Bio-based, selenium/Schiff base-containing co-curing agent enables flame-retardant, smoke-suppressive and mechanically-strong epoxy resins

Epoxy resins (EPs) have excellent overall properties, but their inherent flammability severely limits their industrial applications. Most existing flame-retardant methods rely on phosphorus-based compounds. However, they suffer from bioaccumulation and potential risks to ecosystems and human health. The development of safer and more sustainable phosphorus-free flame-retardant EP systems based on biomass is highly promising but challenging. Herein, a selenium/Schiff base-containing, bio-based flame retardant (SNC) has been successfully synthesized and applied as a multifunctional co-curing agent in EP. The resultant EP containing 15 wt% SNC (EP-SNC15) exhibits enhanced mechanical strength. Additionally, EP-SNC15 achieves a high limiting oxygen index (LOI) of 31.8 % and a vertical burning (UL-94) V-0 rating, and its peak heat release rate (PHRR) and total heat release (THR) decrease by 73.3 % and 56.3 % compared to EP, respectively. Therefore, the excellent flame retardancy and mechanical properties of EP-SNC15 make it superior to previously reported phosphorus-free flame-retardant epoxy systems. The improvement in flame retardancy is attributed to the synergistic catalytic carbonization of selenium-containing and Schiff base groups in SNC in the condensed phase and the free radical quenching of organoselenium groups in the gas phase. Therefore, this work provides a novel design strategy for the development of next-generation, flame-retardant and bio-based EPs. • A selenium/Schiff base-containing, bio-based flame retardant (SNC) is synthesized. • 15 wt% of SNC increases the LOI and UL-94 level of EP to 31.8 % and V-0. • 15 wt% of SNC increases the tensile strength of EP to 75.3 MPa. • Se-based and Schiff base groups act in gas and condensed phases during burning.