Esters and polyesters
Hydraulic fluids - Hydrocarbons and ester-polyesters

Interest in esters began with the discovery of castor oil's outstanding lubricating properties. Naturally, like all natural fats, castor oil has the disadvantage of low oxidation stability. The secondary hydroxyl group in glycerol is responsible for this weakness. As soon as you use an ester obtained from an alcohol with only primary hydroxyl groups as a lubricant, you get good lubricity combined with reasonable thermal stability.

Esterification is an old reaction in organic chemistry that corresponds to the equation : $\text{ acide + alcool}\underset{\text{solvant}}{\overset{\text{catalyseur}}{\rightleftharpoons }}\text{ester + eau}$