23rd International Colloquium Tribology - January 2022 127 Calcium Sulfonate Greases - Improving Biodegradable solution thanks to 1-step process Guillaume Notheaux SEQENS (ex PCAS), Porcheville, France Corresponding author: guillaume.notheaux@seqens.com Laura Hue SEQENS (ex PCAS), Porcheville, France 1. Introduction Over Based Calcium Sulfonate (OBCaS) greases are well known in the industry [10-11,13], confirmed by the growing market demand [1]. During the 22nd ICT in 2019 [2], the possibilities of the “1-step process” have been put forward, especially the advantage to choose 100 % of the carrier of the final grease. The first biodegradable OBCaS grease has been disclosed as example with some excellent results known on OBCaS grease. Thanks to users and market feedback, and to fit the new HPM grease specifications, 3 main items have been selected, and will be studied in this 2 nd step : - Improvement of corrosion preventive properties under dynamic wet conditions according to the ASTM D6138 (Emcor) - Offer a new grade with the same behavior in cold environment / flow pressure according to DIN51805 (Kesternich method) - Improvement of oxidation stability according to ASTM D8206-18 (RSSOT) These 3 refinements may seem independent but are closely related and can be solved with the one step process. 2. Improvement of the corrosion properties under dynamic wet conditions and new grades 2.1 Opportunities High thermal stability, intrinsic anticorrosion properties [3], mechanical stability, water resistance [12] and lubricating properties are driven by the 3D micellar core/ shell structure [4]. Pumpability at low temperature is mainly related to the base oil viscosity but could also be affected by the soap amount and the consistency [5][6]. First proposal in the 22nd ICT 2019 was based on a compromise ISO 46 carrier/ NLGI grade 2. But the market demand pushed 2 other combinations: - ISO150 carrier / NLGI grade 2 (good opportunity to increase performances but not for low temperature behavior) - ISO46 carrier / NLGI Grade 0 (good for low temperature behavior but not for performances) On the two grades requested, expectations were also to increase the Emcor test results, but this could unfortunately also affect all other properties and especially biodegradability. Meanwhile, the initial grade (ISO46/ NLGI grade 2) will also be improved. 2.2 Study follow-up Switching from a carrier to another, or adjusting the consistency are simple to manage with the 1-step process. Working on these 2 new products, the first idea to improve the Emcor test results was to use common additives. Different chemistries were tested to boost the rust inhibitor properties and water resistance (like phosphite/ phate derivatives, imidazoline, amine phosphate, ANsulfonate, or tack. polymer...). However, effects on biodegradability, on consistency/ rheology, on AW performance, or simply no better Emcor results were found. The second idea was to introduce different co-acids during the process in order to reinforce the top layer of the micellar structure, according to the carpeting theory, to improve water resistance. 128 23rd International Colloquium Tribology - January 2022 Calcium Sulfonate Greases - Improving Biodegradable solution thanks to 1-step process There are a lot of examples in the literature for acid and co-acid use in the conventional OBCaS grease 2-step process, such as 12HSA [7], but also acetic acid, boric acid, phosphoric acid... [8] mainly to help the amorphous to calcite conversion or to decrease the amount of soap. In our specific 1-step process, co-acids must be integrated to the top layer of the micelle to strengthen it. The main difficulties were to define how to achieve it, without changing rheological behavior, since the micellar structure is directly impacted. The key is not only the selection of co-acids but also a very well-balanced ratio of each co-acid, and the order of addition. Positive results are shown below. 2.3 Results 3. Improvement of the oxidation stability 3.1 Opportunities These new grades are based on complex esters to ensure biodegradability. Obviously, the impact on oxidation stability is a key topic, especially for OBCaS greases famous for their high temperature stability. 3.2 Study follow-up The first selection of antioxidants was made according to the Lusc-list [9]. Phenolic (ph) and aminic (am) antioxidants (AO) are the common chemistries used, but the specific molecule, quantity and ratio must be finetuned thanks to a DoE (Design of Experiment). For practical reasons, the DoE was performed in the carrier instead of the grease : 40 experiments were selected to cover the disjoined domain. Since the DoE was performed on esters, the possibility of extrapolation on greases need to be checked and validated. The point in time of AO introduction during the process had a surprising effect. This key parameter could dramatically affect the consistency of the grease. If the AO is added at the beginning of the reaction, the final grease will not reach the desired consistency by influencing the micellar organization. Since the reaction is made under nitrogen, the addition of AO at the end is the option adopted. 23rd International Colloquium Tribology - January 2022 129 Calcium Sulfonate Greases - Improving Biodegradable solution thanks to 1-step process 3.3 Results All detailed results will be presenting during ICT. If there are slight interactions, the main effects remain largely prevalent. (Ester type, AO amount) In ISO150 the best combination is 50/ 50 L115/ L06 at 2 % with an estimated RSSOT > 600 min. In ISO46: 60/ 40 L115/ L06 at 2 %, RSSOT > 400 min. Impact on viscosity after oxidation: No statistically significant effect was found, but a natural tendency is visible; higher the amount of AO, less the viscosity increases. Extrapolation on greases: Globally, the RSSOT model is identical in grease and ester (excepted one point which needs further investigation) as shown below in ISO 150. Correlation were made at 200, 400 and 600min results: 130 23rd International Colloquium Tribology - January 2022 Calcium Sulfonate Greases - Improving Biodegradable solution thanks to 1-step process Oxidation mechanism is a free radical reaction (init./ prop./ branch./ term.), and we just studied the 1st option of free radical deactivation. Future other options deserve to be investigated as hydroperoxide decomposition or inhibiting the metal catalytic. 4. Conclusion “One-step process” has interesting advantages by selecting 100 % of the carrier in OBCaS. Biodegradable grease is the best example. Changing the carrier or consistency is quite simple and overcoming the initial carrier’s drawback is easily achievable with this process. Studies on carrier and on grease could be split for quicker experimentations. On top of that, the improvement of performances by dealing on the structure, could be done without using classical additives. Biodegradability or other sensible performances are more easily maintained or even improved. References [1] Annual NLGI meeting (2018), NLGI grease survey [2] G.Notheaux, C.Felix at ICT 2020, Fully Customizable Calcium Sulfonate Greases for Optimum Performances, [3] D.Authier, A.Herman, L. Muntada, E. Ortega, L.Ribera, B.Saillant, ELGI 2013, Calcium sulfonate greases: A solution to water resistance [4] W.Macwood, R.Muir (1998) Calcium Sulfonate Grease … One decade later, NLGI’s 65th Annual meeting [5] D’HOLLANDER V. (2018) Les graisses lubrifiantes, IFP Train. [6] G.Fish, Calcium sulphonate greases “Performance and application overview” Lubrisense White Paper (2014) [7] Olson William D.; Muir, Ronald J.; Eliades, Theo “Sulfonate Grease Improvement”; U.S. Patent No.5,338,467, (1994) [8] J.Andrew Waynick, NLGI spokesman March/ April 2020, vol.84 [9] Lubricant Substance Classification list v24/ 06/ 2021 [10] A.Da Costa d’Ambros, ELGI 2019, Calcium sulfonate complex grease, a legendary technology adapted to future requirements [11] G.Fish, W.C.Ward, STLE 2012, Calcium Sulfonate Grease Formulation [12] Y. Zhou, R. Bosman & P. M. Lugt (2019) On the Shear Stability of Dry and Water-Contaminated Calcium Sulfonate Complex Lubricating Greases, Tribology Transactions, 62: 4, 626-634 [13] Dr. George S. Dodos, Navigating the future; lubrication grease in Marine applications, Eurogrease Oct-Nov-Dec 2020, N°4