With the increasingly demanding engine conditions and the implementation of “double carbon” policies, the demand for high-quality lubricants that are cost-effective and environmentally friendly is increasing. Additives, especially high-performance friction modifiers, play an important role in boosting lubricant efficiency and fuel economy, so their developments are at the forefront of lubrication technologies. In this study, 1,3-dioleoamide-2-propyloleate (DOAPO), which incorporates polar amide, ester, and nonpolar alkyl chains, was synthesized from 1,3-diamino-2-propanol to give an eco-friendly organic friction modifier. Nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HR-MS), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to characterize the structure and thermal stability of DOAPO. Meanwhile, the storage stability and tribological behaviors of DOAPO in synthetic base oil were studied and compared with a commercial oleamide. The results show that DOAPO has better thermal stability and better storage stability in synthetic base oil. Additionally, 0.5 wt.% of DOAPO could shorten the running-in period and reduce the average friction coefficient (ave. COF) and wear scar diameter (ave. WSD) by 8.2% and 16.2%, respectively. The worn surface analysis and theoretical calculation results show that the ester bond in DOAPO breaks preferentially during friction, which can reduce the interfacial shear force and easily react with metal surfaces to form iron oxide films, thus demonstrating a better friction-reducing and anti-wear performance.

Recently, researchers have been committed to boosting the environmental friendliness and functional performance of multifunctional additives. In this study, an eco-friendly methylbenzotriazole-amide derivative (MeBz-2-C18) was designed and synthesized, with ethylamine serving as the linkage between methylbenzotriazole and the oleoyl chain. The structure of MeBz-2-C18 was characterized by nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HR-MS), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). Subsequently, the storage stability and tribological behavior of MeBz-2-C18 and the commercial benzotriazole oleamide salt (T406) were comparatively evaluated. The covalently-bonded MeBz-2-C18 exhibits superior thermal stability, along with boosted storage stability and tribological performance in the synthetic base oil. Specifically, 0.5 wt.% addition of MeBz-2-C18 and T406 can reduce the average wear scar diameter (ave. WSD) by 21.6% and 13.9%, respectively. To further explore the micro-mechanism, the electrostatic potential (ESP) and worn surfaces were analyzed with scanning electron microscope-energy dispersive spectrometer (SEM–EDS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The results show that MeBz-2-C18 possesses stronger adsorption on the metal surface, and its amide bond preferentially breaks during friction. This reduces the interfacial shear force and promotes the film formation of iron oxides, thus resulting in superior tribological performance.

Benzotriazole and its derivatives show good tribological properties, anti-oxidation, anti-corrosion, rust prevention and dispersion capabilities as lubricating additives, becoming the common multifunctional additives. And how to avoid sulfur- or phosphorus-introduction to improve their functionality and the compatibility with hydrocarbons is the forefront research. In this study, methylbenzotriazole and oleic acid were applied to synthesize a new methylbenzotriazole-amide that with long alkyl-chain (E)-N-(2-(5-methyl-2H-benzodiazole-2-yl)ethyl)octadec-9-enamide (MeBz-2-C18), which was characterized by nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HR-MS), FT-IR and thermogravimetric analysis (TGA). The thermal stability and tribological properties of MeBz-2-C18 were compared with the commercially available benzotriazole oleamide (T406). The results show that MeBz-2-C18 has better thermal stability and base oil compatibility than that of T406, and 0.5 wt.% addition of MeBz-2-C18 could decrease the average wear scar diameter (ave. WSD) by 21.6%. The wear surface analysis and DFT calculation show that the amide group in MeBz-2-C18 is preferentially broken during friction, which would reduce the interfacial shear force and easily react with the metal surface to form iron oxide film, thus demonstrating a better anti-wear and friction reducing performance, indicating its potential application as an environmental friendly multifunctional additive.