UV-Assisted Oxidation of Black Phosphorus Enables Green Upcycling of Epoxy Thermosets into Multifunctional Flame Retardant Vitrimers

The flammability and poor recyclability of epoxy thermosets present urgent challenges for sustainable polymer use. Flame retardant epoxy vitrimers offer a promising solution by addressing both issues simultaneously. However, conventional synthesis routes typically rely on complex procedures, catalysts, and solvents, and cannot process existing epoxy waste, limiting their sustainability. Here, we propose a fully solid-state, catalyst-free mechanochemical “waste-to-wealth” strategy to upcycle epoxy thermosets into flame retardant vitrimers. Black phosphorus (BP), synthesized via high-energy ball milling of red phosphorus, was subjected to UV-assisted controllable oxidation, with DFT calculations confirming the energy barrier was reduced by 16.35 kcal/mol under irradiation. The resulting oxidized BP (oBP), rich in P–OH groups, was employed for hot-pressing based vitrimerization of anhydride-cured epoxy waste. Through mixed transesterification, an organic–inorganic interfacial dynamic covalent network was constructed. The upcycled vitrimers exhibited remarkable dynamic adaptability with the lowest flow activation energy of 68.0 kJ/mol and the highest recycle efficiency of 89.3%, efficient infrared-triggered self-healing, and outstanding flame retardancy with V-0 rating in UL-94 test and limit oxygen index improved by 10%. Importantly, the oxidized structures of oBP were found to play a pivotal role in vitrimerization and to act synergistically with elemental phosphorus in enhancing fire resistance. This work provides new insights into the green upcycling of epoxy waste into multifunctional vitrimer composites, advancing both sustainability and performance.