Carbon Fiber (碳纤维 / Inorganic High-Performance Fiber)
Carbon fiber is the defining advanced composite reinforcement material — ≥90% carbon by mass, produced by controlled pyrolysis of an organic precursor fiber (PAN, pitch, or rayon) in an inert atmosphere. It combines the highest specific strength and stiffness of any commercial fiber with the unique ability to withstand 3000°C in the absence of oxygen — a temperature at which all organic fibers have long since vanished. Carbon fiber spans both the inorganic fiber category (it is elemental carbon, an inorganic material) and the high-performance fiber category (its mechanical properties define the HPF class). Global production is dominated by PAN-based carbon fiber (~90%), with Toray (Japan) as the market leader.
Quick Facts
| Type | Inorganic high-performance fiber; ≥90% carbon by mass; produced by pyrolytic carbonization of organic precursor |
| Precursors | PAN (polyacrylonitrile) — ~90% of production; Pitch (petroleum/coal tar) — high modulus; Rayon (viscose) — historical; Lignin, other organics — emerging |
| Production process | Precursor fiber → oxidative stabilization (200–300°C, air) → carbonization (1000–1500°C, inert) → (optional) graphitization (2000–3000°C, inert) → surface treatment → sizing |
| First commercialized | 1960s (rayon-based); 1970s (PAN-based, Toray T300) |
| Density | 1.5–2.0 g/cm³ (1.75–1.80 typical for PAN-based); lighter than aluminum (2.7), ~1/4 of steel |
| Tensile strength | Standard (T300-class): 3.5 GPa (~1.8 cN/dtex equivalent); High-strength (T1000-class): 7.0 GPa; Highest reported: ~9 GPa |
| Tensile modulus | Standard: 230 GPa; Intermediate modulus: 290 GPa; High modulus: 390–590 GPa; Ultra-high modulus (pitch): up to 900 GPa |
| Maximum service temperature | >3000°C in inert atmosphere (unmatched); oxidizes above 400–500°C in air |
| Key manufacturers | Toray (T-series, M-series, Japan), Teijin (Tenax®), Mitsubishi Chemical (Pyrofil®), SGL (Germany), Hexcel (US), Zhongfu Shenying (China) |
Why Carbon Fiber Belongs in Two Categories
The textbook places carbon fiber in the inorganic fiber category (p.49 and p.106–107) because its final composition is elemental carbon — an inorganic material. The organic precursor (PAN, pitch, or rayon) is completely transformed; what remains is >90% carbon with a turbostratic graphite structure. This is fundamentally different from organic HPFs like aramid or UHMWPE, which retain their organic polymer structure. However, carbon fiber also defines the high-performance fiber category by its extreme mechanical properties — specific strength and modulus that no organic fiber can match. It is listed here under HPF and cross-referenced in 3.5 Inorganic.
Classification
| Classification | Types | Key characteristics |
|---|---|---|
| By precursor | PAN-based, Pitch-based, Rayon-based | PAN: best balance, dominant (~90%); Pitch: highest modulus, lower strength; Rayon: historical, low performance |
| By performance (PAN-based) | High-strength (HT, T-series), Intermediate modulus (IM), High modulus (HM), Ultra-high modulus (UHM) | T300 (standard): 3.5 GPa / 230 GPa; T800: 5.5 GPa / 290 GPa; T1000: 7.0 GPa / 290 GPa; M60J: 3.8 GPa / 590 GPa |
| By tow size | Small tow (1K–24K), Large tow (>48K) | Small tow: aerospace, premium; Large tow: industrial, cost-driven (wind energy, automotive) |
| By application grade | General-purpose (GP), High-performance (HP) | GP: refractory, insulation, carbon paper; HP: structural composites |
Properties
| Property | Rating | Engineering implication |
|---|---|---|
| Specific strength | ★★★★★ Highest | Strength-to-weight ratio surpasses all metals and organic fibers; the reason carbon composites dominate aerospace |
| Specific modulus | ★★★★★ Highest | Stiffness-to-weight ratio unmatched; critical for structures where deflection, not failure, is the design limit |
| Thermal resistance (inert) | ★★★★★ >3000°C | Only fiber that survives extreme temperatures without melting; carbon/carbon composites for rocket nozzles, brake discs |
| Elongation at break | ★☆☆☆☆ 0.5–2.4% | Brittle failure; no yield, no plastic deformation; sudden, catastrophic fracture — the critical design constraint |
| Chemical resistance | ★★★★☆ Excellent | Resists most acids, alkalis, and solvents at room temperature; oxidizes in air above 400°C |
| Electrical conductivity | ★★★★☆ Good | Semi-conductive to conductive (depends on heat treatment temperature); can cause galvanic corrosion with metals in composites |
| Thermal conductivity | ★★★★☆ High (pitch-based) | Pitch-based carbon fiber can exceed copper in thermal conductivity; used for thermal management |
| Fatigue resistance | ★★★★★ Excellent | Essentially no fatigue limit in fiber direction (unlike metals); carbon composites outlast aluminum in cyclic loading |
| Compressive strength | ★★★☆☆ Moderate | Weaker in compression than tension (fiber buckling); matrix support critical in composites |
| Cost | ★★★★★ Very high | T300: ~$20–30/kg; high-modulus grades: $100–500+/kg; the dominant barrier to broader adoption |
| Biodegradability | ★☆☆☆☆ None | Essentially permanent; recycling is mechanical (chopped fiber) or thermal (fiber reclamation from composites) |
Yarn Engineering Notes
Carbon fiber is not spun into yarn in the traditional textile sense — it is produced as continuous filament tows, which are then twisted, woven, braided, or used directly as unidirectional prepreg. Key considerations:
- Brittleness: Carbon fiber cannot withstand the bending and abrasion of conventional textile processing. Handling requires low-tension, large-radius guides and ceramic eyelets.
- Sizing: The fiber surface is sized (epoxy, PU, or other compatible coating) immediately after surface treatment to protect the filaments and ensure matrix compatibility. The sizing choice determines composite interlaminar shear strength.
- Twist: Unlike textile yarns, carbon tows are typically used with minimal or zero twist. Twist damages filaments and reduces composite translation of fiber properties.
- Hybrid yarns: Carbon fiber can be commingled with thermoplastic fibers (PA, PP, PPS, PEEK) to produce thermoplastic prepregs — heating melts the thermoplastic matrix around the carbon reinforcement.
Summary
Carbon fiber is the extreme-performance outlier — highest specific strength and stiffness, highest thermal resistance, and highest cost among commercial fibers. It is an inorganic material produced from an organic precursor, sitting at the boundary of inorganic and high-performance fiber classifications. Its brittleness and cost confine it to applications where its unique combination of properties justifies the investment: aerospace structures, high-performance sporting goods, wind turbine blades, pressure vessels, and luxury goods. For the textile engineer, carbon fiber requires a fundamentally different processing approach — it is a reinforcement material handled as filament tows, not a conventional textile fiber. See the Textile Material framework.