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Polyurethane (PU) bilden eine der vielseitigsten Klassen der Polymerwerkstoffe. Kein anderer Kunststoff wird sowohl als Thermoplast, als Elastomer wie auch als Duroplast verarbeitet und eingesetzt. Entsprechend vielfältig sind auch die Anforderungen an den Flammschutz. Je nach Material und Anwendung müssen spezifische Brandnormen erfüllt werden. Der vorliegende Aufsatz gibt einen Überblick über die verfügbaren Ansätze, um durch geeignete Auswahl der Rohstoffe und der Flammschutzmittel diese verschiedensten Anforderungen an das Brandverhalten zu erfüllen.
Polyurethanes (PU) represent one of the most versatile classes of plastics. They are processed and used as thermoplastic, elastomer, and thermoset. The requirements regarding flammability are correspondingly versatile. Depending on the material and the field of application, specific fire tests have to be fulfilled. This paper describes the different concepts used to fulfil these requirements by choosing the right raw materials and flame retardants.
Rigid polyurethane foams (RPUFs) exhibit short times to ignition as well as rapid flame spread and are therefore considered to be hazardous materials. This paper focuses on the fire phenomena of RPUFs, which were investigated through a multimethodological approach. Water-blown polyurethane (PUR) foams without flame retardants (FRs) as well as waterblown PUR foams containing triethyl phosphate as a gas phase-active FR were examined. The aim of this study is to clarify the influence of the FR on the fire phenomena during combustion of the foams. Additionally, materials’ densitieswere varied to range from 30 to 100 kg/m3. Thermophysical properties were studied bymeans of thermogravimetry; fire behavior and flammability were investigated via cone calorimeter and limiting Oxygen index, respectively. During the cone calorimeter test, the temperature development inside the burning specimens was monitored with thermocouples, and cross sections of quenched specimens were examined visually, giving insight into the morphological changes during combustion.
The present paper delivers a comprehensive study, illuminating phenomena occurring during foam combustion and the influence of a FR active in the gas phase. The superior fire performance of flameretarded PUR foams was found to be based on flame inhibition, and on increased char yield leading to a more effective protective layer. It was proven that in-depth absorption of radiation is a significant factor for estimation of time to ignition. Cross sections investigated with the electron scanning microscope exhibited a pyrolysis front with an intact foam structure underneath. The measurement of temperature development inside burning specimens implied a shift of burning behavior towards that of non-cellular materials with rising foam density.
This work investigates the fire phenomena of rigid polyurethane foams (RPUFs) in detail. To elucidate structure-property relationships, systematically varied sets of materials were prepared covering polyurethane, polyisocyanurate-polyurethane and flame retarded polyurethane foams. Advanced cone calorimeter investigations provide insight into the fire behavior under forced flaming conditions. Thermocouples inside specimens give information about the temperature gradient during combustion. Furthermore, fire phenomena were characterized using cross sections of quenched samples and the scanning electron microscope. By using a Multi methodological approach and systematically varied sets of foam materials, new insights into the burning of RPUFs were won. For the flame retarded foams, the dominant flame retardant mode of action changed with density. PIR foams exhibited a cellular structure in the residue leading to the superior fire performance compared to polyurethane foams. The understanding of fire phenomena contributes to future development of tailored flame retardant strategies for RPUFs.
This work investigates the fire phenomena of rigid polyurethane foams (RPUF) in detail. Rigid polyurethane foams (RPUF) are widely used in industry and daily life because of their outstanding mechanical and thermal insulating properties. In case of fire, cellular polymers like RPUF behave differently from bulk materials, the reason for this is their low thermal inertia. The aim of this study is to investigate the fire phenomena of RPUF in detail. Characterized by simultaneous physical and chemical processes which interact, depend, and compete with each other, the combustion of RPUF is a highly complex occurrence. Therefore it is necessary to study all aspects in detail. The fire phenomena that were examined are gasification, liquefaction, charring and structural integrity as well as collapse. The comprehensive understanding of the processes taking place during combustion is the foundation of customized development of successful flame retardant approaches. Advanced cone calorimeter investigations provide insight into the fire behavior under forced flaming conditions. Thermocouples in the inside of specimens give information about the temperature gradient and temperature of the pyrolysis zone during combustion. Changes in the morphology and thickness of the pyrolysis zone were examined using a hot-stage microscope, as well as SEM images of cross-sections of quenched foam specimens. Furthermore, fire phenomena were characterized using LOI and thermal analysis. By using a multimethodological approach and systematically varied sets of Polyurethane and Polyisocyanurate foams, new insights into the burning of RPUF were won. The detailed knowledge of fire phenomena is essential for future development of tailored flame retardant strategies for RPUF.
Flexible polyurethane foams with densities of 40 ± 2 kg m−3 were prepared by combining different ecofriendly fillers such as layered double hydroxides (LDH) and kraft lignin (a byproduct of the pulp and paper industry) with a phosphorous polyol (E560) in order to study their effect on the mechanical performance and fire behavior of the foams. Two series of foams were prepared, some containing lignin or LDH separately, and some with a combination of both: one of the series was prepared without E560 (0E foam series) and the other with 5 parts per hundred of E560 polyol (5E series). The use of fillers resulted in increased viscosity of the reactive mixture, requiring higher blowing agent content in order to hold the density of the foams constant. It was observed that urea phase segregation was favored in the series of 0E foams due to their lower viscosity than the 5E series. This had consequent effects on the resilience, compression force deflection and compression set of these foams. In terms of fire behavior it was observed that while the limiting oxygen index decreased, cone calorimeter results showed that the combination of lignin, LDH and E560 decreased the heat release of the foams. In addition, the combination of fillers and E560 contributed to increase the viscosity of the pyrolysis products, preventing the dripping of the molten polymer, which is a key factor in flame propagation towards adjacent objects in fire scenarios.