Enhanced flame-retardant effect of a montmorillonite/phosphaphenanthrene compound in an epoxy thermoset

A phosphaphenanthrene and triazinetrione group containing flame retardant (TAD) is combined with organically modified montmorillonite (OMMT) in epoxy resin thermosets (EP) to improve the performance of the flame-retardant system. When only 1 wt% OMMT/4 wt% TAD is introduced into the EP, the limited oxygen index (LOI) rises from 26% to 36.9% and a V-0 rating is achieved in a UL 94 test. The decomposition and pyrolysis products in the gas phase and condensed phase were characterized using thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR). The influence on the decomposition of EP, such as the increase in char yield, is limited with the incorporation of OMMT; a large amount of the phosphorus is released into the gas phase. The flame-retardant effect evaluation based on cone calorimeter data testified that OMMT improves the protective-barrier effect of the fire residue of OMMT/TAD/EP on the macroscopic scale, while TAD mainly causes flame inhibition. The fire residues showed a corresponding macroscopic appearance (digital photo) and microstructure (scanning electron microscope [SEM] results). The protective barrier effect of OMMT and the flame-inhibition effect of TAD combined to exert a superior flame-retardant effect, resulting in sufficient flame-retardant performance of OMMT/TAD/EP.