Research supported by pinfa member William Blythe has preliminary assessed around 150 metal compounds for potential as a PIN flame retardant or synergist for polyamide. 151 compounds were produced from low toxicity, water soluble ions or complexes of magnesium, aluminium, calcium, manganese, iron, copper, zinc, tin boron, silicon, phosphorus and nitrogen (NO2).
Of around 200 possible reaction compounds, 142 were successfully isolated. After excluding compounds already known to be marketed as PIN FRs, these were then screened for potential use as FRs by testing in 25% loading in polyamide 6.6 (PA66) with thermal degradation/mass loss tests (char formation potential, compatibility with processing of polyamide at 290°C), so selecting 19 compounds for further study, and finally 7 were selected and successfully synthesised large scale (100g of compound): aluminium, zinc, tin tungstates; tin (II) phosphite, triphosphate and phenylphosphonate; iron (II) aluminate and hyphosphosphite. These showed varying but limited flame retardant effects, including on peak and total heat release rate, leading to the conclusion that they would not be effective flame retardants on their own but could be potentially interesting synergists to FR systems.
“Synthesis and thermal analytical screening of metal complexes as potential novel fire retardants in polyamide 6.6” A. Holdsworth et al., Polymer Degradation and Stability 144 (2017) 420e433 http://dx.doi.org/10.1016/j.polymdegradstab.2017.09.002