Recyclable Thermoset Polymer Composites Based on Degradable and Dynamic Covalent Chemistry

Structural polymer composites for high-performance applications are amongst the most difficult materials to recycle effectively. It is foreseen that the end-of-life scenario of materials and products will have an increasingly more prominent role in material selection. Therefore it is crucial that circular recycling solutions are developed for both the resin and the fibrous/particulate phase of thermoset composite materials. In achieving this goal, thermosets with degradable or dynamic covalent bonds can fulfill an important role as they allow for a certain mobility of the matrix phase. The inclusion of these bonds theoretically allows for the effective separation of the different composite phases. These recyclable thermosets can be subdivided into degradable, associative and dissociative systems based on the molecular linkages that facilitate the stimuli-triggered recycling process. This article will highlight the most illustrative and advanced examples of the different types of recyclable thermoset composites developed throughout the years. In order to contribute to a circular material economy it is important that the thermoset resins are developed from renewable resources. Therefore special attention is given to composite matrices that are (partially) biobased and the chemical pathways that are required to synthesize them.