Zinc compounds as flame retardants and smoke suppressants for rigid PVC

The effect of the concentration of zinc hydroxy-stannate and zinc borate on the fire performance of rigid PVC formulations has been investigated. Fire testing was carried out using cone calorimetry as well as the limiting oxygen index (LOI) test. In addition, further testing was done to check that incorporation of the fire retardant additives did not have any detrimental effects on other properties of the formulated PVC, such as heat stability, colour or impact strength. The results demonstrated that zinc hydroxy-stannate is an excellent fire retardant and smoke suppressant at additions levels of 3 parts per hundred parts of PVC. Zinc borate did not have the excellent fire retardant properties of zinc hydroxy-stannate, but was found to be an efficient and cost-effective smoke suppressant, although the presence of free zinc oxide in the sample affected the thermal stability of the formulation.