Evaluation of the thermal degradation and cone calorimeter parameters of an intumescent composite containing acidic montmorillonites

This work evaluates the effects of the acidity of montmorillonites on the thermal degradation process and in the cone calorimeter parameters of an intumescent composite constituted by polypropylene, ammonium polyphosphate (APP) and pentaerythritol (PER). The cone calorimeter tests showed that the absence of moderate-strength acidic sites is related to the increase in the peak of heat release rate. The composites were burnt at different key-temperatures and the residues were submitted to Fourier transform infrared spectroscopy, Solid State Nuclear Magnetic Resonance Spectroscopy and to X-ray diffraction. The results showed that the addition of the clay minerals is important to preserve the char at higher temperatures (over 430 °C) and that an excess of Brønsted sites over the Lewis ones with moderate-strength could lead to the increase of the esterification reactions between PER and APP. Besides, the addition of the clay minerals did not affect the mechanical properties of the composites.