Hyperbranched polysiloxane (PBDSi) containing P and N shows to be an effective FR in polyamide-6 at only 3% loading. Silica, phosphorus containing DOPO and N containing Schiff-base were combined into one PIN FR oligomeric molecule, PBDSi, by reacting commercially available 3-aminopropyl triethoxysilane (APTES), diphenylsilanediol (DPSD) and DOPO. At 3% loading in polyamide (PA6), LOI (limiting oxygen index) was increased by 30%, peak heat release was reduced by over 30% and melt-dripping was prevented (4mm samples) with only small effects on mechanical properties. The authors suggest that the fire protection mechanisms are generation of a Si-P char layer and release of incombustible gases. This paper shows a potential PIN FR solution to avoid drip without using PTFE anti-drip additive in polyamide.
“A novel phosphorus-nitrogen-based hyperbranched polysiloxane for improving the fire safety of PA6 with suppressed melt droplets and good mechanical properties”, S. Fan et al., Heliyon 9 (2023) e22877, https://doi.org/10.1016/j.heliyon.2023.e22877