Investigating the changing dynamics of processing, temperature‐based mechanics, and flame retardancy in the transfer of ammonium polyphosphate/inorganic silicate flame retardants from epoxy resins to glass fiber composites

Although numerous investigations study the improvement of flame retardancy of epoxy resins using additives, maintaining the flame retardant (FRs) modes of action present in the resins upon transfer to composites is challenging. In this study, ammonium polyphosphate (APP) and inorganic silicate (InSi) are loaded at 10%, 30%, and 50% by weight, in a diglycidyl ether of bisphenol A (DGEBA) resin cured with dicyandiamide and transferred to bidirectional (BD) glass fiber (GF) composites. Although a 50% loading of the FRs impacts the curing kinetics of the resin system, the effect on the glass transition temperature of the resin system remains negligible compared to reactive FRs in the state of the art integrated into the resin's chemical structure. Increasing the FR content improved the heat release characteristics in both the resins and composites. However, the charring mode of action is completely suppressed in the formulation with 10% APP + InSi. A 30% concentration of the FRs restored the charring action in the composite and the GFs provide increased protective layer action upon transfer to the composites. This study highlights the importance of accounting for the changing dynamics related to processing and flame retardancy upon transferring FRs from resins to composites. This study examines the dynamics of varying the combined content of ammonium polyphosphate and inorganic silicate in epoxy resins on processibility and fire performance upon transfer to glass fiber reinforced composites. A 30% loading of the flame retardants was crucial for the recovery of the UL‐94 V‐0 rating and charring action absent in a 10% loading formulation in the composites.