Metal Soap Greases - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 71

FIGURE 8 Lithium soap fatty acid chain length effect on soy grease NLGI hardness (1:1
equivalent ratio of lithium to fatty acid in the thickener; 1:3 wt% ratio of soap to base oil) [25].
6.7 THE EFFECT OF COMPOSITION ON RHEOLOGY IN ROLLING
CONTACT WITH LITHIUM AND ALLUMINUM COMPLEX GREASES
The effect of composition on rheology was investigated with two objectives by Cou-
ronne et al [26, 27]. Firstly, to analyze the influence of the interactions between grease
components on the film thickness in a rolling contact. Secondly, to try to find how the
ability of grease to give fully flooded lubrication is related to its intrinsic properties.
The varying parameters were the base oil type (mineral or ester), the soap type (lithi-
um or alluminum complex and the presence of two macromolecular additives (V and
T, respectively viscosity and adherence improvers). The soap concentration was (12%
w/w) were the same for all the samples. When present V and T concentrations were re-
spectively 5.5 and 0.03% w/w. Film thickness was measured by optical interferometry.
Microstructure and physico-chemical structure were observed by Transmission Elec-
tron Microscopy (TEM). Stress sweep was conducted to evaluate the elastic modulus
(G'). G' is the quantitaive estimation of the grease stiffnes in the low strain range.