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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.
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.
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.
The concreting of prefabricated concrete structures can lead to insufficient bonding or even to remaining cavities. Honeycombs (aggregate clusters without cement) represent potential weakening of the structure and need to be detected non-destructively. In our study we tested the capability of ground penetrating radar (GPR)techniques for this purpose. We applied GPR in reflection mode and zero-offset profiling (ZOP) Transmission mode on a precast concrete twin wall with built-in honeycombs. GPR measurements were performed as twochannel measurement with ground coupled antennas with centre frequencies of 1.5 GHz and 2.6 GHz mounted to an automated scanner system.
Our findings show that ZOP transmission measurements are a more efficient method to detect voids in reinforced concrete structures compared to reflection mode measurements. This holds for both the effort needed for the measurement and the evaluation as well as the validity of the data. Honeycombs (basically representing voids) are usually characterized by strongly reduced amplitudes and earlier arrivals of the transmitted wave.
This work investigates the fire phenomena of rigid polyurethane foams (RPUF) in detail. To elucidate structure-property relationships systematically varied sets of foams were prepared. RPUF were synthesized with different densities using water and pentane as blowing agent. What is more, a flame retarded RPUF and rigid polyisocyanurate-polyurethane foams were examined. 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. Furthermore, fire phenomena were characterized using SEM, LOI and thermal analysis. By using a multi-methodological approach and systematically varied sets of foam materials, 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.
Rigid polyurethane foams (RPUF) are widely used in industry and daily life because of their outstanding mechanical and thermal insulating properties. While their convenient mechanical characteristics predestine these materials for shock absorption, their low thermal conductivity is responsible for their excellent thermal insulation properties. A principal characteristic affecting not only the use properties, but also the burning behaviour, is the density of RPUF.
In case of fire, cellular polymers like RPUF behave differently from bulk materials. The reason for their comparatively high ignitability is the high rate of temperature rise on the surface when exposed to heat, which is due to their cellular structure and characterised as low thermal inertia. The heat build-up on the surface results in a short time to ignition. Therefore foams are able to develop fire and large amounts of smoke within a short period of time. Even though their fire load is quite low because of their low density, their heat release rate is high. These burning properties are not only a consequence of the chemical consistence of such materials, but also a result of their morphology.
The aim of the work is to investigate the fire phenomena of RPUF. Characterised 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 melting of cellular polymers and dripping of pyrolysis products, together with the ability to form pool fires, are the main hazards in fires involving foams. Structural collapse via melting or decomposition, or the retention of the foam’s morphology through charring, are the main characteristics of their burning behaviour. Cellular structure is a further important factor influencing the materials’ response to fire, and deserves examination in greater depth. Since the cells in closed-cell foam are filled with the blowing agent used to produce the material, and this blowing agent can be inert (carbon dioxide) or highly flammable (pentane), this component also affects the burning properties and will be investigated. Examination of the influence of the macroscopic morphology, namely the cell size and thickness of cell walls, will contribute to the study.
In order to provide comprehensive insight into the processes taking place during combustion, and to elucidate structure-property relationships, a set of foams with systematically varied properties was prepared. RPUF was obtained using water and pentane as a blowing agent. Besides RPUF, a flame-retarded RPUF and rigid polyisocyanurate-polyurethane foam were examined, since these foams are known for their higher stability from a thermodanymic point of view. As a flame retardant active in the gas phase, triethylphosphate was used.
Using a multi-methodological approach, the complex interaction of fire phenomena was studied in detail. Cone calorimeter measurements provide insight into fire behaviour under forced-flaming conditions. They were carried out in an horizontal and a vertical orientation to account for the effects of melt flow and dripping. Sample-holders were equipped with glass windows to monitor the materials’ response to forced-flaming conditions with a video camera. Thermocouples were inserted into the specimens, giving information about the temperature gradient in the inside of the sample and the 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. The determination of the Oxygen Index and the use of thermogravimetry measurements rounded out the investigation.
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.