This study demonstrates that low processing rate for producing polyacrylonitrile (PAN)-based carbon fiber is a critical to obtain a homogeneous radial microstructure with high resistance to oxidation, thereby resulting in their improved mechanical strength. The dry-jet wet spun PAN organic fibers were processed (e.g., stabilized and then carbonized) utilizing two different rates; one is 1.6 times longer than the other. The effect of processing rate on the microstructural evolutions of carbon fibers was analyzed by scanning electron microscopy after slow etching in air, as well as Raman mapping after graphitization. The rapidly processed fiber exhibited the multilayered radial structure, which is caused by the radial direction stretching of the extrusion in the spinning. In case of the slowly processed fiber, the layered radial structure formed in the spinning process was changed into a more homogeneous radial microstructure. The slowly processed fibers showed higher oxidation resistance, higher mechanical properties, and higher crystallinity than the rapidly processed one. Raman mapping confirmed that the microstructure developed during spinning was sustained even though fiber was thermally treated up to 2800 °C.

Effect of low processing rate on homogeneous microstructural evolution of polyacrylonitrile-based carbon fibers
    Abstract
    1 Introduction
    2 Experimental
        2.1 Preparation of carbon fibers
        2.2 Etching by oxidation and graphitization
        2.3 Characterization
    3 Results and discussion
        3.1 Cross-sectional microstructure
        3.2 Longitudinal surface of carbon filament
        3.3 Microstructure of the carbon filament
        3.4 Physical and mechanical properties of the CFs
    4 Conclusions
    Acknowledgements 
    References

• Doo‑Won Kim(Institute of Advanced Composite Materials, Korea Institute of Science and Technology)
• Dae Ho Kim(Hyosung Corporation, Jeonju Plant)
• Sung Ryong Kim(Hyosung Corporation, Jeonju Plant)
• Bo‑Hye Kim(Division of Science Education, Chemistry Education Major, Daegu University)
• Yun Hyuk Bang(Korea Institute of Carbon Convergence Technology)
• Duck Joo Yang(Department of Chemistry, University of Texas at Dallas)
• Go Bong Choi(Department of Polymer Engineering, Graduate School, School of Polymer Science and Engineering and Alan G. MacDiarmid Energy Research Institute, Chonnam National University)
• Yoong Ahm Kim(Department of Polymer Engineering, Graduate School, School of Polymer Science and Engineering and Alan G. MacDiarmid Energy Research Institute, Chonnam National University)
• Kap Seung Yang(Department of Polymer Engineering, Graduate School, School of Polymer Science and Engineering and Alan G. MacDiarmid Energy Research Institute, Chonnam National University/Kap Seung YangCarbon Composite Materials R&D Center HPK Inc)