Synergistic Behavior of Graphene and Ionic Liquid as Bio-Based Lubricant Additive

Abstract

The constant utilization of petroleum-based products has prompted concerns about the environment, hence a replacement for these products must be explored. Biolubricants are a suitable replacement for petroleum-based lubricants as they provide better lubricity. Biolubricant performance can be improved by the addition of graphene. However, there are reports that graphene is unable to form a stable suspension for a long period. This study used a graphene-ionic liquid additive combination to stabilize the dispersion in a biolubricant. Graphene and ionic liquid were dispersed into the biolubricant via a magnetic stirrer. The samples were tested using a high frequency reciprocating rig. The cast iron sample was then further observed using various techniques to determine the lubricating mechanism of the lubricant. Different dispersion stability of graphene was observed for different biolubricants, which can be improved with ionic liquids. All ionic liquid samples maintained an absorbance value of three for one month. The utilization of ionic liquid was also able to decrease the frictional performance by 33%. Further study showed that by using the ionic liquid alone, the frictional could only reduce the friction coefficient by 13% and graphene could only reduce the friction by 7%. A smooth worn surface scar can be seen on the graphene-IL sample compared to the prominent corrosive spot on the IL samples and abrasive scars on graphene samples. This indicates synergistic behavior between the two additives. It was found that the ionic liquid does not only improve the dispersion stability, but also plays a role in forming the tribolayer.

A review of advances in tribology in 2020–2021

“…ILs can be added into other lubricants as additives to reduce coefficient of friction (COF) and wear rate [12], such as bio-based lubricant [13], water-based lubricants [14], and oil-based lubricants [15], even at relatively high temperature [16]. ILs can increase the stability of lubricant additives [16], such as NiAl particles and trihexyl(tetradecyl)phosphonium cation [17], and improve their tribological performance.…”

Biolubricant production via esterification and transesterification processes: Current updates and perspectives

“…182 In other studies, mixing ILs with allotropes of carbon like graphene has shown great potential in biolubricants formulation. For example, Hasnul et al, 183 utilized graphene and ionic liquid additives in biolubricants to improve the biolubricants tribological performances. This is because graphene oxide can form a stable colloidal suspension without using surfactant in pure ionic liquid.…”

Physico-chemical and tribological properties of commercial oil – bio-lubricant mixtures dispersed with graphene nanoplatelets

“…Engine oil is crucial in automobiles to prevent heat and corrosion due to friction. Several studies 1–37 explored the commercial use of biobased oils. Ting and Chen 34 proposed the possibility of producing new lubricants with esters from seed oils, thus minimizing toxicity and improving the biodegradability of engine oils over time.…”