Preparation of bimetallic zeolite-imidazole framework and its synergistic flame-retardant application in thermoplastic polyurethane

The development of advanced flame-retardant polymer composites is crucial for enhancing safety in new energy vehicles. Here, we prepared a composite material with excellent flame retardant and smoke suppression properties by the introducing zinc-molybdenum zeolite imidazolium framework (ZIF-ZnMo) and ammonium polyphosphate (APP) into the thermoplastic polyurethane (TPU) matrix, which was denoted as TPU/APP/ZIF-ZnMo. Compared to the pure TPU material, the introduction of 0.5 wt% ZIF-ZnMo significantly reduced the key fire parameters. Among them, peak heat release rate (PHRR), peak smoke production rate (PSPR), and CO₂ yield evidenced by remarkable reductions of 71.8 %, 29.7 %, and 74.3 %, demonstrating excellent flame suppression and smoke reduction capabilities. The composite exhibits a 3.4-fold increase in char residue compared to pure TPU, attributed to the synergistic catalytic carbonization between ZIF-ZnMo and APP. Mechanistic studies reveal a dual-phase flame inhibition mechanism: (1) gas-phase radical quenching through phosphorus-containing species and (2) condensed-phase barrier formation via cross-linked phosphorus-zinc-molybdenum networks. This layered protection system effectively isolates oxygen, combustible gases and heat transfer, providing a promising strategy for producing safer materials for new energy vehicles. In addition, it expands the application of metal–organic frameworks in the field of polymer flame retardancy.