Comparative evaluation of chemically modified Jatropha oils as sustainable biolubricants in boundary lubrication regime

Petroleum lubricants are toxic to the environment and non-biodegradable. The oils extracted from the plants are renewable and could be used as biolubricants. Jatropha curcas oil (JCO) is one such promising biolubricant, whose application is limited due to poor oxidative stability. In this research, JCO is subjected to different chemical modifications viz. transesterification, epoxidation, estolide formation and partial hydrogenation. The functional groups and molecular structure of oils are determined by gas chromatography, Fourier transform infrared and nuclear magnetic resonance spectroscopic techniques. Physiochemical, thermal, rheological, oxidative stability properties are also assessed. A tribological study is conducted with different loads (50 N, 75 N and 100 N) and sliding frequencies (15 Hz and 30 Hz) in boundary lubrication regime with mating surfaces lubricated and the responses like frictional coefficient, surface roughness and wear scar diameter are measured. Under an identical condition, estolides and epoxidized Jatropha reduced the frictional force by about 58% and 57.1% with a corresponding reduction in frictional coefficient by 40% and 46%. Shallow grooves observed on the surfaces, lubricated with epoxide and estolide affirmed the tribological results. Preference selection index (PSI) technique ranked the epoxidized Jatropha atop as potential biolubricant over other chemically modified oils.