Fei Xie

Interfacially reinforced carbon fiber/epoxy composites by grafting melamine onto carbon fibers in supercritical methanol

Melamine used as a coupling agent was functionalized onto a carbon fiber (CF) surface in supercritical methanol to improve the interfacial properties of CF reinforced epoxy composites. Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray photo electron spectroscopy (XPS) confirmed the successful grafting of melamine molecules onto the fiber surface. Scanning electron microscopy (SEM) images showed that melamine was grafted onto the CF surface uniformly and the surface roughness was enhanced obviously. Dynamic contact angle analysis (DCA) revealed the significant improvement in the surface energy and wettability. Compared with the untreated CF composites, the interfacial shear strength (IFSS) and inter-laminar shear strength (ILSS) of composites after melamine modification increased by 41.3% and 36.4%, respectively. The impact properties were also improved significantly. In addition, the reinforcing and toughening mechanisms were also discussed. Meanwhile, supercritical treatment did not decrease the single filament tensile strength obviously.

Controlled growth of silver nanoparticles on carbon fibers for reinforcement of both tensile and interfacial strength

Metal nanoparticles are commonly used for surface modification in fiber reinforced polymer composites because of their large specific surface area and electronic, magnetic and other related properties. In this study, morphology-controllable silver nanoparticles (Ag NPs) were deposited on a carbon fiber surface via a facile and green electro-chemical deposition method in the presence of poly(vinylpyrrolidone) (PVP). It was found that the presence of PVP and its molar ratio (in terms of repeating unit) relative to silver nitrate both played important roles in determining the geometric shape and size of the Ag NPs. Interestingly, electro-chemical deposition of Ag NPs improved both the tensile strength of the carbon single fiber and the interfacial property of the carbon fiber/epoxy composite by as much as 57.2% and 27.2%, respectively. Moreover, the Ag NPs-loaded carbon fibers exhibited superior electrical conductivity, which was a 2-fold enhancement as compared with that of the virgin carbon fibers. It meant that the Ag NPs-loaded carbon fibers could be used as ideal reinforcement materials for advanced aerospace systems.

Mechanical properties of carbon fiber composites modified with nano-SiO2 in the interphase

The performance of carbon fibers-reinforced composites is dependent to a great extent on the properties of fiber–matrix interface. To improve the interfacial properties in carbon fibers/epoxy composites, nano-SiO2 particles were introduced to the surface of carbon fibers by sizing treatment. Atomic force microscope (AFM) results showed that nano-SiO2 particles had been introduced on the surface of carbon fibers and increase the surface roughness of carbon fibers. X-ray photoelectron spectroscopy (XPS) showed that nano-SiO2 particles increased the content of oxygen-containing groups on carbon fibers surface. Single fiber pull-out test (IFSS) and short-beam bending test (ILSS) results showed that the IFSS and ILSS of carbon fibers/epoxy composites could obtain 30.8 and 10.6% improvement compared with the composites without nano-SiO2, respectively, when the nano-SiO2 content was 1 wt % in sizing agents. Impact test of carbon fibers/epoxy composites treated by nano-SiO2 containing sizing showed higher absorption energy than that of carbon fibers/epoxy composites treated by sizing agent without nano-SiO2. Scanning electron microscopy (SEM) of impact fracture surface showed that the interfacial adhesion between fibers and matrix was improved after nano-SiO2-modified sizing treatment. Dynamic mechanical thermal analysis (DMTA) showed that the introduction of nano-SiO2 to carbon fibers surface effectively improved the storage modulus of carbon fibers/epoxy.