23rd International Colloquium Tribology - January 2022 115 Next-generation anti-wear development Christelle Chretien SOLVAY, Bristol, PA - USA christelle.chretien@solvay.com 1. Introduction To protect our health and our environment, cleaner transportation is urgently needed, with an ultimate goal of zero emissions and carbon neutral. To achieve it, the following solutions have to be developed: • Solutions for electric vehicles (EV): more robust anti-wears (AW)/ EP for E-driveline lubricants • Solutions decreasing friction for both Internal Combustion Engines (ICE) and E-drivelines to save fuel and electricity • Solutions free of Metal and Sulfur for cleaner gas emission and better compatibility with E-drivelines. The objective of this paper is to present: • Introduce the technology of next-generation anti-wear • Describe its main benefits 2. Purpose of this project The objective of this project is to develop a next generation of anti-wear additive presenting the following features: • Ashless, Sulfur-free, and low phosphorus content • Providing equivalent or better wear prevention and improving energy efficiency 3. Technology description As the toolbox of chemicals is more and more limited, the idea is to look out-of-the-box and develop a technology of anti-wear not existing today in the industry. The technology we propose as a next-generation anti-wear is very unique as: • The Phosphorous so the anchoring group is outside of the backbone of the polymer bringing a freer access to the surface • It is based on a co-polymer. Different monomers are used to achieve the right balance between surface adhesion and oil solubility. This technology can be depicted as the following: Figure 1: Polymeric Anti-Wear (Polymeric AW) 4. Prior art analysis This analysis of the prior art shows the uniqueness of this Polymeric AW technology as: • It directly coats the surface as a polymer when ZDDP reacts first with the surface to form a polymeric tribofilm on the surface. • It’s anchoring group is easily reachable as it is outside of the backbone. 4.1 Standard anti-wear technology Zinc dialkyldithiophosphate (ZDDP) is the standard anti-wear additive technology in the lubricant industry in a wide majority of applications. To form a tribofilm, ZDDP decomposes into long polyphosphate films which are polymers, under high loads and high temperatures [1]. ZDDP provides very good anti-wear performance at an optimized cost. It is multifunctional as it also provides 116 23rd International Colloquium Tribology - January 2022 Next-generation anti-wear development extreme pressure, anti-oxidation and corrosion inhibition [2]. Its drawback is that it contains Zinc and Sulfur producing harmful vehicle emissions, impacting some types of wear and yellow metallic surfaces. In addition, its performance on fuel economy is quite limited. New regulations, hardware and specifications require today to develop alternatives. 4.2 Polymeric Anti-wear To understand the patent landscape on anti-wear, a patent search was conducted focusing on anti-wears in lubricants. 475 patents appeared from this search. By focusing specifically on polymeric anti-wears, only 5% of the patents claim the use of polymeric antiwears with polyphosphorus and fluorinated polymers. For exemple, the patent application US 2012/ 0309656 claims the use of a polyphosphate in combination with an anti-oxidant to have a better wear prevention in automotive application. Figure 2: Polyphosphate 5. An Innovative solution under development Among the different candidates developed at a lab scale, one candidate has shown leading performances with 11 benefits identified: • Metal-free, Sulfur-free and very low Phosphorus content • Good anti-wear performance • Friction level similar to ZDDP • Tremendous thermo-oxidative stability • Very low sludging tendency • Harmless on viscometrics, foam, and corrosion • Excellent solubility in standard base oils • Very low acidity level Major highlights are: 5.1 Physico and Chemical properties This transparent liquid solution has both a very low phosphorus content at 0.32wt% with a low TAN at 7 mg KOH/ g. 5.2 Anti-wear performances Based on the Falex Pin and Vee wear test, a 45% decrease in wear was observed compared to ZDDP when both used at 1wt% in a Group II base oil. Figure 3: Falex Pin and Vee wear evaluation 5.3 Viscometrics Slight to no increase was observed on the kinematic viscosity after the addition of 1wt% of Polymeric AW. Shear stability and cold flow properties are not impacted when using 1wt% of Polymeric AW in a group II base oil showing a viscosity loss of only 0.3% after a 20 hour KRL. 5.4 Oxidation and thermal stability No impact on a fully formulated oil top treated with 1wt% Polymeric AW after 192 hours at 160C of oxidation: equivalent kinematic viscosity, acid number and deposit formation: Figure 4: After oxidation for 196 hrs at 160C Thermal stability is outstanding as it is above 300C and leaving no residue. 23rd International Colloquium Tribology - January 2022 117 Next-generation anti-wear development 6. Conclusion The Polymeric AW technology shows strong potential as a next-generation anti-wear thanks to the different benefits it provides, on top of anti-wear prevention. Further evaluations are ongoing in fully formulated formulation and specifically in the EV segment to assess its potential. References [1] “Overview of automotive engine friction and reduction trends-Effects of surface, material, and lubricant-additive technologies”: DOI 10.1007/ s40544- 016-0107-9 [2] “ZDDP’s uncertain future” in the TLT Tribology & Lubrication Technology - September 2019