Analyzing the potential of waste cooking oils as biolubricants for electric vehicles

Authors: AYYADEVARA, SESHASAI - Iowa State University; DAS, PIAL - Iowa State University; Sarker, Majher; Sharma, Brajendra; ROY, SOUGATA - Iowa State University

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2026
Publication Date: 3/9/2026
Citation: Ayyadevara, S., Das, P., Sarker, M.I., Sharma, B.K., Roy, S. 2026. Analyzing the potential of waste cooking oils as biolubricants for electric vehicles. ACS Sustainable Chemistry & Engineering. https://doi.org/10.1039/d5ra08832a.
DOI: https://doi.org/10.1039/d5ra08832a

Interpretive Summary: The shift from internal combustion engines (ICE) to electric vehicles (EVs) has necessitated the development of new sustainable lubricants capable of addressing significant lubrication challenges. While numerous studies have focused on vegetable oils as bio-based options, waste cooking oils (WCO) offer a more sustainable alternative; however, their performance under electrified conditions has yet to be thoroughly investigated. In this research, four batches of WCO samples were collected from different sources and tested against regular soybean oil (RSO) through structural, physical, chemical and tribological analysis under both electrified and unelectrified conditions. Structural analyses confirmed that all WCO samples remained intact, but due to variations in fatty acid composition each sample showed unique physical and chemical properties. WCOs with lower unsaturation levels demonstrated greater viscosity and oxidative stability compared to those with higher unsaturation. Conversely, the highly unsaturated oils displayed superior cold flow properties. Tribological assessments indicated that, under electrified conditions, all oil samples experienced increased friction compared to their performance in an unelectrified setting. In unelectrified conditions, certain WCOs exhibited enhanced friction resistance relative to RSO.

Technical Abstract: The transition from internal combustion engines (ICE) to electric vehicles (EVs) has pushed the search for new sustainable lubricants that can withstand relevant lubrication challenges, like high torque loads and stray currents in drivetrains, which can accelerate oxidation and increase component wear, posing a critical challenge for electric powertrain components. Conventional Automatic Transmission Fluids like ATF III and ATF V have shown different wear mechanisms and coefficient of friction (CoF) trends in the presence of simulated stray currents. While many studies have focused on vegetable oils as bio-based oils, waste cooking oils (WCO) offer a more sustainable alternative, yet their performance under electrified conditions is yet to be explored. In this study, four batches of WCO samples were collected from four different sources and evaluated against regular soybean oil (RSO) through structural, physico-chemical, and tribological analysis in electrified and unelectrified sliding conditions. Structural analyses using FTIR, ¹H /¹³C NMR, GC–MS, and CMS confirmed the triglyceride integrity across all samples, with differences in fatty acid composition influencing physicochemical properties. Batch 4 (WCO B-4) version of WCO, with the lowest unsaturation of 3.43 C=C bonds/triglyceride, exhibited the highest viscosity, while WCO B-2 showed higher oxidation resistance due to its lower degree of unsaturation of 3.73 and 66.2% of high oleic acid content, which reduced reactive oxidation sites. WCO B-2 exhibited the lowest cloud and pour points, which can be attributed to its high total unsaturated fatty acid chain (91.7%), dominated by monounsaturated fatty acids, along with its low saturated content. Tribological testing on aluminum–steel contacts showed that, under unelectrified condition, WCO B-3 and B-4 resulted in reduced average coefficients of friction by 18% and 23%, respectively, and had lower average wear depth compared to RSO. Under electrified condition, all batches of lubricants exhibited increased wear and oxidation, yet WCO B-4 maintained the lowest wear depth despite frictional instability. Additional surface characterization via high-resolution microscopy and spectroscopy techniques confirmed more severe oxidation and lower material transfer under current, underscoring the degradation risk in electrically stressed contacts.