Submitted to: Industrial Crops and Products
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/29/2000
Publication Date: N/A
Citation: Interpretive Summary: Automotive stores are filled with oils and greases designed to make cars, lawnmowers, and other equipment run well. These products help moving parts stay fit by providing lubrication, but what makes one product better than another? Oils designed for cars need to stay liquid when the weather is cold, so they need to melt at a low temperature (low melting point). To keep oils from becoming slushy in a car or a container during the winter, they need to pour at low temperatures (low pour point). They also need to be thick enough to coat the parts they protect while still being runny enough to allow the parts to move. The thickness or runniness of a liquid is the liquid's viscosity. Lubricants need a medium viscosity: not as runny as water, not as thick as peanut butter, but somewhere in the middle like shampoo. Most lubricants and greases are made from petroleum and can be bad for the environment. In our lab we make Earth-friendly lubricants by linking together vegetable oils to form products called estolides. Estolides are better for the planet than petroleum products, but they can only be profitable if they have the same low melting point and pour point and the same medium viscosity as regular lubricants. We made estolides that melted as low as -43C (-45F), poured at -27C (-17F), and had a medium viscosity index of 151 to 226. These estolides should keep cars running like regular lubricants while keeping the environment clean.
Technical Abstract: Pour point, melting point and viscosity (40C and 100C) 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, -34C and -43C 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 (PP) of oleic estolides were 5-10C 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 0C; EN of 1.1 had a PP of -27C). In a similar fashion, viscosity increased with higher oligomerization and free acid estolides were generally several hundred centistokes more viscous then the corresponding esters. Viscosity index ranged from 151-226 with the fatty acid esters giving slightly higher indices. Hydrogenation of the estolides resulted in a dramatic increase in the pour point but only changed viscosity slightly.