Synergistic Flame Retardant Effect of Lanthanum Oxide in Ethylene-vinyl acetate/Aluminium Hydroxide Composites

The flammability characterization and synergistic flame retardant mechanism of lanthanum oxide (La2O3) in the ethylene-vinyl acetate/aluminium hydroxide (EVA/ATH) composites were studied by limiting oxygen index (LOI), UL 94 test, cone calorimeter test (CCT), and thermogravimetric analysis (TGA). The results showed that the addition of a given amount of La2O3 apparently increased the LOI value, which for the sample with 1.5 wt% La2O3 reached 37.5. However, the addition of La2O3 cannot enhance the ratings of UL 94 test. The data obtained from the CCT indicated that the addition of La2O3 greatly prolonged the time to ignition, increased the fire performance index (FPI), and predictably reduced the fire growth index (FGI). It has been found that there is a synergistic flame retardant effect between La2O3 and ATH in EVA/ATH/La2O3 composites. The synergistic mechanism between La2O3 and ATH is due to its physical process in the condensed phase, as revealed by CCT data showing that the addition of La2O3 can make the formation of a more thermally stable barrier, and the residual char of the system with La2O3 is higher than that of the system without La2O3. A compact barrier produced by La2O3 collaborating with ATH consequently leads to the decrease of heat release rate, mass, and total release rate as detected by CCT. TGA results showed that La2O3 can enhance the thermal stability of the flame retardant composites at high temperature.