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Lube-Tech


A similar trend is seen in Figure 12 for T 22 and Group III, only slightly larger: the step change in OIT from 3 to 14 minutes (more than 4x) for the initial Addition of 5% NYNAS T 22. At the highest blend rate (25%), a slightly higher OIT can be measured. This is not unexpected, as a more highly refined base oil would respond even better to added antioxidants.


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.119 page 7


oils clearly improves the OIT results. We also note that for many types of finished lubricants, additives of the type showing good effect in this study already are commonly utilised, and good antioxidant response thus is obtained.


For many other formulations, keeping an eye of the overall Sulphur levels, and perhaps trying one of these functional additives, might be a useful strategy for improving the finished lubricant property.


References [1] Norrby, T., Salomonsson, P., and Malm, L. “Group I Replacement Fluids – a Hydraulic Fluid Formulation and Compatibility Study”, Tribologie + Schmierungstechnik, Vol. 64, No. 1 (2017), pp. 31-41.


Figure 12. OIT of NYNAS T 22 and Group III (KV@40°C, 19.9 cSt, KV @ 100°C, 4.3 cSt). A similarly large step-up in OIT is observed, possibly indicating an even better improvement of the oxidation stability.


Conclusions and Outlook


In this work, we have tried to elucidate the effects of primary and secondary antioxidants in relation to overall system Sulphur levels: “base oil” Sulphur and additive Sulphur. We found that the effect on the OIT obtained by HP-DSC gave us a tool to clearly discriminate between the effect of different types of added “base oil” Sulphur, and from six different secondary antioxidant candidate additives. The result was that Sulfide-type and thiocarbamate structures clearly contribute to the improvement in oxidation stability, and that several other types of known secondary antioxidants displayed no effect in the systems studied by HP-DSC.


Thus, oxidation stability improvements can be rationalised by correlation of the Sulphur levels to the observed OIT. Interestingly, adding a Naphthenic base oil to these low-Sulphur Group II and Group III base


38 LUBE MAGAZINE NO.148 DECEMBER 2018


[2] T. Norrby, A.-L. Jonsson, “Antioxidant response in base oils blends – The role of secondary antioxidants and base oil Sulphur content”, Proceedings of the 21st International Colloquium Tribology, January 2018, Technische Akademie Esslingen, Germany.


[3] T. Norrby, A.-L. Jonsson, “Improved Oxidation stability and solvency of naphthenic/ paraffinic blends – a parameter study”, Proceedings of the 73rd STLE Annual Meeting, Minneapolis, May 20-24, 2018.


[4] ASTM D 6186-08, “Standard Test Method for Oxidation Induction Time of Lubricants by Pressure Differential Scanning Calorimetry (PDSC)”


[5] Bala, V., Hartley, R. J., Hughes, L. J., 1996, “The Influence of Chemical Structure on the Oxidative Stability of Organic Sulfides”, Lubr. Eng., 52(12), pp. 868-873


[6] Aguilar. G., Mazzamaro, G., Rasberger, M. in Mortier, R. M., Fox, M. F., Orszulik, S. T., Editors ”Chemistry and Technology of Lubricants”, 3rd Edition, Springer Verlag (2010), p 118.


LINK www.nynas.com


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