Differences in Flame Retardancy of Melamine Polyphosphate Between Fiberglass Reinforced PA66 and PA6

Flame retarded fiberglass reinforced PA66 and PA6 were prepared by adding melamine polyphosphate (MPP). The experimental results show that the effectiveness of melamine polyphosphate is distinctly higher in the fiberglass reinforced PA66 than PA6 in spite of the fact that the elemental composition of PA66 and PA6 remains all the same. By adding 25% MPP to fiberglass reinforced PA66, the LOI was improved from 20.4% to 38.0% and the vertical flammability test of UL94 could reach V-0 class; but the flame retardancy of fiber reinforced PA6 was not distinctive. The increase of LOI was only 5.5% and the vertical flammability performance was not improved. Thermal degradation behavior of the specimen was studied by thermal gravimetric analysis (TGA). It was discovered that the thermal degradation behaviors were different between PA6 and PA66 by adding MPP. The residual char was formed by heating the materials to 600℃ and its structure was observed by scanning electron microscopy (SEM).The test resuls show that it is the difference in the char structure that leads to the difference in flame retardancy.