Poor bonding occurs with resin due to surface inertness of carbon fiber (CF), so CF surfaces were often treated. In some common surface treatments, sizing was a simple and effective modification method. Polyurethane (PU) was used as the main component of sizing agents due to its similar structure to polyamide 6 (PA6). The CF/PA6 composites’ interfacial properties were improved using PU as a sizing agent. Meanwhile, in this paper, glycidol (GLD) was introduced into the PU emulsion so that the epoxy group reacted with the carboxyl group on the acidified CF. After testing, when the content of glycidyl in the sizing agent is 2%, the CF/PA6 composites showed an important improvement in tensile, impact, and flexural strengths, which increased by 49.4%, 94.6%, and 53.2%, respectively. In addition, the effect of modified WPU sizing agents with different GLD contents on the properties of CF/PA6 composites was investigated.

Synthesis of glycidol-modified waterborne polyurethanes as sizing agents for enhancing the mechanical properties of CFPA6 composites
    Abstract
    1 Introduction
    2 Materials and methods
        2.1 Materials
        2.2 Preparation of the WPU emulsions
        2.3 Preparation of WPU sizing agent
        2.4 Preparation of composite
        2.5 Measurement and characterization
            2.5.1 Dynamic light scattering instrument (DLS)
            2.5.2 Thermogravimetric analysis (TG)
            2.5.3 Fourier transform infrared spectroscopy (FTIR)
            2.5.4 Contact angle test
            2.5.5 Scanning electron microscopy (SEM)
            2.5.6 Mechanical performance test
    3 Results and discussion
        3.1 Particle size analysis for WPU
        3.2 Thermal stability analysis of WPU films
        3.3 Infrared analysis of WPU films and CF
        3.4 CF contact angle analysis
        3.5 Surface morphology of CF
        3.6 Mechanical properties of composite materials
        3.7 Brittle fracture surface characterization of SCFPA6 composites
        3.8 Interface enhancement mechanism
    4 Conclusions
    Acknowledgements 
    References

• Pengfei Deng(School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China)
• Shuangquan Wang(School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China)
• Qiuxue Zhang(School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China)
• Songsong Li(School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China)
• Yunjiao Deng(School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China, Engineering Research Center of Synthetic Resin and Special Fiber, Ministry of Education, Changchun University of Technology, Changchun 130012, China) Corresponding author
• Zhongyu Fu(School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China, Engineering Research Center of Synthetic Resin and Special Fiber, Ministry of Education, Changchun University of Technology, Changchun 130012, China)
• Chao Zhou(School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China, Engineering Research Center of Synthetic Resin and Special Fiber, Ministry of Education, Changchun University of Technology, Changchun 130012, China)
• Huixuan Zhang(School of Chemical Engineering, Changchun University of Technology, Changchun 130012, China, Engineering Research Center of Synthetic Resin and Special Fiber, Ministry of Education, Changchun University of Technology, Changchun 130012, China)