Fire reaction properties of flax/epoxy laminates and their balsa-core sandwich composites with or without fire protection

Fire reaction properties of flax/epoxy laminates and their corresponding balsa-core sandwich composites with/without fire protection were evaluated at an applied heat flux of 50 kW/m2. A strategy for improving the fire reaction properties of flax/epoxy composite materials without adversely altering their intrinsic mechanical properties was investigated. A thin glass fiber veil impregnated with ammonium polyphosphate was bonded onto the composite surface intended for heat exposure. There was no significant change in the time-to-ignition with the introduction of the fire retardant glass fiber veil. While similar PHRR values were measured in both flax/epoxy laminates and balsa-core sandwich composites, the total heat release was significantly higher in the later. It is noteworthy, the heat release rates (including the peak values) measured for fire-protected composites were significantly lower than those measured for their unprotected counterparts. Through-thickness temperature profiles across the sandwich composite revealed the effectiveness of the fire retardant veil in minimizing thermal damage of underlying substrate composites.