Kinetics and 13C NMR Study of Oxygen Incorporation into PVC- and Pitch-Derived Materials

The kinetics of oxygen incorporation into a PVC-derived material with pitch-like characteristics was studied by isothermal thermogravimetric analysis at temperatures ranging from 200 to 270 degrees C. Activation energy, Ea, pre-exponential factor, A, and rate constants, k(T), were obtained from the weight-gain curves recorded during reactions of the material with molecular oxygen, which were analyzed following a kinetic first-order model. The numerical values obtained were E-a = 100.5 kJ/mol and A = 1.6 x 10(10) h(-1). The extent of the oxidation at a fixed temperature was monitored by elemental analysis, and the chemical changes in the materials were followed by solid-state C-13 NMR. The study was next extended to the chars obtained from three coal tar pitches with different softening points (55, 85, and I 10 degrees C). Comparisons were then established between the determined kinetic parameters and the chemical/structural aspects and compositions of each analyzed material.