Tribological analysis of palm kernel methyl ester containing polymeric viscosity improver

Nowadays, because of the global concern on environmental protection against pollution produced by petroleum-based lubricants, there is a growing interest in developing biolubricants as a new type of clean and green technology. Vegetable oils have some excellent properties for use as biolubricants due to their biodegradability, renewability, high lubricity and high flash point. Despite these advantages, some vegetable oils have low viscosity, which constrains their potential to be used as biolubricants in many engineering applications. In this experimental study, ethylene–vinyl acetate (EVA) copolymer was tested as a viscosity improver for palm kernel methyl ester (PKME). It was found that the addition of 1% EVA copolymer increased the viscosity of PKME by 137%. The viscosity increment of PKME also contributed to the tribological performance of PKME by reducing the friction coefficient and wear scar diameter. This can be attributed to the ability of the polymer to absorb into metal surfaces to produce thick and viscous boundary films. The results also show that the friction-reducing properties of PKME formulated with 1% EVA copolymer are comparable to those of mineral oil SAE 40.