Effects of carbon nanotube length on interfacial properties of carbon fiber reinforced thermoplastic composites

To improve the interfacial properties between carbon fibers (CFs) and polycarbonate (PC) resin, multi-walled carbon nanotubes (MWCNTs) were deposited onto desized CF surfaces using an ultrasonic-assisted electrophoretic deposition method, forming a multi-scaled hierarchical structure. The results showed that morphologies and geometrical structures of the as-prepared hierarchical structures could be readily tailored by varying in length and concentration of the CNT suspension. The optimum conditions were determined to be CNT length of 1-5 μm with suspension concentration of 0.5–1 wt%. A post-treatment, in combination of a polymer binder and laser irradiation, was followed to solidify the morphology and geometry of the CNT network structures formed by the CNTs with length 1-5 μm, which allowed a 22.9% ± 1.6% improvement in the interfacial bonding strength than that without the post-treatment and 68.1% ± 2.3% improvement than bare CF, evaluated by a single-filament fragmentation test. It was the well-defined CNT porous network structures that are favorable for thermoplastic resin infiltration through channels for resin flow and capillary action, thus enhancing the composite interfacial properties.