Abstract: This article presents a synthetic method for tin phytate-coated zinc hydrox-ystannate (ZHS@Sn-Phyt) particles with different ratios, which were incorporated into soft polyvinyl chloride (PVC) as a composite synergistic flame retardant. The synthe-sized ZHS@Sn-Phyt particles were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The results revealed that a stable coating structure was formed in the form of Sn—O—P—O—Zn ionic bonds at the interface between the zinc hydroxystannate (ZHS) surface and the tin phytate (Sn-Phyt) coating layer. The PVC composites were evaluated through limiting oxygen index (LOI), cone calorimetry, and mechanical studies. When the mass ratio of ZHS@Sn-Phyt in the flame retardant was 1∶9, the best flame retardant properties of PVC were achieved, indicating that combining phosphorus and tin results in a better synergistic flame retardant effect. The LOI of the PVC/ZHS@Sn-Phyt composite was 1.6% higher than that of the PVC composite with only ZHS (without the Sn-Phyt coating). Moreover, the peak heat release rate and total heat release decreased by 18.9% and 31.7%, respectively. In addition, the carbon residue rate increased by 6.1% and the total smoke release of PVC/ZHS@Sn-Phyt and PVC/ZHS were similar. Both the tensile strength and the elongation at break of PVC/ZHS@Sn-Phyt were also better than those of PVC/ZHS at 26.79 MPa and 296.5%, respectively. Thus, this study provides a method for preparing efficient and green flame retardants for PVC. The phosphorus/tin-based synergistic flame retardant prepared by our method has the advan-tageous characteristics of ecofriendliness and simplicity of the preparation process.

Key words: tin phytate, zinc hydroxystannate, polyvinyl chloride, ?ame retardant, environmentally friendly