Behaviour of aeronautical polymer composite to flame: A comparative study of thermoset- and thermoplastic-based laminate

The influence of the fire exposure on the degradation mechanism of thin carbon/epoxy and carbon/polyphenylene sulphide (PPS) laminates has been investigated using a propane burner. The burner used in this work is able to provide a controlled and repeatable heating condition, with the test condition of 106 kW/m2 representative of a severe fire condition. Mass loss and temperature measurements made during the fire aggression coupled with post-fire microscopic analysis aim at providing a better understanding of the physical and mechanical changes on laminates depending on matrix nature and different fire-exposure times. For a high heat flux, a 300s fire exposure is more detrimental for the carbon/epoxy sample (22% mass loss) than for the carbon/PPS (6% mass loss) although ATG results show a similar char yield of around 75% under nitrogen for both materials. Observation and analysis of microscopic images after different fire-exposure times fire suggest that the thermal behaviour of the 2 mm thin laminates is driven by the formation of major delamination and macroscopic pores forming a thermal barrier as the analysis of the images indicates a void content 2 to 5 times higher for the carbon/PPS sample than for the carbon/epoxy specimens. On the one hand, the degradation of the thermoplastic PPS matrix into a viscous product seems to trap pyrolysis gases into macroscopic gaseous cells. These porosities provide an efficient thermal barrier protecting the back surface from the flame high thermal flux. On the other hand the degradation of the thermosetting epoxy matrix forms a dry network of carbon fibres and porous char.