Improving the flame retardancy and smoke suppression of flexible PVC by incorporating zinc borate-modified diantimony trioxide

The properties and structure of flexible PVC by incorporating zinc borate (ZB)-modified diantimony trioxide (Sb₂O₃) were investigated. The results of flame retardancy and smoke suppression testing indicate that there was an obvious maximum Limited oxygen index (LOI) value of PVC/20 wt.% ZB–Sb₂O₃ composites reached 37.5% and passed the UL 94 V-0 rating. An obvious synergistic effect between ZB and Sb₂O₃ was observed by LOI, SDR, and TG. Moreover, remarkable decreases in the smoke density were observed when ZB–Sb₂O₃ was incorporated into PVC. In addition, the tensile strength and elongation at break of PVC/ZB–Sb₂O₃ composites was higher than PVC/Sb₂O₃ composites, and this ameliorative effect was mainly arising from the ZB–Sb₂O₃ nanoparticles, which reduced the degree of fatal defects on PVC. The addition of ZB and Sb₂O₃ greatly increased the amount of residual char and apparently improved the mechanical properties of PVC composites. According to scanning electron microscopy photographs of residual char, after thermal decomposition, there were many fragments linked to the condensed phase and the compact char layer. Fourier transform infrared spectroscopy shows the residues char was composed of benzene ring, the flame retardants occurred and the condensed phase with significant interactions.