A biomass-derived L-proline/glycolic acid deep eutectic solvent for superlubricity under high pressure

Deep eutectic solvents (DESs) are emerging as promising sustainable lubricants. However, most reported DESs, particularly those based on choline chloride, exhibit limited biodegradability due to the presence of halide ions. Herein, halogen-free, fully biomass-derived DESs were synthesized from L -proline and glycolic acid. Among various molar ratios, Pro 1 -GA 2 exhibits moderate viscosity, excellent thermal stability, and the strongest hydrogen bonding interactions. Consequently, under a high contact pressure of 0.43 GPa and entrainment velocity of 250 mm·s −1 , it achieves stable macroscopic superlubricity ( μ = 0.0037) on K9 glass/GCr15 tribopairs, corresponding to an 81.86% reduction in friction compared with PAO 10. The lubrication films were monitored and measured, revealing that an optimal film thickness ratio leads to the superior tribological performance. Combined with worn surface analysis, the performance is attributed to the synergistic effect of opportune fluid lubrication films and interfacial tribofilms. This work demonstrates excellent friction-reduction performance in a fully biomass-derived DES, providing new insights for the development of next-generation green lubricants.