Green Synthesis of Biomass Phytic Acid-Functionalized UiO-66-NH₂ Hierarchical Hybrids toward Fire Safety of Epoxy Resin

A phosphorus abundant biomass phytic acid (PA)-functionalized metal-organic framework (MOF) UiO-66-NH₂ (PA-UiO66-NH₂) was synthesized successfully as a novel fire retardant (FR) to reduce fire hazards and suppress smoke for the epoxy (EP) resin. The complexing and salt formation reaction between phosphate groups and both Zr species or amine groups on UiO-66-NH₂ were verified by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The EP/5PA-UiO66-NH₂ sample exhibited excellent fire retardancy and toxic gases suppression property with a 41% decrease in the peak heat release rate and a 42% reduction in total smoke production. The slightly modified thermal degradation path of the EP/5PA-UiO66-NH₂ sample was evidenced by means of pyrolysis gas chromatography-mass spectrometry, which led to the reinforced char with a strong barrier and a higher polyaromatic structure. Moreover, the amine and phosphorus groups may react with EP, thus providing a better interfacial strength between FRs and EP matrix. Therefore, the enhanced mechanical property was also observed by dynamic mechanical analysis with a light increment of storage modulus (8%). In perspective, functionalization of MOFs to modify the thermal decomposition of FR may provide a possible way for MOFs to become efficient FRs.