Reprocessable and Degradable Siloxane Epoxies and Their Applications in Green Composites

Degradable thermosetting materials provide a promising solution to the recycling challenges associated with solid waste of conventional thermosets and their composites. In this study, three degradable epoxy monomers are synthesized for the first time by incorporating flexible and thermally stable siloxane chains through a hydrosilylation reaction. All three reprocessable siloxane epoxies (RSEs) demonstrate self-healing, reprocessability, and degradability using a cheap and environmentally friendly solvent, which made possible the 100% recycling of flax fibers. Considering viscosity, thermal stability, self-healing and degrading rate, mechanical property and retention of mechanical property after reprocessing, and, more importantly, cost, RSE-1 was found to have the optimum overall performance. Reprocessed RSE-1 retained 92.85% of its original strength. RSE-1 composites reinforced by silane-treated recycled flax fiber retained 88.74% of the strength of the original flax/RSE-1 composites. The results of this study suggest a promising strategy for the fabrication of environmentally friendly and recyclable green composites.