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Lignin is a promising precursor of low-cost carbon fibers. However, the mechanical properties of carbon fibers produced from melt-spinning of raw lignin are poor, restricted by the randomly cross-linked polymer structures of lignin. In the present study, carbon fibers were produced from lignin-derived phenolic oil. Pyrolytic lignin was isolated from pyrolysis oil of red oak and washed with toluene to remove volatile impurities. Upon repolymerizing with 0.5% of sulfuric acid, the toluene-washed pyrolytic lignin became solid with the glass transition temperature (Tg) of 101 °C and the average molecular weight of 1267 Da. The repolymerized pyrolytic lignin was further processed into carbon fibers through melt-spinning, oxidative stabilization and carbonization at 1000 °C. The average tensile strength and modulus of the fibers were 855 MPa and 85 GPa, while the highest values of individual fibers were 1014 MPa and 122 GPa, respectively. The present study suggests that the quality of the carbon fiber produced from pyrolytic lignin could be further improved by process optimization.

The possibility of producing carbon fiber from an industrial corn stover lignin was investigated in the present study. Asreceived, high-ash containing lignin was subjected to methanol fractionation, acetylation, and thermal treatment prior to melt spinning and the changes in physiochemical and thermal properties were evaluated. Methanol fractionation removed most of the impurities in the raw lignin and also selectively removed the molecules with high melting points. However, neither methanol fractionation nor thermal treatment rendered melt-spinnable precursors. The precursors were highly viscous and decomposed easily at low temperatures, attributed to the presence of H, G phenolic units, and abundant hydroxycinnamate groups in herbaceous lignin. A two-step acetylation of methanol fractionated lignin greatly improved the mobility of lignin, while enhancing the thermal stability of the precursor during melt-spinning. Fourier Transform Infrared and 2D-NMR analysis showed that the contents of phenolic and aliphatic hydroxyls, as well as the hydroxycinnamates, decreased in the acetylated precursors. The optimum precursor was a partially acetylated lignin with a glass transition temperature of 85 8C. Upon oxidative stabilization and carbonization, the carbon fibers with an average tensile strength of 454 MPa and modulus of 62 GPa were obtained. The Raman spectroscopy showed the I D /I G ratio of the carbon fiber was 2.53. V C 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45736.

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