Compatibility of Ionic Liquid With Glycerol Monooleate and Molybdenum Dithiocarbamate as Additives in Bio-Based Lubricant

Abstract This study reports the tribological characteristics of trimethylolpropane trioleate (TMPTO) additivated with antifriction and antiwear additives, which are ionic liquid (IL), glycerol monooleate (GMO), and molybdenum dithiocarbamate (MoDTC). In addition, to obtain the ideal composition that results in the minimal coefficient of friction (COF), optimization tool was employed using response surface methodology (RSM) technique with the Box–Behnken design. The IL used in this study was a phosphorus-type IL, namely trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl) phosphinate, [P14,6,6,6][TMPP]. The resulting COF and worn surface morphology were investigated using high-frequency reciprocating rig (HFRR) tribotester and scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. From the experimental results, a second-order polynomial mathematical model was constructed and able to statistically predict the resulting COF. The optimized values that resulted in the lowest average COF of 0.0458 were as follows: 0.93 wt% IL, 1.49 wt% GMO, and 0.52 wt% MoDTC. The addition of IL into neat base oil managed to reduce the COF, while the combination of IL, GMO, and MoDTC at optimum concentration further reduced the average COF and wear as observed through SEM micrographs when compared with those of additive-free TMPTO, suggesting that GMO and MoDTC were compatible to be used with IL.