Nonequilibrium Wetting Process And Interface Properties Regulation Of Carbon/Epoxy RTM Composites

As an advanced composite materials fabrication processing, resin transfer moulding (RTM) was gained the increasingly extensive attention due to the advantages of its low-cost, fast molding speed, good quality and little pollution to the environment. In RTM process, while the matrix flowing through the fiber preform, the components of matrix adsorbed on the surface of fiber to form the load transferring interface, interface properties have a direct effect on the final mechanical properties of composites, so the key to improve the final mechanical properties of composites in RTM process was to form a strong interfacial bond。It is determined by the characteristics of RTM process that the reinforcing material have a short time to contact with resin matrix, so it is easy to form a poor fiber/resin bonding interface because of the fiber impregnated insufficient. On the other hand, because of the surface of fiber have a different adsorption ability to the resin components, there have a competitive adsorption among the resin components, the content of components will changed gradiently along the matrix flow direction, so the composites present different properties at different location, the properties homogeneously of composites was affected. To fabricate high performance RTM composites, it is necessary to modify the surface of reinforing fiber, so as to impove the wetting property, improve the fiber/resin matrix interface bongding properties and control the inhomogeneous properties of composites due to the competitive adsorption effectively.The epoxy resin blend system used for RTM process was studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), rheological properties, gelation properties and mechanics performance testing in this paper. The results indicated that the E-51/TDE-85 blend system present the best comprehensive performance at the rate of 0.3, the system offer higher chemical stability and long enough applicable period at room temperature, can satisfy the basic requirement for the RTM process at temperature range of 45℃～100℃, the most suitable RTM injection temperature range was 45℃～80℃.The carbon fiber surface was treated by the low-temperature oxygen plasma in this paper. The plasma treatment conditions on the surface chemical composition, surface morphologies and roughness, surface free energy of carbon fiber and the interfacial bonding intensities of canbon/epoxy composites were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic contact angle analysis (DCA), dynamic mechanical thermal analysis (DMTA) and interlaminar shear strength (ILSS) test, respectively. The results indicated that the low-temperature oxygen plasma treatment introduced some polar groups (such as-C=O and -COOH/-COOR) to the carbon fiber surface, increased the density of these polar groups on the surface of carbon fiber, oxygen plasma have an obvious etch effect to the surface of carbon fiber. So the surface roughness and surface free energy were increased, and the wettability of carbon fiber was improved significantly. Low-temperature oxygen plasma could increased the interfacial bonding intensities between the canbon fiber and epoxy matrix, thus the interlaminar shear strength of canbon/epoxy composites have improved accordingly.The effect of low-temperature oxygen plasma treatment on the non-equilibrium dynamic wetting process of canbon/epoxy RTM composites and the final mechanical properties were studied by the steady state fluorescence spectroscopy (FS) analysis, interlaminar shear strength and flexural strength test. The results indicated that the adsorption ability of carbon fiber to the matrix components changed after low-temperature oxygen plasma treatment, the curing agent concentration in the matrix changed gradiently along the matrix flow direction in RTM process, thus the composites present inhomogeneous mechanical properties at different location. When the carbon fiber treated with plasma for 5min at power 300W and discharge pressure 15Pa, the composites fabricated with RTM process present the best homogeneous mechanical properties.The ultrasonic technology was used to strengthen the wetting process of RTM canbon/epoxy composites. The effect of ultrasonic on the viscosity of epoxy matrix, composites interface, mechanical properties and microvoids in the composites were studied. The results indicated that the ultrasonic can improved interfacial bonding intensities of composites significantly. The ultrasonic frequency and treatment time have an obvious effect on the mechanical properties, and can affect the microvoids scale and distribution in the composites. The optimal ultrasonic treatment conditions are power 300W, frequency 20KHz and treatment time 30min.The curing process of RTM canbon/epoxy composites was real-time monitored by the fiber Bragg grating (FBG), the results indicated that there were temperature difference and lag effect between the inner temperature of composites and the temperature of oven. The glass transition temperature and gelation temperature of composites were 185℃and 137℃respectively, the gelation appeared after 100min, the residual strain of composites was -243.1μεwhen curing cycle finished.