Investigation of Biobased and Petroleum Base Oils in the Entire Spectrum of Lubrication Regimes

The tribological properties of biobased and petroleum-based base oils in the entire lubrication regime were investigated. High oleic sunflower oil (HOSuO) and commercially available polyalphaolefin (PAO-6) were selected to represent biobased and petroleum-based base oils, respectively. These two oils had similar viscosity and pressure-viscosity coefficient at 40 A degrees C, but differed in their chemical structures and many other properties. Tribological tests were conducted on a high frequency reciprocating rig tribometer at 40 and 75 A degrees C, for 60 min, 1000 gf load, and variable combinations of frequency and stroke length. Lubrication regimes were quantified using the Hersey number (H) which was calculated from lubricant viscosity and test parameters (load, frequency, stroke length). The key tribological test outputs were coefficient of friction (COF); film thickness (h) expressed in % from contact resistance measurement; and ball wear scar diameter (WSD). Analysis of experimental data showed that the biobased HOSuO provided lower COF, thicker lubricant film, and lower WSD than the petroleum-based PAO-6, in all lubrication regimes and at both temperatures (40 and 75 A degrees C). The difference in these properties between the two oils, [Delta(COF), Delta(WSD), Delta(h)], were the greatest in the boundary regimes (low H values) where the polar chemical structure of the biobased lubricant played a dominant role.