Organophosphate-intercalated high-entropy LDHs for high-performance fire-safe thermoplastic polyurethane composites

Polymer materials pose significant fire hazards, including rapid heat release and the emission of toxic smoke. Herein, we report a flame-retardant thermoplastic polyurethane (TPU) composite engineered with organophosphonic acid-intercalated high-entropy layered double hydroxides (HE-LDHs), achieving synergistic flame retardancy, smoke suppression, and mechanical enhancement. Meanwhile, tensile strength was enhanced to 38 MPa. The NiCoFeAlZn/DPA/TPU system demonstrated 42.1 % reduction in peak heat release rate (pHRR), 48.5 % decrease in total smoke release (TSR), and 36.4 % decrease in CO production rate compared to pure TPU, attributed to a hierarchical flame-retardant mechanism involving gas-phase dilution, physical barrier formation, and catalytic charring. The synergistic effect of multi-metal components of HE-LDHs and the intercalation (diphenylphosphoric acid, phenylphosphinic acid) agents restructured the thermal decomposition pathway of the material. Early-stage fire warning through HE-LDHs decomposition of interlayer water and organic acid anions releases CO₂/H₂O to dilute flammable gases; Intermediate flame inhibition through HE-LDHs catalyze dehydrogenation crosslinking of TPU, capture by PO· radicals from phosphonates, effectively suppressing flame propagation; High-temperature protection through collapse of LDH layers generates metal oxides and phosphorus-carbon hybrid barriers, triggering endothermic phase transitions, with an increase in the amount of residual carbon. This work establishes a theoretical framework for regulating the structure-property relationship of HE-LDHs and pioneers an integrated, active-passive design for fire-safe, high-risk polymer applications.