Tribological and Physicochemical Behavior of a Novel Palm Grease Blended with Zinc Oxide and Reduced Graphene Oxide Nano-Additives

Palm oil possesses promising properties which promote them to be a competitive alternative to mineral oils in the lubrication of machinery. Still, marginal oxidation stability, viscosity, and tribological properties remain critical issues for performance improvement. This paper synthesized palm grease with reduced graphene oxide (rGO) and zinc oxide (ZnO) nano-additives at different blending ratios. Grease samples were tested for the physicochemical and tribological characteristics. The results showed that the highest viscosity values are found in case of base oil mixed with 0.1 wt.% ZnO and 2 wt.% rGO, separately. ZnO additives enhanced the oxidation stability by 60% and shifted the pour point from 9 oC to 6 oC. Adding ZnO and rGO to the palm grease increased the load-carrying capacity between 30% and 60%, respectively, and reduced the friction coefficient by up to 60%. The wear scar morphology proved a high competency of the developed palm grease aggregates in comparison with lithium grease.