For years amine surfactants, such as primary amines, ethoxylated amines and polyamines, have been used as friction modifiers in lubricating oils in order to improve fuel economy. This paper describes how the friction performance of amine containing lubricating oils can be improved with the addition of a small amount of molybdenum dithiocarbamate (MoDTC).
Three fatty amines, tallow amine (Armeen® T), tallow propanediamine (Duomeen® T) and tallow dipropylenetriamine (Triameen® T), have been tested with Zinc Dialkyldithiophosphate (ZDDP) and with and without MoDTC in the Minitraction machine (MTM). It is shown that MoDTC improves the friction of Duomeen T and Triameen T while not for Armeen T. It is argued that the packing of Armeen T does not allow MoDTC to reach the surface and to create molybdenum disulphide (MoS2) sheets. Duomeen T and Triameen T have more nitrogen atoms and cannot pack as closely at the surface as Armeen T which allow MoS2 sheets to form. To validate the theory, Scanning Electron Microscopy combined with Energy Dispersive Xray Analysis (SEM-EDX) has been used to determine the amount of sulphur in the tribofilm. The SEM-EDX data show more sulphur in the tribofilm of Duomeen T compared to Armeen T which could be due to the formation of more MoS2.
