Lubricating Performance of Lanzhou Lily Crude Extract as Natural Additive

Due to environmental concerns and multifunctional requirements, natural additives are a promising alternative to traditional enhancers like metal nanoparticles. Lanzhou lily crude extract (LLCE) was investigated as an additive in PEG400 base oil. Firstly, different contents of LLCE as an additive notably improved physiochemical properties, such as thermal stability, viscosity, and the viscosity index. With 5–10 wt.% of LLCE added in PEG400, the thermal degradation temperature increased by 37.3–49.5 °C. Secondly, the addition of LLCE significantly reduced the friction coefficient and wear rate of the steel disc at 50–150 N compared to pure PEG400 base oil with a reduction degree of up to 30% and 92%. The optimum additive content was 7 wt.%, and further increasing the content of the additive did not bring about obvious improvements, even worsening the product in some cases. Thirdly, the lower friction coefficient and wear rate achieved through the addition of LLCE may be due to the higher viscosity facilitating a thicker lubricating film and the higher polarity providing better chemical affinity with the metallic surface. In summary, LLCE is a promising additive that significantly improves the physicochemical properties and lubricating performance of PEG400 base oil.