Unveiling aluminum diethyl phosphinate dual identity: Transfer from epoxy resins to glass fiber‐reinforced composites

Abstract This study examines the transfer of the flame‐retardant aluminum diethyl phosphinate (AlPi) from epoxy resins to composites and the impact of AlPi on fire behavior and fire stability. Further, the effects of different particle sizes and the addition of zinc hydroxy stannate (ZHS) and inorganic silicate (InSi) are investigated. The research provides a detailed analysis of the fire behavior, fire stability, pyrolysis, flame‐retardant modes of action, and flame retardancy index. Interestingly, the particle sizes did not significantly affect the flammability, fire behavior, or fire stability in the systems investigated. AlPi acts primarily in the gas phase, releasing phosphorus that yields flame inhibition. Adding glass fibers (GFs) to the epoxy resin boosts the flame retardancy in the condensed phase, reducing the heat release rate (HRR), total heat release (THR), and peak heat release rate (PHRR) by about 60%. This improvement is largely due to replacing fuel and forming a protective layer during burning. Despite the differences between thermoset and composite, the study demonstrates an effective transfer of flame‐retardant properties from epoxy resins to fiber‐reinforced composites, significantly enhancing the flame retardancy performance in both material systems. Highlights AlPi transfer from resin to composites enhances flame retardancy. Adding glass fibers reduces the heat release rate (HRR) by approximately 60%. Particle size has minimal impact on fire behavior and stability. AlPi acts in the gas phase; with added GFs, the condensed phase is activated. Synergists ZHS and InSi have minimal impact on the composite flame retardancy.