Property evaluation of multi-staged chemically modified used coconut oil for bio-lubricant applications

Bio-lubricant studies in recent years have shown that they can be used as an eco-friendly alternative to petroleum-based lubricants due to their toxicity and the rapidly exhausting nature of petroleum-based products. Coconut oil (CO) is the most used cooking oil in most of the states of India. Earlier studies have already shown the potential of using pure CO as a base oil for various bio-lubricant applications. The extraction and usage of oils for bio-lubricant applications has many feasibility constraints, and used oils can be considered a more viable base stock for bio-lubricant applications. The present study attempts to make used coconut oil (UCO), which is the oil remaining after the cooking process as a potential source for bio-lubricant production. However, the properties of UCO need to be improved to meet the requirements of industrial applications by multi-stage chemical modification process. This study evaluated and compared the physicochemical, oxidative stability, thermal, and tribological properties of CO, UCO, epoxidized used coconut oil (EUCO), and trans-esterified EUCO (MUCO) using various experimental procedures. The chemical properties of MUCO such as acid and peroxide numbers showed a reduction of around 75% and the iodine value decreased by 20% when compared to UCO. The tribological and oxidative stability properties of MUCO were improved by around 20%, and the improvement in viscosity and thermal properties was observed to be around 10% in comparison with UCO. The results showed that MUCO has better thermal stability, a higher viscosity index, and good anti-wear properties compared to EUCO, UCO, and CO. The study concludes that the MUCO has shown the potential to replace petroleum-based lubricants.