Synthesis and tribological properties of bio-based lubricants from soybean oil

The demand for bio-based lubricants has grown considerably in recent years due to increasing environmental awareness among the public, governments, and industries. In this study, soybean-oil-based samples were synthesized via reactions of hydrolysis (FFA, yield>93% wt.), esterification (BL1, yield>92% wt.), epoxidation (BL2, yield>91% wt.), and oxirane ring opening (BLOR, yield>93% wt.), using a long chain alcohol (2-ethylhexanol). The obtained BL1 and BLOR samples were further subjected to tribological testing in the four-ball configuration. The friction coefficients of the BL1 and BLOR samples were evaluated using speed ramps at different loading forces and temperatures. A hydrotreated mineral oil (HMO) sample was used as a reference to evaluate the lubrication performance of the synthesized bio-based samples. The results indicated that these BL1 and BLOR samples had lower friction coefficients than HMO at all assessed sliding speeds, even with increasing load force and temperature. In the test to evaluate the wear, the samples of BL1 and BLOR presented coefficient of friction smaller than HMO in the order of 31.7% and 46.0%, respectively. Furthermore, an assessment of the wear morphologies indicated that the BL1 and BLOR samples yielded smoother surfaces with shallower grooves than the hydrotreated mineral oil sample. Among the studied bio-based lubricants, BLOR yielded the lowest friction coefficients, wear scar diameter, and surface ripples. The tribology resulting from BL1 and BLOR infers that these biolubricants have potential for applications in mechanical systems.