Heat Transfer Study of Polypropylene-Based Intumescent Systems during Combustion

We have studied the fire behavior and the heat transfer in the in tumescent formulations polypropylene (PP)-ammonium polyphosphate (APP)/pentaerythritol (PER) and PP-Hostaflam AP750 (AP750). We have shown that the fire proofing properties (LOI, UL-94 and cone calorimeter) of PP was strongly improved using the commercial additive AP750 in comparison with the system APP/PER. This is explained by the protection of the intumescent coating developed from PP-AP750 which is still efficient at high temperature (450-550°C) and which is developed faster. The measurement of temperature profiles in the conditions of the cone calorimeter shows that the temperatures reached with PP- AP750 are lower than these obtained with PP-APP/PER. Moreover, the tempera ture of PP-AP750 always remains lower than the temperature of the beginning of the fast degradation rate of PP which implies that there is never a fast degrada tion of the polymeric matrix. Finally, the computation of the temperature of the degradation front ( T d ) allows to conclude that low T d and relatively high displace ment rate of the place of the degradation front is needed to increase the efficiency of intumescent systems.