Study on the Effect of CTBN and h-BN Synergistic Toughening on the Damping Properties of Carbon-Fiber-Reinforced Epoxy Composites

Carbon-fiber-reinforced polymer (CFRP) composites possess outstanding specific stiffness and strength but typically exhibit low intrinsic damping, which limits vibration attenuation in lightweight dynamic structures. Herein, a hybrid toughening strategy combining carboxyl-terminated butadiene nitrile rubber (CTBN) and hexagonal boron nitride (h-BN) is developed to enhance the damping of CFRP laminates while preserving cure feasibility and thermomechanical stability. An E51/DICY/accelerator epoxy system (100:6.5:1.2, mass ratio) is used as the baseline matrix. Differential scanning calorimetry shows that both CTBN and h-BN shift the cure peak temperature upward (<i>Tp</i>: 160.6 → 170.3 °C) and reduce the reaction enthalpy (<i>ΔH:</i> 386.5 → 255.1 J/g), indicating dilution/transport effects and altered cure kinetics. Dynamic mechanical analysis (DMA) reveals that CTBN exhibits an optimum damping enhancement at 25 phr (<i>tan δ_max</i> = 0.300), whereas h-BN provides a stronger monotonic increase up to 25 phr (<i>tan δ_max</i> = 0.437). Notably, the CTBN/h-BN hybrid (25/25 phr) delivers a high <i>tan δ_max</i> of 0.468 together with the broadest effective damping window (<i>ΔT_half</i> = 28.6 °C), exceeding 85% of the linear additivity criterion proposed herein. When the materials are transferred into CFRP laminates, free-vibration tests (using the logarithmic decrement method) demonstrate a clear structural damping improvement (<i>ζ:</i> 0.021 → 0.035; <i>δ:</i> 0.132 → 0.221; t₁/₂: 0.48 → 0.27 s). Overall, the results suggest that the damping enhancement arises from a combination of EPBN-mediated ductile energy dissipation and h-BN-related interfacial/interlayer frictional losses, which can be jointly tuned to balance processability, thermal response, and damping performance in CFRPs.