The influence of zinc compounds on thermal stability and flame retardancy of wood flour polyvinyl chloride composites

•Wood flour-polyvinyl chloride(WF-PVC) composites with zinc compounds were prepared.•The charring ability of Zn on WF-PVC composites is higher than that of Sn.•The flame retarding mechanism of the element Zn and Sn was proposed and confirmed. Fire safety is an important issue for wood flour polyvinyl chloride (WF-PVC) composites. Here, three zinc salts are used in WF-PVC composites. Thermogravimetric analysis showed that zinc borate and zinc stannate did some negative effects on the thermal stability of WF-PVC composites at the first thermal decomposition stage, while zinc molybdate had little effects on thermal decomposition of the composites. However, zinc borate and zinc stannate promoted the formation of char. Based on the experiments and theoretical analysis, the charring ability of element zinc (Zn) was stronger than that of tin (Sn). According to the cone calorimetry, zinc stannate and zinc borate were effective flame and smoke retardants, which were mainly reflected in the longer ignition time and reduced heat and smoke release of flame retardant composites. From the char residue, zinc compounds played an important role in the condensed phase, the element tin mainly acted on the surface, while the element zinc worked in the whole phase. Finally, the flame retardants had unfavorable effects on the strength properties of WF-PVC.