A combination of allylamine polyphosphate (20%) and clay (2%) achieved UL-94 V0 (3.2 mm) in polypropylene, showing better fire performance than only APP (ammonium polyphosphate), APP + clay or only allylamine polyphosphate (AAPP). LOI was increased from below 18 (pure PP) to >29. The authors note that literature shows that clay synergist can improve fire performance of PP with ammonium polyphosphate, because the clay reduces melt-dripping and heat release, but that this is limited because of char instability and incompatibility between clay and APP. With allylamine polyphosphate plus 2% clay, there is exfoliation of clay platelets, and formation of dense, continuous, honeycomb structure char. Peak smoke release was around 50% lower than for neat PP, total smoke release was 55% lower, and smoke toxicity (peak carbon monoxide release) was around one third lower.
“Highly efficient flame retardant and smoke suppression mechanism of polypropylene nanocomposites based on clay and allylamine polyphosphate”, D. Xiao et al., J Appl Polym Sci. 2022;139:e52311 https://doi.org/10.1002/app.52311