Recent advances in recyclable thermosets and thermoset composites based on covalent adaptable networks

Recyclable thermosets and thermoset composites with covalent adaptable networks (CANs, or dynamic covalent networks) have attracted considerable attention in recent years due to the combined merits of excellent mechanical and thermal properties, and chemical stabilities of traditional thermosets and recyclable, remoldable, and reprocessable attributes of thermoplastics. In this paper, we present an overview of the current strategies for synthesizing recyclable thermosets based on CANs, which involve recyclability, reprocessability, and possible rehealability. The recent literature examples are categorized based on the underlying controlled-cleavable linkages such as transesterification, DA/retro-DA chemistry, imine bonds, disulfide metathesis, dynamic B-O bonds, hemiaminals/hexahydrotriazines, and acetal linkages. Various degradation and malleability methods and resulting mechanical properties of the recycled thermosets and thermoset composites are presented. The emerging applications of recyclable thermosets and thermoset composites, with emphasis on their usage in adhesives, biomedical materials, wearable devices, coatings, and 3D printing materials, are also illustrated. Finally, a perspective on the challenges and future perspectives is briefly summarized.