Abstract
Vegetable oil based lubricants have good lubricity and biodegradability but often fail to meet viscosity requirements at cold temperatures. These properties for a lubricant are often evaluated by pour point (PP), the minimum temperature at which a liquid will pour. Viscosity and viscosity index also provide information about a fluid's properties where a high viscosity index denotes a fluid that has little viscosity change over a wide temperature range. In order to develop better quality vegetable based lubricants, pour point, melting point and viscosity (40 and 100°C) were determined for a series of esters (methyl, butyl, decyl, oleyl, 2-propyl, 2-ethylhexyl, C18-Guerbet and C24-Guerbet) of meadowfoam, crambe and oleic fatty acids and estolides. Oleic estolide esters had the lowest melting points of all derivatives studied. Of the oleic estolide series the 2-ethylhexyl and C18-Guerbet esters had the lowest melting points, −34 and −43°C, respectively. Similar melting point trends within the series of esters were observed for both fatty acids and estolides. Pour points of the oleic estolides were also determined on a series of both free acid estolides and their 2-ethylhexyl esters. The series compared the effect of oligomerization on pour point. Pour points of oleic estolides were 5–10°C higher than the corresponding derivative's melting point. The extent of oligomerization (estolide number, EN) played a significant role in the pour point with higher oligomerization giving higher pour points (EN of 2.96 had a PP of 0°C; EN of 1.1 had a PP of −27°C). In a similar fashion, viscosity increased with higher oligomerization and free acid estolides were generally several hundred centistokes (cSt) more viscous than the corresponding esters. Viscosity index ranged from 151 to 238 with the fatty acid esters giving slightly higher indices than estolide esters. Hydrogenation of the estolides resulted in a dramatic increase in the pour point but only changed viscosity slightly.
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