The influence of novel zinc hydroxystannate-coated fillers on the fire properties of flexible PVC

Abstract

Zinc hydroxystannate (ZHS), at levels of 2-5 phr, and the hydrated fillers, magnesium hydroxide (MH) and alumina trihydrate (ATH), at levels of 20–50 phr, are effective flame retardants and smoke suppressants for flexible PVC. Novel ZHS-coated hydrated fillers are found to exhibit markedly improved fire-retardant properties, particularly with regard to increasing LOI values, reducing heat release rates and suppressing smoke generation, when compared with conventional uncoated forms. The ZHS coating appears to change the filler particle morphology and there is evidence that the coating is largely retained on the filler surface after melt processing into the PVC. The improved dispersion of the active tin compound in the polymer matrix leads to enhanced fire retardancy and this, in turn, allows significant reductions to be made in overall filler loading, with no loss in flame-retardant or smoke-suppressant performance. © 1997 John Wiley & Sons, Ltd.