Synthesis and tribological properties of air plasma polymerized soybean oil with N-containing structures

Abstract

In this study, polymerized oils with different viscosity grades were synthesized by the polymerization of soybean oil (SO) in an air plasma environment. The results of the elemental analysis, infrared spectroscopy, and pyrolysis gas chromatography revealed that the carbonyl, organic amine, and nitrogen heterocyclic groups were incorporated into the molecule of the polymerized oil (PAIR9); the GPC chromatogram of this oil revealed that the product consisted of dimers and oligomers with higher molecular weights. The tribological behaviors of the polymerized oils were evaluated using a four-ball friction and wear tester. The maximum non-seizure loads of all the polymerized oils surpassed that of SO, and the PB value of PAIR9 reached 1,186 N. Meanwhile, PAIR9 exhibited much better anti-wear performance when the tested loads were lower than 350 N. The worn surfaces lubricated by SO and PAIR9 were analyzed using the X-ray photoelectron spectra (XPS). The results of the XPS analysis proved that during the frictional process, the polymerized oil could not only promote the adsorption of the oil on the metal surface because of the oxygen-containing species (such as esters and carbonyl groups) with higher polarities but also promote the interactions with the metallic iron to form compact and stable tribochemical films containing organic nitrogen complexes. © 2014 AOCS.