A semi-interpenetrating polymer network for enhancing mechanical, thermal and dielectric properties of carbon nanotube-reinforced epoxy composites

The intrinsic brittleness of epoxy resin (EP) severely limits its use in applications requiring both strength and toughness. Herein, methoxy polyethylene glycol-functionalized carbon nanotubes (mPEG-CNTs) were prepared via an in-situ grafting strategy, leveraging the outstanding structural characteristics of carbon nanotubes (CNTs). The obtained mPEG-CNTs were subsequently incorporated into an epoxy matrix to fabricate mPEG-CNTs-filled composites. The effects of mPEG-CNTs on the structure and properties of epoxy composites were systematically investigated. At an optimal loading of 1.25 wt.%, the tensile strength, tensile toughness, and Young’s modulus increased by 30.7%, 61.27%, and 28.57%, respectively, compared with neat EP; furthermore, the storage modulus at 30°C and 170°C increased by 8.8% and 77.10%, respectively, demonstrating improved rigidity and thermal stability. Microstructural analysis confirmed the uniform dispersion of mPEG-CNTs within the epoxy matrix and the formation of a semi-interpenetrating polymer network (semi-IPN) at the filler/matrix interface, strengthening interfacial interactions. The composites also exhibited an increased dielectric constant while maintaining low dielectric loss over a wide frequency range. The semi-IPN structure suppressed conductive leakage pathways and limited dielectric loss despite enhanced interfacial polarization. These results indicate that the mPEG-CNTs-induced interfacial architecture contributes to a balanced enhancement of mechanical, thermal, and dielectric properties.