Zinc hydroxystannate- or zinc stannate-coated calcium carbonate as flame retardant for semirigid poly(vinyl chloride)

The flame retardant and smoke suppressant properties of semirigid PVC treated with CaCO3, zinc hydroxystannate, zinc stannate, zinc hydroxystannate-coated calcium carbonate, and zinc stannate-coated calcium carbonate have been studied through the limiting oxygen index, anaerobic char yield, and smoke density rating (SDR) methods. The thermal degradation in air of the treated semirigid PVC is studied by thermogravimetry (TG) and differential thermal analysis (DTA) from ambient temperature to 1073 K. The morphologies of the additives and the unaerobic char formation are studied through SEM. The mechanical property is also studied. The results show that the semirigid PVC treated with zinc hydroxystannate-coated calcium carbonate or zinc stannate-coated calcium carbonate has a higher limiting oxygen index and anaerobic char yield, lower SDR and starting decomposition temperature, a more compact structure of char formation and reduced tensile strength and elongation, and improved impact strength than the semirigid PVC without flame retardant.