Abstract
Rigid polyurethane foams (RPUFs) typically exhibit low thermal inertia, resulting in short ignition times and rapid flame spread. In this study, the fire phenomena of RPUFs were investigated using a multi-methodological approach to gain detailed insight into the fire behaviour of pentane- and water-blown polyurethane (PUR) as well as pentane-blown polyisocyanurate polyurethane (PIR) foams with densities ranging from 30 to 100 kg/m3. Thermophysical properties were studied using thermogravimetry (TG); flammability and fire behaviour were investigated by means of the limiting oxygen index (LOI) and a cone calorimeter. Temperature development in burning cone calorimeter specimens was monitored with thermocouples inside the foam samples and visual investigation of quenched specimens’ cross sections gave insight into the morphological changes during burning. A comprehensive investigation is presented, illuminating the processes taking place during foam combustion. Cone calorimeter tests revealed that in-depth absorption of radiation is a significant factor in estimating the time to ignition. Cross sections examined with an electron scanning microscope (SEM) revealed a pyrolysis front with an intact foam structure underneath, and temperature measurement inside burning specimens indicated that, as foam density increased, their burning behaviour shifted towards that of solid materials. The superior fire performance of PIR foams was found to be based on the cellular structure, which is retained in the residue to some extent.
Highlights
Rigid polyurethane foams (RPUF) are widely used as an insulation material in the construction industry, for refrigeration, and in the pipe and tubing industry
The time to ignition for thermally thick combustible materials is proportional to their thermal inertia, which is described as the product of thermal conductivity (λ), density (ρ) and heat capacity (c) [3,4]
All examined materials were divided into three groups, namely pentane-blown polyurethane foam (PUR-P), water-blown PUR (PUR-H), and pentane-blown polyisocyanurate-polyurethane foam (PIR-P) and named indicating the density of the material
Summary
Rigid polyurethane foams (RPUF) are widely used as an insulation material in the construction industry, for refrigeration, and in the pipe and tubing industry Due to their extremely low thermal conductivity, RPUFs typically offer excellent insulating properties and outperform other commercially available insulating materials [1,2]. The reason for these unique characteristics is their cellular structure. For a given heat flux the surface temperature of a cellular polymer rises more rapidly than for high values of λρc [5] Because of their low thermal inertia, which benefits their ignitability and their flame spread, RPUFs are considered hazardous [6,7,8]
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