Release and flammability evaluation of pyrolysis gases from carbon-based composite materials undergoing fire conditions

In the event of fire, composite materials can be exposed to high heat flux leading to a significant release of smoke and toxic fumes that can contribute to the growth of the fire. This can be problematic in the aerospace industry where strict fire regulations are imposed for designated fire zones. Research has therefore been carried out in recent years to estimate the volatile emissions and self-ignition risk during the development phase of composite parts. In the present study, gaseous emissions and lower flammability limits (LFL) were evaluated during the degradation of three carbon-reinforced composites. The thermoplastic polyetherketoneketone (PEKK), belonging to the polyaryletherketone (PAEK) family, which is known for its high-temperature stability, was compared with two thermosetting resins: a classic phenolic resin and a fire improved epoxy. The former is well known and already used as thermal protection whereas the latter could be used as ablative protection for internal thermal insulation. Gaseous emissions were measured using an analytical pyrolyser (heated platinum filament) coupled with a gas chromatograph and a mass spectrometer (Py-GC-MS) for four different temperatures: 360, 450, 590 and 750 °C. From the suspected species given by the pyrolysis experiments, the LFLs were determined by means of a Quantitative Structure-Property Relationship. The classification of the three materials in terms of combustibility (degradation temperature and mass loss) and ignitability (gaseous emissions and lower flammability limit) revealed superior performances of PEKK composites. The benefit of the fire treatment on the carbon-epoxy was demonstrated by a higher value of LFL whereas the carbon-phenolic resin had a lower mass loss even if it presented a lower degradation temperature.