A polyphosphazene – iron – nitrogen – organic hybrid at 1% in epoxy passed UL94-V1. The polyphosphazene was combined with iron 2-methylimidazole metal–organic framework (Fe–MOF) then mixed into epoxy (DGEBA). 1% loading of the hybrid PIN FR achieved UL94-V1 @ 3 mm (but 3% achieved only V2 due to poorer dispersion). At 1% loading, LOI (limiting oxygen index) increased from 26 (pure epoxy) to 30 and peak smoke production rate (SPR) was reduced by around one third. The authors suggest that the FR effect is result synergies generating compact ceramified char.
“Polyphosphazene‑wrapped Fe–MOF for improving flame retardancy and smoke suppression of epoxy resins”, L. Sang et al., J Therm Anal Calorim (2020) https://doi.org/10.1007/s10973-020-09481-6