Thermal Decomposition of Flexible Polyurethane Foams in Air

The oxidative thermal decomposition of a non-fire retardant and a fire retardant polyurethane foam is investigated over 1 – 60 °C/min of heating rate. From the thermogravimetry results under the oxidative environment of air, additional oxidative reactions which are heating rate dependent compete with the pyrolysis reactions over similar temperature range. The decomposition behaviour differs for the foams and the heating rates investigated. Due to the presence of fire retardant additives, the oxidative thermal decomposition from heating rates of 1 – 20 °C/min occurs at a higher rate and over a narrower temperature range for the fire retardant foam. However, at 60 °C/min, the fire retardant foam shows a reduced decomposition rate spreading over a wider temperature range. This shows the fire retardant foam can decompose rapidly at low heating rate, under the condition of low temperature with ample of oxygen. This is similar to the incipient phase of a fire, and ignition inhibition is possible when coupled with the gas phase fire retardant mechanisms of the fire retardant foam. The char residue formed by the solid phase fire retardant mechanism slows the decomposition rate, and as the heating rate increases, the decomposition extends over a greater temperature range due to improved thermal stability. For both foams, the increase in heating rate shows a gradual reduction to the influence from oxidative reaction of foam, shifting towards the pyrolysis reaction of polyol. Kinetic properties of Arrhenius equation governing the decomposition rate are estimated graphically using the Inflection Point Methods and the model shows reasonable agreement with the experimental results. From the heat flow results, the heat of reaction for the oxidative thermal decomposition of foams is calculated and is found to be exothermic