Reprocessable, chemically recyclable, and flame-retardant biobased epoxy vitrimers

Conventional epoxy thermosets exhibit outstanding mechanical performances, excellent thermal and dimensional stabilities, and prominent resistances to chemical/solvent corrosions but are limited because they are dependent on fossil resources, cannot be reprocessed, and are not fire safe. Herein, we reported biobased, flame-retardant, reprocessable, and chemically recyclable epoxy thermosets synthesized with bio-based glycerol triglycidyl ether (GTE) as an epoxy monomer, vanillin derived imine compound as a hardener, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as a reactive fire-retardant agent. The curing kinetics investigation manifested that the curing reaction was activated with increasing DOPO content. The relationship between structure and properties of the vitrimers were studied in detail. The BEVs showed excellent physical properties with a tensile strength and glass transition temperature higher than 80 MPa and 100 °C, respectively. They possessed outstanding reprocessability and could be chemically recycled easily owning to the presence of the exchangeable imine bonds. The BEV with 6 wt% DOPO showed excellent fire resistance with a UL-94 V-0 rating and a LOI at 26.4% as well as much lower peak heat release rate and total heat release than the control vitrimer without DOPO. The BEVs with combination of excellent mechanical properties, reprocessability, chemical recyclability, and flame retardancy showed a bright future as an alternative to conventional epoxy thermosets for better sustainability and fire-safety.