Micron-sized magnesium oxide (MgO <75 µm) at 0 – 0.5 % loading, and AlPi (aluminium diethylphosphinate) at 0 – 14 % loading, were tested as synergistic PIN FRs in polyamide PA66, after extrusion and injection. A combination of 0.3% MgO and 9.7% AlPi achieved fire performance (LOI, heat release) similar to 12 – 14 % AlPi (without MgO), including UL94-V0 at 1.6 mm. The authors indicate that MgO reacts with diethylphosphinic acid, produced by AlPi in burning, to create magnesium phosphates which improve char yield, giving a compact and homogeneous char.
“The study on flame retardancy synergetic mechanism of magnesium oxide for PA66/AlPi composite”, Z. Zhan et al., Materials Res. Express 6 (2019) 115317 https://doi.org/10.1088/2053-1591/ab4737