Triethanolamine-Mediated Covalent Adaptable Epoxy Network: Excellent Mechanical Properties, Fast Repairing, and Easy Recycling

Early epoxy vitrimers in the literature rely on an inequivalent epoxy/anhydride stoichiometry and a large amount of catalyst to achieve a decent transesterification rate within the crosslinked network. This design approach raises a number of concerns such as poor miscibility of the catalyst with other ingredients, poor mechanical properties owing to insufficient crosslinking, the toxicity of the catalyst, etc. In this study, a hydroxyl-amine compound, triethanolamine (TEOA), is incorporated as a catalytic co-curing agent to a typical BPA epoxy-cyclic anhydride curing system to give a TEOA-mediated covalent adaptable network system. The hydroxyl groups and tertiary amine of TEOA catalyze the curing process, and the tertiary amine and the regenerated hydroxyls in the crosslinked network accelerate dynamic transesterification. The resulting epoxy vitrimer exhibits a high glass transition temperature (similar to 135 degrees C), excellent tensile strength (similar to 94 MPa), and fast repairing rate (10 min at 190 degrees C). Recycling of the TEOA-mediated epoxy vitrimer and reuse of the recyclate are also studied. In an experiment, the vitrimer is ground into powder, and in another, it is degraded in an aqueous solution. The recyclates collected from both experiments are incorporated into the fresh resin, and the new vitrimer materials exhibited similar T(g)s and moduli to that of original vitrimer samples. This work provides a solution to eliminate the performance gap between conventional epoxy and epoxy vitrimer and offers simple recycling methods of epoxy vitrimer for new epoxy.