A combination of zinc hydroxystannate [ ZnSn(OH)6 ] inorganic zinc tin compound ZnHS) and ammonium polyphosphate (APP) was tested in thermoplastic polyurethane (TPU) with 12-15% loading of APP and 0-3% ZnHS.
1% ZnHS plus 14% APP showed optimal mechanical characteristics (better tensile strength than other combinations but still worse than pure TPU, better elongation at break than pure TPU or other combinations) and best fire performance (peak heat release rate PHRR < 12% of pure TPU, highest LOI Limiting Oxygen Index. All APP-ZnHS combinations achieved UL V0 (pure TPU did not). Inclusion of ZnHS at all tested levels significantly reduced the smoke density (c. 50% reduction after 8 minutes) and both of the two measured toxic gases in smoke (carbon monoxide, hydrogen cyanate, both reduced by more than 15%).
“The influence of zinc hydroxystannate on reducing toxic gases (CO, NOx and HCN) generation and fire hazards of thermoplastic polyurethane composites”, B. Wang et al., Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2016.04.029