Effect of polyphosphate flame retardant compounded montmorillonite and ammonium polyphosphate on flame retardancy of epoxy resin

Abstract

<p indent=0mm>A new polyphosphate flame retardant, polyphosphate-2-10-hydrogen-9-oxa-10-phosphaphenanthrene-10-oxide hydroquinone p-tolyl ester (POTP), was successful synthesized by p-methyl dichlorophosphate acid phenyl ester and 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB). The chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (³¹P-NMR, ¹N-NMR and ¹³C-NMR). The POTP with ammonium polyphosphate (APP) and montmorillonite (MMT) was added to epoxy resin (EP) for Flame retardant modified. The flame retardancy and thermal performance of epoxy composites were investigated by vertical burning (UL-94), limiting oxygen index (LOI), thermal weight loss (TGA), cone calorimetry (CONE) and scanning electron microscope (SEM). The results showed that epoxy composites obtained a UL<sc>-94 V-0</sc> grade when 5% flame retardant added. When the added amount of flame retardant was increased to 9%, a higher LOI value of 27.6% can be achieved. The cone test showed that the residual carbon content was as high as 29%, and the peak of heat release rate (Pk-HHR) and total heat release (THR) decreased by 41.7% and 31.1%, respectively. The thermal stability and flame retardant properties of flame retardant EP at high temperatures have been improved. The morphology of residual carbon after the CONE test shows that flame retardant EP forms a more stable and dense expanded carbon layer at high temperature. Its carbon structure can isolate the exchange of combustible gas and air, and effectively inhibit the release of toxic gases in the flue gas.