Tribological study of leaf-surface wax extracted from sorghum leaves as a lubricant additive

The leaf-surface wax was extracted from the sorghum bicolor (L.) Moench (abbreviated as sorghum) leaves and evaluated as a kind of new lubricant additive in poly-alpha-olefin (PAO) for steel/steel, steel/aluminum and steel/copper contacts using a MFT-R4000 friction and wear tester at room temperature. A gas chromatography-mass spectrometry (GC-MS) analysis system was used to analyze the compositions of sorghum leaf-surface wax (SLW). Scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (SIMS) were employed to characterize the worn surfaces to explore the lubrication mechanisms. The results show that the SLW could effectively reduce the friction and wear for steel/steel and steel/copper friction pairs. The analysis of the worn surfaces suggest the good tribological properties were attributed to the protective films including physical adsorption film and tribochemical reaction film generated during the friction process.