Recycled carbon fibers: Recycling strategies and materials engineering for multifunctional applications

The increasing use of carbon fiber reinforced polymers (CFRPs) has generated growing amounts of manufacturing scrap and end of life composite waste. This study critically examines mechanical, thermal, and chemical recycling strategies for recycled carbon fibers (rCFs), with emphasis on the relationships among recycling conditions, recovered fiber state, material design, and multifunctional performance. Recycling route, processing severity, and feedstock characteristics collectively determine fiber morphology, graphitic structure, defects, surface chemistry, and interfacial characteristics, which subsequently govern mechanical, electrical, dielectric, and functional properties. Recycling induced structural changes are not solely associated with degradation; when appropriately controlled, they can serve as design variables for network and interface engineering. The reviewed evidence shows that the optimum rCF state is application dependent. Interconnected conductive networks favor electromagnetic interference shielding, while controlled dielectric loss, polarization, and impedance matching promote microwave absorption. Deformation sensitive and electrically stable networks further enable self sensing and electrothermal functions. Based on these relationships, an application oriented framework is proposed to connect target performance with network and interface requirements, recovered fiber characteristics, and recycling conditions. This perspective shifts rCF utilization from property recovery toward application oriented material design, providing a pathway for higher value structural and multifunctional applications of CFRP waste.