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Polyolefine and Poly(alkyl methacrylate) mixed additives as lubricating mineral oil rheology modifiers

Some rheological properties of mineral lubricating oils containing polyolefine (OCP)(ethylene/propylene copolymer) and poly(alkyl methacrylate) (PAMA) mixed additives have been examined. The viscosity and shear stability of solutions become significantly increased by increasing the OCP content in the mixture, whereas the viscosity index and pour point temperature are directly proportional to the PAMA content. Viscosities of the mixed dilute additive solutions obey typical Krigbaum-Wall equation and due to the negative viscosimetric interaction parameter values, the OCP/PAMA mixture was found not be miscible. The immiscibility becomes more pronounced by increasing the overall polymer concentrations. However, decreasing the polymer concentration to practical quantities as well as increasing the temperature viscosity values approaches the ideal additivity law. Based on the ratio of specific viscosities at 40 and 100 C (Q) the OCP additive solution showed a better thickening effect at lower temperatures (Q<<1). Contrary, the PAMA additive solution showed a better efect as higher temperatures (Q>1) with more coherent thickening by temperature change. The mixed polymer additive containing ~ 10 wt.% OCP and ~ 90 wt.% PAMA is a nearly ideal candidate for the viscosity index improver showing the same thickening effect at different temperatures. The obtained results give the prospects for design of lubricant formulations with mixed polymeric additives.

lubricant rheology; polymeric mixed additives; miscibility; viscosity; viscosity index improver; pour point depressant

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