Enabling Closed-Loop Recycling of Carbon Fiber-Reinforced Composites: A Dynamic Network Strategy Based on...

Developing sustainable high-performance composites is crucial for achieving circularity in advanced structural materials. Herein, we report a fully bio-based strategy for constructing recyclable carbon fiber-reinforced composites (CFRCs) based on dynamic non-isocyanate polyurethane (NIPU) matrices. Three cardanol-derived amine curing agents with tunable functionalities were rationally designed and synthesized from renewable cardanol, and subsequently reacted with lignin-derived cyclic carbonates (LCCs) to form a robust yet reprocessable NIPU network. Structure-property analyses reveal that the molecular architecture of the cardanol-derived curing agents governs the balance between network rigidity and flexibility, thereby tailoring the thermomechanical performance of the NIPUs. Optimizing carbonate structures and amine functionality yields polymers that combine high mechanical strength (tensile strength: 44.5 MPa) with excellent thermal and solvent resistance. The presence of hydroxyurethane linkages confers dynamic covalent character via reversible transcarbamoylation, imparting efficient reprocessability and pronounced multiple-shape-memory effects. Notably, the reprocessed NIPU retains >75% of its initial tensile strength after three hot-pressing cycles. As CFRC matrices, the optimized NIPU ensures outstanding interfacial adhesion and closed-loop recyclability, allowing solvent-assisted deconstruction to recover carbon fibers with nearly preserved mechanical integrity. This research establishes an eco-friendly and scalable approach to producing entirely renewable, recyclable and superior-performance composite materials for sustainable engineering applications.