24th International Colloquium Tribology - January 2024 249 New Technologies of Antiwear and Antioxidant Additives Used for Designing Nonhazardous Turbine Oils and Sustainable High-Performance Lubricants Including Greases Grégoire Hervé 1 , Florence Severac 1 1 NYCO, Paris, France 1. Introduction Sustainability is increasingly vital in technological developments, with final users desiring non-hazardous materials that pose minimal environmental and safety risks for their operations. Evolving regulations are unveiling the true toxicity of various chemicals, particularly affecting performance additives, transcending industries. Thus, the quest for effective and safer additive chemicals remains a big challenge for the global industry. 2. Methods Toxicity assessment is a complex and multifaceted domain, characterized by numerous uncertainties. It depends on various factors, including the type and level of exposure, sensitivity of the organisms involved, individual differences such as gender, and more. Usually, a thorough evaluation spanning several years and incurring high costs is required to gain a comprehensive understanding of chemical toxicity. In some cases, conflicting results from toxicity studies have led to prolonged debates within the scientific community. In our research, we employ a holistic approach that integrates both modeling and practical experiments to assess the toxicity of anti-wear and antioxidant additives effectively. 2.1 Modeling Approach [1] For the modeling aspect of our assessment, we have established two types of models: - Quantitative Structure-Activity Relationship (QSAR) Models - 3D Models based on the Harmonic Spheric methodology as previously reported in the literature. [2] 2.2 Biotesting Experiments - In Vitro Experiments - In Vivo Experiments using the freshwater planarian model [3] The combination of these modeling and biotesting approaches forms the foundation of our holistic toxicity assessment, which aims at comprehensively evaluating the toxicity level of anti-wear and antioxidant additives used in lubricants. 3. Main results 3.1 Antiwear toxicity assessment In our assessment of antiwear and organophosphate substances (OPs), we modeled several classes of OPs. Our 3D and QSAR models revealed that most conventional antiwears fall into a group of molecules with an undesirable toxicity profile. Figure 1 illustrates the distinct 3D model patterns, emphasizing variations in shape and chemical functionalities. Additionally, our modeling tool quantifies the accessibility of the potent phosphate functions directly linked to toxicity. The alignment between our in vitro and in vivo experimental results corroborates our modeling findings. For instance, Figure 2 illustrates the disparate neurotoxicity patterns observed in vitro aligning with the 3D models. 3.2 Antioxidant toxicity assessment In the assessment of antioxidants (AOs), we primarily employed QSAR models, encompassing four types: C, M, R, and N models (N for neurotoxicity). Reprotoxicity (R) emerged as the most critical endpoint among these. Our in vivo experiments validated the potential toxicity of most commercial aminic and phenolic AOs. Encouragingly, our in-house developed polyaminic antioxidant technology exhibits a significantly safer profile based on our both predictive and in vivo data. 3.3 Performance evaluation Subsequently, we formulated our safer and nonhazardous antiwear and polyaminic antioxidant additives, resulting in various finished lubricants, including turbine oils, gear oils, and greases. Thermal and tribological evaluations underscore their superiority over existing market lubricants. Our bearing rig, as depicted in Figure 3, recorded outstanding thermal properties when subjecting turbine oils to high temperatures and rigorous conditions (260-°C, 200-h, 10,000-rpm). Furthermore, we observed reduced coke formation compared to commercial references. Notably, our new antiwear molecules demonstrate excellent frictional antiwear performance, with some exhibiting remarkable extreme pressure properties, as illustrated in Figure 4. This latter achievement is exceptional as it relies solely based on phosphorus, oxygen, carbon, without the need for other heteroatoms like N, F, Cl, or S. Turbine oils and gear oils derived from these innovative chemistries find applications with excellent seal and material compatibilities, thanks to the low additive aggressiveness. Additionally, greases stand to benefit from these technologies as hazardous phosphorus additives can be replaced, allowing for the formulation of pictogram and risk-free materials. It is noteworthy that biodegradability can be further enhanced, particularly in ester/ PAO-based grease formulations) using such carefully selected additives. 250 24th International Colloquium Tribology - January 2024 New Technologies of Antiwear and Antioxidant Additives Used for Designing Nonhazardous Turbine Oils and Sustainable High-Performance Lubricants 4. Conclusion Our research addresses the complex toxicity issue through an innovative, holistic approach that integrates modeling and practical experiments on anti-wear and antioxidant additives. Both computational and experimental approaches align harmoniously, providing robust consistency and clear trends. This enables us to judiciously select the safest chemistry of additives for antioxidant and anti-wear applications. Our lubricant formulations, including greases, exhibit exceptional thermal and tribological performance. This research demonstrates the harmonious coexistence of safety, sustainability and performance, in accordance with industry and environmental needs. Figure 1: 3D models predict different bioactivity-toxicity patterns between the class of standard organophosphate antiwears (cluster A) and the new class of AW molecules (cluster B). Calculated phosphate access is considerably reduced in cluster B versus cluster A. [1] Figure 2: In vitro results specific to neurotoxicity assessment based on the Elman’s method (cholinesterase (ChE) inhibition). [4] IC50: OP concentration (in mg/ L) for 50% of inhibition. Figure 3: Bearing rig used for assessing the level of cokefaction of turbine oils. Figure 4: AW Standard 1 is the commercial benchmark, AW1, AW2, AW3 the new safer antiwears. Load resistance performance using MTM2 tribometer. Conditions: 0,2 m/ s speed, 50 N load, slide-to-Roll Ratio: 30 s step from 300% and up to failure, 100-°C. References [1] Modeling work on OP toxicity assessment is under publication. [2] Karaboga et al. Journal of Molecular Graphics and Modelling 2013, 41, 20-30. [3] Hagstrom, D., Hirokawa, H., Zhang, L., Radic, Z., Taylor, P., & Collins, E. S. Archives of toxicology 2017, 91(8), 2837-2847. [4] Ellman, G. L., et al. Biochem. Pharmacol. 1961, 7, 88-95.