A Mxene-Reinforced Chitosan-Gelatin Adhesive “Brick-and-Mud” System Inspired by Nacre for Fire-Resistant High-Performance Wood Composites

Inspired by the “brick-and-mud” structure of nacre, this study successfully prepared a biomass-based composite adhesive, GMCS@MXene, through a biomimetic design strategy. The material features rigid MXene nanosheets as the “bricks” and a flexible chitosan-gelatin hybrid network as the “mud”, constructing a multilevel structure with excellent interfacial compatibility via a three-step synthesis method. The incorporation of only 0.8 wt % MXene resulted in a synergistic enhancement of multiple performance metrics. Unlike conventional polymer-MXene blends that rely on simple physical mixing, this nacre-mimetic “brick-and-mud” architecture achieves a previously unattainable balance between ultralow filler loading and high flame-retardant efficiency. Compared to the unmodified system, the plywood exhibited substantially improved shear strength, achieved a V-0 classification in the UL-94 vertical burning test, and demonstrated an increased limiting oxygen index of 28.8%. Furthermore, total smoke production was reduced by 68.2%. Mechanistic investigation elucidated the dual role of MXene during combustion. On the one hand, MXene catalyzed the polymer matrix to form a compact and protective char layer. On the other hand, thermal oxidation of MXene generated nanoparticles that became embedded within the char layer, thereby reinforcing its structural integrity and enhancing its barrier properties. This work proposes a plausible dual flame-retardant pathway of MXene featuring promoted carbonization and nanoscale char reinforcement, while also providing insights for developing formaldehyde-free, inherently flame-retardant, eco-friendly wood adhesives.