Submitted to: Fuel
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2021
Publication Date: 10/13/2021
Citation: Bantchev, G.B., Cermak, S.C. 2022. Correlating viscosity of 2-ethylhexyl oleic estolide esters to their molecular weight. Fuel. 309. Article 122190. https://doi.org/10.1016/j.fuel.2021.122190.
DOI: https://doi.org/10.1016/j.fuel.2021.122190

Interpretive Summary: Being able to predict the viscosity (resistance to flow or how sticky) of an oil is important in determining what industrial applications the oil can be used for. We have discovered a set of mathematical models which predict the viscosity/temperature relationships of estolide esters. Estolide esters are a commercially available and renewable biobased lubricant made from vegetable oils (soybean and sunflower), and the ability to model their viscosity will further their range of applications. With this viscosity data, tailoring the estolide esters viscosity to specific applications will be enhanced by allowing users to accurately select the appropriate structure (size) of the estolide material. This will enable use as engine oils, hydraulic fluids, and metalworking fluids and thus limit our impact on the environment (climate change) and help reduce our dependence on petroleum sources.

Technical Abstract: Estolides are a relatively new class of biobased materials, and their properties are not thoroughly investigated. Since they have been recently commercialized as lubricants, a deeper investigation of their viscosity was warranted. Five 3-parameter viscosity models with theoretical derivations were found in the literature. Additionally, several empirical 2- and 3-parameter models, including one empirical 4-parameter model, used to describe the viscosity of lipids, were selected for investigation. These models were used to fit the experimental viscosity of 13 oleic estolide ester samples. The viscosity was measured at six temperatures between 20 and 100 °C. The jackknife procedure was used to estimate the uncertainty of the fitted parameters. For the theory-based models, correlations were derived between the fitted coefficients and the molecular weight of the sample. The results allowed for simple prediction of the viscosity of estolide esters as a function of the temperature, based only on number-average molecular weight (or on the estolide number). The best model required additional knowledge of the weight-average molecular weight.