Multifunctional TP-P-Co-MOF for epoxy resins: Simultaneously achieving flame retardancy, smoke suppression, and mechanical reinforcement

The design of low-smoke and low-toxicity epoxy resin (EP) composite materials remained a significant challenge. In this study, a multifunctional MOF-based flame retardant (TP-P-Co-MOF) was synthesized using ZIF-67 as the framework via a three-step modification process. TP-P-Co-MOF incorporated Schiff base-conjugated structures, Co P synergistic flame-retardant sites, and a porous architecture, while exhibiting excellent compatibility with EP. At a 4 wt% loading, the EP/TP-P-Co-MOF composite attained a UL-94 V-0 classification and an LOI of 31.3%. Additionally, in comparison with EP, the EP/TP-P-Co-MOF composite exhibited marked reductions in the peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR), and total smoke production (TSP), which decreased by 43.1%, 14.9%, 64.0%, and 52.6%, respectively, thereby demonstrating outstanding flame-retardant efficiency and toxic-smoke suppression performance. Investigation of the flame-retardant mechanism indicated that TP-P-Co-MOF not only significantly improved the quality of the graphitized carbon layer in EP, but also reduces the concentration of combustible gases, thereby exerting synergistic flame-retardant effects in both the condensed and gas phases. With respect to mechanical properties, the incorporation of TP-P-Co-MOF improved both the toughness and strength of the EP. The tensile strength and impact strength increased by 11.1% and 24.7%, respectively, in comparison with neat EP. This study provided a promising strategy for developing highly efficient MOF flame retardants while offering a novel approach to designing low-smoke, low-toxicity flame-retardant EP.