Tribological Behavior of Plant Oil-Based Extreme Pressure Lubricant Additive in Water-Ethylene Glycol Liquid

A water-soluble lubricant additive (RSOPE) was prepared by esterification reaction using fatty acid from rubber seed oil. The RSOPE was added into water-ethylene glycol (W-EG) solution as lubricant additive. Dispersion stability and rheological properties were investigated. We used a four-ball tribotester to assess the lubrication performance of W-EG based fluid with the RSOPE additive. The stainless-steel surface was analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Good dispersion stability was observed in the RSOPE/W-EG solutions. Furthermore, nonNewtonian fluid behavior at low shear rates and Newtonian fluid behavior at high shear rates was exhibited. The addition of RSOPE into water-glycol reduced the friction coefficients (COF) and wear scar diameters (WSD). The maximum nonseizure loads (PB) increased from 98 N to 752 N and the W-EG solution with RSOPE had good corrosion resistance properties. Good tribological performances for W-EG solution with RSOPE were attributed to the boundary tribofilm composed of iron oxide, iron phosphide and so on.