration for your system.
Carbon fibers are made from organic polymers such as poly (acrylonitrile). Although a full description of polymers is not really appropriate at this point, it should be noted that polymers are giant molecules comprised of repeating units. Poly (acrylonitrile) is a polymer with chains of carbons connected to one another. To make carbon fibers, the polymer is stretched into alignment parallel with what will eventually be the axis of the fiber. Then, an oxidation treatment in air between 200 and 300 °C transforms the polymer into a nonmeltable precursor fiber. This precursor fiber is then heated in a nitrogen environment. As the temperature is raised, volatile products are given off until the carbon fiber is composed of at least 92% carbon. The temperature used to treat the fibers varies between 1000 °C and 2500 °C depending on the desired properties of the carbon fiber. Each carbon fiber is very thin; the total diameter of a carbon fiber is 6-10um or about five times thinner than an average human hair. When carbon fibers are used in industry, they are woven into sheets, tubes, or other desired shapes. Epoxy resins or other binders are often added to the carbon fibers. The resulting composite of epoxy and carbon fibers is stronger than either component individually.