Formulation, rheology and thermal ageing of polymer greases—Part I: Influence of the thickener content

•Four polymer thickened greases of different formulation were tested.•Rheological tests were performed on fresh and thermally aged greases.•Thermal ageing evaluated through IR spectroscopy, oil loss and oil-bleed rate.•Influence of the thickener content analysed.

The aim of this work is to show the correlation between polymer greases’ rheology and its formulation. The tested polypropylene (PP) thickened greases were evaluated regarding their thickener content and its effect on the rheological properties. An artificial ageing procedure was performed by heating fresh grease samples in an oven to study the thermal degradation. The ageing evaluation was performed through rheological measurements, FT-IR spectra, oil loss, bleed-oil viscosity changes and bleed rate. The rheology measurements were performed on a rotational rheometer, emphasizing on the storage and loss moduli values at the Linear Visco-Elastic (LVE) region. The flow curve of each grease was also measured. A modified Herschel–Buckley model was applied and the data was correlated to the thickener content.