High-Performance, Closed-Loop Recyclable Polyimine Elastomers Based on Covalent Adaptive Networks for Polyimine/Carbon Fiber Elastomeric Composites

Thermoset composites are essential in modern engineering yet suffer from an intrinsic lack of recyclability due to their permanently cross-linked structures. Herein, we report a series of biobased thermoset polyimine elastomers with intrinsic self-healing and closed-loop recyclable properties, which were further employed as a polymer matrix for polyimine/carbon fiber elastomeric composites. The synthesized PIm-TFBx elastomers exhibited excellent mechanical properties (tensile strength up to 2.8 MPa and an elongation at break of 123%) and room-temperature self-healing, achieving a healing efficiency of 92.9% within 24 h at room temperature. All-atom molecular dynamics simulation models were constructed for different elastomers, providing molecular-level insight into the nonlinear dependence of tensile strength on cross-linking density and imine bond exchange in covalent adaptive networks (CANs). More importantly, the elastomers demonstrated efficient closed-loop recyclability under mild conditions, with recycled samples retaining over 92.9% of their original tensile strength and nearly unchanged Tg and cross-linking density. When employed as matrices, these polyimine/carbon fiber elastomeric composites achieve a tensile strength of 10.4 MPa and maintain over 90% of their original strength after five recycling cycles, which is accompanied by the high-yield recovery of intact carbon fiber. This study combines experiments and molecular simulations to elucidate the structure–property relationships of imine-based CANs, offering a sustainable pathway for advanced recyclable thermosets.