Studies on the thermal stability and kinetic parameters of naturally aged Octol formulation

Abstract

A study on the thermal stability and kinetic parameters of an Octol formulation stockpiled for prolonged period a 20 year under natural environment conditions was investigated. The thermal stability of the naturally aged was studied by an employing thermogravimetry and differential scanning calorimetry methods and compared with freshly prepared Octol formulation. The results showed that the thermal stability did not significantly vary for aged Octol samples. The kinetic parameters of aged and freshly prepared Octol samples were also studied by means of the Kissinger and isoconversional Kissinger–Akahira–Sunose (KAS) methods. The values of apparent activation energy derived from the Kissinger method using DSC data for aged and fresh samples were obtained around 228.8 and 234.4 kJ mol‒1, respectively. The isoconversional KAS method was also used for computation of the activation energy at different values of conversion for two stages of thermal degradation using TGA data. The determined average activation energy for the first stage was obtained around 88.9 ± 4.1 kJ mol−1 for aged and 94.6 ± 6.5 kJ mol−1 for fresh sample, while average activation energy for the second stage was obtained 212.7 ± 14.5 kJ mol−1 and 218 ± 14 kJ mol‒1 for aged and fresh Octol formulations, respectively. These values were found to be consistent and close to those obtained from the Kissinger method. These results indicated that there was no any significant change in the kinetic parameters for aged and fresh samples. The pre-exponential factor for different values of conversion was also determined by the use of the so-called compensation effect. Conversion of aged and fresh samples using the kinetic parameters was found to be in good agreement with the experimental conversion data, and the maximum error limit was observed to be 8.0% between experimental and predicted conversion.