Grease thixotropy: evaluation of grease microstructure change due to shear and relaxation

Purpose – The thixotropy of lubricating grease thickened with lithium 12-hydroxystearate with mineral base oil was investigated. The thixotropy has a significant influence on the flow resistance and pressure drop in the structural components of lubrication systems, which is of major importance as today the latter are being centralized and automated. The paper aims to discuss these issues. Design/methodology/approach – Rheometer studies on thixotropy were carried out and the grease microstructure was visualized using atomic force microscopy (AFM). Total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the physicochemical interactions which indicate the disintegration and recovery of the grease microstructure. Findings – A qualitative assessment of the physicochemical interactions between lithium soap floccules was made and a theory of the self-ordering effect of lithium 12-hydroxystearate associated molecules during shearing and their aggregation and flocculation during relaxation has been proposed. Originality/value – Because of the complexity of the disintegration and recovery of the lubricating grease thickener microstructure, there is still limited physical understanding of the mechanism of this process. Therefore, the present research was undertaken to identify the phenomena involved.