Influence of Phosphomolybdates on Flame Retardancy and Smoke Suppression of PVC Matrix Flame Retardant Composites

Four types of phosphomolybdates (iron, cobalt, nickel, and zinc) were each combined with antimony trioxide (Sb₂O₃) to prepare polyvinyl chloride (PVC) composites. The effects of the phosphomolybdates on the combustion behavior, smoke release, and mechanical properties of the PVC composites were studied by thermogravimetric analyzer, limiting oxygen index (LOI) tester, smoke density tester, cone calorimeter, scanning electron microscopy (SEM), and universal tensile tester. The results indicate that phosphomolybdates exhibit a significant synergistic flame-retardant effect with Sb₂O₃ in the PVC matrix. Compared with Sb₂O₃ alone, the addition of phosphomolybdates can significantly improve the LOI of PVC composites. It can also reduce smoke release, lower the heat release rate (HRR) of PVC composites, and produce more char residual, which is more continuous and denser. Meanwhile, there is no significant loss of mechanical properties. Overall, nickel phosphomolybdate has been determined to be the most effective of these four phosphomolybdates. Compared with PVC-1, the peak heat release rate (PHRR) of PVC-4 with nickel phosphomolybdate decreased by 13.3%, the total smoke production (TSP) decreased by 37.3%, and the peak smoke production rate (PSPR) decreased by 28.9%. This study demonstrates that replacing some of the Sb₂O₃ with phosphomolybdate can achieve efficient flame retardancy and smoke suppression in PVC. And the results of this study can also provide a reference for future research on the application and promotion of flame-retardant PVC.