24th International Colloquium Tribology - January 2024 245 How can Esters Improve the Sustainability of Both Intrinsic and Extrinsic Factors? Gareth Moody 1 , Gemma Stephenson 2* 1 Cargill, York, United Kingdom 2 Cargill, York, United Kingdom * Corresponding author: Gemma_Stephenson@Cargill.com 1. Introduction Sustainable development is happening on a global basis [1]. At the core is a call for concerted efforts towards building an inclusive, sustainable and resilient future for people and planet. For this to happen, it is crucial to harmonize the three elements of social development, economic growth and environmental protection. Central to environmental protection is the recognition that greenhouse gas levels, particularly CO 2 , in the atmosphere need to be reduced to slow down the global temperature rise and avoid catastrophic events [2]. It has been realized that within the lubricants industry, decarbonization is required across the whole value chain and collaboration is essential in making this happen. Initiatives are underway to reduce carbon embedded in raw materials (scope 3 emissions), as well as reduce reliance on fossil-based processes within manufacturing (scope 1 and 2). Within the scope 3 emissions umbrella, the “use of sold products” [3] allows for lubricant additive manufacturers to design technologies that allow for carbon reductions and savings. As an industry, product performance is the primary consideration when designing additives, base oils and finished lubricants. A product MUST deliver performance benefits to the customer that are second to none. These are known as the extrinsic benefits. It is also desirable to maximize intrinsic benefits at the same time, e.g., biodegradability or bioaccumulation potential. However, we understand that with product performance will also come a carbon footprint, or an environmental footprint of some kind. Reports have indicated that up to 80% of a materials carbon footprint can be attributed to carbon embedded in raw materials [4]. It is therefore a balancing act, but also vital to create products which are safe and sustainable by design, and to use innovation as a tool to create ingredients that deliver maximum performance benefits, but which also have a minimal carbon/ environmental footprint. Biobased materials are derived from biomass and are defined as renewable resources, which can be replenished over time. Biobased materials allow for the consideration of CO 2 sequestration as the raw materials are grown and can lead to reductions in the CO 2 footprint of a product. Care must be exercised when calculating product carbon footprints (PCFs) and appropriate methodologies should A simple way to evaluate base fluid traction coefficient is by measuring them using a Mini Traction Machine (MTM), the test conditions for which are shown in Table 2.be followed. Similarly, it is important to consider other complex factors when assessing sustainability of such biobased materials (e.g., land use change) to ensure that a positive effect in one area is not being cancelled out by a negative effect elsewhere. Continuing efforts to minimize product carbon footprints can help reduce CO 2 levels, however extrinsic factors can save even more over the lifetime of a vehicle if a fluid can be more efficient or have a longer lifespan. Choosing a lubricant which has a low product carbon footprint, but which is inefficient in use may well have a negative effect overall. In order to evaluate which of the lubricants is the best choice overall both the intrinsic and the extrinsic benefits must be evaluated. In this paper, the intrinsic and extrinsic properties of both petrochemical and highly biobased formulations have been tested. Base fluids for EV transmission oils have been evaluated using a suite of tribological tests. Fully formulated EV transmission oils have also been considered. Additionally, an ester whose structure is optimally designed for film formation within EV transmission oils has also been evaluated. 2. Maximizing Efficiency and Biobased Content in Esters The properties of biobased esters having a viscosity similar to typical base fluids (group III, PAO 4) are shown in Table 1. Table 1: Neat base oils for evaluation Product kV at 40-°C (mm 2 / s) kV at 40-°C (mm 2 / s) Biobased content (%) Group III 20 4.2 0 PAO 4 19 4.1 0 Ester 1 19 4.5 31 Ester 2 25.3 5.5 47 Ester 3 19.6 4.4 82 Ester 4 9.6 2.9 0 Ester 5 6.1 2.0 85 A simple way to evaluate base fluid traction coefficient is by measuring them using a Mini Traction Machine (MTM), the test conditions for which are shown in Table 2. 246 24th International Colloquium Tribology - January 2024 How can Esters Improve the Sustainability of Both Intrinsic and Extrinsic Factors? Table 2: MTM Test Conditions Parameter High speed, low severity Samples Base oils Test type Traction curves Load/ N 16 SRR 0-100 Temperature/ °C 40, 100 Figure 1 shows the traction coefficient curves for these tests. The solid line shows the traction coefficient curve at 100-°C, and the dotted line shows the traction coefficient curve at 40-°C. Figure 1: Traction coefficients by MTM at 40 and 100-°C The first thing to notice is that the traction values at 40-°C (dotted line) are higher than their corresponding lines at 100-°C (Solid lines), this is because of viscosity and the general trend that the lower the viscosity, the lower the traction. At 40-°C there is a large difference between the base oil types. Group III has the highest traction, next are Ester 1 and PAO. Ester 1 is a predominantly petrochemical based ester and has some branching which can give it higher traction. Esters 2 and 3 have a higher biobased content and were designed to have lower traction. This occurs at both 40-°C and 100-°C. Esters 4 and 5 are designed to have maximum efficiency and lowest possible traction as shown in Figure 1. There are two approaches to achieving this. The first is to use petrochemical derived raw materials which have a higher PCF value but have the lowest possible traction and Ester 5 which uses biobased raw materials but still has very low traction. 3. Conclusion Using esters can greatly benefit the intrinsic and extrinsic properties of a lubricant. For the intrinsic properties the choice of raw materials (petrochemical vs biobased), the way they are processed and the way they are transported will influence the product carbon footprint of a molecule. Even if a material is 100% biobased it does not mean that it will be the most sustainable option over the lifetime of an oil as it must also perform in use. When evaluating a lubricant for an application, the intrinsic and extrinsic properties must both be considered to make the most sustainable choice. Esters shown in this paper demonstrate that it is possible to improve EV transmission fluid efficiency through designing molecules that deliver significant reduction of traction. References [1] United Nations. The Sustainable Development Goals Report, 2022. [2] United Nations Climate Change UNFCCC. The Paris Agreement - Publication 2018 [3] Carbon Chain, 2023. Scope 1, 2 and 3 emissions. Available at https: / / www.carbonchain.com/ carbon-accounting/ scope-1-2-3-emissions/ [4] C. Cherel-Bonnemaison, G. Erlandsson, B. Ibach & P. Spiller. Buying into a more sustainable value chain. Mckinsey & Company, 2021. Available online at https: / / www.mckinsey.com/ capabilities/ operations/ our-insights/ buying-into-a-more-sustainable-value-chain