Carbon fiber is primarily made by processing organic polymers that consist of long strings of molecules held together by carbon atoms.
The manufacturing process involves several steps to transform precursor polymers into the strong, lightweight carbon fibers used in various applications today.
The Main Manufacturing Processes
According to industry practices, carbon fiber is predominantly produced using one main method and two less common ones.
The PAN Process (Polyacrylonitrile)
About 90 percent of carbon fibers are made by using the polyacrylonitrile (PAN) process. This is the most common and widely used method due to its efficiency and the quality of fibers produced. In this process, PAN fibers are heated in a controlled environment through various stages:
- Stabilization: The PAN fibers are heated in air at temperatures around 200-300°C (392-572°F) for several hours. This adds oxygen to the fiber structure, rearranging the molecular bonds and preparing the fibers for carbonization.
- Carbonization: The stabilized fibers are then heated to much higher temperatures, typically 1000-3000°C (1832-5432°F), in an inert atmosphere (like nitrogen) for a few minutes. This process removes non-carbon atoms, leaving behind tightly bonded carbon atoms in crystal structures.
- Surface Treatment: The surface of the carbon fibers is often treated chemically to improve adhesion with the matrix material (like epoxy resin) when forming composite materials.
- Sizing: Finally, a protective coating (sizing) is applied to protect the fibers during handling and processing into composite materials.
Other Processes
The remaining 10 percent are made using either the rayon or petroleum pitch process. These methods are less common than the PAN process but are still used for specific types of carbon fibers or applications.
- Rayon Process: Historically significant, this method uses rayon as the precursor. It involves steps similar to the PAN process, including stabilization and carbonization, but typically produces fibers with different properties, often less strong and stiff than PAN-based fibers.
- Petroleum Pitch Process: This method uses petroleum pitch (a residue from oil refining) as the precursor. Pitch-based carbon fibers can achieve very high stiffness, making them suitable for certain specialized applications.
Here's a simple summary of the primary methods:
| Process | Precursor Polymer | Percentage of Production | Key Characteristics |
|---|---|---|---|
| PAN | Polyacrylonitrile | ~90% | High strength and stiffness, most common. |
| Rayon | Rayon | Part of the remaining 10% | Less common, historical method. |
| Petroleum Pitch | Petroleum Pitch | Part of the remaining 10% | Can achieve very high stiffness. |
Understanding these processes highlights how different organic polymers are transformed through heat and chemical treatments into the strong, lightweight fibers known as carbon fiber.
