Electrochemical treatment has a significant effect on the properties of carbon fibers (CFs). In this study, the effect of mild electric field action on the microstructure and properties of polyacrylonitrile (PAN)-based high-modulus CFs (HMCFs) and high-strength CFs (HSCFs) was investigated. Under the action of a mild electric field, CFs did not show obvious defects, but their microstructure, mechanical properties and electrical properties were affected. For HMCFs, the graphitization degree in both axial and radial directions of the fibers had a decreasing trend, the grain spacing increased, and the grain size and degree of orientation decreased, which led to a decrease in the tensile strength, tensile modulus and axial conductivity. However, for HSCFs, the pattern of change was exactly opposite to that of HMCFs. The results of this study can provide useful guidance for optimizing the production process and surface modification of CFs.

Evolution of microstructure and properties of various types of PAN-based carbon fibers under the action of a mild electric field
    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Energizing carbon fibers
        2.3 Characterization
            2.3.1 Scanning electron microscope
            2.3.2 X-ray photoelectron spectroscopy
            2.3.3 Raman spectroscopy
            2.3.4 X-ray diffraction
            2.3.5 Mechanical properties of carbon fiber
            2.3.6 Conductivity of carbon fiber
    3 Results and discussion
        3.1 SEM observation of carbon fibers
        3.2 Analysis of carbon-fiber surface functional groups
        3.3 Fiber Raman analysis of various regions
        3.4 XRD analysis of carbon-fiber crystal structure
        3.5 Mechanical properties analysis of carbon fibers
        3.6 Electrical resistivity analysis of carbon fibers
    4 Conclusions
    Acknowledgements 
    References

• Hongshuo Cao(State Key Laboratory of Organic‑Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China)
• Yanhong Tian(State Key Laboratory of Organic‑Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China)
• Jiangman Sun(State Key Laboratory of Organic‑Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China)
• Xuejun Zhang(State Key Laboratory of Organic‑Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China)