Thermal Behaviours of Ammonium Polyphosphate-Pentaerythritol and Ammonium Pyrophosphate-Pentaerythritol Intumescent Additives in Polypropylene Formulations

Abstract

The comparative study of the intumescent formulations (poly propylene-ammonium polyphosphate-pentaerythritol) and (polypropylene- ammonium pyrophosphate-pentaerythritol) shows that the highest fire retar dance property of the second system may be related to the existence of a protective carbonaceous coating stable in the temperature range 300-550°C. Comparatively, the stability of the carbonaceous coating on the first system is only observed between 300 and 420°C. A 31P N.M.R. study shows the presence (in the carbon-based layers) of acidic phosphate species (Lewis acids) which result from the thermal degradation of the additive mixtures. In the particular case of (PP-PPA-PER), these species degrade at 420 ° C to give phosphorus oxide. The study reveals that, with (PP-PY-PER), an additional protective char (stable in the temperature range 420-550°C) is formed by a reaction between the Lewis acids and the oxidized products of the thermo-oxidative degradation of the polymer.