Diels-Alder Macromolecular Networks in Recyclable, Repairable and Reprocessable Polymer Composites for the Circular Economy - A Review

In the expanding field of high-performance materials, polymer-based thermoset composites play an important role due to their favorably-high strength/weight ratio and their mechanical performance, thermal stability, and chemical resistance. However, their chemically-crosslinked nature hampers their re-processability and efficient recyclability, thus making them not compliant with the principles of the circular economy and of end-of-life valorization. Dynamic covalent polymers able to modify their network topology upon thermal stimulus can be considered valid alternatives to commonly used thermosets as they offer advantages in terms of recyclability and reusability, normally not achievable with conventional cross-linked systems. Within the broad field of dynamic polymers, thermally-triggered Diels-Alder based materials represent reliable platforms with enormous technological and industrial potential as repairable, reusable and recyclable matrices in composites given their chemical versatility, suitable mechanical performance and ease of production and processing. In this review, a comprehensive discussion of the most recent demonstrations of the reversibility, reprocessability and recyclablability of such systems is provided, in the context of their use as polymer matrices in composites. It is hoped that this work will stimulate further discussion and research in the area of reversible polymer composites with increased functionality and extended lifetime, in view of their application in future circular economy scenarios.