24th International Colloquium Tribology - January 2024 257 Hybrid Lubricating Grease Formulations: A Sustainable Approach for Utilizing Renewable Resources within a Circular Economy Model George S. Dodos *1 , Mehdi Fathi-Najafi 2 , Christina Dima 1 , Nora Kaframani 1 , Andreas Dodos 1 1 ELDON’S S.A., Athens, Greece 2 Nynas AB, Stockholm, Sweden * Corresponding author: g.dodos@eldons.gr 1. Introduction The UN’s Sustainable Development Goals sets 2030 as the year by which certain key targets should be achieved including the responsible consumption and production, aiming to reduce waste and protect natural resources. Waste minimization can be achieved in an efficient way by focusing primarily on the first of the 3Rs, “reduce,” followed by “reuse” and then “recycle”. “Zero Waste” is an approach that promotes the goal of reducing the amount of material we throw away and instead reincorporating by-products of one system for use for another system. The idea of the so-called Industrial Symbiosis the process by which wastes or by-products of an industry or industrial process become the raw materials for another can substantially contribute to the creation of circular development and “Zero Waste Goal”. Waste may include bio-waste, mineral-waste, and food-type waste. Particularly for the latter there is a global social and economic need to recover high added value components and to produce energy and bio-commodities. Valorizing the vast amount of food and food processing industry waste and by-products can provide economic benefits and reduce GHG emissions [1, 2]. Moreover, the industrial utilization of components with a lower nutritional value means that there is no element of competition between current food or feed streams. In the recent past, a series of successful projects to valorize waste streams, such as used cooking oil to produce sustainable greases have been presented. Also, it has been demonstrated that the reduction of the energy consumption in the grease production can contribute to an increasing sustainable profile of lubricating greases [3,4]. To move forward, the utilization of waste materials or the re-use of end-of-life components as renewable feedstock in the production of greases, can promote further the sustainable performance within a circular model. 1.1 Scope The aim of this work is to employ innovative renewable raw material streams for the formulation of lubricating greases that can show improved performance characteristics compared to a conventional base grease formulation model. Specifically, this study: • Investigate the potential of the Hybrid Concept in grease formulation. Within the hybrid approach, bio-components and waste material can be efficiently incorporated to already studied matrix and this will allow for elimination of the risk of incompatibilities and provides flexibility in the selection of efficient additive chemistries. • Assess the efficiency of incorporating crude fatty oils in the grease matrix instead of refined ones. Renewable feedstock from plant or animal sources are a good starting point as most of them do not pose classification issues. The utilization of crude (instead of refined) species of these oils is one more asset to the LCA of the final greases due to the lower GHG emissions involved in the overall processes and the potential gain in the water footprint. • Examine the incorporation of renewable particles in the grease matrix. By adding solid particles to a lubricating grease, certain properties can be enhanced. These renewable solid particles can further increase the renewable partition in the final formulation. • Create possibilities for the evolution of a new roadmap towards low carbon intensity greases. 2. Experimental 2.1 Grease formulations Lab scale grease formulations based on Ca and Li 12-HSA thickener were utilized and evaluated per the effect of a series of renewable components (liquid and solid) on certain key grease performance characteristics. A naphthenic specialty product was utilized as an effective conventional and compatible foundation to highlight the benefits of the renewable materials added. The target was to replace at least 50 percent by weight of the formulation with bio-components. 2.1.1 Natural esters Two different types of renewable straight run/ crude natural esters were incorporated in the dispersion medium that represent oils with different fatty acid composition that could be either of low nutrition value or by-products of the food sector. Cottonseed oil (CCSO) has increased levels of saturated fatty acids while olive pomace oil (COPO) is abundant in oleic acid. CCSO has certain advantages for climate change compared to other seed oils (low water footprint, potential for reduced climate change impacts). COPO is a byproduct of olive oil processing. It is intended for refining for use for human consumption, or for technical use. It is a non-GMO High Oleic Fatty acid profile which is beneficial for industrial uses. 2.1.2 Renewable solid particles Two types of renewable particles (RSP-1 & RSP-2) were added at a treating rate between 5 - 15 wt. percent. These are by-products of the food processing industry that were selected as inert components instead for chemically active compounds. 258 24th International Colloquium Tribology - January 2024 Hybrid Lubricating Grease Formulations: A Sustainable Approach for Utilizing Renewable Resources within a Circular Economy Model Li Formulations Ca Formulations Figure 1: Hybrid Grease Formulations: Effect of the various renewable bio-components on grease’s characteristics Moreover, Calcium carbonate (CaCO 3 ), a natural solid particle, was added as a controlling agent particle at 2 wt. percent. 3. Results and Discussion Figure 1 gives a summary of the effect of the various bio-components on fundamental quality parameters of the hybrid grease formulations. 3.1 Natural Esters Consistency: A penetration equal to NLGI #1 was determined in most cases with a trend of a higher consistency in Ca formulation, especially when COPO was incorporated. Dropping Point: No adverse effect on thermal properties of greases after the addition of the crude vegetable oils. Anti-wear Properties: Reasonable Four Ball wear scars were generated after the addition of the natural esters. Cold flow properties: COPO is capable of substantially upgrading the low temperature performance due to the positive effect of high monounsaturated fatty acid profile. Lower flow pressure values were measured in the Li formulations. Oxidation Stability: Results are acceptable for this type of formulations. There is a clear effect of the variant FA profile of the two natural esters. 3.2 Renewable solid particles Consistency: A thickening effect of the particles was depicted in almost all cases. Dropping Point: The addition of renewable particles shows a positive effect on Ca formulations, with no negative effect in the rest of the samples. Antiwear Properties: RSP1: at 5wt. % treating rate the wear scar was dramatically decreased from around 2.6 mm to <- 0.5- mm. RSP2: this type of particle is more efficient at higher treating rates of 15 wt.% Cold flow properties: COPO formulations show overall lower impact on low temperature flow pressure after the addition of the RSPs. Oxidation Stability: No adverse effect on oxidation stability 4. Conclusions In a holistic approach to formulate lubricating greases in a sustainable way, this study demonstrated that by-products or waste material from the food processing industry may be introduced in the grease matrix and can be compatible with conventional chemistries and base oils. The incorporation of these renewable materials produces cost-effective greases that are competitive in terms of their characteristics and performances. Hybrid formulations are advantageous in terms of the versatility they can offer in the selection of materials and additives. Finally, the authors believe that this study demonstrates as a successful benchmark of an efficient life-extension of regional by-products or/ and wastes. Moreover, the global extensions of this type of concept to other regions may contribute to a localized vertical (food) waste valorization in grease formulations that can promote the ideas of industrial symbiosis and zero-waste society. References [1] Roy, et al. (2023). ACS Environmental Au, 3(2), 58-75. [2] Tropea, A. (2022). Fermentation, 8(4), 168. [3] Dodos G. S., Eurogrease 2, 2016. [4] Fathi-Najafi M. et al. NLGI Spokesman, 84-2, 2020.