Location: Bio-oils Research Unit
Title: Pressure viscosity coefficient of vegetable oils Authors
Submitted to: Tribology Letter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 25, 2012
Publication Date: March 1, 2013
Citation: Biresaw, G., Bantchev, G.B. 2013. Pressure viscosity coefficient of vegetable oils. Tribology Letters. 49(3):501-512. Interpretive Summary: Vegetable oils provide a renewable and environmentally friendly alternative raw material to petroleum for use in lubricant application. The use of vegetable oils as a replacement to petroleum in lubrication also provides economic benefits to farmers and rural communities. However, successful commercialization of vegetable oil-based lubricants requires understanding their lubrication properties relative to petroleum-based formulations. In this work, researchers from the National Center for Agricultural Utilization Research in Peoria, IL, investigated the film-forming properties of ten vegetable oils from commodity and new crops. They also conducted similar investigations on two petroleum-based oils to see how these two groups of oils perform. The investigated vegetable oils include soybean, canola, cottonseed, jojoba, meadowfoam, and lesquerella. The researchers found that the vegetable oils have comparable film-forming and pressure-viscosity properties as the petroleum-based fluids. This result indicates that replacement of petroleum oils with vegetable oils in lubricant formulations will not cause performance problems related to film-forming and pressure viscosity. Such knowledge is useful to researchers who develop vegetable-based lubricant formulations as a replacement to petroleum-based formulations.
Technical Abstract: The elastohydrodynamic (EHD) pressure viscosity coefficient (PVC) of ten vegetable oils from commodity and new crops, and two petroleum-based oils, polyalphaolefin (PAO) and hexadecane, were investigated. PVC was measured using three different methods: the So and Klaus (S-K) procedure from oil viscosity and density; the Hamrock-Dowson (H-D) relationship from analysis of EHD film thickness; and the Barus relationship from EHD traction and film thickness. Measured PVC data for the vegetable and petroleum-based oils decreased with increasing temperature and pressure, which was expected. PVC values from the S-K method were generally much higher than the values from the literature or from the other two methods. PVC values from the S-K and H-D methods increased with increasing viscosity of the tested oils, but no such correlation was observed with the PVC data from the Barus method. Comparison of the PVC of petroleum-based vs. vegetable oils obtained from the three methods showed that these two groups fall within the same PVC range. It appears that these two groups of oils have common structural features that provide them with intermediate PVC properties; between liquid crystals in the low PVC range and oils that are highly naphthenic (cyclic and branching), halogenated, and polyaromatic in the upper PVC range. Vegetable oils belong to a category of structures with PVC values in the range 10–20 GPa-1 that includes PAO, polyalkyl glycols, polyol esters, and paraffinic mineral oils such as hexadecane.