Preparation and properties of intumescent flame retardant thermoplastic polyurethane composites

Environmentally friendly intumescent flame retardant thermoplastic polyurethane (TPU) composites were prepared using ammonium polyphosphate (APP), melamine cyanurate (MCA) and boric acid as additives. The combustion, smoke suppression and thermal stability of the composites were characterized by a cone calorimeter and smoke density tests. The results show that this flame retardant greatly reduces the peak heat release rate by up to 80% and the total heat release and generates a compact char layer which effectively prevents volatile releases. The limit oxygen index (LOI) results show that this flame retardant increases the LOI. The TPU composites with the mass fraction of 15% APP, 2.5% MCA and 2.5% boric acid have the highest UL-94 level and LOI (32%). In addition, a thermal gravimetric analysis shows that the TPU composites have better thermal stability. APP, MCA and boric acid additives enhance the smoke suppression and flame retardant effects in the intumescent flame retardant TPU composites.