Biobased polyalphaolefin base oil: Chemical, physical and tribological properties

Authors: Biresaw, Girma

Submitted to: Tribology Letter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2018
Publication Date: 5/14/2018
Citation: Biresaw, G. 2018. Biobased polyalphaolefin base oil – chemical, physical and tribological properties. Tribology Letter. 66:76. doi: 10.1007/s11249-018-1027-9.
DOI: https://doi.org/10.1007/s11249-018-1027-9

Interpretive Summary: Base oils comprise >60% of oil-based lubricant formulations. Thus, successful substitution of petroleum based base oils with biobased base oils will have a big impact on the biocontent of the lubricant formulation. This in turn will have a very positive effect on the environmental impact of the lubricant, increase the demand for agricultural products and strengthen the rural economy. In the work described here, a biobased polyalphaolefin (BPAO-40), synthesized from vegetable oils using proprietary technology, was evaluated relative to a commercial petroleum-based polyalphaolefin (PAO-40) of similar viscosity (40 cSt. at 100°C). The findings of this study indicate that, in addition to providing biodegradability, renewability, low toxicity and many other benefits, BPAO-40 also provides superior lubrication properties. These results will be useful additions to the database available to scientists and engineers engaged in the development of biobased lubricants from polyalphaolefins.

Technical Abstract: The properties of a biobased polyalphaolefin with a viscosity of 40 cSt at 100 °C (BPAO-40) were investigated relative to a commercial petroleum-based PAO of similar viscosity at 100 °C (PAO-40). BPAO-40 was synthesized by oligomerization of a mixture of alpha olefins, with and without terminal methyl esters. These olefins were obtained from vegetable oils via a biorefinery process. In contrast to BPAO-40, commercial PAO-40 is synthesized only from non-functionalized alpha olefins. Thus, BPAO-40 is not only biobased, but also has a unique chemical structure, which makes it a functionalized PAO. The effect of chemical structure (presence or lack of methyl ester functionalization) on chemical, physical, and tribological properties of these two base oils was investigated. The investigation showed that, relative to the commercial non-functionalized PAO-40, the functionalized BPAO-40 displayed the following properties: higher density at 40-100 °C, lower number average molecular weight, higher polydispersity index, higher viscosity index, lower oxidation stability (pressurized differential scanning calorimetry), higher total acid number, higher free fatty acid, lower four-ball anti-wear coefficient of friction (COF) and lower wear scar diameter (WSD), higher elastohydrodynamic (EHD) lubricant film thickness under boundary conditions (low speeds and high temperature), lower EHD traction coefficient at 40 and 100 °C, similar pressure-viscosity coefficient, lower COF, lower WSD, and higher relative film thickness on a high-frequency reciprocating rig tribometer under boundary conditions (low speeds).