Carbon Fiber's Classification and Raw Materials

The ranking of carbon fiber is based on the tensile modulus of the fiber. Tensile modulus can be defined as the measure of the amount of pulling force exerted on an object before it breaks. The unit used to measure the tensile modulus of an object is psi (pounds of force per square inch). Carbon fibers classified as low modulus have a tensile modulus below 34.8 million psi. The other classifications of carbon fibers based on their tensile modulus include standard modulus, intermediate modulus, high modulus, and ultrahigh modulus. Ultrahigh tensile modulus carbon fibers have a tensile modulus of 72.5-145 million psi. In comparison, steel has a tensile modulus of about 29 million psi. Thus, the most durable form of carbon fiber is about five times stronger than steel.

The raw material used to make carbon fiber is called the precursor. 90% of the carbon fibers produced are made from polyacrylonitrile. The remaining 10% is made from rayon or petroleum pitch. All of these materials are organic polymers. The characterization of organic polymers is formed by a long string of molecules bound together by carbon molecules. During the manufacturing process, certain gases and liquids are used. Some of these elements react with the fiber to bring about a specific effect. Other materials are designed not to respond or to prevent certain reactions with the fiber.