Flame retardancy of ammonium polyphosphate–montmorillonite nanocompounds on epoxy resin

Ammonium polyphosphate–montmorillonite nanocompound was used to retard epoxy resin with a comparison to the physical mixture of ammonium polyphosphate and montmorillonite. The thermal decompositions of the epoxy resin composites were investigated by thermal gravimetric analysis. The flame retardancy of epoxy resin composites was studied by limited oxygen index measurements, UL-94 testing, and cone calorimeter test. The ammonium polyphosphate–montmorillonite nanocompound shows better flame retardancy (limited oxygen index, UL-94, time to ignition, peak of heat release rate, etc.) than the ammonium polyphosphate + montmorillonite mixture. The morphology of epoxy resin composites is studied by scanning electron microscopy. The ammonium polyphosphate and montmorillonite intimately mixed or pre-reacted give a reaction that quickly helps to form char during burning, whereas in the ammonium polyphosphate + montmorillonite mixture, the ammonium polyphosphate particles and montmorillonite particles are separated in the epoxy resin matrix, the polymer burns away before ammonium polyphosphate and montmorillonite can interact with one another. The quickly effective char layer formation should be the main reason that the ammonium polyphosphate–montmorillonite nanocompound shows better flame retardancy than the ammonium polyphosphate + montmorillonite mixture.