Robust and fire-safe thermoplastic polyurethanes via guest–host confinement in bio-derived metal–organic frameworks

The development of sustainable, multifunctional flame retardants that do not compromise the inherent mechanical properties of polymers remains a formidable challenge. Herein, we report a novel guest–host architecture engineered by encapsulating a flame retardant (PCU) within a bio-derived metal–organic framework (Bio-MOF) to fabricate robust, fire-safe thermoplastic polyurethanes (TPU). The resultant PCU@BioMOF nanocomposite exhibits exceptional fire retardancy at a low loading of 6 wt%, achieving a UL-94 V-0 rating, a limiting oxygen index (LOI) of 28%, and remarkable reductions in peak heat release rate (62.3%) and total heat release (51.1%).Mechanistically, this molecular confinement promotes synergistic gas- and condensed-phase interactions, facilitating robust char formation to extinguish combustion and drastically suppress smoke production (38.6% reduction). Crucially, bypassing the traditional trade-off between fire safety and mechanical performance, the PCU@BioMOF acts as a multifunctional nano-reinforcement. It simultaneously enhances the tensile strength of the TPU by 16.2% (at 2 wt% loading) while imparting excellent UV-shielding capabilities. This molecular encapsulation strategy provides a highly efficient, sustainable platform for designing next-generation, multifunctional polymer nanocomposites.