Study of the mechanism of intumescence in fire retardant polymers: Part V—Mechanism of formation of gaseous products in the thermal degradation of ammonium polyphosphate

On heating, ammonium polyphosphate eliminates ammonia and water in two successive steps. The first (T = 165–280°C) involves a limited weight loss (ca. 3%) and the formation of some branched structures. The transition from one crystalline form of ammonium polyphosphate to another, more stable, form, may prevent further elimination of NH3 and H2O which occurs in the second step (T > 280°C). The final product of degradation is characterised by a crosslinked POP structure formed by elimination of H2O between POH groups freed by the evolution of NH3.