Effect of CNT Grafted Carbon Fibers Catalyzed by Pulsed Electrolytic Nickel Plating on Mechanical Properties and Fracture Morphology of CFRTP Laminates

Carbon nanotube grafted carbon fibers (CNT-CFs) have high fiber-matrix interfacial shear strength and excellent resin impregnation properties, suggesting their potential to enhance the mechanical properties of Carbon Fiber Reinforced Thermoplastic (CFRTP) laminates. However, when CNT-CFs are used as a reinforcement for CFRTP laminates, it has been reported that aggregated CNTs can hinder resin impregnation and act as crack initiation sites. Therefore, it is necessary to control the density and diameter of CNTs grafted on the carbon fiber surface. In this study, carbon fibers with grafted in low density, large-diameter CNTs were grafted by using Ni, which was electroplated with pulse current as a catalyst. Micro-droplet tests, three-point bending tests, and DCB (double cantilever beam) tests were performed to clarify the effect of CNT grafting on carbon fibers. The CNT-CFs showed high fiber-matrix interfacial shear strength, and CFRTP laminates with these CNT-CFs exhibited high bending modulus. However, their bending strength and mode I fracture toughness showed low value. During the bending test, CFRTP laminates with these CNT-CFs buckled easily, and the fracture surface had areas where the fiber surface was exposed. This was also observed on the fracture surface of the Mode I fracture toughness test. These results indicate that while CNT-CFs have a high fiber matrix interfacial shear strength, the interfacial adhesion strength perpendicular to the fiber axis remains low. Therefore, it is necessary to develop a method to firmly bond CNTs to the carbon fiber surface.