Lubricity and mechanical stability of bio-grease formulated from non-edible vegetable oil

Abstract

This study proposes the formulation of a novel grease material using biological resources, which displayed satisfactory mechanical and lubrication properties. This bio-grease material was formulated using non-edible vegetable oils (such as castor, neem and jatropha oils), with a beeswax thickener and hexagonal Boron Nitride (hBN) as the nano additive. Thereafter, the optimal formulation of the bio-grease material was conducted using the Taguchi-based Grey Relational Analysis technique. The lubricity and mechanical stability of the formulated bio-grease material was tested with the help of a 4-ball tribometer based on the modified sliding frictional wear test, described in the ASTM D2266 standard. The fundamental wear mechanism occurring between the contact surfaces was also determined by investigating the surface morphology using Scanning Electron Microscopy embedded with Energy Dispersive X-Ray Analysis (SEM-EDX). The results of the study indicated that base oil was the most significant factor that affected the Coefficient of Friction (COF) and the mechanical stability loss of the formulated bio-grease. Furthermore, the optimised bio-grease material contained 5 wt.% of thickener in castor oil and showed the lowest COF value of 0.04 and the highest delay in the mechanical stability loss (13,200 s). The acquired results were compared with those of the conventional grease material and observed that the SEM images of conventional grease material showed higher adhesive wear and rougher surface compared to the micrographs of the samples that were lubricated using the optimally-formulated bio-grease material.