Basic Properties Necessary for Lubricants

The normal rules used for the selection of lubricants are as follows [17]  

Metal soaps, mainly stearates, function as external lubricants, since they possess low affinity to all polymers. 

Long-chain fatty acids, alcohols, and amides act as internal lubricants for polar polymers such as PVC, polyamides, and so on, but have low affinity to nonpolar polymers such as polyolefins. 

Long-chain dialkyl esters have medium affinity to most polymers and can act both as external and internal lubricants for polymers they are often used to obtain a balanced lubrication [9]. 

High-molecular-weight paraffin waxes function as external lubricants for polar polymers because of their low affinity to them, but they have a high affinity to polyolefins and are used then as internal lubricants. 

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