Classification of carbon fiber

Carbon fiber can be divided into polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, phenolic-based carbon fiber and vapor-grown carbon fiber according to the source of raw materials. According to the performance, it can be divided into ordinary carbon fiber, high strength carbon fiber, medium strength carbon fiber, high modulus carbon fiber and ultra-high modulus carbon fiber. According to the state, it is divided into filament, short fiber and short fiber; According to mechanical properties, it can be divided into general type and high performance type. Generally, the strength of carbon fiber is 1000 MPa, and the modulus is about 100G Pa. High-performance carbon fiber can be divided into high-strength type (strength 2000 MPa, modulus 250G Pa) and high-modulus type (modulus above 300G Pa). Strength greater than 4000 MPa is also called ultra-high strength type; Modulus greater than 450G Pa is called superelevation model. With the development of aerospace industry, carbon fiber with high strength and high elongation has appeared, and its elongation is more than 2%. Polyacrylonitrile-based carbon fiber is the most widely used. More than 90% of carbon fibers in the market are mainly polyacrylonitrile-based carbon fibers. Because the mystery of carbon fiber has not been completely unveiled, people can't directly use carbon or graphite to make carbon fiber. They can only use some carbon-containing organic fibers (such as nylon, acrylic fiber and rayon) as raw materials, and combine organic fibers with plastic resin to make carbon fibers.

The production process of polyacrylonitrile-based carbon fiber mainly includes two processes: precursor production and precursor carbonization: firstly, polyacrylonitrile fiber or precursor is treated by a series of processes such as acrylonitrile polymerization and spinning, and these precursors are oxidized in an oxidation furnace at 200-300℃, and then carbon fiber is made in a carbonizer at 1000-2000℃.

Pitch-based carbon fiber The United States invented pitch containing metal mesophase for spinning pitch-based carbon fiber. After the precursor was stabilized and carbonized, the tensile strength of the carbon fiber was 3.5G Pa and the modulus was 252G Pa. France developed mesophase pitch-based carbon fiber with heat resistance and high conductivity; Poland has developed a new method of metal coating carbon fiber. For example, pitch-based carbon fibers coated with copper are manufactured by a hybrid method. Firstly, copper salt and isotropic coal tar pitch were mixed evenly, then spun by centrifugal spinning, stabilized in air and treated in high temperature hydrogen to obtain alloy copper carbon fiber. The production capacity of pitch-based carbon fiber is small in the world, and the research and development of pitch-based carbon fiber in China is earlier, but there is a big gap in development, production and application compared with foreign countries.

Carbon fiber can be divided into aviation grade and industrial grade according to different product specifications, also known as small tow and large tow. Generally, carbon fibers above 48K are called large tow carbon fibers, including 360K and 480K. Aviation-grade carbon fiber was mainly 3K at first, and gradually developed to 12K and 24K. It is mainly used in national defense and high technology, as well as sports and leisure products, such as airplanes, missiles, rockets, satellites, fishing rods, clubs and rackets. Industrial grade carbon fiber is used in different civil industries, including textile, medicine and health, electromechanical, civil construction, transportation and energy.