Environmentally friendly inorganic lubricating greases enhanced with modified bentonite clay for improved performance and sustainability in the engine industry

Abstract The rapid demands of the engine industry for greases that can perform under a wide range of operating conditions focused on developing environmentally friendly, inorganic lubricating greases free from soap-based components. Utilizing bentonite clay as an innovative porous thickener, combined with two base oils blend with soft and hard paraffin wax additives, seeks to economically synthesize greases that are versatile and suitable for a wide range of service conditions. Acid post-treatment of raw bentonite was undertaken to activate the bentonite clay and alter its surface from hydrophilic to organophilic, enhancing its dispersion in organic base oil. The activated bentonite exhibited significant modifications in surface area, porosity, and crystal morphology, which directly influenced the grease's physical properties and performance. Notably, activated bentonite treated by nitric acid showed superior efficacy in homogeneously integrating with both base oil types and paraffin waxes compared to other acid post-treatments, producing greases with higher dropping points similar to lithium complex and organic clay grease, lower working penetrations as normal grease as classified by National Lubricating Grease Institute (NLGI) consistency grade. This study contributes to the development of inorganic grease formulations by systematically evaluating the rheological and thermal performance of modified bentonite. On the other hand, it highlights the flexibility of modified bentonite as a universal thickener for lubricating greases, demonstrating its efficiency as a multifunctional thickener that meets the evolving demands of various industrial engines.