Study On Surface Structure Of High-Modulus Carbon Fiber And Interfacial Properties Of HM-CF/TDE-85

As an important advanced structural materials in the area of aerospace, the properties of carbon fiber reinforced polymer (CFRP) highly depend on the properties of the carbon fiber (CF) and the resin matrix, and the properties of interface. So, it is extremely significant for studying on the high-performance CF and the interface strength of CF/resin.Surface of polyacrylonitrile (PAN) carbon fiber with different modulus had been studied by means of scanning electron microscopy (SEM), atomic force microscope (AFM) and laser scanning confocal microscope (LSCM). Results show that: surface of high-modulus carbon fiber (HM-CF) was rough, and there were lots of ridge-like prominences and grooves, cross section showed a"C"shape. Microstructure of CF studied by means of XRD and Raman spectrum, results indicated that the high modulus of carbon fiber profit from the high degree of graphite of the carbon fiber. Modulus of CF can be improved by increased size and the interplanar spacing of microcrystal, and higher degree of structural ordering.Contact angle of CF with water, diiodomethane and TDE-85 epoxy had been studied by means of dynamic contact angle method. Completely opposite trends in the contact angle of CF with different polar liquid was observed. Surface free energy of CF was calculated, contact angle with water and diiodomethane used, by OWRK methods, so were the dispersion component and the polar component. Surface free energy of different modulus CFs was similar, but components of surface energy were different. Higher contact angle with water and smaller polar component, with higher modulus of CF. Results showed that surface of HM-CF was non-polar surface, this kind of surface was harmed for forming good wettability between CF and epoxy. Improvement of wettability between CF and epoxy should start with the increase of non-polar component of surface energy. Chemical composition and functional group on the surface of sized and unsized CF and the interface of CF/resin was studied by means of XPS. Results show that content of C element and functional group increased with the increase of modulus of CF. Content of functional group was increased dramaticly, higher than 50%, after interface was formed, and N element and high oxidation functional group were detected, indicated that chemical linking was formed at the interface.Microbond test had been taken out for measuring IFSS of CF/TDE-85. Two methods were used in calculating IFSS, difference between the results of this two methods was less than 5%. Strong interface between CF and TDE-85 was formed, IFSS of CF/TDE-85 was 59.81MPa. Difference of IFSS between sized and unsized CF/TDE-85 indicated that major resources interface strength were mechanical engagement at the interface, increase surface roughness of CF could be an effective means in improving interface strength between CF and resin.