We have already discussed grease properties and why grease is an alternative to oil. Now let’s get a little more in-depth and discuss the thickeners that give grease its properties. Grease thickeners can be divided into two categories, soap and non-soap. More than 90 % of thickeners are soap based. These thickeners can be broken into three groups:
Simple – A simple soap resulting from the reaction of a single acid, usually 12 HSA and a metallic hydroxide, usually lithium, aluminum, calcium or sodium. The metal used defines the type of soap, with lithium being the most common.
Mixed – Produced by a reaction of acid with two metallic hydroxides. Not common.
Complex – Reaction of an acid with a short chain complexing acid, like azelaic acid. Usually has much better high temperature properties.
Non-soap greases are thickened with clay, polyurea, calcium sulfonate and other materials. These greases provide strong heat and water resistance without sacrificing other properties. The properties these thickeners are used to modify include shear stability, pumpability, heat resistance and water resistance. Thickeners impact greases as follows.
Calcium – Provides good water resistance and shear stability at the cost of pumpability and heat resistance
Sodium – Provides good heat resistance while sacrificing utility in the other properties
Barium – Good heat and water resistance, but poor pumpability
Lithium 12 OH Stearate – Makes improvements to all areas, particularly to shear stability and water resistance
Lithium complex – Provides a boost to all properties
Calcium Complex – Provides strong water resistance, but not very pumpable
Aluminum complex – Good heat and water resistance.
Clay, Polyurea and Calcium Sulfonate – Good water and heat resistance.