Thermo-oxidative-kinetic study of cinnamyl diesters

The thermo-oxidative behavior and kinetic study of cinnamyl diesters having different aliphatic chain lengths in the structure were studied by the TG/DSC/FTIR coupled method. The degradation processes on the studied esters occurred through several overlapping steps, between 150 and 450 °C, linked to different gaseous products emitted and with changes of E(α) values as (α) increased. The initial stage of cinnamyl diester degradation (for α ≤ 0.15) was independent of the kind and length of the aliphatic chain, and the energetic barrier necessary to break the ester linkages was independent of the transformation degree (ca. 60-80 kJ mol−1). A progressive increase in the E(α) values from ca. 80 kJ mol−1 to 200-250 kJ mol−1 (for 0.15 ≤ α ≤ 0.40) suggested the existence of competitive reactions which were due to chemical recombination processes in the gas phase, involving oxidation reactions of volatile organic fragments with oxygen. However, as α is changed between 0.40 ≤ α ≤ 0.75, the high data dispersion and the marked increase in experimental error in the E(α) values indicated a strong dependence of the kinetic parameters on conversion degree and complexity of chemical processes taking place. Finally, for 0.8 ≤ α the decrease in E(α) values suggested modifications of degradation mechanism and indicated that the easy oxygen accessibility toward the sample promotes the fast gasification reaction of the carbonaceous residues.