Effect of the Flame Retardants and Glass Fiber on the Polyamide 66/Polyphenylene Oxide Composites

In this work, polyamide 66/polyphenylene oxide (PA66/PPO) composites, including the flame retardants 98 wt% aluminum diethylphosphinate + 2 wt% polydimethylsiloxane (P@Si), Al(OH)₃-coated red phosphorus (RP*), and glass fiber (GF), were systematically studied, respectively. The limiting oxygen index (LOI), UL-94 vertical burning level, and thermal and mechanical properties of the PA66/PPO composites were characterized. The results showed that the P@Si and RP flame retardants both improved the LOI value and UL-94 vertical burning level of the PA66/PPO composites, and PA66/PPO composites passed to the UL-94 V-0 level when the contents of P@Si and RP* flame retardants were 16 wt% and 8 wt%. On the other hand, the mechanical properties of the PA66/PPO composites were reduced from a ductile to a brittle fracture mode. The addition of GF effectively made up for these defects and improved the mechanical properties of the PA66/PPO composites containing the P@Si and RP*, but it did not change the fracture mode. P@Si and RP* flame retardants improved the thermal decomposition of PA66/PPO/GF composites and reduced the maximum mass loss rates, showing that the PA66/PPO/GF composites containing the P@Si and RP* flame retardants could be used in higher-temperature fields.

Synthesis, Structures, and Properties of a New Pentaerythritol-Derived Flame Retardant Used in Polyamide 66

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.