Preparation and Tribological Properties of Sulfide Transesterified Black Soldier Fly Oil

In order to solve the environmental pollution problem caused by mineral lubricants, it is crucial to develop a highly biodegradable lubricant. Sulfurized transesterified black soldier fly oil (STBSO) was synthesized with black soldier fly lipid by transesterification and sulfurization reactions, and its structure was characterized by FTIR. The effect of STBSO on the viscosity-temperature property, oxidation stability and corrosion resistance of the base oil 150N was investigated. The influence of STBSO on the tribological behavior of the base oil 150N was evaluated by four-ball friction tester and SRV oscillating friction and wear tester. The wear surface morphology and elemental composition of the tribofilms were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX) analysis, respectively. Based on SEM and EDAX analysis, combined with X-ray photoelectron spectroscopy (XPS) analysis, the anti-wear mechanism of STBSO was explored. The results demonstrated that the addition of STBSO can effectively improve the viscosity and viscosity index of the base oil 150N. With the increase of STBSO addition, the viscosity and viscosity index of the base oil 150N gradually increased. The oxidation stability test results manifested that the addition of STBSO can greatly increase the oxidation stability of the base oil 150N. The addition of 1% STBSO to the base oil 150N increased the induction time from 105 min to 121 min. The base oil 150N with addition of 5% STBSO had a corrosion degree of 1b. The simple friction wear test results showed that the addition of 1% STBSO to the base oil 150N significantly reduced the wear mass loss of the steel ball, however, when the STBSO addition was above 5%, the improvement in the anti-wear performance of the lubricant was no longer significant as the STBSO addition increased. The four-ball test results revealed that the maximum non-seizure load (P_B) of the base oil 150N with 5% STBSO was 1 254 N, an improvement of 12.3% in the maximum non-seizure load and a 6.4% reduction in scar diameter compared with RC 2411. The SRV test results indicated that the friction coefficient of the base oil 150N with 5% STBSO remained stable (0.127), and was lower than that of the base oil 150N with 5% RC 2411 at a constant load of 300 N. The friction coefficient of the base oil 150N with 5% STBSO was always less than that of the base oil 150N with 5% RC 2411 for a given load at a continuous variable load from 50 N up to 700 N. When the load increased to 600 N, the original boundary lubrication films formed by the base oil 150N with RC 2411 broke down, but the base oil 150N with 5% STBSO still showed good anti-wear performance.