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Graphene oxide (GO) has been widely used as an additive of polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) to optimize its crystal structure and improve the mechanical performances of nanofibers. However, the homogeneous dispersion of GO nanosheets among entangled PAN molecular chains is always challenging, and the poor dispersion of GO severely limits its positive effects on both the structure and performances of CNFs. Considering this issue, this paper provides for the first time an effective solution to achieve rapid and uniform introduction of GO in PAN-based nanofibers via in situ polymerization, and the optimization of the nanofiber structure by GO is systematically studied in three consecutive stages (polymerization, electrospinning, and carbonization) of the production process. During in situ polymerization, PAN is tightly attached on GO nanosheets to form PAN/GO nanocomposites, and this interaction is maintained throughout the spinning process. Not only the arrangement of PAN molecular chains but also the crystal size of the final turbostratic structure of CNFs is considerably improved by the interaction between PAN and GO. Besides, the direct proof that GO nanosheets promote the crystallization and orientation of the nanofiber matrix is presented. As a result, the tensile strength of CNFs is remarkably increased by 2.45 times with 0.5 wt % addition of GO. In summary, this paper provides a method for efficiently introducing nanoscale additives into PAN-based nanofibers and gives insights into the production of high-performance CNFs with the addition of GO.

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The high quality polyacrylonitrile (PAN) fibers, which were used to manufacture the high performance carbon fibers, were prepared by the dry‐jet wet spinning process. The fiber samples were treated by using the ultrathin sectioning and solution etching methods. Subsequently, the changes of the fibril structures and mechanical properties were investigated by utilizing scanning electron microscopy, high‐resolution transmission electron microscopy and mechanical tester. The fiber titer and diameters, the amount of the pores decreased during the spinning process. The microfibrils were oriented along the fiber axis to form the fiber backbone in PAN fibers. Furthermore, the microfibrils with small size were incorporated into the large fibrils and some fold chains formed the interfibril transverse joint bridges to reinforce the connection of the fibril elements. The fibrils served as self‐reinforcing element to efficiently resist the cracks propagation and dissipate much energy to increase the tensile strength and initial modulus. Consequently, the PAN precursor fibers with the homogeneous, compact, well‐oriented, and closely interlinked fibrils, presented high tensile strength and initial modulus. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47336.