Laser pyrolysis of hydroxyl-terminated polybutadiene

Abstract

A method was developed for measuring the dynamic regression rate and plume transmission loss during laser pyrolysis of polymeric binder materials. This method was applied to an investigation of the thermal decomposition of hydroxyl-terminated polybutadiene. Measurements of steady regression rate and surface temperature during constant flux laser pyrolysis were correlated using a zeroth-order, single-step model to obtain global decomposition kinetic constants and the heat of decomposition. At these heating rates (102-104 K/s) the activation energy was Ec = 11 kcal/mole (E, = 5.5 kcal/mole). This is substantially lower than the values that have been obtained by lower heating rate (0.1-1 K/s) methods such as thermogravimetric analysis, differential thermal analysis, and differential scanning calorimeter, indicating that the rate-controlling decomposition step is a strong function of heating rate. It was also found that the addition of carbon black as an opacifier lowers the regression rate significantly, probably due to carbon accumulation on the surface. Pulsed laser pyrolysis tests gave a two-peaked, nonlinear response with one peak near 1 Hz corresponding to condensed phase processes and another peak near 300 Hz corresponding to gas phase processes.