Long Way Education

By Eman Abdallah Kamel

Eman is a writer and engineer. She has her bachelor’s degree in textile science from the College of Applied Arts.

Carbon Fibers

Carbon fibers are polymers with a near-perfect graphitic structure—a pure form of carbon in which the atoms are arranged in large sheets of hexagonal rings. This structure provides high levels of stiffness and strength.

Carbon is a chemical element; its symbol is C, and its atomic number is 6. It is a tetravalent non-metallic element, meaning that its atoms are capable of forming up to four covalent bonds due to its valence shell containing 4 electrons.

Carbon fibers are composed of at least 92% carbon and are typically between 5 and 10 micrometers in diameter. Carbon fibers possess excellent thermal, electrical, and mechanical properties.

Toray Industries, Teijin, and Japan’s Mitsubishi Chemical are the world’s largest producers of carbon fiber. Other major players include Hexel (USA), Syensqo (Belgium), and SGL Carbon (Germany), with China and Hyosung (South Korea) also making significant and growing contributions to the industry.

Did You Know?

The properties of carbon fibers depend primarily on the raw materials. Carbon fibers are continuously produced and bundled into bundles ranging from 1,000 to 48,000 fibers. Carbon fibers are classified according to their modulus of tensile strength and elasticity.

Classification

There are five different types of carbon fibers.

1. HT: Stands for low modulus of elasticity (<100 GPa) and high tensile strength (>3.0 GPa).
2. IM: Medium modulus of elasticity (modulus of elasticity > 350 GPa, > 200 GPa).
3. SHT: Tensile strength greater than 4.5 GPa.
4. HM: High modulus of elasticity (modulus of elasticity > 450 GPa, greater than 350 GPa).
5. UHM: Ultra-high modulus of elasticity (modulus of elasticity > 450 GPa). Carbon fiber tubes with an extremely high modulus of elasticity (UHM) are characterized by exceptional rigidity, exceeding that of aluminum by four to five times or steel by 1.5 times. They are not recommended for applications requiring high stress tolerance.

Properties

The stiffness of carbon fibers is determined by the alignment and regularity of their atomic structures, allowing the production of carbon fibers with different elastic moduli. Depending on the processing conditions, properties of carbon fibers can be achieved. Here are some properties of carbon fibers.

• Carbon Content: The carbon content must be high to obtain properties close to those of graphite.
• Mechanical Resistance: The mechanical resistance varies from 700 MPa to 6,000 MPa depending on the nature of the precursor.
• Young’s Modulus: The Young’s modulus ranges from 33 to 800 GPa.
• Strength: High
• Model of Elasticity: High
• Stress Resistance: High
• Thermal Conductivity: High

In addition, other properties include thermal stability, corrosion resistance, and electrical conductivity.

Did You Know?

Cost, both in terms of energy and money, is the main obstacle to the widespread use of carbon fibers. Producing one kilogram of carbon fiber requires 286 megajoules of energy. Therefore, numerous studies are currently underway to reduce production costs and the energy required.

Precursor Types

The majority of commercially used raw materials for carbon fiber production are polyacrylonitrile (PAN), rayon, and tar; however, a range of other raw materials can also be utilized, including cellulosic materials, heterocyclic aromatic polymers, non-heterocyclic aromatic polymers, linear polymers, and coal.

1. Polyacrylonitrile: Polyacrylonitrile (PAN) is composed of at least 85% acrylonitrile and up to 15% co-monomers like methyl methacrylate, methyl acrylate, vinyl acetate, vinyl chloride, and other vinyl monomers.

Manufacturing method,

Polyacrylonitrile is produced through radical polymerization of acrylonitrile. It is spun into fibers and then undergoes coagulation, finishing, and winding to produce finished fibers.

2. Cellulose: Cotton, linen, ramie, sisal, hemp, and flax are all raw materials, but rayon is more commonly used.

3. Pitch: Tar feedstocks produce high-performance carbon fibers due to their high carbon content. Certain fractions of asphalt and tar have been converted into carbon and graphite fibers through a process that involves heat treatment, extrusion, spinning, stabilization, carbonization, and graphitization, resulting in carbon fibers with moderate strength and modulus of elasticity.

4. Aromatic heterocyclic: These polymers are characterized by their linearity and high content of aromatic compounds. Polyimides, polybenzimidazoles, polybenzimidazonium salts, and polytriadiazoles are examples of polymers that have been transformed into highly elastic carbon fibers.

5. Non-heterocyclic aromatic polymers: These materials have a high carbon content. Converting these materials to a graphitic structure and removing non-carbon atoms is a straightforward process. Several compounds have been tested, including phenolic polymers, polyacetylene, polyacrylate ether, polyamides, phenol-formaldehyde resin, and polyvinylene. The tensile strength and modulus of elasticity of these fibers range from 1600 to 2170 MPa and 350 to 490 GPa, respectively.

Did You Know?

General Electric has patented a continuous method for manufacturing polyacetylene-based carbon fibers.

6. Linear Polymers: Several studies on specific types of linear thermoplastic polymers have yielded carbon fibers with poor mechanical properties, such as a low modulus of elasticity and strength. Examples of polymers used as raw materials include polyethylene-polypropylene blends, polyvinyl chloride (PVC), and polyvinyl ketone.

Remember,

These carbon fibers are typically non-carbonizable and have a high number of voids, resulting in poor mechanical properties.

7. Coal: Carbon fibers have been prepared from specific coal extracts obtained by digesting coal at high temperatures and pressures using a high-boiling aromatic solvent. These fibers are homogeneous and have very low strength.

Did You Know?

Currently, work is being done using lignin as a raw material for carbon fibers.

Why Lignin?

1. Lignin is considered waste in paper mills because it doesn’t produce paper with the required properties. Therefore, most of these mills burn the excess lignin as fuel. Because lignin is considered waste in both the paper and biofuel industries, these industries would be willing to sell it to carbon fiber manufacturers.
2. It has been found that blending lignin of different types improves fiber spinning, stability, and the properties of lignin-based carbon fibers.
3. Producing carbon fibers from lignin may be a solution to reduce carbon fiber costs while using renewable resources, promoting more sustainable and cost-effective carbon fiber manufacturing.

Uses

Carbon fibers are used in sectors that include,

• Aerospace,
• Defense,
• Wind energy,
• Sports.

Examples of these applications include,

• Aircraft wings,
• Wind turbine blades,
• Tennis rackets.

Sources

• Ultra High Modulus
• Carbon Fiber Properties
• compositesuk.co.uk/Carbon Fibre Report 2016.pdf
• Lignin-Derived Carbon Fibres: Opportunities and Challenges
• Top 10 Carbon Fiber Companies Driving Market Innovation and Growth Through 2030

©Eman Abdallah Kamel, 2026

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The Long Way Education Site path is based on self-learning. Here you will learn about science, education, and religion. You will also learn about fiber and its manufacture. And different disciplines of engineering, such as mechanical and industrial engineering.