Multifunctional epoxy/P-N Co-modified MXene composites: Achieving concurrent toughening, flame retardancy and self-alarm functionality via interfacial engineering

The development of advanced epoxy resin (EP) composites that simultaneously integrate mechanical toughness, flame retardancy, and early fire-warning functionality represents a challenge for safety-critical engineering applications. To overcome these limitations, this study designed a multifunctional EP/HMN-MXene system through the incorporation of phosphorus-nitrogen (P-N) co-modified MXene (HMN-MXene) into EP matrix. This innovative material was fabricated by first synthesizing a water-soluble P-N compound (HMN) via nucleophilic substitution reaction, subsequently grafting it onto hydroxylated Ti 3 C 2 T x MXene, and finally introducing the resulting HMN-MXene into EP precursors to yield a composite exhibiting a remarkable negative temperature coefficient (NTC) effect, significantly enhanced toughness, and exceptional flame retardancy. The EP/HMN-MXene system demonstrates three distinct advantages: the synergistic combination of phosphorus-nitrogen-rich HMN with MXene's catalytic charring effect improves both thermal stability and flame retardancy, the unique wrinkled morphology of HMN-MXene effectively deflects crack propagation, resulting in toughness improvement compared to pure EP, and the intrinsic NTC effect of MXene enables rapid resistance response to temperature at 100 °C (∼1.25 s) and direct flame exposure for fire-warning activation. Furthermore, the system exhibits excellent ambient-temperature curing behavior, achieving rapid gelation within approximately 20 min. These combined functionalities position EP/HMN-MXene as a promising candidate for demanding safety-critical applications requiring multifunctional performance.