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The grafting of trisilanolphenyl-polyhedral oligomeric silsesquioxanes (trisilanolphenyl-POSS) onto carbon fibers (CFs) was achieved using toluene-2,4-diisocyanate (TDI) as the bridging agent. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed the successful modification of trisilanolphenyl-POSS. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed that trisilanolphenyl-POSS nanoparticles were grafted uniformly onto the surface of CFs and the surface roughness increased significantly. The results of dynamic contact angle (DCA) measurements demonstrated an improvement in the surface energy and wettability that related to the increased polarity of the obtained hybrid fibers (CF-g-POSS). The effects of trisilanolphenyl-POSS grafting on the interfacial, impact, and heat-resistant properties of methylphenylsilicone resin (MPSR) composites were also studied. The interlaminar shear strength (ILSS) and impact resistance of methylphenylsilicone resin (MPSR) composites after POSS modification were improved significantly with increasing amplitudes of 41.91% and 28.65%, respectively. Moreover, the interfacial reinforcing and toughening mechanisms of composites have also been discussed. In addition, the thermal oxygen aging experiments indicated a remarkable improvement in the heat oxidation resistance by the introduction of trisilanolphenyl-POSS in the interphase. Meanwhile, the grafting processes do not decrease fiber tensile strength (TS).

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.

Raw carbon nanotube (CNT)/carbon fiber (CF) hybrids were achieved through a two-step aryl diazonium reaction in mild, eco-friendly conditions. Raman spectra, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirmed the grafting of CNT onto the CF surface. The surface topography and surface free energy of the modified CFs were examined by scanning electron microscopy (SEM), transmission electron microscope (TEM) and dynamic contact angle (DCA) tests, respectively. The resulting CNT/CF hybrid formed a strong chemical bond between the fiber and matrix and enhanced the surface wettability of the modified CFs. The interfacial shear strength (IFSS) of the CNT/CF hybrid reinforced composites increased by 104% compared with that of the untreated CFs. Moreover, the mechanical properties of the CNT/CF hybrid showed a slight improvement after modification.

The surface of poly(p-phenylene benzobisoxazole) (PBO) fibers was modified by Zinc oxide nanowires (ZnO NWs) using a mild hydrothermal method to enhance the interfacial properties of PBO fiber/epoxy composites. A functionalization technique was developed to improve the bonding between the PBO fiber and ZnO NWs and was validated by X-ray photoelectron spectroscopy (XPS). Energy dispersive spectrometry (EDS), X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), wettability testing and single fiber tensile testing were performed to characterize the hybrid fibers. The quantitative relationships between the process parameters (solution concentration ratio and growth time), structure and interfacial shear strength (IFSS) of ZnO NW-grown PBO fibers were systematically investigated. Moreover, the possible interfacial property enhancing reasons were explored. Experimental testing showed that the ZnO NWs interphase developed here offered a significant increase in the IFSS (increased by 50.7%) without degrading the base fiber. It was also shown for the first time that dense ZnO NWs could serve as barriers to protect the PBO fiber underneath from atomic oxygen (AO) erosion, which resulted in their potential applications.

In order to understand the effects of chain length on the interfacial adhesion of PAN-based carbon fiber (CF)/epoxy composites, dendritic hexamethylenetetramine (HMTA) was functionalized on carbon fibers through quaternary ammonium salt reaction using alkyl dihalide of varying chain length [Cl(CH2)nCl, n = 2, 6 and 12]. Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray photoelectron spectroscopy (XPS) confirmed the successful grafting of dendritic HMTA and alkyl dihalide. AFM images showed that dendritic HMTA modified CF surfaces enhanced roughness, and this effect was more pronounced with increasing alkyl dihalide chain length. The results of dynamic contact angle (DCA) and interfacial shear strength (IFSS) demonstrated that the surface energy and interfacial adhesion increased and then decreased with the chain length of alkyl dihalide. The tensile strength and impact roughness of the composites enhanced as the alkyl dihalide chain length grew. Moreover, the reinforcing and toughening mechanisms were also discussed.