Comparative evaluation of lubricant properties of biodegradable blend of coconut and mustard oil

Abstract

Abstract The vegetable oils are preferred over mineral oil as lubricating base oil due to their high biodegradability, renewability and low toxicity. Among vegetable oils, coconut oil as a lubricant exhibits low coefficient of friction at metallic interfaces but high wear rate and pour point compared to mineral oils, limits its application as a commercial lubricant. Mustard oil exhibits better wear resistance. In the present work, the saturated coconut oil was blended with unsaturated mustard oils by varying volume (%) of mustard oil from 10 to 50%. The composition of saturated and unsaturated fatty acids present in the blend was analysed by using gas-chromatograph mass-spectroscopy analyzer. The thermal and oxidative stability tests were performed on the blend using thermogravimetric analysis and differential scanning calorimetry. The physicochemical, thermal, rheological and tribological (using four-ball tester) analyses of the blended oil were carried out and the corresponding properties were compared with those of coconut oil, mustard oil and mineral oil (SAE20W40). The results showed that the tribological performance (in terms of wear) and cold flow properties (in terms of pour point) of the blends were superior to that of coconut oil and the blend (50%) exhibited the best performance. The wear scar diameter and pour point of the blend (50%) were 0.486 mm and −11.6 °C with a reduction of 18.45% and 159.7%, respectively, with respect to those of coconut oil. Compared with coconut oil the kinematic viscosity of the blend (50%) demonstrated an enhancement of 18.18% with a value of 32.88 mm2/s. The thermo-oxidative stability (in terms of on-set temperature) of the blend (50%) was better than that of coconut oil. Also, the friction and wear of the blended oil (50%) were lower than that of mineral oil. As a lubricant, the blend (50%) is the best biodegradable alternative for mineral oil for cleaner production.