The synthesis of meltable and highly thermostable triazine‐DOPO flame retardant and its application in PA66

A melting phosphorous‐nitrogen flame retardant was synthesized via the addition reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and 2,4,6‐triallyloxy‐1,3,5‐triazine (TAC). The synthesized product from DOPO and TAC (DT) flame retardant possesses high thermal stability with T 5wt% at 340°C, which can meet the high‐temperature processing for polyamide 6,6 (PA66) and other engineering plastics. The chemical structures of DT were characterized by nuclear magnetic resonance and infrared spectrometry. The PA composites were fabricated via blending PA66 with DT and poly‐phenyl ether (PPO) as charring agent. The results show that the PA composites exhibit strong flame retardancy with limited oxygen index reaching to 29.0%. As compared to the neat PA66, the total heat release and the effective heat of combustion were decreased by 27% and 21%, respectively. The mechanism study revealed that the thermal cleavage of DT gave the phosphorus‐containing free radicals and incombustible nitrogen‐containing gas, indicating the ability of DT to flame‐inhibition in the gas phase. Moreover, the char formation of the PA66‐based composites was facilitated by the synergistic effect from DT and PPO. This study may gain a potential technical route to manufacture the flame‐retardant PA66 materials for the melt spinning of fibers.