Effect of grease thickener and surface material on rheological properties of boundary layer

•The behaviour of the greases in the vicinity of five different materials was examined.•Two greases thickened with lithium soap, and also a polyurea grease were studied.•Thermoplastic materials PA 6 and PE have the highest ability to form a surface layer.•Elastomeric material MVQ/VMQ has the lowest ability to form a surface layer.

This paper presents the results of studies into the formation of a surface layer and a boundary layer in simple and complex lithium greases and in polyurea grease. The behaviour of the greases in the vicinity of walls made of five different materials, i.e. two elastomeric materials (MVQ and NBR), two thermoplastic materials (PE and PA 6) and aluminium alloy 2017, was examined. The studies have shown that thermoplastic materials PA 6 and PE have the highest ability to form a surface layer. A zone with a reduced thickener concentration, characterized by a lower structural viscosity, forms in the vicinity of these materials. Elastomeric material MVQ/VMQ has the lowest ability to form a surface layer. In this case, the structural viscosity of the tested greases within the boundary layer was the highest.

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