Synergistic flame retardant effect of aluminum hydroxide and ammonium polyphosphate on epoxy resin

Abstract Epoxy resin is an attractive traditional thermoset that is widely used in a variety of applications. And its flammable problem has drawn an increasing number of researchers to solve it. As flame retardants, ammonium polyphosphate (APP) and aluminum hydroxide (ATH) were mixed in the epoxy matrix to create composites with an interesting synergistic flame retardant effect, and its mechanism were thoroughly investigated. When 10 wt% APP and ATH were added at a mass ratio of 3/1, the peak of heat release rate and total heat release were reduced by 48% and 38%, with a LOI of 28.9% and a UL‐94 of V‐0 rating. During the combustion process, polyphosphoric acid formed by the decomposition of APP could catalyze matrix decomposition to form a charring barrier and react with alumina formed by the decomposition of ATH to produce extremely stable aluminum metaphosphate, which covered the surface of burning matrix and hampered further combustion.