Development of Vegetable Oil-Based Greases for Extreme Pressure Applications: An Integration of Non-toxic, Eco-Friendly Ingredients for Enhanced Performance

Several permutations and combinations of the ingredients have been tried to develop eco-friendly alternatives to conventional mineral/petroleum oil-based greases; however, a potential solution is not yet reached. Surprisingly, the incorporation of environmentally benign additives and their synergy with the greases was least explored in this area. The present study explores a maiden effort to enhance the extreme pressure (EP) characteristics of eco-friendly greases (based on vegetable oil and organoclay) using calcium carbonate (CaCO 3 ) nanoparticles as an additive. The developed nano-greases displayed an improved EP behavior (as per ASTM standards) at all concentrations of the nanoparticles (0.1–4% w/w), and the performance ameliorates with increasing concentration (up to 60% increment achieved). The enhanced performance is attributed to the calcination of nano-CaCO 3 into nano-CaO under extreme conditions. The worn surfaces revealed the formation of a more robust (high melting point, low shear strength, rapidly formed, and tribosintered) tribofilm incorporating the organoclay and the nano-CaO. The formulated greases also demonstrated biocompatible behavior toward human osteoblast-like cells (MG-63) in MTT and Live-dead cell assays. Graphical Abstract