Plasticized Melt Spinning of Lignin Precursor Fibers and Carbonization Assisted by Electron Beam Irradiation

Although previous work demonstrated that the thermostabilization of fatty-acid-functionalized lignin (FAFL) can be effectively accelerated by UV irradiation, utilizing FAFL as a melt-spinnable carbon fiber precursor has presented a significant challenge: the solidification of lignin melts before they can be spun. This phenomenon arises from the uncontrollably rapid rheological transition of molten lignin from a predominantly viscous state to an elastic one. To overcome this problem, in this study, stearic acid (SA) was employed for both the chemical modification and plasticization of lignin precursors. Stearic acid-functionalized lignin (SAFL) was homogeneously blended with SA, followed by melt spinning, electron beam irradiation (EBI), and thermal treatments. SA containing an octadecyl group effectively plasticized SAFL to form plasticized SAFL (SLS) melts at lower temperatures compared to pristine SAFL. Notably, even after prolonged heating (∼2 h) at the spinning temperature, the predominantly viscous state of SLS was maintained without the formation of cross-links among SAFL macromolecular precursors. Moreover, EBI-treated SLS fibers were more rapidly thermostabilized without experiencing melt deformation and subsequently converted to carbon fibers with measurable mechanical properties (tensile strength = 0.74 GPa, tensile modulus = 65 GPa).