A novel flame-retardant modification strategy for UiO66-NH₂ by encapsulating triethyl phosphate: preparation, characterization, and multifunctional application in poly (lactic acid)

This work reports a strategy to improve the flame-retardant efficiency of metal organic frameworks (MOFs). Herein, triethyl phosphate (TEP) was in situ encapsulated into the cavity of a zirconium-based MOF (UiO66-NH₂) to prepare a compound flame retardant UiO@TEP_x. The morphology, composition, crystal, and pore structure of UiO@TEP_x were fully characterized. The introduction of UiO@TEP₅₀ significantly improved the flame retardancy of poly (lactic acid) (PLA). The presence of 2% UiO@TEP₅₀ upgraded the UL-94 level to V-0, improved the limiting oxygen index value to 24.2%, reduced the total smoke production by 29.5%, and decreased the peak heat release rate by 14.2% compared with that of the control PLA sample. The ‘thermosensitive release’ flame-retardant mechanism was proposed and porous smoke suppression function was demonstrated. Besides, PLA composites also showed excellent mechanical properties and apparent anti-UV effects. The tensile strength was increased to 59.7 MPa from 50.5 MPa, and the UV radiation transmittance was decreased to 6.4% from 71.3% compared with that of PLA. This work provides a novel flame-retardant modification strategy for encapsulating TEP into MOFs, which has not been reported so far.