Bio-based Ti₃C₂T_x/NiCo layered double hydroxides/sodium lignosulfonate system for multifunctional EVA composites: ultra-efficient fire safety and solar-to-thermal conversion

To overcome the inherent flammability and excessive smoke emission of ethylene vinyl acetate (EVA), this study innovatively designed a heterogeneous flame retardant system based on Ti₃C₂T_x, nickel-cobalt layered double hydroxides (NiCo LDHs), and sodium lignosulfonate (LS). This system achieves high-efficiency flame retardancy in EVA through multicomponent synergistic effects. By leveraging the anti-agglomeration properties of metal-organic frameworks (MOFs), NiCo LDHs nanosheets were uniformly anchored onto Ti₃C₂T_x surfaces and interlayers. Simultaneously, LS modification enhanced hydrophobicity (water contact angle increased from 21.7° to 63.4°), effectively resolving interfacial incompatibility issues in the EVA matrix. The renewable LS component not only replaced toxic halogenated additives but also synergized with transition metals to catalyze the formation of a dense, graphitized carbon layer during combustion. This enabled dual-phase flame inhibition via radical quenching and physical barrier effects. At a low loading of 5 wt%, the composite exhibited exceptional fire safety performance: a limiting oxygen index of 28.6 %, UL-94 V-0 rating, and reductions in peak heat release rate (26.9 %), peak smoke production rate (29.3 %), and total smoke production (13.4 %). The char residue increased 4.1-fold compared to Neat EVA. Additionally, the composite demonstrated efficient photothermal conversion capabilities, indicating suitability for applications in intelligent fire protection. This work establishes a sustainable, scalable paradigm for designing high-performance flame-retardant polymers.