Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/3/2010
Publication Date: 2/11/2011
Citation: Liu, Z., Biresaw, G. 2011. Synthesis of soybean oil-based polymeric surfactants in supercritical carbon dioxide and investigation of their surface properties. Journal of Agricultural and Food Chemistry. 59:1909-1917. Interpretive Summary: Currently, there is an oversupply of farm products that have suppressed the price that farmers get for their crops. One way of countering this trend is developing new uses for agricultural products. A promising new application area for farm-based products is in detergents and surfactants, which are currently manufactured almost exclusively from petroleum-based raw materials. In this research, soybean oil was converted to a surface active polysoap in carbon dioxide media. CO2 is inexpensive, readily available and nonflammable. It also offers environmentally friendly processing and reaction medium and no toxic residues in the final products. Such polysoaps have a variety of potential applications, such as for personal care and cleaning purposes. These soy-based polysoaps were evaluated using a variety of surface and interfacial techniques. The results showed that they possess the required surface and interfacial characteristics for such applications.
Technical Abstract: This paper reports the preparation of polymeric surfactants (HPSO) via a two-step synthetic procedure: polymerization of soybean oil (PSO) in supercritical carbon dioxide and followed by hydrolysis of PSO with a base. HPSO was characterized and identified by using a combination of FTIR, 1H NMR, 13C NMR and GPC. The effect of HPSO polysoaps on the surface tension of water and interface tension of water-hexadecane was investigated as a function of concentration of HPSO and counter ion chemistry. HPSO polysoaps were effective at lowering surface tension of water and interfacial tension of water-hexadecane. They have displayed minimum values of surface tension in the range of 20.5 - 22.5 dyn/cm at a concentration of 3.2 - 32 µm and minimum values of interfacial tension in the rage of 15.6 to 23.4 dyn/cm for K+ and Na+. The minimum value of surface tension and interfacial tension are higher for amine salt, 39.6 dyn/cm and 31.4 dyn/cm, respectively at a concentration of 13 µm and 15.9 µm. These results suggest that a very low level concentration of surfactant can be used to reduce the surface tension of water and interface tension of water-hexadecane. Water-hexadecane interfacial energy was also calculated from measured surface tension data using Antonoff, harmonic mean (HM) and geometric mean (GM) methods. Measured values agreed well with those calculated using the HM and GM. The HM method predicated slightly higher than the GM method, but the Antonoff method did not agree with measured values.