Enhancing interfacial strength and hydrothermal aging resistance of silicone resin composites by different modification of carbon fibers with silica nanoparticles

Besides the well‐designed combination of the fibers and matrix resin, the fiber‐matrix interface plays a key role in bulk properties of composites. Here, the chemical grafting of silica nanoparticle (SiO₂) onto fiber surface (CF‐g‐SiO₂) using the bridging toluene‐2,4‐diisocyanate has been achieved and compared with the physical adsorption one (CF‐ad‐SiO₂). Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy confirmed the covalent bonding nature between SiO₂ and CF. By atomic force microscopy observation, coating or grafting SiO₂ on the surface of CFs also enhanced fiber surface polarity and roughness. However, CF‐g‐SiO₂ showed a better uniform distribution of SiO₂ on the fiber surface compared with CF‐ad‐SiO₂ with the serious agglomeration of SiO₂. These results of dynamic contact angle measurements indicated that CF‐ad‐SiO₂ and CF‐g‐SiO₂ had the similar increase degree of surface free energy, which contributed to improve the wettability between CFs and matrix resin. Interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) showed great enhancements, especially for CF‐g‐SiO₂ composites, which increased 10.92% in ILSS and 10.71% in IFSS compared with those of CF‐ad‐SiO₂ composites. Moreover, the interfacial reinforcing mechanisms have also been studied. Additionally, the introduced Si‐O‐Si bonds at the interface by SiO₂ coating or grafting resulted in the different improved degree of the hydrothermal aging resistance. The results showed that the quality of fiber‐matrix interface could be tuned by varying the bonding natures between CFs and the modifiers, and chemically grafting SiO₂ onto the fiber surface is the promising multifunctional reinforcement. POLYM. COMPOS., 40:E975–E982, 2019. © 2018 Society of Plastics Engineers