Biobased Polyalphaolefin Base Oil: Chemical, Physical, and Tribological Properties
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).