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.