Composite materials have become one of the widely used material systems for applications such as aircraft structural components, wind turbine blades, interior, and exterior automotive components, boats, and surfboards. Composite materials being non-homogenous, their structures can delaminate and disintegrate, mostly due to poor interlaminar strength since there is no reinforcement between the laminae to bear the load. One of the unique solutions to improve the interlaminar strength is the use of nano-scale reinforcement between the laminae, within the resin, and between the fiber filaments. Carbon nanotubes (CNTs) are one such nanomaterial with superior mechanical, electrical, optical, magnetic, and thermal properties. CNTs have been extensively studied in recent decades because of their exceptional properties. However, they react poorly with polymeric resin molecules, because of their inertness. One way to improve their interaction with polymer molecules is through covalent chemical functionalization. The functionalization treatment creates defects and attaches functional groups on the surface of the individual CNTs thereby modifying its interfacial interaction with the polymers. Our previous research has shown that helical CNTs (HCNTs) perform better than straight CNTs, because of their geometrical configurations. In this research, HCNTs that were chemically functionalized using mixtures of nitric, sulfuric, and hydrochloric acids through 8 different procedures by varying sonication time, molarities of the nitric, sulfuric, and hydrochloric acids (i.e., 3, 6, and 16) in different sequences. Nanocomposite panels were made using epoxy reinforced with three different weight percentages of these functionalized HCNTs (FHCNTs) and then tested and characterized per ASTM 638-03 and ASTM 5045 standards for tensile and fracture toughness properties, respectively. The test results for nanocomposite samples were all compared against the samples with pristine HCNTs reinforcements and the neat epoxy. Results showed considerable improvements in mechanical properties of the samples containing FHCNTs and the best functionalization processes were identified. Copyright 2024. Used by CAMX – The Composites and Advanced Materials Expo.