Synergistic effects of inorganic tin compounds and Sb2O3 on thermal properties and flame retardancy of flexible poly(vinyl chloride)

The effects of inorganic tin compounds such as zinc hydroxystannate (ZHS), tin dioxide (SnO2), and tin monoxide (SnO), Sb2O3, and their mixtures on the flame retardant and smoke suppressant properties of flexible poly(vinyl chloride) (PVC), and their flame retardant and smoke suppressant actions, were studied using the limiting oxygen index (LOI) test, the smoke density rating (SDR) test, thermogravimetric analysis/differential thermogravimetry/differential thermal analysis (TGA/DTG/DTA), scanning electron microscopy (SEM), and quantitative analysis. The results showed that the incorporation of small amounts of inorganic tin compounds and their mixtures with Sb2O3 can increase the LOI of PVC and decrease the SDR during combustion. Partial replacement of Sb2O3 in flexible PVC by ZHS resulted in a significant synergistic improvement in flame retardant behavior. TGA/DTG/DTA, SEM, and quantitative analysis showed that ZHS acts as a flame retardant in the solid phase, Zn2+ can catalyze dehydrochlorination of PVC and promote early cross-linking, leading to rapid charring, and Sn4+ can react with the char, thereby increasing the char stability. These actions, combined with the vapor-phase role of Sb2O3, can significantly enhance the flame retardancy of PVC.

► Tin compounds and Sb2O3 have a good synergistic effect on the flame retardancy of flexible PVC.
► Sb2O3/ZHS is the most effective fire retardant for flexible PVC.
► ZHS can catalyze dehydrochlorination of PVC and increase the stability of the char.