Investigation of biobased and petroleum base oils in the entire spectrum of lubrication regimes

Authors: Biresaw, Girma; Bantchev, Grigor; Murray, Rex

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2017
Publication Date: 7/24/2017
Citation: Biresaw, G., Bantchev, G.B., Murray, R.E. 2017. Investigation of biobased and petroleum base oils in the entire spectrum of lubrication regimes. Journal of the American Oil Chemists' Society. 94(9):1197-1208.

Interpretive Summary: Development of biobased lubricants requires understanding their triblological properties under all possible application conditions, also known as lubrication regimes. Unfortunately, most standard lubricant tests are conducted under a narrow set of test conditions of speed, load, temperature, and time. The result from such tests, while important, cannot be used to accurately predict performance in the broader lubrication regime. To remedy this, the high frequency reciprocating rig (HFRR) tribometer was used to investigate the tribological properties of biobased and petroleum based base oils in the entire lubrication regime. High oleic sunflower oil (HOSuO) and commercially available polyalphaolefin (PAO6) were selected to represent biobased and petroleum based base oils, respectively. Tests were conducted at 40 and 75 °C in which coefficient of friction (COF), film thickness, and wear scar diameter (WSD) were measured as a function of test conditions (load, speed, lubricant viscosity) expressed in terms of the Hersey number (H). Analysis of experimental data showed that the biobased HOSuO provided lower COF, thicker lubricant film, and lower WSD than the petroleum based PAO6, in all lubrication regimes and at both temperatures. The biobased HOSuO performed especially well in the boundary lubrication regimes because of its highly polar chemical structure relative to the non-polar PAO6. It is clear from the results that the petroleum based PAO6 will need to be blended with rather expensive lubricant additives (such as anti-wear, anti-friction, viscosity modifier) in order to match the performance of the biobased base oil without additives. The results of this work will be of great interest to scientists and engineers engaged in biobased lubricant development. It demonstrates that vegetable oils and their derivatives can be used as cost-effective base oils in lubricant formulations for use in all lubrication regimes.

Technical Abstract: 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 °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 °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 °C). The difference in these properties between the two oils, ['(COF), '(WSD), '(h)], were the greatest in the boundary regimes (low H 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 °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 °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 °C). The difference in these properties between the two oils, ['(COF), '(WSD), '(h)], were the greatest in the boundary regimes (low H 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 °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 °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 °C). The difference in these properties between the two oils, ['(COF), '(WSD), '(h)], were the greatest in