First commercialised 70 years ago, silicone rubber is widely used in varying applications, because of its bio-compatibility, chemical, temperature and UV resistance and electrical properties. However, it is flammable, even if less so than organic rubber. A polymer nitrogen and phosphorus based flame retardant, cyclotriphosphazene based HPPT, was synthesised and tested in silicone rubber.
This showed to generate a compact and stable char layer in case of fire, through mechanisms including melamine release and reaction with silica in the rubber. The PIN flame retardant improved fire performance characteristics measured, including LOI (limiting oxygen index) and heat release ratings (peak heat release was reduced by 40% at 18% flame retardant loading) enabling to achieve UL94-V0. Smoke emission (peak SPR) was reduced by the PIN FR by 15 – 40%. However, the HPPT did negatively affect the rubber mechanical performance (tensile strength, elongation at break).
“An efficient flame retardant for silicone rubber: Preparation and application”, C. Zhu et al., Polymer Degradation and Stability 121 (2015) 42-50 http://www.sciencedirect.com/science/article/pii/S014139101530063X