What is carbon fiber?

Before answering this question, let's first understand what fiberglass is. People are familiar with it, and glass fiber and epoxy resin are the raw materials for manufacturing fiberglass reinforced plastic. Fiberglass and asbestos are both inorganic fibers. Carbon fiber, as the name suggests, is a fiber composed of carbon elements with a carbon content of over 90%. At the microscopic level, the structure of carbon fiber is somewhat similar to graphite, both composed of layered carbon plate-like crystals. These carbon flake crystals have a name called graphene. It has only one layer of atomic thickness, with carbon atoms arranged in a hexagonal pattern within its surface, resembling a honeycomb shape.

How is such high-performance carbon fiber made?

Although carbon fiber is mainly composed of carbon, people still cannot directly use carbon or graphite to produce carbon fiber. They can only use some organic fiber materials containing carbon to combine organic fibers with plastic resin and carbonize them to produce carbon fiber. The organic fibers selected for preparing carbon fibers mainly include polyacrylonitrile fibers, asphalt fibers, viscose fibers, or phenolic fibers, among which polyacrylonitrile carbon fibers and asphalt carbon fibers are more commonly used. In this process, it is generally necessary to go through four processes: fiber spinning, thermal stabilization (pre oxidation), oxidation, and carbonization, accompanied by chemical changes such as dehydrogenation, cyclization, pre oxidation, oxidation, and deoxidation. After these processes, we can obtain the precursor of carbon fiber.

Preparing raw fibers does not mean that the process of preparing carbon fibers is over. After preparing the raw silk, it still needs to go through the processes of sizing and curing. The so-called sizing is the process of mixing raw silk and epoxy resin. There are many methods used in the sizing process, including automatic placement of machinery to immerse carbon fibers in epoxy resin, or manual mixing of epoxy resin and other polymers with carbon fibers. After the sizing process is completed, the final step is solidification. The commonly used methods in the curing process are heating or placing the epoxy resin under vacuum pressure. Curing mainly involves hardening the carbon fibers coated with epoxy resin; In addition, during the curing process, carbon fibers may undergo chemical reactions, generating carbon free substances in the raw material, resulting in stronger agglomeration forces between fiber particles. At this point, the carbon fiber product is truly ready.

Carbon fiber is an inorganic polymer fiber with a carbon content of over 90%. Graphite fibers are those with a carbon content higher than 99%. In addition to the typical characteristics of carbon materials, carbon fiber woven fabrics have significant anisotropic softness in appearance and can be processed into various fabrics. Due to their low specific gravity, they exhibit high strength along the fiber axis. Carbon fiber reinforced epoxy resin composite materials have the highest comprehensive indicators of specific strength and modulus among existing structural materials. The tensile strength of carbon fiber resin composite materials is generally above 3500 megapascals, which is 7 to 9 times that of steel, and the tensile modulus of elasticity is 230 to 430 megapascals, which is also higher than that of steel.