In the late 1970s, the International Union of Theoretical and Applied Chemistry (IUPAC) established regulations for the classification and naming of carbon fibers. Firstly, PAN (polyacrylonitrile), MP (mesophase asphalt), and VS (adhesive) are used to represent the category of carbon fibers. Then, lowercase English letters are used to represent the heat treatment temperature, such as lht (representing heat treatment temperature below 1400 degree ) and hht (heat treatment temperature above 2000 degree ). Then, performance symbols are added (such as HT for high strength, HM high modulus, SHT ultra high strength, HTHS high strength and high strain, IM medium modulus, and UHM ultra high modulus, etc.). It is also pointed out that polyacrylonitrile based, adhesive based, and ordinary pitch based carbon fibers are all difficult to graphitize polymer carbon, while mesophase pitch based carbon fibers and vapor grown carbon fibers are easy to graphitize carbon.
At the Third International Conference on Carbon Fibers (London, 1985), it was proposed to classify carbon fibers into the following 5 levels based on their mechanical properties.
Ultra High Mode Magnitude (UHM): modulus above 395GPa;
High mode magnitude (HM): modulus between 310 and 395GPa;
Medium modulus level (IM): modulus between 255 and 310 GPa;
Ultra High Strength (UHT): Strength above 3.5GPa,
Modulus below 255GPa;
High strength level (HT): The strength reaches 3.5GPa.
Both grading methods have shortcomings. Nowadays, the classification of high-performance carbon fiber products is indicated by manufacturers themselves: type of raw fiber, number of single fiber pores, diameter, arrangement method (such as parallelism, entanglement, twisting, etc.), whether there is surface treatment (and its type), whether there is sizing (and the type of sizing agent), etc. Some important high-performance product names and properties can be seen in polyacrylonitrile based carbon fibers and asphalt based carbon fibers.