Initial polymer degradation as a process in the manufacture of carbon-carbon composites

The fundamental pyrolysis step in carbon-carbon composite processing utilizing a 2-D phenolic resin-carbon fiber composite was investigated both experimentally and analytically. The gas permeabilities of a degrading composite in the in-plane and the through-thickness directions were measured and analyzed as a function of porosity by the Kozeny-Carman eqn. Degradation kinetics of the polymer matrix was determined by the composite degradation methodology capable of describing different stages of gas evolution. Subsequently, a mathematical model was developed combining heat, mass and momentum-transport phenomena with the degradation kinetics of the matrix. Integrating kinetic and thermodynamic variables and experimentally determined material correlations, the model could provide pressure, temperature and degree of degradation as a function of processing time and through-thickness position in the composite. The effect of composite size and heating rate was investigated by the model, verifying practical experiences in the carbonization step during carbon-carbon manufacturing processes.