The formation of estolides was detected during the studies on dimerization of meadowfoam oil fatty acids. By adjusting the reaction conditions, it was possible to produce monoestolides with little dimer or trimer formations. Estm lides have potential use in lubricant, cosmetic and ink formulations and in plasticizers. This paper reports the conditions for production of estolides from mixed meadowfoam fatty acids, commercial oleic acid, high-oleic sunflower oil fatty acids, c/s-5¢e/s-13-docosadienoic acid, petroselinic acid and linoleic aCid. KEY WORDS: c/~5, c/~13

Starch-oil composites comprising purified foodgrade corn starch (PFGS) and soybean oil (SBO) were investigated as potential ingredients for water-based solid lubricant formulations. Current solid lubricants are almost exclusively petroleumbased and are used for protecting sheet metal and/or as sheet metal forming lubricants. Starch-oil composites are preferred ingredients for formulating solid lubricants because they are based on renewable and abundantly available raw materials and also have superior environmental and health characteristics. Steel sheets coated with the PFGS-SBO containing solid lubricant were evaluated for boundary coefficient of friction (COF) and wear properties using ball-on-flat test geometry. The COF was highly dependent on the SBO to PFGS ratio in the composite. In the absence of SBO, the COF was high (~0.8) and decreased sharply with increasing SBO content to a minimum value of 0.07. Wear evaluation showed no scratches or lubricant transfer on the ball. There were also no wear tracks observed on the flat sheet before or after the solid lubricant was washed off. It was concluded that waterbased solid lubricants formulated with the PFGS-SBO starch-oil composite have acceptable friction and wear properties and should be evaluated further for use in sheet metal forming. SOLID LUBRICANT FORMATIONS WITH STARCH-SOYBEAN OIL COMPOSITES 293 JAOCS, Vol. 79, no. 3 (2002) FIG. 1. Typical run time vs. friction force data of a solid lubricant obtained on a ball-on-flat friction tester.

The monomers produced from thermal high‐pressure conversion of meadowfoam or oleic acids into estolides were characterized as a complex mixture of fatty acids. Mild reaction conditions produced little change in the starting acids. However, vigorous reaction conditions,e.g. ≥3 h at 250°C with stirring, significantly altered the starting fatty acids.Cis/trans isomerization occurred readily, with the proportion oftrans isomers reaching 57%. In addition, the double bonds migrated throughout all positions of the hydrocarbon chain with concentrations diminishing outward from the starting double bond position. Branching was also observed to a small extent under these conditions and was even more pronounced in the absence of water. Lactones were also identified in the reaction mixture, with contents near 16% in the meadowfoam series. All products can be explainedvia carbocation rearrangement mechanisms that result from protonation of the starting olefins.

The boundary coefficient of friction (COF) of starch-oil composite dry film lubricants was investigated as a function of starch type (waxy vs. normal purified food grade corn starch), oil chemistry (hexadecane vs. oleic acid and various vegetable oils), and starch-to-oil ratio. Based on the results, a mechanism of starch-oil interaction in these composites was proposed. According to the proposed mechanism: (a) the oil in the composite is distributed between the bulk and the surface of the starch; and (b) the fraction of the oil trapped in the bulk and that adsorbed on the surface are related to each other by an equilibrium constant, and are functions of the total oil concentration in the composite. In line with the proposed mechanism, an adsorption model was used to quantify the free energy of adsorption (᭝G ads ) of the polar oils onto the starch surface. The analysis gave ᭝G ads values that were higher than those reported for the adsorption of the same polar oils onto steel surfaces. This result is consistent with the effect of the relative surface energies of steel and starch on the adsorption of polar oils. The adsorption property of the non-polar hexadecane relative to the polar oils was estimated by comparing their interfacial tensions with starch. The result showed a higher interfacial tension for hexadecane-starch than that for the polar oil-starch composites. This result predicts a relatively poorer compatibility with, and, hence, poorer adsorption of hexadecane onto starch leading to higher COF, as was observed in the friction measurements.