Surface free energy is an important parameter in surface and interface properties of fiber reinforced polymer composite. The BET (Brunauer, Emmett, and Teller) surface area and surface energy of the sample can be obtained by Inverse Gas Chromatography (IGC) based on the adsorption principle. In this paper, surface energy of carbon fiber bundle was tested by means of IGC under different conditions to find reliable test parameters. The main parameters involved include length, mass, and packing density of sample, target fractional surface coverage, flow rate, and maximum elution time. It is demonstrated that IGC has the advantages of simple sample preparation, stable test data, high automation, and high sensitivity for carbon fiber. Among all test conditions, packing density and flow rate have the greatest influences on the experimental results. The optimized test parameters are suitable for various kinds of carbon fiber bundles, including polyacrylonitrilebased and pitch-based carbon fibers with different tensile properties and tow sizes. Moreover, IGC can acutely characterize the surface properties of carbon fibers after carbon nanotube modification and heat treatment, which are hard to carry out using contact angle method.

Optimization for testing conditions of inverse gas chromatography and surface energies of various carbon fiber bundles
    Abstract
    1 Introduction
    2 Materials and methods
        2.1 Materials
        2.2 Theoretical considerations
        2.3 Surface treatment
        2.4 Characterization
    3 Results and discussion
        3.1 Determination of test conditions
            3.1.1 Length, mass, and packing density of fiber
            3.1.2 Target fractional surface coverage
            3.1.3 Flow rate
            3.1.4 Maximum elution time
        3.2 Verification of IGC applicability for various carbon fibers with the optimized test parameters
        3.3 Surface treatment
            3.3.1 Desizing and CNTs modification
            3.3.2 Heat treatment
    4 Conclusions
    Acknowledgements 
    References

• Min Li(School of Materials Science and Engineering, Beihang University, Beijing 100191, China)
• Shaokai Wang(School of Materials Science and Engineering, Beihang University, Beijing 100191, China)
• Yizhuo Gu(Research Institute for Frontier Science, Testing and Evaluation Center for High-Performance Fibers of Beihang University, Beihang University, Beijing 100191, China)
• Yuwei Liu(School of Materials Science and Engineering, Beihang University, Beijing 100191, China)