Structural evolution of pitch fibers during low temperature carbonization

Isotropic pitch-based carbon fibers (IPCFs) were prepared at various carbonization temperatures from 400 to 1200 °C using pitch fibers stabilized at 290 °C to investigate their structural evolution during the carbonization process. The chemical structure changes of IPCFs as a function of carbonization temperature were thoroughly analyzed using various characterization tools, such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and laser desorption/ionization time-of-flight mass spectrometry. The characterization results were systematically compared with those of the ordering structures obtained from Raman spectroscopy and X-ray diffraction. The results demonstrated that the transformation of the chemical structure, ordering structure, and physical properties of IPCFs proceeds with three distinct steps depending on the carbonization temperature: fusion of small aromatic structures of pitch, random stacking of the fused structure and conversion into mostly disordered carbon structures. In addition, we found a correlation of the chemical and ordering structure changes with the enhancement of physical properties, such as density, tensile modulus, and strength.