Ultra-Low-Temperature Growth of Carbon Nanofilament on Continuous Carbon Fiber for Simultaneous Tensile and Interfacial Enhancement

The construction of a nanostructure on the surface of carbon fiber (CF) is one of the most promising technologies to improve the properties of CF-reinforced composites. Achieving the growth of a carbon nanofilament (CNF) on CF at lower temperatures can effectively relieve the damage to the CF strength, but traditional processes cannot be conducted below 400 °C. In this work, with CuNi nanoalloy as the catalyst, a continuous CNF–CF product was obtained at 300 °C, whose strength and interfacial properties were simultaneously improved. Mechanical tests show that the interfacial and interlaminar shear strengths of the CNF–CF/epoxy composite are, respectively, 64.9 and 69.6% higher than those of pristine CF. After sizing, its tensile strength, interfacial shear strength (IFSS), and interlaminar shear strength (ILSS) reached 5.21 GPa, 122, and 131 MPa, respectively, significantly outperforming the commercial-sized CF. The catalytic behavior of the CuNi catalyst at low temperatures is compared with those of other catalysts; thereby, the ultra-low-temperature catalytic mechanism is deeply discussed. The ultra-low-temperature production is also conducive to saving energy, reducing cost, and lowering the equipment requirement for mass production.