ZINC HYDROXYSTANNATE - A COMBINED FLAME-RETARDANT AND SMOKE SUPPRESSANT FOR HALOGENATED POLYESTERS

Zinc hydroxystannate (ZHS) has been found to exhibit exceptional flame-, smoke- and toxic gas-retardant properties in unsaturated polyester resins based on the reactive halogenated compounds, chlorendic anhydride (CA) or dibromoneopentylglycol (DBNPG). At a 2 phr incorporation level, ZHS rendered polymers containing either 28% Cl (as CA) or 10% Br (as DBNPG) self-extinguishing in the UL-94 vertical test, and gave reductions in smoke and carbon monoxide emission of ca. 50 and 80%, respectively, for the chlorinated plastic, and ca. 20 and 25%, respectively, for the brominated formulation. Thermoanalytical and related mechanistic experiments suggest that, whereas in the DBNPG resin the fire-retardant action of the tin additive involves both the condensed and vapour phases, its effects in the CA system appear to be almost exclusively due to vapour phase activity.