Thermal decomposition of some Diels–Alder adducts of resin acids: Study of kinetics process

Abstract

The thermal behaviors of three Diels–Alder adducts of rosin acids were studied using thermogravimetry coupled to Fourier transform infrared spectroscopy and mass spectroscopy (TG-FTIR–MS) analysis in non-isothermal conditions. The TG data processing at three heating rates was performed using Netzsch thermokinetics software. The dependence of the activation energy (E) of the degradation process versus conversion degree (α) was evaluated using Friedman and Ozawa–Flynn–Wall model-free analyses. This dependence suggests that the degradation process is a complex one and can be divided in one or two steps, depending on the chemical adduct structures. The degradation processes and the thermal kinetic parameters were also estimated, using the multivariate non-linear regression method. The kinetic parameters and the most probable thermal degradation mechanisms were given. FTIR–MS analysis of the evolved gaseous products (on low temperatures interval 200–350°C) shows the presence of ammonium derivatives, carbon dioxide and water. With temperature increase, acids, anhydride, alkane and alkene derivatives, aromatic amines, aromatic compounds (benzene, alkyl benzene, toluene, naphthalene) are eliminated. At temperatures near 500°C tricyclic diterpene isomers, retene, are identified, as a result of dehydrogenation, dealkylation, dehydration and scission of hydrophenathrene moieties.