A Carbon Layer Modulation Mechanism of 4‑Formylphenylboronic Acid Reactive Flame-Retardant PA66

Polyhexamethylene adipamide (PA66), a prominent engineering thermoplastic and chemical fiber material, plays a crucial role in industrial applications and daily life. However, its inherent flammability accompanied by substantial heat release during combustion presents significant fire safety hazards. To address this limitation, we developed a reactive flame-retardant modification strategy using 4-formylbenzeneboronic acid (FBA) through simple melt blending with PA66. It is revealed that incorporating 4 wt % FBA effectively enhanced the flame retardancy, achieving a limiting oxygen index (LOI) of 28%. Notably, this formulation demonstrated a 49.9% reduction in peak heat release rate (pHRR) and an 8.3% decrease in total heat release (THR) compared with pristine PA66. Mechanistic investigations indicated that FBA primarily functions via condensed-phase flame retardation. Specifically, FBA facilitates the formation of a compact carbonaceous char with improved structural regularity and graphitization degree. This enhanced char layer architecture effectively impedes heat and oxygen transfer while exhibiting superior thermal shielding capability and structural stability.