Combustion behaviour of polyurethane flexible foams under Cone Calorimetry test conditions

Abstract

The first part of this study focuses on the &ect 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, i.e. conventional slabstock foams, high-resilience slabstock foams and all-MDI (methylene diphenyldiisocyanate) 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 25 mm. 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 m-' were found to be very severe to test flexible polyurethane foams. Under such conditions, foams that show large 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, are defined. These effects were clearly pronounced at radiant flux levels of 15 -25 kW m-'. 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 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.

Flame retardancy working mechanism of methyl‐DOPO and MPPP in flexible polyurethane foam

“… With increasing methyl‐DOPO content in the PU a decrease in the THR from 12.1 to 10.4 MJm −2 for the PU samples without and with 5 and 7.5 phpp methyl‐DOPO can be observed indicating initiation of flame retardancy. In comparison, the samples with MPPP show only minor changes in the THR. The combustion of the samples during the cone calorimeter test left only small amounts of residue compared with other cone calorimeter experiments of low‐density flex PU foams with ATH or melamine 52. The insufficient formation of a char layer is also indicated by the low phosphorus content of the residue (<0.5% of 5 and 7.5 phpp methyl‐DOPO and <0.8% of 5, 7.5 and 10 phpp MPPP in the foam) after the cone calorimeter test (results are not shown here). Another parameter that can be detected by the cone calorimeter is the smoke density and its integral, the total smoke release, shown in Table IV.…”

Heat release and structural collapse of flexible polyurethane foam

“…In such cases, the foam collapse generally occurred under the flame front and not ahead of the flame [27]. Therefore, the situation found in many cone calorimeter experiments, where the foam may first collapse and then ignite [5,8,9], is not desirable.…”

“…The cone calorimeter is a useful tool for testing the flammability of flexible polyurethane foam, provided that careful consideration is given to the sample size, choice of external heat fluxes and test configuration [5,8]. Lefebvre found that the heat release rate during the foam collapse stage and the fire growth rate parameter (FIGRA 1 ) of both the collapse stage and pool fire stage correlate to the flame spread rate resulting from exposure to a small flame according to Federal Motor Vehicle Safety System (FMVSS) standard no.…”

Experimental assessment of bench‐scale ignitability parameters

“…However, the corner areas of a square sample receive a lower heat flux from the irradiating cone . The effect of this nonuniform heat exposure is more pronounced in the burning of some materials, eg, shrinking flexible polyurethane foam or low‐combustibility materials . Previous studies have therefore also elaborated with larger cones and samples or cylinder‐shaped samples, in order to eliminate some of the effects of nonuniform exposure …”