Through-Thickness Fire-Retardant Distribution Influence on Fire Retardancy Properties of Glass Fibre Powder Epoxy Composites

: Despite advances in novel fire retardants, how they are incorporated into a flammable substrate and the impact of this on fire retardancy remains underexplored. This study investigates how different fire-retardant (FR) distribution modes affect the flammability of an epoxy-based glass fibre composite. Specifically, three distribution modes are examined: homogenous (i.e., evenly distributed FR across layers), gradient (i.e., controlled variation in-depth), and top (i.e., all FR concentrated in the top layer). The study also varied the volume fraction of DOPO (9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) in each plate to observe its effect on fire performance. Nine glass fibre reinforced polymer (GFRP) plates were manufactured with different distribution modes and DOPO volumes using a manual layup method. The fire performance of these plates was assessed using the cone calorimeter, analysing heat release rate (HRR), carbon monoxide (CO) generation and time to ignition (TTI). Results indicate that the gradient and top distribution modes are more effective in reducing the flammability with a lower total volume of DOPO compared to the homogeneous mode. Optimising the distribution mode by mainly placing DOPO on the surface layer with a lower total volume is more effective than using a higher volume of DOPO distributed homogeneously. This research exemplifies how FR loadings can be modified to allow optimisation of fire performance, material properties and cost.