Energy-efficient recovery of high-value carbon fiber from waste CFRP via phosphoric acid pyrolysis and its application in enhancing flame retardancy of VER

CFRP waste is growing at an increasing rate. This study proposes a novel atmospheric-pressure phosphoric acid pyrolysis method to efficiently recover high-value carbon fibers from waste CFRP, which are then applied to enhance the flame retardancy of VER. Waste CFRP was immersed in phosphoric acid at 80 °C under atmospheric pressure. The acid acted as a solvent to degrade the epoxy resin, achieving an 80% degradation rate. Comprehensive characterization (SEM, XPS, TGA, XRD, Raman) confirmed that the recycled carbon fibers (rCFs) possess a clean surface with their microstructure largely intact. Mechanical testing revealed excellent property retention, with a tensile strength of ∼97% and interfacial shear strength comparable to virgin fibers. This method is advantageous due to its lower temperature, reduced energy consumption, and operational simplicity compared to traditional recycling techniques. Halloysite nanotubes (HNTs) were employed to modify both recycled carbon fibers (rCFs) and virgin carbon fibers (vCFs), followed by the fabrication of HNTs/CF/VER composites. SEM confirmed that carbon fibers were successfully modified, and the modification effect of rCFs was superior to that of vCFs. Tests demonstrated that rCFs and HNTs exhibit a favorable synergistic flame retardant effect, modified recycled carbon fibers (m-rCFs) at 1 wt% exhibited relatively excellent flame-retardant performance (LOI: 28.3%, UL-94: V-1 rating, Lowest pHRR and THR), superior to modified virgin carbon fibers (m-vCFs) at the same addition level and a slight improvement in tensile strength relative to pure VER. The above research provides a promising solution for the degradation and reuse of waste CFRP.