Acrylic (PAN) as Carbon Fibre Precursor

PAN-based acrylic precursor fibre is the dominant raw material for carbon fibre manufacturing, accounting for 95% of global carbon fibre production — with precursor quality (molecular weight, co-monomer composition, void content, defect density, filament diameter uniformity) being the single most important determinant of carbon fibre mechanical performance and manufacturing yield. Precursor requirements: high molecular weight PAN homopolymer or copolymer (Mn 100,000–200,000 g/mol, narrow MWD PDI <2.5 — low PDI reduces oxidation stage non-uniformity), co-monomer content 1–3% itaconic acid (IA) or methacrylic acid (MAA) — carboxylic acid co-monomers catalyse cyclisation reaction, reduce stabilisation temperature by 20–30°C and stabilisation time by 30–40%; filament diameter 5–7 µm (aerospace grade) or 7–12 µm (industrial grade); void content <0.1% volume (voids become defects in final carbon fibre, reducing tensile strength by 5–15% per 0.1% void); surface irregularity <5 nm Ra. Precursor production differentiation: aerospace carbon fibre precursor (Toray T800, T1000 grade) — solution wet-spun from DMSO or DMF, 5–6 µm diameter, defect-free, $8–15/kg precursor cost → $25–45/kg carbon fibre; industrial carbon fibre precursor (Toray T300 equivalent) — 7–12 µm, lower quality control, $4–6/kg precursor → $15–25/kg CF. Carbon fibre conversion process: precursor → stabilisation (oxidative, 200–280°C, air atmosphere, 60–90 minutes — PAN ladder polymer formation by cyclisation, dehydrogenation → black oxidised fibre density 1.35–1.40 g/cm³) → low-temperature carbonisation (LTC, 300–800°C, nitrogen, 3–5 minutes — evolution of N₂, HCN, CO, CO₂, non-carbon elements) → high-temperature carbonisation (HTC, 1,000–1,600°C, nitrogen, 1–3 minutes — graphitic carbon layer development, carbon content >93%) → surface treatment (anodic oxidation, 0.3–1.0 A/dm², increases -COOH, -OH functional groups for matrix adhesion) → sizing (epoxy emulsion 0.5–1.5% OWF, protects during handling) → final carbon fibre. CF properties versus precursor: T800 CF tensile strength 5,880 MPa, modulus 294 GPa, strain to failure 2.0%, density 1.80 g/cm³ — conversion efficiency 50% (1 kg PAN precursor → 0.5 kg carbon fibre by mass loss of non-carbon elements). Global carbon fibre market: 190,000 tonnes (2023, Lucintel), $4.5 billion market value — Toray 37% share, Teijin Toho 14%, SGL Carbon 9%, Hexcel 10%; aerospace 25%, wind energy 28%, automotive 15%, sports/leisure 12%.