# Studying the Tribological Properties of Coffee Oil-Loaded Water-Based Green Lubricant
## 4 Conclusions  
In this study, green lubricating fluid was formulated using coffee oil from spent coffee grounds and protic ionic liquid bis(2-hydroxyethyl)ammonium oleate as additives in the water-based lubricating fluid. In order to evaluate the potential of this lubricant, physicochemical and tribological properties were investigated. As a result, the following conclusions could be reached:  
* The extracted coffee oil comprises almost equal amounts of saturated and unsaturated fatty acids. Moreover, it has a high acid number which could result from the coffee preparation process. As an additive, coffee oil increases fluids' viscosity. * Protic ionic liquid facilitated the dispersion of coffee oil into the water. With the introduction of one wt.% of PIL, ten wt.% of coffee oil was dispersed. Moreover, PIL was found to be responsible for improved wettability and corrosion prevention ability. * With the introduction of investigated additives, the lubricity of water could be significantly improved. The adsorption layer and viscosity were assigned responsibility for this. Conceptualisation, R.K.; investigation, M.G., A.K., J.T. and K.K. ; methodology, R.K. and A.K. ; project administration, R.K.; resources, E.S. ; supervision, E.S. and R.K.; validation, R.K., M.G. and A.K. ; visualization, J.T., R.K. and M.G. ; writing--original draft, R.K. and E.S. ; writing--review and editing, R.K. and E.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. * _[PERSON] et al. (2019)_ [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON] Extraction and Esterification of Waste Coffee Grounds Oil as Non-Edible Feedbackstock for Biodiesel Production. _Renew. Energy_**2019**, _133_, 1414-1425. [CrossRef]
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* _ISO 660:2020_ Animal and Vegetable Fats and Oils--Determination of Acid Value and Acidity. International Organization for Standardization: Geneva, Switzerland, 2020. * _ISO 659:2009_ Oilseeds--Determination of Oil Content. International Organization for Standardization: Geneva, Switzerland, 2009. _ISO 5508:1990_ Animal and Vegetable Fats and Oils--Analysis by Gas Chromatography of Methyl Esters of Fatty Acids. International Organization for Standardization: Geneva, Switzerland, 1990. * _ISO 5509:2000_ Animal and Vegetable Fats and Oils--Preparation of Methyl Esters of Fatty Acids. International Organization for Standardization: Geneva, Switzerland, 2000. * _[PERSON] et al. (2022)_ [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] Spent Coffee Waste: A Sustainable Source of Cleansing Agent for a High-Performance Makeup Remover. _Sustain. Chem. Pharm._**2022**, _29_, 100826. [CrossRef]
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