Kinetic Study of Thermal Degraded Drying Oils

Abstract

At a fire scene caused by spontaneous combustion of drying oils and semi-drying oils, long heat storage is thought to produce thermal degraded oils in the vicinity of the fire occurrence point. In other words, even if the cause of a fire scene is difficult to judge from the appearance of the damaged scene where spontaneous combustion occurred, the possibility of spontaneous combustion might be considered more clearly by proving the existence of thermal degraded parts in oily debris. Results derived from both appearance and evidence are forensically reliable. It is considered that not only are changes of fatty acid composition observed in thermal degraded parts, but also changes of physical and thermodynamic properties. This paper focuses on thermal analyses as the method to distinguish these changes. The purpose of this paper is also to discuss the validity of thermal analyses as the method to prove the existence of thermal degraded parts in oily debris. Differential scanning calorimetry and thermogravimetry were applied to thermal degraded samples produced in experiments, and so the freezing point and thermal decomposition temperature were measured. Furthermore, a kinetic study was carried out based on the isoconversion method; using the value of activation energy derived from the line gradients, master curves were drawn. In the course of considering the freezing point, thermal decomposition temperature, the parallel relation among the lines and convergent state of master curve, and the distinguishable possibility of thermal degraded samples were discussed. In conclusion, this paper clarified that a kinetic study based on the isoconversion method allowed us to distinguish parts of a slight thermal degradation. This method is effective in proving thermal degraded parts existing in oily debris.