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The fire behaviour of carbon fibre (CF) reinforced polymers differs in comparison to polymers. Fibres behave often inert with respect to pyrolysis, they change the melt flow and dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue and so on. Flame and fire retardancy concepts are needed not only suitable for the different fire protection goals typical for each application, but also tailored for composites. This field is illuminated by examples taken from different projects carried out in the group of the author in the recent years. The examples target on different applications through achieving reduction in reaction to fire controlling the fire risks (flammability, heat release) in the beginning and development of a fire and investigating the fire stability, when a severe flame is directly applied (key property in fully developed fires). Approaches to halogen-free flame retardancy in CF reinforced thermosets are presented as well as building up a bench and an intermediate scale testing of composites in fire applying mechanical load (up to 1 MN compression) and direct flame exposure (180 kW/m2) simultaneously. Indeed, e.g. we have investigated the fire stability of stringer reinforced shell components taken out from the fuselage of an aircraft.
The understanding of fire behaviour, fire resistance, and fire retardant modes of action in composites is a promising basis for target-oriented development. The role of flame inhibition, charring, and protective layer formation is discussed. Successful concepts are presented for fire retardancy tailored for different application as well as general guidelines for future development. Different phosphorus flame retardants are proposed to achieve halogen-free flame retardancy with respect to ignition and developing fires. Different protective approaches are sketched for addressing the fire stability of composites that is the most important fire risk for the fire resistance in structural applications.
Intumescent coatings are used for decades to increase the fire resistance of steel or wood constructions. Intermediate and full scale tests are used to assess their protection performance. For the product development and screening, cheaper and faster bench-scale tests are demanded that provide information about thermal protection, foaming dynamics and mechanical resistance. In the recent years, we have developed several bench-scale fire resistance tests and used them in different research and developing projects. The influence of distinct binders and fillers, respectively, was studied in intumescent coatings using the Standard Time Temperature modified muffle furnace (STT Mufu+). This bench-scale test evaluates the fire resistance (by means of temperature measurements) and the foaming behaviour (by means of a high-temperature endoscope) during a standard time-temperature exposure. The fire residues were suitable for advance residue analysing techniques like nondestructive μ-computed tomography (μ-CT). Also, scanning electron microscopy was used to investigate the microscopic structure of the surface and inside of the residues. The mechanical resistance of the residues was tested by an impact resistance experiment.
The binder influence on the insulation of the coating was small for the investigated systems. Nevertheless, it was interestingly noted, that coatings with high expansion did not provide the best protection. The great influence of the binder material on the inner structure of the foamed residues was revealed by the μ-CT images. Clear differing morphologies were observed. These led to distinct mechanical resistance properties of the tested coatings. Also the change of a low amount of fillers, such as fibres and clay was investigated with similar effects. What is more, a transition of the residue from black, carbonaceous foam with closed cells into an inorganic, residual open cell sponge occurs at high temperatures during the test. This transition is due to the loss of carbon; the change in microstructure is analysed by scanning electron microscopy.
The bench-scale tool presented outreaches screening; the investigation based on the STT Mufu+ delivers a deeper understanding of the phenomena controlling the performance of intumescent coatings.