One-step hydrothermal synthesis of nano zinc carbonate and its use as a promising substitute for antimony trioxide in flame retardant flexible poly(vinyl chloride)

In this article, zinc carbonate with a nano size (nano ZnCO₃) was prepared by the reaction of zinc nitrite and urea in a one step hydrothermal synthesis. The effects of antimony trioxide (Sb₂O₃), nano ZnCO₃ and their mixture with different weight ratios on the flame retardancy of flexible poly(vinyl chloride) (PVC) were studied by using a limiting oxygen index test (LOI), a vertical burning test (UL-94) and a cone calorimeter test (CCT). The thermal stability of flame retardant flexible PVC composites was detected by thermogravimetric analysis (TGA). Very interestingly, it was found that substituting 75% Sb₂O₃ with nano ZnCO₃ in the flexible PVC obviously improved the dripping behavior in a UL-94 test, increased the LOI value and greatly reduced the peak heat release rate and total heat release simultaneously in comparison to using them separately, suggesting a significant synergistic effect between nano ZnCO₃ and Sb₂O₃ on improving the flame retardancy of flexible PVC. Importantly, tensile tests showed the addition of nano ZnCO₃ significantly enhanced the mechanical properties of flexible PVC. This work has offered a new approach to develop low or non Sb₂O₃ containing flame retardant flexible PVC composites.