Submitted to: Surfactants in Tribology
Publication Type: Book / Chapter
Publication Acceptance Date: May 5, 2010
Publication Date: April 15, 2011
Citation: Biresaw, G. 2011. Characterization of surface active materials derived from farm products. In: Biresaw, G., Mittal, K.L., editors. Surfactants in Tribology. Volume 2. Boca Raton, FL: Taylor & Francis. p. 353-386. Interpretive Summary: There is a large quantity of surplus soybean, corn, wheat, barley, and other major crops relative to market demand in the United States. As a result, prices farmers get for their crops have declined over the years which has negatively impacted their incomes. One way of increasing the demand for agricultural products, and thereby improve the income of farmers, is to develop new uses for the surplus crops. However, converting farm products into competitive consumer and industrial products requires developing a thorough understanding of their chemical/physical properties. Also required is developing efficient and cost-competitive methods of converting and manufacturing farm-based raw materials into products that are competitive to petroleum-based products currently in the market. Surface activity is one of the most important raw material properties for materials development. It affects a number of critical processing and performance properties including: friction, film thickness, compatibility, adhesion, wetting, emulsification, etc. In the work described here, chemically modified plant proteins, starches and oils were investigated for their surface and interfacial properties. The materials were found to be effective at reducing the surface tension of water solutions and the interfacial tension between water solutions and various oils. The results suggest that, with further development, chemical modification can open up new opportunities for application of surplus crops in a variety of consumer and industrial products.
Technical Abstract: Surface active materials obtained by chemical modification of plant protein isolates (lupin, barley, oat), corn starches (dextrin, normal, high amylose, and waxy) and soybean oil (soybean oil based polysoaps, SOPS) were investigated for their surface and interfacial properties using axisymmetric drop shape analysis. All of the materials were effective at reducing the surface tension (ST) of water, and the interfacial tension at the water-hexadecane or water-soybean oil interface. From concentration vs. equilibrium ST data, the surface energy (SE) of the materials were determined. The SE of chemically modified starches were in the 41-48 dyn/cm range. The SE of proteins varied in the 31-55 dyn/cm range and were dependent on the crop origin. The SE of SOPS was in the 20-33 dyn/cm range, and displayed mol wt. dependence. The SE data was analyzed to predict interfacial energy using the Antonoff, geometric mean (GM) and harmonic mean (HM) methods. Predictions of the Antonoff method relative to measured values were substantially low for SOPS–hexadecane, substantially high for starch ester–hexadecane and reasonably good for lupin protein isolate–soybean oil. In the GM and HM analysis, the fraction of non-polar SE component (Xsd) was used as a fitting parameter. The result showed that Xsd values that predict interfacial energies close to measured values increased in the order: SOPS < starch esters < protein isolates. This suggests that the surface polarities of the surface active agents increased in the order: protein isolates < starch esters < SOPS.