Flame-retardant Properties and Transformation of Flame-retardant Mechanisms of EVA: Effect of ATH/ADP Ratio

To improve the flame retardancy of Ethylene-Vinyl Acetate Copolymer (EVA) with Aluminum Hydroxide (ATH), a blend of aluminum diethylphosphite (ADP) and ATH was used.The flame-retardant properties of the composites were evaluated by using Vertical Burning (UL-94), Limiting Oxygen Index (LOI), and Cone Calorimeter (CONE) tests.The results indicated that at the mass ratio of ATH to ADP of 2:1 and 1:2, compared to the EVA/ATH composites, the Vertical Burning rating improved from no rating to V-0, and the LOI increased from 34.5% to 37.8% and 42.8%, respectively.Different methods were used to analyze the flame-retardant mechanism of samples with these two ratios.For the sample with a 2:1 ratio of ATH to ADP, the content of phosphorus-containing compounds released during thermal decomposition was extremely low, and the formation of Aluminum Phosphate (AlPO4) strengthened the char layer, making it more continuous and dense, resulting in a significantly higher residue mass than theoretical values.Therefore, the proposed flame-retardant mechanism at this ratio involves the formation of a substantial amount of AlPO4 during the thermal decomposition of ATH and ADP, which enhances the char layer, thereby improving the composite material's flame retardancy.For the sample with a 1:2 ratio of ATH to ADP, the char layer had more pores, and the residue mass in the TGA test was significantly lower than the theoretical value, but high-intensity phosphorus-containing compoundsVol.