Frictional Behavior and Tribofilm Formation of Organic Friction Modifiers under Severe Reciprocating Conditions

Area of Science:

• Tribology
• Materials Science
• Green Chemistry

Background:

• Environmentally friendly lubrication requires organic additives free from heavy metals, phosphorus, and sulfur.
• Organic friction modifiers (OFMs) reduce friction and wear by forming adsorbed boundary films, but their mechanisms are not fully understood.

Purpose of the Study:

• Investigate the lubrication mechanism of OFMs using a novel approach with acylglycerol mixtures.
• Evaluate the tribological performance of glycerol monooleate (GMO), glycerol trioleate (triolein), and glycerol dioleate (GDO) mixtures in PAO4 base oil.

Main Methods:

• Utilized a combination of glycerol monooleate (GMO), glycerol trioleate (triolein), and glycerol dioleate (GDO) in varying ratios.
• Evaluated lubricating performance under boundary lubrication at 60 °C and 100 °C.
• Employed High-Resolution Transmission Electron Microscopy (HRTEM), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and Near-Edge X-ray Absorption Fine Structure (NEXAFS) analyses.

Main Results:

• Mixtures of acylglycerols exhibited synergistic effects, significantly reducing friction and wear compared to individual additives.
• HRTEM analysis revealed thicker tribofilm formation with additive mixtures.
• ToF-SIMS and NEXAFS indicated that at 60 °C, GMO decomposition products and oleate ions formed the tribofilm, suggesting chemisorption's role in friction reduction.

Conclusions:

• Acylglycerol mixtures offer enhanced tribological performance in environmentally friendly lubrication.
• Synergistic effects and thicker tribofilms contribute to improved friction and wear reduction.
• Chemisorption of decomposition products plays a crucial role in friction reduction at lower temperatures.