Tribological evaluation of environmentally friendly ionic liquids derived from renewable biomaterials

Unlike most of the conventional ionic liquids (ILs) derived from non-renewable resources, five environmentally friendly ILs ([Ch][AA] ILs) derived from amino acids (AAs) and choline (Ch) were synthesized using biomaterials by a simple, green route: acid–base reaction of Ch and AAs. The thermal and corrosion properties, as well as viscosity, of the prepared ILs were examined. The results revealed that the anion structure of ILs plays a dominant role in their thermal and viscosity behavior. These ILs exhibited less corrosion toward copper, related to their halogen-, sulfur-, and phosphorus-free characteristics. The tribological behavior of the synthesized ILs was examined using a Schwingungs Reibung und Verschleiss tester, and the results indicated that these ILs exhibit good friction-reducing and anti-wear properties as lubricants for steel/steel contact. Results from energy-dispersive spectroscopy and X-ray photoelectron spectroscopy indicated that the good tribological properties of [Ch][AA] ILs are related to the formation of a physically adsorbed film on the metal surface during friction.