Submitted to: Journal of Polymer Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/8/2006
Publication Date: 5/30/2006
Citation: Doll, K.M., Shogren, R.L., Willett, J.L., Swift, G. 2006. Solvent free polymerization of citric acid and D-sorbitol. Journal of Polymer Science A. 44:4259-4267. Interpretive Summary: Non-degradable, petroleum-based polymers are used in many consumer and industrial products in the U.S. It would be desirable to make similar polymers from agricultural commodities such as corn to improve biodegradability, reduce imported petroleum and create new markets for surplus corn. Sorbitol and citric acid, two chemicals made from corn by fermentation, were heated together to form water-soluble polymers and gels having a strong negative charge. Such sorbitol/citrate polymers have the potential to soften water similarly to oil-based polyacrylate polymers now being used in detergents and other applications. The corn-based polymer has no toxic components and would safely biodegrade after use rather than accumulating in lakes and rivers. These results could benefit corn processors and industrial chemical manufacturers by providing a simple method to make water soluble and swellable polymers using safe, renewable, corn-derived raw materials.
Technical Abstract: Copolymers of citric acid and D-sorbitol have been synthesized with molar ratios of citric acid to D-sorbitol from 1/1 to 6/1, using a solvent free vacuum oven synthesis. The extent of reaction was followed by monitoring the residual acid content of the system. As expected, the reaction occurs much more rapidly at 150 than at 110 deg C. The FTIR spectra of the products show the expectd FTIR bands at less than 1735 cm-1 and less than 1188 cm-1 indicative of ester formation. Gel Permeation Chromatography (GPC) shows a major product with a MW less than 3500 Daltons. Insoluble material with a water absorbance index (WAI) of up to 17 was also synthesized, leading to possible applications as absorbers, thickeners or bio-based seed coatings. Additionally, the mono- and di- sodium salts of citric acid were also polymerized with D-sorbitol in a similar manner to the citric acid system. Soluble polymers were synthesized with a residual acid content of 5 meq per g of polymer. These materials show CA+2 sequestering ability, of up to 0.56 mmol Ca+2 per gram of product.