Synergistic toughening and electrical conductivity enhancement in epoxy nanocomposites via hybrid carbon nanotube-acetylated cellulose nanocrystal networks

Epoxy resins are widely used in structural and functional applications. However, their high crosslink density leads to brittleness, low toughness, and limited multifunctionality. In this study, hybrid epoxy nanocomposites were developed using carbon nanotubes (CNTs) at 0–0.2 wt% and acetylated cellulose nanocrystals (ACNC) at 0.1–1 wt% through a solution casting method to overcome these limitations. At low content of 0.02 wt%, CNTs significantly increased the flexural strength from 45.73 to 68.67 MPa and the flexural modulus from 1398.46 to 2384.18 MPa due to efficient stress transfer resulting from their homogeneous dispersion and strong interfacial interactions with the epoxy matrix. Electrical conductivity was increased by more than three orders of magnitude, reaching 2097.35×10⁻ 9 S/cm at 0.2 wt% CNT, along with enhanced hydrophobicity. However, higher CNT contents led to agglomeration and reduced tensile strength. The addition of ACNC improved ductility, with elongation at break increasing from 3.06% to 5.93%, although tensile strength decreased. This behavior is attributed to a cooperative reinforcement mechanism in which CNTs act as load-bearing and conductive networks. At the same time, ACNC serves as a dispersion regulator and toughening agent through crack deflection and particle pull-out. The optimal balance of mechanical, surface, and electrical properties was achieved at epoxy with 0.02 wt% CNT and 0.5 wt% ACNC. Overall, the CNT-ACNC hybrid system enables simultaneous improvement in toughness and electrical conductivity at ultralow filler contents and offers a sustainable approach for multifunctional epoxy materials.