Thermal decomposition behavior and kinetics of nanocomposites at low-modified ZnO content

Abstract

In this study, a titanate coupling agent (TCA) was used to modify the surface of nano ZnO. The thermal properties of room temperature vulcanized silicone rubber (RTV) nanocomposites with modified nano ZnO were compared at nano-filler weight fractions ranging from 0% to 2%. The results indicated that the titanate coupling agent was successfully grafted on the surface of nano ZnO. The size and shape of the nanoparticles were not changed after modification and all particles were about 36 nm. With increasing amounts of nanoparticles, the initial thermal decomposition temperature increased from 344.6 °C to 420 °C and reached maximum at 1.5% ZnO addition. The thermal decomposition process of RTV can be divided into three different stages. In the first stage, the temperatures at maximum decomposition rate (T_1max) for the five samples were similar. In the second and third stages, T_2max and T_3max increased 79.1 °C and 88.9 °C, respectively, upon addition of the modified nano ZnO. The thermal decomposition kinetics results showed that the activation energy (E_α) of RTV was lower than that of 1% ZnO/RTV at the low thermal conversion rate (α). The average E_α values of the two samples were similar, at 144.29 kJ mol⁻¹ and 146.78 kJ mol⁻¹, respectively. The kinetic energy index (n) of RTV was 3.84. Compared to pure RTV, 1% ZnO/RTV showed a more complex thermal decomposition process, as its n value was 0.66 higher than that of RTV. Comparing E_α and n values, it was found that the nanocomposites were less likely to transform into an activated complex due to their higher potential energy barrier.