Influence of pyrolytic decomposition on the microstructure evolution of benzoxazine-derived carbon–carbon composites

The microstructural evolution of a T800 2 × 2 twill weave carbon fiber/benzoxazine resin composite was quantified through the pyrolytic decomposition region of 250–800°C. In performing kinetic analysis, three stages of mass loss were identified and quantified through a non-isothermal kinetics model. The kinetics model parameters were determined at each state of the reaction, and the corresponding decomposition gases were analyzed to gain insight into pyrolytic reactions. The kinetics model was then used to design a heat treatment cycle that isolated each stage of the reaction so that the effects on the progression of the porous microstructure could be characterized. In the first stage of the reaction, the nucleation and growth of voids were dominant. In the second stage, the initiation of microcracks within the matrix was observed. The third stage saw the formation of an interconnected porous network in which cracks propagated throughout the composite and formed a continuous pathway from the surface to the centermost voids. To evaluate these microstructural features, X-ray computed tomography was utilized. In doing so, the various damage phenomena including void size, the degree of open and closed porosity, and the crack density were quantified. Graphical Abstract