To address the need for a suitable thermoplastic resin-based sizing agent for accommodating the increasing demands of carbon fiber-reinforced plastic, in this work, alcohol-soluble polyamide 6 (PA6) and silane were chemically combined in a certain ratio to improve the mechanical interface properties of the carbon fiber/PA6 composite, and the enhancement in the mechanical interface strength of the final composite according to the treatment time was confirmed. Carbon fiber surface properties were analyzed through ultrahigh-resolution field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy, and Fourier transform infrared spectrometry. The tensile strength of carbon fibers before and after hybrid sizing treatment and the mechanical interfacial shear strength of the final composite were analyzed using tensile and universal testing machines, respectively. After the hybrid sizing treatment, the introduction of the sizing agent to the carbon fiber surface was confirmed through FE-SEM, and a simultaneous increase in the surface roughness was observed. Moreover, the interfacial adhesion was confirmed to increase significantly, as compared to that of the desized carbon fiber. Therefore, this modified sizing agent treatment serves as an effective method for improving the mechanical interfacial adhesion between the carbon fiber and the PA6 matrix.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Sizing process
        2.3 Characterization
        2.4 Physical properties
    3 Results and discussion
        3.1 Surface characteristics of the sized carbon fiber
        3.2 Physical characteristics of the sized carbon fibers
    4 Conclusion
    Acknowledgements 
    References

• Dong‑Kyu Kim(R&D Office 1st, Korea Carbon Industry Promotion Agency, Department of Carbon Materials and Fiber Engineering, Jeonbuk University)
• Seong‑Hyun Kang(R&D Office 1st, Korea Carbon Industry Promotion Agency, Department of Carbon Materials and Fiber Engineering, Jeonbuk University)
• Woong Han(R&D Office 1st, Korea Carbon Industry Promotion Agency, Department of Carbon Materials and Fiber Engineering, Jeonbuk University)
• Kwan‑Woo Kim(R&D Office 1st, Korea Carbon Industry Promotion Agency)
• Byung‑Joo Kim(Department of Carbon‑Nanomaterials Engineering, Jeonju University)