Tannic acid-etched ZIF-8 encapsulating phosphorus-containing ionic liquid for synergistically enhancing the fire retardancy and smoke suppression of thermoplastic polyurethane

A facile and eco-friendly strategy was developed to synthesize IL@MOF hybrid FR. • The optimized composite achieved a UL-94 V-0 rating with a LOI value of 27.1%. • The peak heat release rate and total smoke production were reduced by −76.1% and −83.1%. • The reaction to fire and its underlying mechanisms were systematically characterized. The deployment of thermoplastic polyurethane (TPU) in high-safety applications is critically hindered by its inherent flammability and the emission of toxic smoke during combustion. To address these limitations, this study proposes a new strategy driven by structural engineering and spatial confinement. Specifically, a zeolitic imidazolate framework-8 (ZIF-8) precursor was selectively etched using an eco-friendly tannic acid to engineer a mesoporous host architecture (TZIF-8). By encapsulating a bespoke phosphorus-containing ionic liquid (PMDP) within these tailored cavities, a highly efficient inorganic-organic hybrid (PM@TZ) was synthesized. It was subsequently compounded with piperazine pyrophosphate (PAPP) to construct a synergistic fire-protection network within the TPU matrix. The optimized composite (incorporating 6.5 wt% PAPP and 1.5 wt% PM@TZ) demonstrated excellent flame retardancy, achieving a UL-94  V -0 rating alongside a limiting oxygen index (LOI) of 27.1%. Forced-flaming evaluations confirmed dramatic reductions in the peak heat release rate (−76.1%), total heat release (−62.1%), and total smoke production (−83.1%) relative to the TPU. Mechanistic investigations across the volatile and condensed phases elucidated a robust synergic reaction to fire. The liberation of active phosphorus radicals facilitates profound gas-phase flame quenching, whereas the confined ionic liquid and MOF-derived catalytic zinc nodes cooperatively accelerate the formation of a highly graphitized, heteroatom-doped (P/Zn) char barrier. In summary, this study provides a versatile structural engineering route for resolving the interfacial incompatibilities of ionic liquids, paving the way for next-generation, high-performance, fire-safe elastomers. Download: Download high-res image (170KB) Download: Download full-size image