Poly(m-xylylene adipamide) (MXD6) has good gas barrier properties and high mechanical strength. However, in nature, this resin has a low rate of crystallization. In order to overcome this obstacle in its applications, this study prepares a new, efficient modifier for MXD6 by combining the synthesized DOPO derivative (DT) and P22. It is found that the use of the binary modifier exhibits obvious effects on the crystallization of MXD6. When 11.0 wt.% DT is added together with 0.1 wt.% P22 (DT/P22), the crystallization temperature of MXD6 shifts to a higher temperature of 19.7 °C, and the crystallinity degree of MXD6 is significantly increased by 60%. Meanwhile, this modifier exhibits obviously intumescent flame-retardancy on MXD6 by increasing the limited oxygen index (LOI) from 26.4% to 33.4%. The results of the cone calorimeter test (CCT) reveal that the peak heat release rate (PHRR), total heat release (THR) and average effective heat release (av-EHC) are obviously suppressed due to the use of this modifier. Moreover, the influences of this modifier on the crystal structures, mechanical and rheological properties of MXD6 are analyzed in detail. This study can provide an efficient modifier for MXD6.

A melting phosphorous-based flame retardant (FR) named as diphenyl phosphoryl (DPP)–PEPA is synthesized from 2,6,7-trioxa-1-phosphabicyclo-(2.2.2)-octane-4-methanol (PEPA) and diphenyl phosphoryl chloride. The melting DPP–PEPA FR possesses high thermostability with T 5wt% at 344 °C, which can match the melt-spinning of engineering plastics at high temperatures. The structure of DPP–PEPA is defined by nuclear magnetic resonance and infrared spectrometry. The influences of DPP–PEPA on polyamide 6,6 (PA66) are assessed in terms of rheology parameters and crystallinity. It is observed that the flame retardancy of PA66 is greatly improved when DPP–PEPA is added to the PA66 resin. The results show that the modified PA66 has limited oxygen index as high as 29.4%, and the compact char layers are obviously formed on top of the burned samples. As compared to the pure PA66, the peak heat release rate and the average effective heat of combustion are decreased by 26.5 and 19.3%, respectively. It is obtained that the value of flame retardancy index is 1.4, indicating high efficiency of the entire flame retardancy. Moreover, pyrolysis of DPP–PEPA is carried out at different temperatures for identifying gaseous products and types of flame retardancy.

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 T5wt% 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.

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