Friction Behavior of Some Seed Oils: Biobased Lubricant Applications

Seed oils are renewable and an environmentally friendly alternative to mineral based oils in lubrication and other important industrial applications. They are generally triesters having a complex distribution of fatty acid (FA) chains. All the physical and chemical properties of seed oils are dependent on their FA distribution, composition, and additional functional groups in the chain structure. In this work, various seed oils are studied for their boundary lubrication properties using the Langmuir adsorption model for their possible use as industrial lubricants. This information can be used to design suitable lubricant molecules that will have optimum structure for effective metal adsorption as well as exhibit excellent boundary lubrication properties. The free energy of adsorption ((delta)Gads) of cottonseed, canola, olive, and meadowfoam oil is investigated in boundary lubrication regime using steel ball-on-disk geometry. Adsorption values were compared with monoesters with varying chain lengths. It was observed, based on computed (delta)Gads, that molecular polarity, hydrocarbon chain length, and relative distribution of unsaturation in the FA chain can affect adsorption on the metal surface. Statistical analysis on FA distribution and (delta)Gads was helpful in making a generalized assumption on adsorption behavior. The results are consistent with theoretical assumptions on surface adsorption as a function of molecular structure.