Facile preparation of hyperbranched polysiloxane-grafted carbon fibers with improved interfacial strength of silicone resin composites

New hybrid carbon fibers (CFs) were facilely prepared via in situ synthesizing hyperbranched polysiloxane with epoxy groups onto the fiber surface with the aim to enhance interfacial strength of composites. CFs were grafted with phenyl amine groups through an aryl diazonium reaction, and then modified with hyperbranched polysiloxane obtained by the sol-gel polymerization of gamma-glycidyloxypropyltrimethoxysilane. Surface structures of different CFs were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy, indicating the successful modification. The introduced hyperbranched polysiloxane enhanced fiber roughness, polarity, wettability, and surface free energy. Hence, the interfacial shear strength and impact toughness of polysiloxane modified composites (CF-g-Polysiloxane) increased sharply compared with those of untreated composites. Moreover, Interfacial reinforcing and toughening mechanisms have also been studied, and polysiloxane modification maintained fiber tensile strength. The obvious improvement of anti-hydrothermal aging behaviors after modification could be due to the introduction of strong Si-O-Si bonds at the interface.