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 (SiO 2 ) onto fiber surface (CF‐g‐SiO 2 ) using the bridging toluene‐2,4‐diisocyanate has been achieved and compared with the physical adsorption one (CF‐ad‐SiO 2 ). Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy confirmed the covalent bonding nature between SiO 2 and CF. By atomic force microscopy observation, coating or grafting SiO 2 on the surface of CFs also enhanced fiber surface polarity and roughness. However, CF‐g‐SiO 2 showed a better uniform distribution of SiO 2 on the fiber surface compared with CF‐ad‐SiO 2 with the serious agglomeration of SiO 2 . These results of dynamic contact angle measurements indicated that CF‐ad‐SiO 2 and CF‐g‐SiO 2 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‐SiO 2 composites, which increased 10.92% in ILSS and 10.71% in IFSS compared with those of CF‐ad‐SiO 2 composites. Moreover, the interfacial reinforcing mechanisms have also been studied. Additionally, the introduced Si‐O‐Si bonds at the interface by SiO 2 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 SiO 2 onto the fiber surface is the promising multifunctional reinforcement. POLYM. COMPOS., 40:E975–E982, 2019. © 2018 Society of Plastics Engineers