Comparative study on synergistic effect of LDH and zirconium phosphate with aluminum trihydroxide on flame retardancy of EVA composites

Flame-retardant ethylene vinyl acetate (EVA) composite based on aluminum trihydroxide (ATH), layered double hydroxide (LDH) and organo-modified zirconium phosphate (mZrP) were prepared by melt-compounding method. The synergistic effect of LDH and mZrP with ATH on the fire behavior and thermal stability of EVA composites was studied by limiting oxygen index, UL-94 test, cone calorimeter and thermogravimetric analysis. EVA composite with ATH and LDH passed the V-0 rating while EVA composite with ATH and mZrP exhibited relatively low peak heat release rate. EVA/ATH composite with 10 mass% LDH exhibited a char yield of 34 % at 700 °C, while its counterpart with 10 mass% mZrP showed 29 %, indicating LDH possessed superior flame-retardant synergistic efficiency with ATH over mZrP in terms of promoting char formation. Regarding the heat release rate (HRR), EVA/ATH composite with 10 mass% mZrP displayed a 73 % reduction in PHRR, whereas its counterpart with the equivalent loading of LDH showed a lower flame-retardant synergistic efficiency (a 58 % reduction in peak HRR). The results above demonstrated that LDH mainly functioned as catalyst in char formation, while mZrP was beneficial to restraining heat release.