Kinetics of Thermal and Oxidative Decomposition of Printed Circuit Boards

Abstract

The kinetics of thermal and oxidative decomposition of printed circuit boards is investigated under various heating rates (5, 10, 15, 20, and 25 K/min) and oxygen concentrations (5, 10, and 15%) in the nitrogen-oxygen atmosphere by means of thermogravimetric measurements. Results show that there is only one reaction stage in the inert atmosphere, with an initial reaction temperature of 564–584 K and an activation energy at 181.59 ± 21.80 kJ/mol. But there are two reaction stages when oxygen is present in the carrier gas. The activation energy is in the range of 170.79–184.98 kJ/mol for the first-stage reaction and 113.69–138.85 kJ/mol for the second-stage reaction. The fractional residue is reduced by 14.1–18.8% in the oxidative atmosphere. The rate equations for various oxygen concentrations can be modeled by Arrhenius-type equations, from which kinetic parameters such as activation energy, preexponential factor, and reaction orders for unreacted material and oxygen concentration are determined using an extended Friedman's method. The cutoff conversion factor between the first and second reactions is in the range of 0.46–0.54, depending on the oxygen concentration. The complete rate equations when two-stage reactions are involved can be obtained by summing the individual weighted rate equations; the weighting factor are determined from the cut-off conversion factor.