LASER PYROLYSIS OF HYDROXYL-TERMINATED POLYBUTADIENE

A method was developed for measuring the dynamic regression rate and p lume transmission loss during laser pyrolysis of polymeric binder mate rials. This method was applied to an investigation of the thermal deco mposition of hydroxyl-terminated polybutadiene. Measurements of steady regression rate and surface temperature during constant flux laser py rolysis wee correlated using a zeroth order, single-step model to obta in global decomposition kinetic constants and the heat of decompositio n. At these heating rates (10(2)-10(4) K/s) the activation energy was E(c) = 11 kcal/mole (E(s) = 5.5 kcal/mole). This is substantially lowe r 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 ra te. It was also found that the addition of carbon black as an opacifie r lowers the regression rate significantly, probably due to carbon acc umulation on the surface. Pulsed laser pyrolysis tests gave a two-peak ed, nonlinear response with one peak near 1 Hz corresponding to conden sed phase processes and another peak near 300 Hz corresponding to gas phase processes.