Mechanical Recycling of CFRP Composites—Part I: Characterization of Carbon Fiber and Epoxy Constituents as Reinforcing Phases

The increasing use of carbon fiber-reinforced polymers (CFRP) has raised critical challenges for their end-of-life management, particularly given the limited recyclability of thermoset matrices. This work presents the first stage of a mechanical recycling strategy based on the evaluation of CFRP constituents as functional reinforcing phases.

Carbon fiber fabrics were converted into short carbon fibers (SCF, ~5 mm) through ZÜND cutting machine, while epoxy-derived chips were produced via controlled End Milling cutting in the face and peripheral milling of epoxy blocks. These macroscopic reinforcements were incorporated into an epoxy matrix at 1–5 wt.%. Subsequently, all constituents were processed via high-energy ball milling (HEBM) to obtain microparticles, which were incorporated at 3–10 wt.% to evaluate the effect of reinforcement scale.

Mechanical performance was evaluated through tensile, flexural, and Izod impact testing. The results demonstrate that reinforcement efficiency is governed by a transition from geometry-controlled mechanisms at the macroscopic scale to interfacial interaction-driven behavior at the micrometric scale. SCF improved impact resistance at low contents but led to mechanical degradation at higher loadings due to agglomeration and stress concentration. Epoxy-derived particles exhibited a more stable but less effective reinforcing response, particularly under flexural loading.

HEBM processing enhanced stiffness and strength at intermediate contents (~3 wt.%) in tensile loading, while flexural performance showed maximum improvement at higher contents (10 wt.%). Impact behavior exhibited a non-monotonic response, with a critical reinforcement concentration required to activate effective energy dissipation mechanisms.

These findings allow progress towards the development of new mechanical recycling strategies for CFRP composites in order to reuse recycled materials as effective reinforcements in polymeric matrices, positioning recycling as a materials design strategy within a circular economy framework.