Influence of Carbon Nanotubes on Conductive Capacity and Tribological Characteristics of Poly(ethylene Glycol-Ran-Propylene Glycol) Monobutyl Ether as Base Oil of Grease

Carbon black (CB) and three kinds of carbon nanotubes (CNTs) including multiwalled CNTs (MWCNTs), carboxyl multiwalled CNTs (CMWCNTs), and single-walled CNTs (SWCNTs) were doped as conductive additives in poly(ethylene glycol-ran-propylene glycol) monobutyl ether (denoted as PAG) to afford conductive greases in the presence of polytetrafluoroethylene (PTFE) as the thickener and acetone as the polar dispersant. The effects of the conductive additives on the conductive capacity and tribological characteristics of the PAG grease were investigated, and the tribological action mechanisms of the conductive additives were analyzed in relation to worn surface analyses by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Results indicate that the SWCNTs can reduce the volume resistivity of the base grease by over 10,000 times. In the meantime, the CB and the three kinds of CNTs as conductive additives can improve the tribological characteristics of the base grease to some extent, and the CNTs are advantageous over the CB in improving the friction-reducing and antiwear abilities of the base grease. The reason lies in that CNTs with a small size and a large specific surface area can be easily adsorbed on sliding steel surfaces to form a surface protective film.