Activation energy of structural development for phenol formaldehyde resin-based carbon fibers Original Research Article

Activation energy of the structural development for phenol formaldehyde resin-based glass-like carbon fibers has been investigated in comparison with those for the pitch- and polyacrylonitrile (PAN)-based carbon fibers. The fibers were isothermally heat-treated using the internal resistance heating, and the resistivity change during heat-treatment and the variation of the structural parameters of the fibers heat-treated with various conditions were measured. The activation energy was determined from the shift factors for superimposing resistivity curves. The PAN-based carbon fibers showed a lower activation energy in the lower temperature region due to the effects of the external and the internal stresses. The phenol formaldehyde resin-based carbon fibers showed a higher activation energy in the lower temperature region. For the phenol formaldehyde resin-based carbon fibers, the temperature dependence of the activation energy was an apparent phenomenon and resulted from successive structural change with two different activation energies. The activation energies for the pitch-, PAN- and phenol formaldehyde resin-based carbon fibers observed in the higher temperature region were about 1000 kJ mol−1, which was close to the values reported for various graphitizing carbons. This suggested that although the crystallite sizes and the perfection of the structure are quite different between graphitizing and non-graphitizing carbons, the rate-determining, fundamental thermally activated processes are similar.