Leaves Based Lubricant Additive Towards Improving Tribological Properties

Abstract

Three kinds of crop leaf-surface waxes were extracted from wheat, corn and broomcorn leaves, respectively. The crop leaf-surface waxes as lubricant additives were added to synthetic ester and the friction and wear properties of prepared lubricants for steel-aluminum and steel-copper friction pair were investigated in detail. The scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS) were employed to explore the friction mechanisms. The results show that crop leaf-surface waxes could successfully reduce the friction and wear of steel-aluminum and steel-copper sliding friction pairs as compared with pure synthetic ester. For example, when the concentration of wheat leaf-surface wax as additive was 2%, the COFs was decreased by 58%; the four additives can be ranked by the anti-wear capability as follows: Corn > Wheat > Glycerol >Broomcorn to steel-aluminum sliding friction pairs. The SIMS spectra of positive and negative ions on the worn surfaces have reduced the exposure of Al and increased short chain ions counts. The good friction reduction and antiwear abilities are attributed to the adsorption or reaction films formed by leafsurface wax on worn surface.

Brasenia Schreberi mucilage as a green lubricant additive exhibiting good tribological properties for steel/steel and steel/aluminium friction pairs

“…Meanwhile, with the frequency ranging from 2 to 5 Hz, all the lubricants exhibited a slow increase in COFs and wear widths. It also can be found that BS mucilage exhibited the biggest reduction in COFs and wear widths, which indicated that BS mucilage could generate a high-performance lubricating film on the friction surface at various frequencies [28]. Therefore, BS mucilage possessed a superior friction reduction and anti-wear abilities for steel/steel contact pair under various frequencies.…”

“…Obviously, the COF and wear scar widths also slowly increased with the frequency ranging from 2 to 5 Hz. Among the additives, SE+BS mucilage still exhibited lower COFs and wear scar widths, indicating that BS mucilage could effectively separate the friction interface to exhibit a better friction reduction and anti-wear abilities than others for steel-aluminium friction pair at different frequencies [28].…”

“…As compared with pure SE, it reduced the COF and wear width by 29.6% and 22.4%. The good tribological properties of BS mucilage was mainly attributed to the sufficient lubricating film formed by physical adsorption and chemical reactions on the worn surfaces [19,24,28]. Therefore, the optimal concentration of the three kinds of additives was 1.5 wt%, and in the following experiments for steel/steel friction pair all the concentration of the additive was adjusted as 1.5wt%.…”

“…When BS mucilage is used as lubricant, these long-chain components will fracture to form a lot of short-chain components under the action of contact pressure and friction interface interaction. And these short-chain components usually carry negative charge [19,28,34]. Meanwhile, in the process of friction, electrons on the metal surface are easy to escape, so that the metal surface usually carries positive charge [39].…”

“…It is well known that positive and negative charges could attract each other. Thus, the genitive short -chain components could tightly adsorb on the worn surface to form a form a lubricating film to improve the tribological properties [19,28]. Apart from the physical adsorption lubricating film, there is also existing a tribochemcial lubricating film to enhance the tribological performances.…”