Natural emulsifier assisted lubricity of the colloidal system: Effect of natural emulsifier concentration

[Display omitted] •GA concentration controls stability, lubricity, and antifriction response of FFs.•Chemisorption of GA molecules to steel surface controls the wettability of FFs.•Packing of GA molecules at the oil–water interface decides the stability of FFs.•Active participation of GA molecules assists in lubricious (stable) film formation.•GA stabilized environmental friendly FFs have potential to replace commercial MWFs. Environmental needs, human health issues, government regulations have motivated this work to explore an alternative to mineral oil-based systems to vegetable oil-based environmental friendly lubricants. The present study is an attempt to use natural products (soybean oil and Gum Arabic) to develop environmental friendly oil-in-water emulsion to be used as metalworking fluid. The role and effect of Gum Arabic (GA) concentration on emulsion stability, wettability, and lubricity is explored. Three concentrations of GA corresponding to critical micelle concentration (CMC), below CMC and above CMC are selected to formulate the emulsions (Formulated fluids (FFs)). The emulsion characteristics (droplet size and zeta potential), pH, wetting dynamics, and lubricity are evaluated using dynamic light scattering (DLS), pH glass electrode, Goniometer, and four-ball tester (FBT), respectively. Worn surfaces are analysed using Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscope (FESEM). The physical characteristics and tribological responses suggest that the FF @ CMC of GA exhibited better stability, lubricity, and antiwear properties than other formulations. Different responses of FFs are benchmarked with that of mineral oil-based commercial fluid (CF). FF @ CMC of GA showed a better anti-friction and similar anti-wear response as compared to CF. The excellent lubricity of the FF @ CMC of GA is attributed to the formation of the low shear strength stable lubricious film due to the active participation of GA molecules at the tribo-pair interface.