F+L Week 2018 | Ian Elliott | Olefin Copolymers Designed to Provide Robust Low Temperature Performance with High Thickening Efficiency
Viscosity modifiers allow lubricating oils to maintain a suitable operating viscosity at high temperatures found in engines. In automotive applications, they can have an impact on performance areas such as piston deposit formation, fuel economy and wear. Viscosity modifiers keep formulated finished oil viscous enough at high temperatures to provide wear protection and can provide fuel economy benefits based on how they impart shear-thinning characteristics to the oil and interact at lower temperatures. High amounts of polymer in the oil can lead to piston deposits, so reducing the viscosity modifier treat rate with a high thickening efficiency polymer is generally desirable. Olefin copolymers (OCP) are widely used in engine oil applications as viscosity modifiers. The amount of viscosity modifier needed to reach a given viscosity is determined by its thickening efficiency. High ethylene OCPs are known to provide better thickening efficiency than low ethylene OCPs, but often at the cost of low temperature performance. This low temperature tradeoff can be observed in tests such as pour point, MRV and aged oil MRV (i.e. ROBO). This presentation will explore the development of a new mid-SSI (shear stability index) OCP, with the goal of achieving uncompromised low temperature performance while maintaining high thickening efficiency and thus yielding low polymer treat rates in formulated finished oils. Different candidates were evaluated on a number of criteria. Rheology profiles were generated which can provide information on the crystallinity of the polymer, and the structure performance tradeoff between crystallinity and thickening efficiency was modeled to select process parameters with the biggest impact on low temperature properties. Extreme gel formation tests were also conducted, and results evaluated against several polymer properties. The impact of each property was quantified by creating a statistical predictive model, which could account for changes in gel formation behavior from changes made to the polymerization reaction. Parameters such as ethylene content, extent of branching and segment molecular weight were evaluated, and by understanding the statistical significance and magnitude of each, modifications were made which allowed for robust low temperature performance in multiple areas. Data will be shared demonstrating the effect of polymer design on pour point, MRV and aged oil MRV as well. Further to lab testing, polymers are being tested in the field to evaluate real world performance in multiple countries.