Thermal decomposition of flexible polyurethane foams in air

Abstract

The oxidative thermal decomposition of a non-fire retardant and a fire retardant polyurethane foam is investigated using thermogravimetric analysis and differential scanning calorimetry over 1–60 °C/min of heating rate, in both air and nitrogen environments. From the thermogravimetry results, the oxidative environment of air results in additional oxidative reactions which are heating rate dependent. These reactions compete with the pyrolysis reactions for the same reactants over similar temperature range. For both foams, increasing heating rate gradually reduces the influence from the oxidation of foam while favouring the pyrolysis of polyol. At low heating rate, in oxidative air environment, the fire retardant foam shows significant decomposition across low temperature range. This environment mimics the incipient phase of a fire, and ignition inhibition is possible when this low temperature decomposition is coupled with gas phase fire retardant mechanisms such as neutralisation of reactive radicals. Fire retardant additives also form char residue which notably lowers the decomposition rate while extending the decomposition temperature range, improving the overall thermal stability. Lastly, the kinetic properties governing the oxidative thermal decomposition of foams are estimated graphically using Inflection Point Methods, and the corresponding exothermic heat of reaction is determined from the heat flow results.