Green Tribology Enabled by Fully Biodegradable Amino Acid-Based Lubricant Additives with Robust Lubricity

With the escalating scarcity of energy resources and the rising emphasis on environmental sustainability, water-based lubrication has emerged as a focal area in tribological research. In this paper, two kinds of eco-friendly and biodegradable amino acid-based ionic liquids (AAILs), Lys-LGA and Arg-LGA, were successfully synthesized through a sample proton exchange process and applied as water-based lubricant additives. Both AAIL additives demonstrated superior thermal stability and effectively retarded the corrosion of cast iron in aqueous environments. The coefficient of friction and wear volume of water-based lubricants were reduced by approximately 70% and 92%, respectively, when Lys-LGA or Arg-LGA was used as an additive. During the friction process, tribochemical reaction films and physical/chemical adsorption films formed by Lys-LGA and Arg-LGA at the interface synergistically prevent direct contact between the sliding friction pairs, endowing water-based lubricants with superior tribological performance. After a 28 day biodegradation test, both Lys-LGA and Arg-LGA exhibited degradation rates exceeding 90%, highlighting their exceptional biodegradability. These compounds exhibit significant potential as key lubricant additives for water-based metal-working fluids and fire-resistant hydraulic fluids.