Synthesis and physical properties of pennycress estolides and esters

Authors: Cermak, Steven - Steve; Durham, Amber; Isbell, Terry; Evangelista, Roque; Murray, Rex

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2015
Publication Date: 3/5/2015
Publication URL: http://handle.nal.usda.gov/10113/5428955
Citation: Cermak, S.C., Durham, A.L., Isbell, T.A., Evangelista, R.L., Murray, R.E. 2015. Synthesis and physical properties of pennycress estolides and esters. Industrial Crops and Products. 67:179-184.

Interpretive Summary: A series of new pennycress estolides were synthesized that have properties suitable for cold weather applications. Pennycress is a winter annual belonging to the mustard family. A common agricultural weed, Pennycress, is readily adaptable to various climatic conditions, requires minimal agricultural inputs, can be harvested with existing farm equipment, and has a high seed yield. Vegetable oil-based lubricants have excellent lubricity, as well as biodegradability properties. However, the combination of poor cold temperature performance and low resistance to thermal oxidation is a problem for most lubricant applications. The pennycress estolides have properties that overcome these common vegetable based pitfalls. Additionally, these pennycress estolides are materials that have higher viscosities (thicker) than other estolides. Pennycress is currently being developed for "green" diesel applications; the development of other industrial applications is a necessity for the success of an alternative crop. The combination of high viscosity and modest cold temperature properties of these pennycress estolides could fill a specialty niche as a high viscosity industrial lubricant.

Technical Abstract: A new series of pennycress (Thlasphi arvense L.) based free-acid estolides was synthesized by an acid-catalyzed condensation reaction, followed by an esterification reaction to produce the 2-ethylhexyl (2-EH) esters of the initial estolides. The physical properties of the estolides are highly affected by the length and unsaturation level of the capping fatty acid, the base fatty acid unit, and estolide linkage position. Both the free-acid estolides and the estolide 2-EH esters produced proved to have marked viscosity increases over previously synthesized estolides. Kinematic viscosities of the free-acid estolides were higher than the corresponding estolide 2-EH esters, ranging from 494.4 cSt to 870.5 cSt at 40°C and 53.6 to 75.3 cSt at 100°C with viscosity indices (VI) from 134 to 163. Viscosities of the estolide esters ranged from 116.3 to 245.75 cSt at 40°C and 18.2 to 33.6 cSt at 100°C with VI from 169 to 183. The highest viscosity values belonged to the pennycress estolides made with pennycress fatty acids in the reaction acting as the base material, as well as the capping material. The oleic-capped pennycress estolide 2-EH esters had the best low-temperature properties with a pour point (PP) of -33°C and cloud point (CP) of -31°C. With the exception of palmitic acid, there was very little variation in the low-temperature properties of the remaining saturate capped estolide 2-EH esters, PP ranging from -18 to -21°C. Pennycress is currently being developed for "green" diesel applications; the development of other industrial applications is a necessity for the success of an alternative crop. The combination of high viscosity and modest cold temperature properties of these pennycress estolides could fill a specialty niche as a high viscosity industrial lubricant.