Influence of oxidation and distribution of carbon nanotube on mechanical properties of buckypaper/epoxy composites

In order to elucidate the effects of carbon nanotube surface modification and carbon nanotube distribution on mechanical properties of the buckypaper composites, two oxidation processes were developed to prepare functionalized buckypapers. The tube geometries, the entanglement, and stacking state of the carbon nanotubes were characterized by scanning electron microscope, transmission electron microscope, and atom force microscopy. Surface morphology and volume density of the buckypapers indicate that denser and homogeneous carbon nanotube skeletons are achieved by acidification on carbon nanotube powders, while only slight change can be observed from the oxidized buckypaper. The contact angles suggest that both oxidation and carbon nanotube distribution can affect the wettability of buckypapers with epoxy at 120 degrees C, in which homogeneous and dense carbon nanotube skeleton exhibits relatively low wettability. The tensile moduli and strengths of the functionalized buckypaper composites are increased by 20-37% and 42-68%, respectively, with respect to the pristine buckypaper composite. Further analysis demonstrates that the mechanical property improvement is caused by dense carbon nanotube network and strong adhesion of oxidized carbon nanotube to the matrix. Moreover, dynamic mechanical analysis shows that the order of magnitude of storage moduli is consistent with that of the tensile Young's moduli for different buckypaper composites.