Tribological characteristics of some environmentally friendly lubricants

The lubricating properties of a new class of esters were studied using a pin on disc tribometer. These molecules are peresters (full esterified esters) of sugars. These peresters are compared to a set of classical esters: esters of pentaerythritol, of trimethylol propane or glycerol. In terms of wear and friction, esters of sorbitol are equivalent if not superior to the classical esters. Moreover, they allow a larger range of viscosity. The structure of the polyol and the length of the fatty acid chains are two important parameters in wear and boundary friction. An increase in the number of ester groups, the length of fatty acid chains and linearity of the polyol explain the higher lubricating performance by the esters. Besides their attractive tribological properties, they show high oxidative stability, excellent biodegradability, and potentially low toxicity. These properties are due to their structure (totally esterified, β-hydrogen, etc.) and this structure makes these peresters strong candidates for replacing mineral oils in the food, pharmaceutical and cosmetic industries; in fact they could be used wherever lubricants may directly or indirectly come into contact with animals or humans.