Three types of β resins, namely, β-1, β-2, and β-3 were obtained from a medium coal tar pitch, modified pitch A, and modified pitch B, respectively. The pyrolysis characteristics of these three β resins were studied by TG/DTG analysis, FTIR spectroscopy, and curve-fitting method. The pyrolysis of β-1 showed a two-step mass loss, and the pyrolysis of β-2 showed a one-step mass loss. However, the pyrolysis of β-3 showed a three-step mass loss. This difference in pyrolysis among the three β resins was caused by the dissimilarity in their aromaticity index (Iar) and CH3/CH2 ratio; these factors significantly affect the aromaticity and number of aliphatic side chains in β resin. The polarized microscopic structures of the pyrolysis products β-1-P, β-2-P, and β-3-P obtained from β resins show that β-1-P mainly has a coarse fibrous structure, whereas β-2-P and β-3-P have a mosaic structure and fine fibrous structure, respectively. The results of XRD and Raman analysis combined with curve-fitting method show that the content of ordered carbon microcrystalline structure in β-3-P is higher than the contents of other two samples, and β-2-P has the lowest content of this microcrystalline structure. In fact, the lower Iar (<0.5) corresponded to a mosaic structure, and the higher Iar (>0.8) corresponded to a fibrous structure. Moreover, oxidation linking reaction inhibited the formation of plane macromolecules, thus hindering the formation of an optically anisotropic fibrous structure during the pyrolysis of coal tar pitch.
Yaming Zhu, Xuefei Zhao, Lijuan Gao, Jun Lv, Junxia Cheng, Shiquan Lai