CO₂ as a Viscosity Index Improver for Wind Turbine Oils

A high viscosity index (VI) is crucial for lubricants in industrial gearboxes exposed to changing load or weather conditions. Especially in the field of wind turbine oil, viscosity indices of 150 or higher are demanded to reduce power losses and ensure reliability at the same time. In this context, the use of dissolved CO₂ to improve viscosity–temperature behavior has been investigated for task-specific, halogen-free ionic liquids and benchmarked against poly­(α-olefins). By measuring the viscosity and density of the lubricants with dissolved CO₂, it was proven that the VI can be increased significantly, even at moderate pressures. In addition, measurements and simulation on CO₂ solubility and studies on corrosion and tribology under CO₂ pressure are presented.