Dynamic imine bonds enable closed-loop recycling of high performance PEEK/CF composites

Carbon fiber reinforced resin matrix composites are widely used across various industries. However, with their growing, there is an increasing demand for effective and sustainable recycling strategies. Chemical recycling of carbon fiber reinforced poly(ether ether ketone) (PEEK/CF) composites remains challenging due to the inherent chemical inertness of PEEK and the economic inefficiency of recovering carbon fiber only. In this work, a dynamic covalent chemistry strategy is employed to enable the closed-loop recovery of PEEK/CF composites through acid catalyzed imine bonding. Trifluoroacetic acid initiates the protonation of the carbonyl groups in crystalline PEEK, converting it into amorphous poly(aryl ether ketone) (KPEEK) with an activation energy of 35.1 kJ/mol. Under acidic conditions, the dynamic chemistry of imine bonds facilitates KPEEK to revert to crystalline PEEK, achieving a recovery rate of 95 %. As a result, the recycled PEEK retains excellent properties, including a tensile strength of 97 MPa and thermal stability (T_{d5 %} ≥ 550 °C). The recycled carbon fiber is undamaged and fully reusable. The reprocessed PEEK/CF composites exhibit tensile strength of approximately 1900 MPa mechanical properties. This strategy avoids energy intensive degradation of PEEK and offers the potential for scalable production through compatibility with existing industrial infrastructure.