Combustion Behaviour of Polyurethane Flexible Foams under Cone Calorimetry Test Conditions

Abstract

The first part of this study focused on the effect of cone calorimeter test variables on polyurethane flexible foam properties such as ignitability, heat release rate, effective heat of combustion and mass loss. Three of the main commercial foam types were used; viz. conventional slabstock foams, high resilience slabstock foams and all-MDI moulded foams. A decrease in heat flux (down to. 40%) with increasing distance from the conical heater was measured. As a consequence, results were found to depend to a large extent on the thickness and the melting behaviour of the foam samples. To achieve a sufficiently constant and uniform heat flux exposure, sample thickness had to be limited to 2.5 cm. In addition, repeatability was found to be good under various conditions, with percentage standard deviations for effective heat of combustion, peak rate of heat release and mass loss below 10%. Levels of radiant flux above 25 kW/m2 were found to be very severe to test flexible polyurethane foams. Under such conditions, foams that show big differences in combustion performance in small scale flammability tests, performed almost identically in the cone calorimeter. In the second part of this study, the effects of foam variables, such as foam type, density and melamine content, were defined. These effects were clearly pronounced at radiant flux levels of 15 to 25 kW/m2. Density was found to be the key variable in controlling ignition resistance. In addition, high-resilience slabstock foams and all-MDI moulded foams performed better than conventional slabstock foams of the same density. Melamine addition resulted in a delay of ignition for all three foam types and an incomplete combustion, decreased heat release and effective heat of combustion, in case of HR slabstock and all-MDI moulded foams. However, melamine is not effective as a heat sink in conventional slabstock foams. The different performance of the foam types under study can be explained by a different melting behaviour.