Recycled carbon fiber (rCF)

Definition (what it is)

Recycled carbon fiber (rCF) is carbon fiber recovered from post‑industrial scrap (e.g., prepreg offcuts, trim waste, out‑of‑spec parts) or post‑consumer/end‑of‑life carbon‑fiber‑reinforced polymer (CFRP) components. Recycling removes or depolymerizes the original matrix and preserves the fiber reinforcement to varying degrees, after which the fibers are cleaned, classified, and typically reprocessed into new intermediate forms such as chopped fibers, milled fibers, nonwoven mats/veils, sheet molding compounds (SMC), or pellets/compounds for thermoplastics. Long, aligned, or near‑continuous rCF forms exist but are less common.

Key technical characteristics

Fiber morphology and forms: Most commercial rCF is discontinuous (e.g., chopped lengths from a few millimeters up to ~100 mm) or supplied as random nonwoven mats. Milled rCF is a very short, powder‑like filler for property modification. Longer, aligned, or tow‑like rCF products are emerging but remain niche.
Mechanical properties: At the filament level, stiffness (tensile modulus) is largely retained; tensile strength can be reduced by fiber shortening, surface defects, and loss of original sizing. Composite‑level performance depends strongly on fiber length distribution, orientation, volume fraction, and fiber–matrix adhesion.
Surface chemistry and sizing: Recycling often strips original sizings/coatings. Re‑sizing (epoxy‑, polyester‑, or thermoplastic‑compatible) is commonly applied to restore interfacial bonding and improve composite performance.
Processability: rCF is readily used in injection molding (as chopped/compounded), compression molding (as SMC/BMC or with nonwoven mats), resin transfer molding (RTM) with mats, and thermoplastic press molding and overmolding. Managing shear to preserve fiber length during melt processing is a key constraint.
Density and conductivity: rCF shares carbon fiber’s low density (~1.75–1.9 g/cm³) and high electrical/thermal conductivity, enabling lightweight structures, EMI shielding, and tailored thermal pathways relative to glass‑fiber solutions.
Cost and environmental profile: rCF reduces embodied energy and greenhouse‑gas footprint relative to virgin carbon fiber (vCF) and can be cost‑competitive with high‑performance glass fiber or lower‑grade vCF, depending on quality, form, and supply chain.
Variability and quality control: Properties vary with feedstock, recycling route, and post‑processing. Important quality metrics include fiber length/length distribution, single‑fiber strength, surface condition/sizing, impurity content, and moisture. Industry efforts are ongoing to standardize rCF grading.

Applications and relevance

Lightweighting at lower cost: Substitutes metals or glass fiber in weight‑sensitive, cost‑constrained parts where continuous vCF is excessive, including automotive/EV interior structures, underbody/aero panels, brackets, load floors, instrument panel carriers, housings, and covers.
Battery and electronics components: Electrical conductivity supports EMI shielding and ESD control in enclosures and covers; with appropriate matrices and barriers, rCF composites can contribute to thermal management and fire performance strategies.
Industrial and consumer products: Used in power‑tool housings, consumer electronics for EMI control, sporting goods, and infrastructure components where discontinuous carbon reinforcement suffices.
Circularity and compliance: Diverts CFRP waste from landfill/incineration and helps meet regulatory and corporate sustainability targets, including recycled content and embodied‑carbon reduction.

Recycling and recovery methods (typical)

Thermal processes (pyrolysis, fluidized bed): Thermally decompose thermoset matrices in inert or controlled atmospheres. Widely used; yield clean fibers with sizing removed. Strength can be reduced relative to vCF; modulus is typically retained.
Chemical processes (solvolysis, including supercritical fluids): Depolymerize or dissolve the matrix using solvents/reactants, often at elevated temperature/pressure; can better preserve fiber surface and strength and may enable partial resin constituent recovery.
Mechanical processes (shredding, milling): Physically reduce CFRP into flakes/short fibers; lowest cost and simplest but produce shorter fibers with lower structural performance.

Post‑processing and intermediate products

Fiber cleaning, classification by length/diameter, and application of new sizings.
Nonwoven mats/veils (random orientation) for RTM or compression molding.
rCF‑SMC/BMC (thermoset) for structural and semi‑structural compression‑molded parts.
Chopped or pelletized rCF compounds with thermoplastics (e.g., PP, PA, PBT, PEI, PEEK) for extrusion and injection molding.
Milled rCF concentrates for stiffness, wear, and electrical/thermal property modification.

Design and processing considerations

Structural role: Best suited to quasi‑isotropic laminates and molded discontinuous‑fiber parts; generally not a direct substitute for continuous‑fiber laminates in primary, highly loaded structures without hybridization.
Fiber length retention: Optimize compounding and molding to minimize fiber breakage (low‑shear screws, gate design, melt temperature and residence time control).
Orientation and geometry: Use ribbing and thoughtful flow path design to align fibers where beneficial and mitigate weld‑line weaknesses.
Interfaces and sizings: Match sizing chemistry to the target matrix; consider compatibilizers/coupling agents where needed.
Hybrid strategies: Combine rCF with vCF, glass fiber, or thermoplastic fibers to balance performance, cost, impact resistance, and surface finish.
Electrical behavior: Account for conductivity in tooling, part design, and assembly to avoid unintended shorting; consider EMI/ESD requirements and insulation strategies.
Surface quality and finish: Compression‑molded rCF SMC can achieve good cosmetics; injection‑molded compounds may need paint or coatings for Class‑A surfaces.
End‑of‑life: Thermoplastic rCF composites can often be remelted/reprocessed; thermoset rCF composites can be mechanically or thermally recycled again, supporting circularity.

Health, safety, and handling

Handle as for carbon fiber and conductive dusts: use appropriate PPE and dust extraction to control respirable particles and reduce electrical shorting risks. Manage waste and offcuts per local regulations.

Synonyms and related terms

Synonyms: recycled carbon fibre, reclaimed carbon fiber, recovered carbon fiber.
Related: carbon fiber reinforced polymer (CFRP), chopped carbon fiber, milled carbon fiber, carbon fiber nonwoven mat/veil, rCF‑SMC/BMC, thermoplastic rCF compound, pyrolysis recycling, solvolysis, mechanical recycling, sizing (fiber surface treatment).