Vincent Rerat, Dow Corning Europe, outlined challenges for performance flame retardants in transparent polycarbonates, which are increasingly in demand for specialist applications in electronics (e.g. screens), transport and architecture (e.g. sky domes).
The company’s specialist silicones provide efficient synergists for PIN flame retardants.
In fire, with KSS (Potassium Diphenylsulfone Sulfonate) or HES (Complex sulfonate salt blend), they react with the polycarbonate polymer to accentuate char formation. They also offer transparency, good dispersion and improve flow, so facilitating production of complex and thin-walled components, and enabling mechanical performance to be maintained by adjusting the polycarbonate grade. UL94-V0 at 1mm and EN 445/545 railway standards can be achieved, with a 50% reduction in smoke (probably because the porous char formed dampens and adsorbs fumes). These silicones are short, linear polymers (without Si5 rings) and so are not persistent, and are recognised as safe (used in cosmetics).