Synthesis of New Sulfur-free and Phosphorus-free Ether-ester and Study on Its Properties As Ashless Friction Modifier

With the upgrading of mechanical equipment and the implementation of the "double-carbon" policy, the demand for high-quality lubricants with longer drain period, more clean and environmental friendly is increasing day by day. The study on new additives and base oils, as well as the compatibility law between the two has always run through the development of high-performance lubricants. As an important additive to improve the durability of lubricating protection and fuel economy, the design and development of friction modifier is the forefront of the development of lubrication technologies. Based on these, a new sulfur-free and phosphorus-free ether-ester DOA-mPEG350 was designed and synthesized, and characterized by nuclear magnetic resonance (NMR), high resolution mass spectrometer (HR-MS), Fourier transform infrared (FT-IR) and gel permeation chromatography (GPC). Meanwhile, the thermal stability of DOA-mPEG350 and its compatibility with synthetic hydrocarbon base oil were analyzed by thermogravimetric analysis (TGA) and ultraviolet visible spectroscopy (UV-Vis). The tribological behaviors of DOA-mPEG350 as an ashless friction modifier in synthetic hydrocarbons were studied using a four-ball friction and wear tester. The results show that DOA-mPEG350 has good thermal stability and compatibility with synthetic hydrocarbon base oil, and can effectively shorten the running-in period, and 1.0% (w) addition of DOA-mPEG350 could decrease the ave. coefficient of friction (COF) and wear scar diameter (WSD) of synthetic hydrocarbons such as CTL6 and PAO6 base oils by 20.6%, 20.1% and 28.9%, 34.8%, respectively. The comprehensive friction reducing and anti-wear performance of DOA-mPEG350 is better than that of the selected commercial friction modifier and extreme pressure anti- wear additives, which are usually contain sulfur, phosphorus, or metals that can not meet the increasingly stringent environmental requirements, that is, the synthesized DOA- mPEG350 has the potential to replace these additives. Through analyzing the worn friction surface and density functional theory (DFT) calculation, the micro-lubrication mechanism of ether-ester is revealed, namely, it can combine the "line contact" of ether with the "point contact" of ester to form a thick and dense protective film on metal surfaces, thus showing better tribological performance than that only contain ether chain or ester group.