Synergistic Enhancement of Flame Retardancy Performance in Glass Fiber‐Reinforced Polyamide 6 Through the Incorporation of Aluminum Diethylphosphinate and Hexa (4‐aldehyde phenoxy) Cyclotriphosphazene

ABSTRACT To improve the flame retardancy of glass fiber (GF)‐reinforced polyamide 6 (PA6/GF) composites and alleviate the “candlewick effect” caused by GF, this work synthesized hexa (4‐aldehyde phenoxy) cyclotriphosphazene (HAPCP) via the reaction of hexachlorocyclotriphosphazene (HCCP) and p ‐hydroxybenzaldehyde (PHB). Subsequently, HAPCP was combined with aluminum diethylphosphinate (ADP) to fabricate glass fiber‐reinforced polyamide 6 (PA6/GF) composites. The structural characterization of HAPCP was conducted, and the thermal stability, flame retardancy, and mechanical properties of PA6/GF composites were systematically investigated. The results indicated that compared with neat PA6/GF, the limiting oxygen index (LOI) of PA/1H/9ADP (adding 1 wt% HAPCP and 9 wt% ADP in PA6/GF) increased from 21.7% to 34.4%, and the UL‐94 rating achieved V‐0, with no melt droplets during combustion. The peak heat release (PHRR) and the total heat release (THR) respectively decreased by 51.2% and 29.4%, and the fire performance index (FPI) increased by 107.4%, demonstrating significantly enhanced flame retardancy. HAPCP existed a strong synergistic effect with ADP, promoting the formation of a continuous and compact protective layer during combustion, and generating non‐combustible gases that reduce the concentration of flammable species. This effectively mitigated the “candlewick effect” and improved the overall flame retardant performance of PA6/GF composites.