What is carbon fiber made of?

In this era of rapid technological advancement, carbon fiber materials have become a favorite in numerous fields due to their exceptional properties. With advantages such as high strength, high modulus, low density, and corrosion resistance, they are widely used in aerospace, automotive manufacturing, sports equipment, and more. So, how is carbon fiber produced? Let’s explore the origin, development, manufacturing methods, and applications of carbon fiber.

The history of carbon fiber dates back to the late 19th century. In 1860, British scientist Joseph Swan invented carbon fiber while developing filaments for light bulbs. However, the performance of carbon fiber at that time was far from ideal, limiting its widespread use. It wasn’t until the mid-20th century, with the rapid development of aerospace technology and the growing demand for high-performance materials, that carbon fiber began to gain attention for its outstanding properties. In 1959, Akio Shindo of the Osaka Industrial Research Institute in Japan developed a method for producing carbon fiber using polyacrylonitrile (PAN) as the raw material, laying the foundation for large-scale carbon fiber production. Since then, carbon fiber technology has continued to advance, with its performance constantly improving.

In the aerospace sector, carbon fiber composites have gradually replaced traditional metals, becoming a crucial structural material for aircraft, satellites, and other spacecraft. In automotive manufacturing, carbon fiber is increasingly used to reduce vehicle weight, improve fuel efficiency, and enhance safety and comfort. In sports equipment, carbon fiber has become synonymous with high-end products, such as golf clubs, bicycles, and tennis rackets.

Carbon fiber is an inorganic fiber composed primarily of carbon atoms (over 90%) arranged in a carbon backbone structure. It is formed through the pyrolysis and carbonization of organic fibers such as polyacrylonitrile (PAN), pitch, or rayon under high temperatures. Below is a detailed introduction:

PAN-based carbon fiber:
Using polyacrylonitrile as the raw material, it undergoes polymerization to form polyacrylonitrile, which is then spun into PAN fibers through a spinning process. The fibers are then pre-oxidized by heating to 200–300°C in air, causing cyclization and oxidation reactions that create a heat-resistant ladder-like structure. Next, the fibers undergo carbonization in an inert atmosphere at 1,000–2,000°C, removing non-carbon atoms to form carbon fiber. For high-performance carbon fiber, an additional graphitization process is applied, heating the carbonized fibers to 2,500–3,000°C in an inert atmosphere to refine the crystal structure and enhance the fiber's modulus.

Pitch-based carbon fiber:
Using petroleum or coal pitch as the raw material, the pitch is first refined to remove impurities and increase its softening point and viscosity. It is then spun into pitch fibers via melt spinning or solution spinning. The fibers undergo stabilization (or "infusibilization") by heating to 200–400°C in air, inducing cross-linking reactions in small molecules to form a heat-resistant structure. Finally, the fibers are carbonized in an inert atmosphere at 1,000–2,000°C, removing non-carbon atoms to produce carbon fiber.