In situ interfacial assembly of P-MXene@COF hybrids for flame-retardant and smoke-suppressive epoxy resin

Abstract

Epoxy resin (EP) is intrinsically flammable and generates dense smoke and toxic gases during combustion, which severely restricts its application in fire-sensitive environments. In this work, an in situ interfacial assembly strategy was developed to construct a P-MXene@COF hybrid, where covalent organic framework (COF) layers were grown on amino-functionalized MXene nanosheets and subsequently integrated with phosphorus species. At a low loading of 3 wt%, EP/P-MXene@COF maintained satisfactory mechanical performance, while achieving remarkable fire safety. The limiting oxygen index (LOI) reached 27.2%. Cone calorimetry revealed substantial reductions in combustion intensity, with the peak heat release rate (pHRR) and total heat release (THR) decreased by 43.4% and 22.2%, respectively. Moreover, smoke and toxic gas emissions were effectively suppressed, as reflected by a 22.6% reduction in the peak smoke production rate and a 44.8% decrease in the CO₂ release rate. Char residue analyses confirmed the formation of a compact, highly graphitized phosphorus-rich protective barrier, while TG-FTIR demonstrated significant inhibition of volatile evolution. These results indicate that the synergistic integration of P/N-containing COF layers with Ti-based MXene, combining gas-phase radical quenching, inert-gas dilution, and condensed-phase catalytic charring, endows EP/P-MXene@COF with superior flame retardancy and smoke suppression. This study provides new insights into the scalable design of multifunctional flame-retardant fillers for epoxy composites.