Abstract
Although lubricants play an essential role in reducing wear and friction in mechanical systems, environmental issues persist. In the past decades, Ionic Liquids (ILs) have arisen as environmentally friendly alternatives to conventional lubricants and additives. ILs are low-volatile and non-flammable salts that possess low melting points (below 100 °C). Their tunable properties, achieved by selecting the appropriate cation and anion, make them ideal candidates for different applications, including lubricants. In recent times, Protic Ionic Liquids (PILs) have attracted attention in the tribological community as a cost-effective alternative to conventional aprotic counterparts.
In this work, a choline-amino acid ionic liquid, derived only from renewable, biodegradable, and biocompatible products, was synthesized, and investigated as both neat lubricant and additive to non-polar oil. The lubricating properties of [CHO][GLY] were studied both as a neat lubricant and as a 1 wt. % additive to a polyalphaolefin (PAO) oil using a ball-on-flat reciprocating friction tester. AISI 52100 steel disks were tested against AISI 52100 steel balls using either [CHO][GLY] or the mixture of PAO+[CHO][GLY]. For comparison purposes, the commercially available base oil, PAO, was also tested. Preliminary results showed no major differences in friction between the lubricants used. Nevertheless, the addition of 1 wt.% to the PAO demonstrated a remarkable 30% reduction in wear on the steel disk. This encouraging improvement in anti-wear characteristics raises the potential advancement of lubrication technology with the choline-amino acid ionic liquid, coupled with its environmentally friendly nature. Energy-dispersive X-ray (EDX) spectroscopy, non-contact profilometry, and scanning electron microscopy (SEM) were used to study the worn steel surfaces and elucidate the wear mechanisms.
