The combined effects of zinc stannate and aluminium diethyl phosphinate on the burning behaviour of glass fibre-reinforced, high temperature polyamide (HTPA)

The effect of changing the ratio of aluminium diethyl phosphinate (as Exolit OP1230) and zinc stannate (as Flamtard S) present within a glass-reinforced high temperature polyamide (HTPA/GF) at a constant total flame retardant level of 15 wt% is shown to have fire performance properties that depend on the ratio of both these agents. Aluminium diethyl phosphinate (AlPi) alone at 15 wt% gives LOI > 40 vol% and a V-0 rating. The introduction of zinc stannate (ZS) at levels up to 3.75 wt% maintains the LOI at about 40 vol% and the V-0 rating. Similarly, glow wire ignition temperatures and cone calorimetry results, in terms of minimal peak heat release rate, show that optimum fire performance also occurs at the [ZS] ≤ 3.75% and [AlPi] ≥ 11.25% condition. Smoke generation reduces only slightly when highest levels of AlPi are present compared with the HPTA/GF sample and then reduces further as the ratio [ZS]/[AlPi] increases. Tensile and impact properties are also optimal for the [ZS] ≤ 3.75 wt% and [AlPi] ≥ 11.25 wt% condition. At the mechanistic level, TGA studies show that for HPTA/GF, the presence of oxygen increases char residue in the 450–550 °C region compared to when heated under nitrogen. Air oxidation further increased residues above 450 °C when AlPi is present and confirms other published work that the reported volatilization occurring during pyrolysis under nitrogen is now in competition with its oxidation to aluminium phosphate. Thus residues above 450 °C in air comprise both increased char from HTPA plus residual aluminium phosphate with the latter remaining above 600 °C after the former has oxidized.