Carbon Fiber from Isotropic Petroleum Pitch Doped with Carbon Nanotubes

The comprehensive investigation results of surface morphology, the internal structure, and the physical and physicomechanical properties (thermal conductivity coefficient, specific electrical resistance, tensile strength, Young’s modulus) of carbon fiber obtained from isotropic pitch based on heavy oil pyrolysis resin are shown in this paper. The pristine isotropic pitch was doped with ultralong double-walled carbon nanotubes with a single filament length exceeding 10 000 nm, with their content varying from 0 to 1.0 wt %. The moulded carbon fiber, after stabilization by thermal oxidation unfusible state, was exposed to various heat treatment regimes: carbonization at 2000°C, as well as graphitization at 2500 or 2800°C. It was shown that carbon nanotubes content increase leads to different effects. Compared to undoped carbon fiber, there is an increase in the thermal conductivity coefficient (from 6.61 to 12.72 W/(m K)) and a decrease in specific electrical resistance (from 33.90 to 5.41 μΩ m). However, this is accompanied by inhomogeneities formation in doping component distribution within the carbon fiber filament, resulting in a significant degradation of the physicomechanical properties. Typical surface and structural defects of the final filament (overstretching, protrusions, hollows) that appear during its moulding and depending on the carbon nanotube content in the pitch material are discussed.