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From halogenated flame retardants to non-halogenated to nanocomposites, each milestone in flame retardancy research led to an increase in performance and safety. With the rise of ceramic precursors in flame retardants, a new field of applications in extreme fire scenarios has become accessible. Intumescent coatings combined with precursors for ceramics show a high temperature transition to a ceramic foam, which provides much better fire resistance than conventional coatings at temperatures beyond 1200°C. Even a protection at 2000 °C for several minutes can be achieved. Combining the expansion property of traditional intumescent coatings with a ceramification at high temperatures leads to high-performance coatings, whose unique properties may prove useful for emergency insulation systems for re-entry bodies in the aerospace industry or special fire protection applications.
In this study, the protection performance in extreme fire conditions, the development of the expansion and the following ceramic transition of a high-performance coating are investigated. To this end, a small scale high-performance burner setup was created. The coated (2.5/4 mm) steel plates (75 x 75 x 2 mm) were exposed to direct flame treatment of a propane-oxygen-burner controlled by two flow controllers. During the test, temperatures above of 1800 °C were reached and steel and flame temperature were recorded. Fire tests of different durations (1, 2.5, 5, 10 and 20 min) were performed. The residues of the different development stages were analysed with non-destructive µ-computed tomography and scanning electron microscopy. The 3D images of the computed tomography provide an insight into the developing cell structure and state of ceramification of the residues.
Research and development of flame retarded polymeric materials generate a strong demand for bench-scale fire testing saving costs, time, and material. Hereby the good correlation to the fire tests mandatory for later products is the key challenge. Three examples are presented for tailored bench-scale fire test set-ups based on recent projects in my working group:
- STT MuFu+: A bench-scale set-up was designed to investigate intumescent coatings protecting steel. An electric oven was modified, so that the standard time temperature curve is applied to a 75 mm x 75 mm coated steel plate. The plate is tested in a vertical position the temperature increase is measured at its back. A high temperature endoscope is used for online observation of the intumescence. Perfect fire residues are produced ready for further investigation.
- Rapid Mass Calorimeter: A bench-scale set-up was designed to speed up cone calorimeter testing. Specimen size reduction and using a modified mass loss calorimeter deliver crucial reduction in time and material needed for screening materials. More than 70 different materials, polymers and flame retarded polymers, have been used to understand the meaning of the results and to check the correlation with cone calorimeter results.
- Bench-scale Cable Testing Module: A bench-scale set-up was designed to screen cables with respect to their performance in the large scale test (EN 50399). A module is proposed replacing the cone heater and balance in the cone calorimeter. Thus the whole set-up of the cone calorimeter is used determining the heat release by means of oxygen consumption, whereas the novel cable module become cheap and easy. A good correlation to EN 50399 was observed indicating the module being an excellent screening tool for the development of flame retardant cables.
The three examples show how close tailored bench-scale testing comes to simulate the performance in larger mandatory fire tests. Proper bench-scale approaches are used for reliable inexpensive assessment when screening novel materials and products.
Acknowledgements
Thanks go to Michael Morys, who has elaborated the STT MuFu+ in his PhD, and Sebastian Rabe, who has elaborated the Rapid Mass Calorimeter in his PhD. Thanks go to Corning Optical Communications (Emanuela Gallo and Waldemar Stöcklein) for the joint project developing the Bench-scale Cable Testing Module. Thanks go to Patrick Klack elaborating the cable module.
Modern flame retardant polymeric materials often stand for multicomponent systems consisting of different ingredients. Using a variety of flame retardants, fillers, additives, synergists and adjuvants as well as applying different concentrations, particle size distributions, encapsulation, and so forth lead to a vast multidimensional matrix of possible formulations. Actual, comprehensive elucidations are no longer possible due to time, material and cost limitations. The task is dying for accelerated procedures, for high-throughput methods. Therefore we developed the Rapid Mass Calorimeter based on a Mass Loss Calorimeter with attached thermopile chimney and a linear motion unit for semi-automatic sample change. Together with the reduction in specimen size (2 cm x 2 cm), a saving of time around 70% and a saving of material of 96% is achieved not considering the strongly reduced calibration and maintenance efforts required for the Mass Loss Calorimeter. The correlations between the results of the Rapid Mass Calorimeter and the Cone Calorimeter as well as to the Oxygen Index and UL94 classification are described; the effects such as when reducing the specimen size are discussed.