Yann Bourgeois, Huber Engineered Materials, presented testing of different combinations of commercially available PIN flame retardants in polyamides for railway electrical applications. FRs tested were: melamine poly(zinc) phosphate, melamine poly(magnesium) phosphate, magnesium hydroxide (amino silane surface treated), aluminium phosphinate (DEPAL), zinc borate, zinc phosphate complex.
A combination of these (without using borate) achieved UL94-V0, 600V GWIT (glow wire ignition test) and considerably reduced smoke, enabling to meet the EU Railway standard EN 45545 R22 – HL3. Zinc phosphate complex showed to be effective in reducing smoke toxicity, in particular by chelating nitrogen species generated by the polyamide. Melamine poly(zinc) phosphate, magnesium hydroxide and DEPAL combinations display interesting synergistic effects through the improvement of charring, the development of a strong intumescence or high CTI values (comparative tracking index).