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Nitrogen compounds present in mineral base oils at low concentrations are known to accelerate oil oxidation and to reduce the useful lifetime of formulated lubricants. Both Partial Least Squares and Neural Network analyses were employed to establish correlations between base oil composition and performance in industry standard thermal stability and oxidation tests. These correlations show that the “basic nitrogen” (BN) content of a base oil is a very important compositional feature determining its ultimate performance in a formulated lubricant which may be especially important for API Group II and III base oils that are relatively free of other pro-oxidants and naturally occurring, sulfur-containing antioxidants. The effect of BN species was also studied using model nitrogen compounds and it was confirmed that the pro-oxidant effect appears only in “basic” nitrogen containing molecules involving pyridine and quinoline derivatives.

Viscosities were measured on 1% solutions of olefin copolymer (OCP) VI improvers in oils using a variety of techniques to obtain comparisons under different shear rates. OCPs with 60-70 mole % ethylene were amorphous; those with 80 mole % contained small amounts of crystallinity. Kinematic viscosities at 40 and 100 ° C increased with molecular weights, regardless of OCP composition. Haake Viscometer data showed that at room temperature and low shear rates solutions of all copolymers were Newtonian. When the temperature was lowered, amorphous copolymers remained Newtonian while partially crystalline OCPs became non-Newtonian and gave viscosities that were much lower than expected from molecular weight. At -20 °C, high shear rates in the CCS reduced the dependence of viscosity on OCP molecular weight and viscosity changed very little with increase in Mw from 106,000 to 336,000; at low shear, however, in both the MRV and Haake, viscosities increased appreciably as Mw rose.