Kinetics of pyrolysis mass loss from cured phenolic resin

Abstract

Knowledge of the kinetics of phenolic resin pyrolysis is critical to the accurate modeling of ablatives used in rocket nozzle and re-entry environments. Most employ thermogravimetry to study this phenomena. Nearly all of the previous studies on ablative materials have utilized fairly slow heating with respect to the use environment. This has forced analysts to extrapolate to the much higher rates occurring in the use environment. The high heating rate predictions of these models suggest that pyrolysis can be postponed to much higher temperatures. This has had dramatic effects on the predicted mechanical response of the material under flight conditions. To avoid these large extrapolations, laboratory data was required at or near the high heating rates seen in the use environment. A new facility was constructed that is capable of obtaining data at substantially higher heating rates than are currently available. Cured SC 1008 phenolic resin in powdered form was heated at eight heating rates ranging from 0.25 to 2500°C/min. The data indicates that the weight loss behavior of this material at very high heating rates exhibits a much reduced kinetic response over what was previously predicted, and that this may be due to a change in chemical reaction mechanism.