Mineral additives reduce smoke and fire toxicity with a PIN FR, and improve and modify flame retardant effects. Four mineral PIN smoke suppressants (zinc stannate, zinc phosphate, titanium oxide and hydrotalcite) were tested at 1 % loading (and 5% for zinc stannate) with 18% of the PIN flame retardant AlPi (diethyl aluminium phosphinate) in polyamide 6.6 + 25% glass fibres. In cone calorimeter tests, all four smoke suppressants reduced peak heat release rate (PHRR) of the PIN FR polyamide glass fibre compound, but at 1% only hydrotalcite reduced total smoke production. In a smoke density chamber, only zinc stannate and hydrotalcite reduced peak smoke density but hydrotalcite significantly reduced time to ignition. At 5%, zinc stannate reduced PHRR by 30%, total smoke production by over 40%, peak smoke density by 60% and toxic emissions of carbon monoxide and hydrogen cyanide by 70% as well as reducing smoke particle size. The authors conclude that the mode of action of AlPi was switched from gas to condensed phase, resulting in increased dense char, suppressing smoke release and improving fire protection.
“No business as usual: The effect of smoke suppressants commonly used in the flame retardant PA6.6 on smoke and fire properties”, S. Goller et al., Polymer Degradation and Stability 209 (2023) 110276, https://doi.org/10.1016/j.polymdegradstab.2023.110276