Development of eco-friendly nano-greases based on vegetable oil: An exploration of the character via structure

Abstract The grease industry today is saturated with products based on petroleum/mineral oils and harsh (containing harmful chemicals) thickeners and additives. Such greases pose severe threats to the environment during their entire service life and even after being discarded as waste. To acknowledge the issue, researchers have developed a few eco-friendly alternatives (from natural and/or eco-friendly ingredients) so far; however, a potential solution is never reached. The present study puts forward a maiden combination to develop a series of greases using soybean oil as base oil, organo-montmorillonite as a thickener, and CaCO3 nanoparticles (0–3 %w/w) as additives. The developed gels were characterized for fundamental properties (consistency, thixotropy, and rheology) against an equivalent commercial grease to justify the signatures of a typical lubricating grease. Deep exploration of the microstructures was also carried out to understand the mechanism(s) behind the observations. In general, the developed gels exhibited equivalent characteristics to that of the commercial grease. However, the concentration of nanoparticles appeared to influence grease behavior significantly. The distribution of and the level of agglomeration among the nanoparticles were recognized as the two crucial parameters. Among all the formulations, the grease with 2% doping of CaCO3 nanoparticles displayed the optimum properties (thixotropy and rheology) closest to that of the commercial reference grease. Models are proposed to develop an explicit understanding of the grease structure, and TEM (Transmission Electron Microscope) micrographs are presented to support the hypothesis. The structure of the grease and the interaction(s) among various ingredients was observed as the fundamental factor governing the grease character.