As a key component of composite materials, the interface quality is crucial for determining the mechanical properties of composites. Carbon fiber sizing treatment significantly enhances the fiber-matrix interface, a process extensively utilized in the carbon fiber industry. This study synthesized an environmentally friendly waterborne polyurethane sizing agent and investigated the impact of molecular weight, a critical factor, on composite performance by varying the soft segment type in the polyurethane. This research provides insights into cost-effective and eco-friendly surface treatment methods for carbon fibers and the design of robust interface structures.

Effect of molecular weight of aliphatic dicarboxylic acids polyester on properties of the waterborne polyurethane sizing agent
    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Synthesis of WPU
        2.3 Modification of CF surface
        2.4 Preparation of CFRPs
        2.5 Characterization
            2.5.1 Composition characterization
            2.5.2 Micromorphology characterization
            2.5.3 Thermal analysis and particle size analysis
            2.5.4 Tensile strength (TS) and interlaminar shear strength (ILSS)
    3 Results and discussion
        3.1 Chemical structure of WPU
        3.2 Surface chemical composition
        3.3 Contact angle
        3.4 Surface morphology analysis
        3.5 Tensile strength of fiber monofilament
        3.6 Mechanical properties of composites
        3.7 AFM
        3.8 The section of composites analysis
    4 Conclusion
    Acknowledgements 
    References

• Shuoyao Song(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China)
• Yuxuan Xing(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China)
• Dongliang Wu(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China)
• Xuhao Qin(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China)
• Xiaodong Liu(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China)
• Chuanxiu Hu(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China)
• Manman Kong(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China)
• Lei Liu(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China)
• Ruliang Zhang(School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China) Corresponding author