Green Tribology Enabled by Fully Biodegradable Amino Acid-Based Lubricant Additives with Robust Lubricity
Xuemin Sun, Xiao Liu, Yongqiang Wang, Kun Zou, Pingxia Guo, Qiang Chen, Meirong Cai, Feng Zhou
Abstract
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.