Synergistic flame retardant behavior and mechanism of based on DOPS/triazine-trione groups flame retardants in epoxy resins

Abstract Epoxy resin (EP), as a widely used polymer material, is inherently flammable. Bestowing it with high-efficiency flame-retardant properties has always been the focus of attention. Herein, Using triallyl isocyanurate (TAIC) and 9,10-dihydro-9-oxa-10-phospha phenanthrene-10-sulfide (DOPS) as raw materials, a novel bismaleimide flame retardant, tris(3-(9,10-dihydro-9-oxa-0-phosphaphenanthrene-10-sulfide)-propyl)triazine-2,4,6-trione(DOPS-TAIC), was synthesized via a one-step method. Before curing, the structure was characterized using FT-IR, ¹H NMR, and ³¹P NMR. Subsequently, the flame retardant DOPS-TAIC was applied to EP, and a series of testing methods were employed to investigate the effects of DOPS-TAIC on the thermal stability, flame retardancy, and mechanical properties of EP. Furthermore, the flame retardant mechanism of DOPS-TAIC in the gas phase and condensed phase was further explored. The results showed that EP/DOPS-TAIC achieved UL-94 V-0 rating with an LOI value of 31.6% when added at 12.5 wt%. In addition, the total heat release (THR), peak heat release rate (PHRR), and average heat release rate (av-HRR) of EP/DOPS-TAIC-12.5 wt% were significantly reduced by 35.05%, 61.83%, and 51.68%, respectively. The SEM-EDS results indicate that DOPS-TAIC can form a more complete and dense char layer, with a higher phosphorus content in the char layer. Meanwhile, TG-IR and Py-GC/MS demonstrate its radical quenching effect in the gas phase, indicating that DOPS-TAIC possesses both condensed-phase and gas-phase flame-retardant mechanisms. Therefore, this study provides a simple and effective method for developing flame-retardant epoxy resins.