Manufacturing Process of Carbon Fiber
Anup Kumar Mohanta
Dept. of Textile Engineering
College of Engineering and Technology,
Bhubaneswar, Odisha, India
Carbon fibers are manufactured from two pre cursors known as PAN (poly acrylonitrile) and pitch. It is a high performance fiber. A carbon fiber is a long, thin strand about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the axis of the fiber. This crystal alignment makes the fiber incredibly strong. Several thousand carbon fibers are joined together to form a yarn.
Manufacturing Process of Carbon Fiber
Carbon fiber can be manufactured from PAN and PITCH. These processes are described below.
A typical process used to manufacturing of carbon fiber from PAN includes spinning, stabilization, carbonizing, surface treating, and sizing.
1. PAN contains highly polar C-N groups that are randomly arranged on either side of the chain.
2. Carbon filaments are wet spun from a solution of PAN and stretched at an elevated temperature during which the polymer chains are aligned in the filament direction. Then the filament are heated at 200 to 3000C for a few hours.
3. At this stage the C-N groups located on the same side combine to form a more stable and rigid ladder like structure and some of the CH2 groups are oxidized.
4. In the next stage the PAN filaments are carbonized by heating at a controlled rate between 1000 to 20000C in an inert atmosphere.
5. Tension is maintained on the filament to prevent shrinkage and to improve molecular orientation.
6. Subsequently the carbonized filaments are heated above 20000C, where their structures becomes more oriented and turns towards a true graphite form with increasing heat treatment temperature.
7. At this stage the graphitized filaments attain a high tensile modulus, but their tensile strength may be relatively low.
8. Tensile strength can be increased by hot stretching above 20000C.
1. Pitch is a byproduct of petroleum refining, and is a lower cost raw material than PAN.
2. The carbon atoms in pitch are arranged in low molecular weight aromatic ring patterns.
3. Heating to temperature above 3000C polymerizes these molecules into long two dimensional sheet like structure.
4. The highly viscose state of pitch at this stage is called mesophase.
5. Pitch filaments are produced by melt spinning the mesophase pitch through a spinneret.
6. The filaments are cooled to freeze the molecular orientation and then heated between 200 to 300 0C in oxygen atmosphere to stabilize them and make them infusible.
7. In the next step the filaments are carbonized at 20000C.
8. Rest of process of transferring the structure to graphitic form is similar to that followed for PAN precautions.
USES OF CARBON FIBER:
The carbon fibers are an important part of many products, and new applications are being developed every year. Carbon fiber-reinforced composite materials are used in the automotive and aerospace industry, sports and many other components where light weight and high strength are needed. Carbon fibers have high electric conductivity (volumetric impedance) and at the same time have excellent EMI shielding property. This successfully brings CFRP (Carbon fiber reinforced plastics) to the field of EMI shielding. Carbon fibers have low heat expansion ratio and high dimensional stability, and sustains its mechanical performances even under high temperature region. CFRP is superior to steel or glass fiber reinforced plastics (GFRP) in its specific tensile strength and specific elastic modulus (specific rigidity). Fatigue resistance of Carbon fiber surpasses that of other structural material. Carbon fibers are used in the following fields: Aerospace industry, sporting goods, automobiles, wind turbine blades, military, medical applications and many more fields.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.