Based on the precursor material, carbon fibers can be classified into three categories: polyacrylonitrile-based (PAN-based), pitch-based, and rayon-based. Among these, PAN-based carbon fiber features a relatively simple production process and superior performance characteristics. Since its inception in the 1960s, it has gradually emerged as the dominant sector within the carbon fiber industry, accounting for over 90% of total global production; consequently, the term "carbon fiber" generally refers to PAN-based carbon fiber in current usage. Pitch-based carbon fiber involves complex raw material preparation and exhibits lower performance characteristics; currently, its production scale remains relatively small. Rayon-based carbon fiber is characterized by low carbonization yields, significant technical challenges, complex equipment requirements, and high production costs; its output is limited, and it is primarily utilized in ablative-resistant and thermal insulation materials.
Carbon fiber precursors can also be classified according to tow size (i.e., the number of individual filaments contained within a single bundle). This is typically denoted by a "K-number" (representing thousands of filaments)-such as 1K, 3K, 12K, 24K, 48K, and so forth. The greater the number of filaments, the larger the tow size. Based on the range of K-numbers, tows ranging from 1K to 24K are generally classified as "small-tow" fibers, while those at 48K and above are designated as "large-tow" fibers. Large-tow fibers are primarily geared toward large-scale, cost-effective manufacturing applications.
