Molecular dynamics insights into Ti₃C₂ MXene/chitosan composite as a flame-retardant barrier

Abstract

Two-dimensional Ti3C2 MXenes exhibit remarkable thermal stability and flame resistance, while hybridisation with bio-based chitosan (CS) enhances their effectiveness as flame-proof coating. However, the underlying flame-retardant (FR) mechanisms remain insufficiently resolved at the atomistic scale. Herein, reactive molecular dynamics simulations (MD-ReaxFF) alongside experiments (TGA-FTIR, SEM, XRD, XPS) elucidate the FR pathways of MXene/CS nanosheets. MXene/CS exhibits flame retardancy through three synergistic pathways: (1) releasing organic volatiles to dilute oxidisers; (2) depositing hydroxyl and nitrogen groups to passivate reactive sites; and (3) reinforcing char formation by strengthening C-C and Ti-C bonding. Multilayer MXene/CS coatings exhibit sequential FR behaviour, where sacrificial TiO2 layers, interlayer carbonisation, and volatile exclusion collectively maintain structural stability under extreme heating. Experimental validation confirms the organic volatiles, enhanced char yield, TiO2 transformation, and surface functionalisation. These insights establish a mechanistic framework for MXene-based hybrids and highlight CS as a sustainable charring agent, offering design principles for future lightweight and multifunctional flame-retardant coatings.