23rd International Colloquium Tribology - January 2022 89 Naphthenic Base Oils - Tailoring Emulsion Stability Thomas Norrby Nynas AB, Naphthenics TechDMS, Nynäshamn, Sweden Corresponding author: thomas.norrby@nynas.com Jinxia Li Nynas AB, Naphthenics TechDMS, Nynäshamn, Sweden Linda Malm Nynas AB, Naphthenics TechDMS, Nynäshamn, Sweden 1. Introduction In this study, several MWF Soluble oil and Semi-synthetic emulsions based on two different naphthenic base oils were created. The purpose was to elucidate any and all influence on the properties of these emulsions arising from difference in the fundamental properties of the base oils employed. The naphthenic base oils utilized were two 22 cSt oils, one straight cut (narrow cut) and one blended oil (a wider cut). Two Soluble oil non-ionic emulsifier systems, and four different semi-synthetic (anionic and non-ionic blends) formulations were investigated in soft and hard water, with respect to emulsion droplet size and stability over time. The emulsion particle size, and the emulsion stability as a function of time, was determined by static light scattering utilizing a Malvern MasterSizer equipment, and a TurbiScan unit. The results show that the two base oils yield emulsions with very similar properties under a wide variety of chemistries and conditions. 1.1 Base oils • Base Oil B has a slightly higher colour ASTM <1.0 (vs. <0.5) • Base Oil A and B have similar Aniline Point 77 °C (vs. 77 °C) • Very similar Carbon Type Content by ASTM D 2140 in both base oils • Base Oil A has about 10 °C higher Flash Point by ASTM D 93 Penske-Martin; (A) 173 °C vs. (B) 162 °C • An average of six brands in a previous Nynas study was found to be 159 °C • NB! Blended base oils are rather common in the market Distillation curves by ASTM D 86 and ASTM D 2887 also display different cure shape, and the blended Base oil B displays more lighter ends (lower IBP) and more high boiling components (Higher FBP) 1.2 Emulsions Stability Experiments 90 23rd International Colloquium Tribology - January 2022 Naphthenic Base Oils - Tailoring Emulsion Stability Soluble oil experiments were done across HLB values ranging from 9 to 13, as published previously [2]. The main correlation was found to be Aniline Point and viscosity, and no major differences between Base oil A and B can be seen in the Soluble oil non-ionic model formulations. 1.3 MWF concentrates We have previously published a study of Semi-synthetic Metalworking fluids [1]. We could see that small changes in the complex formulations (15 + components) in the case of Semi-synthetics did display different emulsion stability and droplet size distribution, depending on base oil viscosity and water hardness. In the present study, either the straight cut Base oil A or the Base oil blend B was tested versus a number of different MWF concentrates. As seen in the graph below, Base oil A prefers concentrate MWL 3, and Base oil B performs better with MWL 2 2. Conclusion The careful selection of components in the case of the Semi-synthetic formulations thus can be made so that either the straight cut Base oil A, or the blended Base oil B displays smaller droplet size and higher emulsion stability. Additive concentrates thus can and should be tailored to match also the finer details of the differences between even closely related base oils. References [1] T. Norrby, J. Li., L. Visuri, ”Model MWFs based on Naphthenic base oilsstraight cut or blend? ”, STLE Annual Meeting 2021. [2] T. Norrby, L. Malm, P. Wedin, G. Ponti, “Emulsion Stability in Semi-Synthetic MWF formulations”, Proceedings of the 21 st International Colloquium Tribology, January 2018, Technische Akademie Esslingen, Germany