Evaluation of fire-retardant biocomposites exposed to various heat fluxes at medium and large scales

This study aims to enhance the understanding of fire behavior in biosourced composite materials for potential aeronautics and automotive applications. Experimental tests include NexGen burner trials for Federal Aviation Administration fire certification and cone calorimeter tests on a medium scale. The research also explores the development of biosourced composite materials, addressing the non-biodegradability of synthetic counterparts and contributing to the understanding of their physical and chemical characteristics under varying heat flux densities (20, 35, and 50 kW/m 2 ). The heat fluxes of 25, 35, and 50 kW/m 2 were selected to provide a range of moderate- to high-intensity heat exposures that are relevant for assessing the thermal performance and fire behavior of biocomposite materials. The composites were fabricated using the Vacuum-Assisted Resin Transfer Molding method, augmented with an intumescent flame-retardant layer to bolster their fire safety attributes. The parametric study focused on the fire performance index, the fire growth index, the mass loss, the gas emission species, the surface temperature of the front face of the sample using a Telops infrared camera, and the gaseous emissions obtained for each test configuration. The sample dimensions are 100 × 100 × 5 mm 3 for the cone calorimeter and 500 × 500 × 5 mm 3 for the NexGen burner. Our experimental findings provide a detailed quantitative analysis of their fire performance, highlighting the significant variance in thermal properties and degradation behavior contingent on fiber type and heat flux exposure. Time-to-ignition ranged from 144.9 to 36 s for flax composites and 125 to 32.5 s for banana composites across the tested heat flux densities. The peak heat release rate was notably higher for banana composites (753.1–908.6 kW/m 2 ) compared to flax (495.4–823 kW/m 2 ). This study underscores the critical dependency of thermal and fire safety properties on composite material composition and heat flux exposure, providing valuable insights for the development of safer, biosourced composite materials.