Phosphonate-influenced Diels-Alder chemistry toward multi-path recyclable, fire safe thermoset and its carbon fiber composites

Dynamic covalent chemistry offers a solution to tackle the recycling issue of epoxy resins (EPs) and their carbon fiber-reinforced composites; however, the vulnerability to creep associated with the inflammable nature of the EPs are the key obstacles for their applications. Herein, we propose a feasible and facile strategy to overcome these obstacles by incorporating phosphorus-influenced Diels-Alder (DA) chemistry to construct dynamic epoxy networks. In the strategy, the electron-withdrawing phosphonate in the dienophile maleimide greatly promotes the thermal stability of the DA reaction, exhibiting excellent creep resistance, repairability, and malleability; while its flame-retardant activity improves the fire safety of the resultant thermosets. Meanwhile, nondestructive recycling of carbon fiber is achieved. The ease with which EP and its composites can be manufactured, used, recycled and re-used–without losing service performance–points to new orientation in sustainable composites.