Influence of thermo-oxidative aging and thermal shock testing on the fire performance of high-Tg epoxy-based GFRP systems

In fire-critical sectors like transportation and construction, flame-retardant composite systems must adhere to stringent safety standards. However, their long-term fire performance is often unexplored, as most studies assess fire behavior only in the as-received state, neglecting potential degradation due to environmental exposures. This study addresses this gap by examining the effects of thermo-oxidative aging and thermal shock testing on glass fiber reinforced composites, comparing both neat and flame-retardant modified version using aluminum diethyl phosphinate (AlPi). An initial assessment was carried out to identify the optimum concentration of AlPi and the impact of glass-fiber reinforcement on the fire behavior. Thermo-oxidative aging at 200 °C for 1000 h showed only slight effects. The maximum average rate of heat emission (MARHE) and effective heat of combustion (EHC) decreased, suggesting enhanced gas-phase flame inhibition and increased char stability. Visual inspections confirmed more stable char layers and reduced delamination in aged, flame-retardant composites. In contrast, thermal shock testing led to significant mechanical degradation, evidenced by up to a 30 reduction in interlaminar shear strength. This degradation is attributed to microcrack formation from internal stresses. Fire performance also deteriorated, with increases in MARHE and total smoke production (TSP) indicating more complete combustion.