The realization of industrial applications of plant-based lubricants depends on well-dispersed lubricant additives. Herein, microwave-assisted ball milling directly grafted L-phenylalanine (LP) onto graphene oxide. The reaction does not require a pretreatment step and avoids high temperatures and catalyst involvement. The prepared LP-functionalized graphene oxide (LP-GO) exhibited hydrophobicity with a water contact angle of up to 133° and could maintain stable dispersion in castor oil for more than 80 days. 0.2 wt% of LP-GO improved the thermal conductivity of castor oil by 11.1 % and contributed to the enhancement of tribological performance under three different conditions. In particular, wear and friction decreased by 7.31 % and 11.54 % under the medium speed medium load condition, respectively. The friction decreased by 25.27 % in the low-speed high-load condition, and the wear decreased by 18.65 % under the high-speed low-load condition. The characterization of the tribological interface revealed that the lubrication mechanism of LP-GO was attributed to its protective and repairing effects at the friction interface. The surface functionalization approach in this paper is rapid and green. It can be extended to other functionalizing agents and nanomaterials, facilitating further applications of vegetable oils in tribology.
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