Novel Recycling of Epoxy Thermosets by Blending with Reversible Diels–Alder Epoxy Resin

The introduction of Diels–Alder (D-A) bonds into epoxy resins is a promising pathway to convert these unrecyclable materials into sustainable materials. However, D-A bonds make epoxy resins extremely brittle materials and hinder their practical usability. Nonetheless, the reversibility of D-A bonds allows the transition of the material to a de-crosslinked network formed by separated oligomers that can melt above 90–100 °C. This means that D-A epoxy resins can be reprocessed after being cured like thermoplastics. In the present work, a thermoset blend is made by adding spent epoxy particles to a D-A epoxy resin to increase its thermal and mechanical properties and to evaluate a possible reuse of conventional thermoset wastes. The application of hot-pressing to a mixture of epoxy particles and powder of cured D-A epoxy creates a material in which the interaction of the particles with the D-A resin increases the thermal resistance of the material and prevents the D-A epoxy from melting at high temperatures. In addition, the flexural strength is increased by 80% and the chemical resistance against organic solvents is also improved.