Views: 0 Author: Site Editor Publish Time: 2025-11-24 Origin: Site
Carbon fiber manufacturing is a complex thermo-chemical transformation of polymer precursors into crystalline carbon structures. The process includes five key stages.
Over 90% of carbon fiber worldwide is produced from polyacrylonitrile (PAN) precursor. PAN is a long-chain polymer consisting of repeating –CH₂–CH(CN)– units. Its linear structure and nitrile groups make it ideal for later conversion into ladder polymers and graphitic structures.
Alternative precursors include:
Pitch (mesophase or isotropic)
Rayon (rare today)
PAN remains dominant because it provides the best combination of high strength, high modulus, and processing efficiency.
In this stage, PAN fibers are heated in air at 200–300°C. Several critical reactions occur:
oxidative cross-linking
cyclization of nitrile groups
dehydrogenation
formation of a thermally stable ladder polymer
Stabilization prevents the fibers from melting during subsequent high-temperature processing. It also determines the ultimate performance of the carbon fiber—poor stabilization leads to defects and reduced strength.
Stabilized fibers are heated to 1000–1500°C in an inert atmosphere (typically nitrogen). At this stage:
hydrogen, nitrogen, and oxygen are removed
carbon content increases to 90–95%
turbostratic carbon layers begin to form
The resulting fiber becomes black, stiff, and electrically conductive.
For high-modulus grades, fibers undergo further heating at 2000–3000°C. At these extreme temperatures:
crystallites grow
graphitic layers align more perfectly
modulus increases significantly
High-modulus (HM) or ultra-high-modulus (UHM) fibers used in aerospace and robotics require extensive graphitization.
Carbon fibers are naturally inert and smooth, which makes bonding to resins challenging. Therefore:
fibers are oxidized or electrochemically etched to create surface functional groups
a sizing layer (typically epoxy-compatible) coats the fiber to protect it during weaving and improve composite adhesion
Sizing chemistry is important because it determines how well the fiber interacts with epoxy, vinyl ester, or thermoplastic resins.
The extraordinary performance of carbon fiber originates from its microstructure.
Carbon atoms form hexagonal sheets resembling graphene. These layers are:
extremely strong in-plane
stiff due to strong covalent bonds
lightweight because of low atomic mass
The alignment of these layers along the fiber axis gives carbon fiber its high modulus.
The degree of preferred orientation—known as texture—determines:
modulus
tensile strength
electrical conductivity
Higher orientation → higher modulus.
Smaller crystallites → higher tensile strength (fewer catastrophic flaws).
Common defects include:
voids
misaligned crystallites
surface flaws
incomplete stabilization
Strength in carbon fiber is controlled by the “weakest link,” meaning a single micro-crack may limit performance.
Carbon fiber alone is strong, but when combined with a polymer matrix:
the matrix transfers shear loads
fibers carry tensile loads
interfacial bonding determines performance
This is why surface treatment is critical in composite engineering.
Understanding what is carbon fiber requires a look at its most important performance indicators.
Typical values:
Grade | Tensile Strength | Tensile Modulus |
Standard Modulus (SM) | 3.5–4.5 GPa | 230–250 GPa |
Intermediate Modulus (IM) | 4–5.5 GPa | 275–320 GPa |
High Modulus (HM) | 2.5–4.0 GPa | 350–450 GPa |
Strength depends heavily on defect distribution; modulus is controlled by graphitization.
Typical density: 1.75–1.95 g/cm³
Compare:
Aluminum: ~2.7 g/cm³
Steel: ~7.8 g/cm³
Fiberglass: ~2.5 g/cm³
Carbon fiber delivers higher strength at much lower weight.
Very low or negative coefficient of thermal expansion
High thermal stability
Anisotropic thermal behavior
This is why carbon composites maintain dimensional precision in aerospace and robotics.
Graphitic structure makes carbon fiber electrically conductive—unlike fiberglass. This must be considered in lightning strike protection and EMI shielding.
Carbon fiber composites show:
excellent fatigue resistance
minimal creep compared to polymers and metals
This is why carbon fiber is used in repetitive load environments (wind blades, aircraft wings).
Carbon fiber is not a single material—it is a family of engineered materials.
Standard Modulus (SM) – most common
Intermediate Modulus (IM) – aerospace and high-end sporting goods
High Modulus (HM) – robotics, precision machinery
Ultra-High Modulus (UHM) – telescopes, optical systems
PAN-based (high strength, common)
Pitch-based (high modulus, lower strength)
Rayon-based (legacy, niche applications)
Rather than listing industries, it is more educational to link applications with engineering motivations.
Aerospace primary structures
Satellite components
Robotic arms
Optical benches
High modulus and low thermal expansion are key benefits.
EV structural components
UAV airframes
Sporting goods (bicycles, rackets, skis)
Lower mass improves performance, range, and efficiency.
Audio equipment
High-speed machinery
Precision measuring devices
The combination of stiffness and energy dissipation makes carbon fiber ideal for dynamic systems.
Marine structures
Chemical processing equipment
Infrastructure reinforcement
Carbon fiber does not rust and tolerates aggressive environments.
No material is perfect. Carbon fiber has strengths and weaknesses determined by its physics and chemistry.
exceptional strength-to-weight ratio
low density
high fatigue resistance
corrosion resistance
low thermal expansion
customizable anisotropy
brittle failure mode
electrically conductive (may be undesirable)
expensive energy-intensive processing
machining difficulties (delamination)
requires expertise in composite design
Primarily PAN precursor, converted through stabilization and carbonization.
Its graphitic planes have extremely high in-plane covalent bond strength.
It is brittle; cracks propagate rapidly through aligned crystalline regions.
Energy-intensive heat treatments up to 3000°C dominate cost.
Surface roughness, weave style, and resin type affect optical appearance.
Filaments are the raw fibers; fabrics are woven or stitched assemblies.
Epoxy provides excellent adhesion, toughness, and thermal stability.
Carbon fiber is a scientifically remarkable material: lightweight, strong, stiff, corrosion-resistant, and dimensionally stable. Understanding what is carbon fiber requires an appreciation of polymer chemistry, high-temperature carbonization, crystallite orientation, and composite engineering. Meanwhile, the phrase “what is the carbon fiber” refers to a specific grade or form within this broad material family.
Today, carbon fiber enables engineering achievements from aerospace structures to electric vehicles, renewable energy, robotics, and advanced sporting goods. Its unique combination of microstructure, anisotropy, and composite compatibility continues to drive innovation across multiple high-performance industries.
