Sub-atmospheric pressure environment enabled flame-retardant MXene-Al2O3 nanohybrid for polyethylene composites

Low-pressure environments significantly compromise the performance of conventional intumescent flame-retardant systems by accelerating ignition and inducing excessive yet fragile char expansion, which easily cracks and compromises its protective function. To overcome these challenges, MXene has attracted considerable attention due to its ability to promote char layer formation and serve as an effective physical barrier. In this work, a novel flame-retardant PE composite was developed by incorporating a silane-coupling-agent-modified Al₂O₃-supported MXene nanohybrid (MXene@Al₂O₃). The nanohybrid exhibited uniform morphology, strong interfacial bonding, and excellent dispersion within the PE matrix, significantly reducing the fire risk of PE under sub-atmospheric conditions. With only 1 wt% of MXene@Al₂O₃, the composite achieved a 26.9 % and 31.8 % reduction in peak heat release rate and total heat release, respectively, along with a 25.9 % decrease in maximum smoke density and significant suppression of carbon monoxide evolution. Under reduced pressures (55–99 kPa), the system formed more graphitized and compact char layers, demonstrating enhanced thermal stability and suppressed volatile release. Mechanistic insights obtained via synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) revealed a shift from oxygen-driven oxidation to condensed-phase carbonization under low pressure. These improvements are attributed to the early char templating and barrier-forming capabilities of MXene, while Al₂O₃ contributes by catalyzes carbonization reactions and suppresses smoke precursors. This work demonstrates a pressure-adaptive flame-retardant strategy for polyolefin materials and offers theoretical guidance for designing next-generation nanohybrid flame-retardant systems for sub-atmospheric pressure environments.