Functionalizing Carbon Nanotubes by Plasma Modification for the Preparation of Covalent-Integrated Epoxy Composites

A novel method for preparing a fully integrated nanotube composite material through the use of functionalized multi-walled carbon nanotubes (MWNTs) is presented in this study. The functionalization of MWNTs was performed via plasma treatment; subsequently, maleic anhydride (MA) was grafted onto the MWNTs (CNTs-MA). Nanotube-reinforced epoxy polymer composites were prepared by first mixing the CNTs-MA and a diamine curing agent, followed by a further reaction with the epoxy matrix. In this hybrid nanocomposite system, the CNTs-MA were covalently integrated into the epoxy matrix and became part of the cross-linked structure rather than just a separate component. Fourier transform infrared (FT-IR) and high resolution X-ray photoelectron (XPS) spectroscopes were used to characterize the functional groups on the surface of the MWNTs after the plasma modification. In addition, observations of scanning electronic microscopy (SEM) and transmission electron microscopy (TEM) images showed that the functionalized nanotubes, CNTs-MA, had a better dispersion than the unfunctionalized nanotubes, u-CNTs, on either the composite fracture surfaces or inside the epoxy matrix. Moreover, CNTs-MA/epoxy nanocomposites presented obvious improvements in mechanical properties and conductivity (from 10<sup>-12</sup> to 10<sup>-4</sup> S/m) with only a small quantity (0.1−1.0 wt %) of the CNTs-MA addition.