Lubricant quality and oxidative stability of Cruciferae oils

Abstract

In the current research, oil derived from several Brassica species, and related oilseeds, was investigated for use as a lubricant base-oil. Oils obtained from B. rapa L. were selected because of their superior cold temperature performance over Sinapis alba L., B. carinata A., B. napus, and B. juncea L. The commercial antiwear additive zinc dialkyl dithiophosphate (ZDDP) was added (800 ppm) to B. rapa oils to determine the impact on oxidative stability and lubricity. It was found that the B. rapa oil ACS-C7 had a low cloud and pour point. B. rapa oils had poor oxidative stability at 97.8 °C when compared to a mineral oil (petroleum-based) standard. ZDDP had little effect on oxidative stability and cloud point. It was concluded that B. rapa oils have sufficient low temperature performance for use as a lubricant base oil. However, for continued use in a motor oil formulation, further modification of the oxidative stability will be necessary. All B. rapa oils with and without ZDDP were subjected to lubricity testing in a Plint High Frequency Wear Tester (TE-77). Lubricity testing simulates the high temperature and pressure in a motor system. The coefficient of friction and resultant wear scar width were measured. B. rapa oils lower coefficients of friction and decrease wear scar widths when compared with a mineral oil standard. Addition of ZDDP to B. rapa oils slightly increased lubricity performance of the oils. The wear scars produced on the polished stainless steel disk were subjected to X-ray Absorption Near Edge Structure (XANES) analysis using two synchrotron beamlines at the Canadian Light Source. XANES analysis confirmed the presence of a lubricating tribofilm on the surface of the stainless steel disks following B. rapa lubricity testing. These results indicate that B. rapa oils are suitable candidates as lubricant base oils for motor oil formulation.