Synergistic Enhancement of Mechanical and Interfacial Properties in Carbon Fiber Epoxy Nanocomposites via Dual Functionalization of Fiber and Exfoliated Hexagonal Boron Nitride Nanosheets

ABSTRACT A dual interfacial engineering strategy is proposed to enhance the mechanical and interlaminar performance of carbon fiber (CF)‐reinforced epoxy (EP) nanocomposites by simultaneously silanizing CF and exfoliated hexagonal boron nitride nanosheets (hBNNs). Sodium hydroxide assisted hydroxylation, followed by 3‐aminopropyltriethoxysilane (APTES) functionalization, enabled covalent integration at the fiber–matrix and filler–matrix interfaces. XPS analysis confirmed the formation of SiOSi and SiOB linkages on APTES functionalized hBNNs, establishing a chemically interconnected interface. Wettability improved significantly, with the contact angle reducing from 85.48° for untreated CF to 74.46° after salinization of CF. The dual‐functionalized epoxy composite exhibited a tensile strength of 409 ± 9 MPa and modulus of 32.05 ± 2 GPa, corresponding to enhancements of 22% and 67.45%, respectively, over pristine CF/EP. Flexural strength increased from 492 ± 6 MPa to 537 ± 11 MPa, while interlaminar shear strength improved from 37.08 ± 0.06 to 43.50 ± 0.04 MPa, demonstrating superior resistance to shear‐driven failure. Fiber volume fraction was consistently maintained within 41% with void content less than 5%, confirming that the performance gains arise from interfacial engineering. The chemically integrated hybrid network induces constrained interphase regions and cooperative stress‐transfer pathways in the polymer matrix, generating a positive synergistic effect beyond additive reinforcement behavior.