Reaction kinetics and morphological changes of a rigid polyurethane foam during combustion

A three-step series mechanism is shown to provide a good description of the oxidative degradation of a rigid polyurethane foam. Kinetic constants have been estimated by the simultaneous evaluations of four weight loss curves measured for heating rates between 5 and 20 K/min and a final temperature of 873 K. The following parameters have been obtained for the three reaction steps: (I) A1=2.6×1012 s−1, E1=133.6 kJ/mol; (II) A2=3.3×104 s−1, E2=81 kJ/mol; (III) A3=8.7×108 s−1, E3=180 kJ/mol. The thermal response of the foam has also been examined in a cone calorimeter for low (25 kW/m2) and high (50 kW/m2) radiation intensities, which lead to flaming combustion for a period of 90 and 75s, respectively. In the latter case, a transition from flaming to slow smoldering also takes place. Finally, for both radiation intensities, SEM micrographs show the complete loss of the initial closed-cell structure.