How Polymers Behave as Viscosity Index Improvers in Lubricating Oils

Abstract

One of the requirements of engine lubricating oil is that it must have a low enough viscosity at low temperatures to assist in cold starting and a high enough viscosity at high temperatures to maintain its load-bearing characteristics. Viscosity Index (VI) is one approach used widely in the lubricating field to assess the variation of viscosity with temperature. The VI of both mineral and synthetic base oils can be improved by the addition of polymeric viscosity modifiers (VMs). VI improvement by VMs is widely attributed to the polymer coil size expanding with increasing temperature. However, there is very little physical data supporting this generally accepted mechanism. To address this issue, intrinsic viscosity measurements and Small-Angle Neutron Scattering (SANS) have been used to study the variation of polymer coil size with changing temperature and concentration in a selection of solvents. The results will show that coil size expansion with temperature is not necessary to achieve significant elevation of viscosity index.

Síntese, caracterização e estudo reológico de melhoradores do índice de viscosidade para óleos lubrificantes automotivos

“…Nesse caso, com a elevação da temperatura, a força das interações intra e intermoleculares diminui, acarretando um aumento no volume hidrodinâmico das moléculas poliméricas e, também, da viscosidade. COVITCH e TRICKETT [10] descreveram o comportamento de vários polímeros nos chamados solventes "pobres", relatando as interações atrativas entre os segmentos de polímero. Contrariamente, na presença de "bons" solventes, segundo os autores, forças repulsivas entre segmentos de polímero são predominantes, resultando numa expansão das cadeias.…”

Epoxidized Oleic Acid‐Based Polymethacrylates as Viscosity Index Improvers

“…For this purpose, the RV between lube oils and lube oil‐polymer (5 wt.%) blends were calculated and plotted with respect to temperature. As the calculated RV represents the influence of the polymer on oil's viscosity, the RV should increase with temperature in the case of coil copolymer expansion as previously reported (Covitch and Trickett, ). The properties of rheological FA‐based polymers were compared to those previously reported for PMAEO.…”

Shear Thinning and Hydrodynamic Friction of Viscosity Modifier-Containing Oils. Part II: Impact of Shear Thinning on Journal Bearing Friction

“…Their primary role is to enhance the lubricant viscosity index of their blends [3][4][5]. This enables the development of multigrade engine oils that combine a reasonably low viscosity at low engine temperatures with sufficient viscosity at high temperature to produce effective hydrodynamic films in engine components.…”