Detailed analysis of species production from the pyrolysis of the Phenolic Impregnated Carbon Ablator

Many modern materials that are being developed to protect space vehicles entering planetary atmospheres use phenolic impregnated carbon fiber substrates as the basic material architecture. To mitigate the heat flux into the material, the decomposition of phenolic phase generates protective gases that blow into the boundary layer and help shield the material. The goal of this paper is to measure the decomposition products of cross-linked phenolic as used in the NASA's Phenolic Impregnated Carbon Ablator (PICA). A custom batch reactor was designed to quantitatively determine detailed species production from the pyrolysis of PICA. A step-wise heating procedure using 50 K increments from room temperature up to 1250 K was followed. An initial PICA mass of 100 mg was loaded in the reactor, and the mass loss was measured after each 50 K step. Species production after each step was quantified using gas-chromatography techniques. The quantitative molar yields of pyrolysis products as a function of reaction temperature are compared to those from resole phenol-formaldehyde resin pyrolysis reported in the literature. The differences in product distributions between PICA pyrolysis and resole phenol-formaldehyde pyrolysis confirm that the decomposition products are sensitive to the composition of the material and the cross-linking process. These results indicate that characterizations need to be performed for all variations of phenolic-matrix based ablators. Such information is also critical for the development of next generation material response models.