Friction and wear reduction by glycerol oleates: The molecular basis for performance variations in the presence of water and acetic acid

Friction and wear reduction by pure and technical grade glycerol monooleates (GMOs) was investigated in commercial and model base oils, including the influence of water and acetic acid (AA) impurities. Small-angle X-ray scattering (SAXS) indicated they cause micelle swelling and elongation. AA reduces the separation of OFM from oil at room temperature (RT). Tribotests in a mini-traction machine with white light interferometry (WLI) show that OFMs decrease the traction coefficient, especially at higher temperatures. AA addition also lowered the traction coefficient at RT. X-ray photoelectron spectroscopy (XPS) revealed surface chemical changes that depend on both tribotest conditions and lubricant composition. Wear was associated with the oxidation of metallic iron. The effects of impurities intrinsic to technical GMO appeared to be significant.