Function of the thickener
The thickening agent is a vital component that allows the lubricant to pass from one fluid appearance to a more or less consistent appearance. Its function is to retain the base oil inside its structure and to dispense it when the grease is under pressure, in order to lubricate the elements in contact. In the same way, the thickener should act as an element of oil recovery after the effort and maintain its consistency with small variations for an acceptable duration. The nature of the thickener has an important influence, with the proper choice of base oil, on the basic properties of the grease, such as water resistance, corrosion protection, welding ability and resistance to extreme loads and temperatures.
Types of thickeners
A grease can be formulated with a metallic thickener, organic or inorganic. The thickeners based on metal soaps are obtained from the saponification reaction of fatty acids or esters of plant or animal origin. Depending on the nature and the number of fatty acids used, simple or complex metallic soaps are obtained, the latter having general properties increased compared to those of simple soaps. Organic thickeners, such as polyurea and polytetrafluoroethylene (PTFE) components, are the ideal solution in extreme temperature conditions. They are applied more and more in the industry and in the automobile industry thanks to excellent properties such as resistance to loads and surrounding environments. Inorganic thickeners provide a grease through a fairly simple manufacturing process. Silica gel and bentonite or modified clay are solutions that are limited in its resistance to high loads. They can be used under very specific conditions when other thickeners can not be used: ionizing radiation, extreme acid and alkaline media, food applications).
Choice of thickener
As with oil, the choice of thickener for a fat depends on several factors. The table on pages 14 and 15 summarizes the most important properties of each type of thickener and base oil.