Study On Interfacial Strength Of Atmospheric Pressure Plasma Modified PAN-Based Carbon Fiber/Polyimide

Carbon fiber (CF) is an inorganic fiber, which is frequently used to manufacture high performance fiber reinforced polymer composites. Carbon fiber has a series of excellent properties, such as low density, high strength, high modulus, endurance to high temperature, high resistance to chemical erosion and so on. However, its surface is composed of highly crystalline structure of the graphite substrate and it shows a higher reaction inert. So the interfacial bonding strength of carbon fiber reinforced composites is very weak and the good mechanical properties of composites can't be guaranteed. It is because the interface plays an important role for the performance of the carbon fiber reinforced composites, it is very critical to enhance the interfacial bonding strength for improving the mechanical performance of composites through surface treatment to carbon fiber.There are several methods in surface treatment to carbon fiber, for example, plasma treatment, gas phase oxidation, liquid phase oxidation, electrochemical oxidation, coupling agent coating, etc. In this thesis, Atmospheric Pressure Plasma Jet (APPJ) treatment was used to modify the surface properties of carbon fiber in order to enhance interfacial bonding strength. At the same time, the effect of atmospheric pressure plasma treatment on the mechanical properties of carbon fiber was investigated. And the tensile test of the single fiber was used to investigate the mechanical properties of carbon fiber. And the Weibull Theory was used to evaluate high-degree-dispersion strength data of the carbon fiber. Through statistical processing of data, the shape parameter (Weibull modulus) and scale parameter of simplified two-parameter Weibull distribution can be known. In this experiment, polyimide (PI) resin was used as matrix resin.The interfacial shear strength of CF/PI composite was characterized by Single Filament Composite Method which was also used to evaluate the improvement of bonding strength after APPJ treatment. Morphology of carbon fiber surface was investigated by SEM and AFM. Functional groups on carbon fiber surface were analyzed by XPS. Surface energy was computed according to the contact angle.It was found that APPJ treatment with different time on the carbon fiber surface made little effect on the fiber strength. After 16 seconds and 32 seconds of treatment, the interfacial bonding strength between carbon fiber and polyimide matrix was enhanced to 86.15 Mpa and 92.57 Mpa respectively, and 12.4 and 20.7% higher than the one without treatment.SEM test shows that AAPJ treatment can clean the surface of carbon fiber. Through analyzing the roughness indexes from AFM test, it was also found that the mean roughness was at least improved by 38.4%. But if the carbon fiber was treated for long time, the roughness had no big change. Computing the surface energy from contact angle shows that the surface energy of treated carbon fiber was enhanced by more than 10%. APPJ treatment made oxygen content and the number of functional groups with oxygen element of carbon fiber surface increase obviously and provided more reactive groups and the active sites to bond effectively for fiber and matrix.Through research and analysis of this issue, it was evaluated that the modification mechanism of APPJ treatment on interface of carbon fiber reinforced composites and the law of surface treatment with AAPJ. It lays a good foundation of further research.