Submitted to: Macromolecular Chemistry and Physics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/8/2008
Publication Date: 5/14/2008
Citation: Selling, G.W., Woods, K.K., Sessa, D.J., Biswas, A. 2008. Electrospun zein fibers using glutaraldehyde as the cross-linking reagent-effect of time and temperature. Macromolecular Chemistry and Physics. 209(10):1003-1011. Interpretive Summary: With the fast-growing bio-ethanol industry, it is very important to use the co-products generated during ethanol production in a fashion that will improve the economics of this new industry. Zein, the dominant corn protein, is present in large amounts in the main co-products of both wet-milling and dry-milling ethanol plants. It is typically isolated from corn gluten meal (generated by ethanol producers using wet milling techniques). The main use of zein historically was in the textile fibers market. Zein needed to be modified (using formaldehyde, a suspect carcinogen) to be suitable in the textile market. To achieve the best properties formaldehyde was used both before and after the fiber was formed. Improved derivatization techniques are needed that would avoid the use of formaldehyde. It would also be advantageous to avoid chemical treatment of the fiber after it is formed. Glutaraldehyde has been shown to increase the tensile strength and reduce the solubility of zein in films. In order to economically produce fibers in the lab, the electrospinning technique is preferred. When zein was modified with glutaraldehyde and electrospun to make non-woven fiber mats, surprisingly the fibers produced readily dissolved in standard zein solvents. The non-woven fabrics were found to have more than triple the tensile strength of the control. However, reduced solubility is important as well. It was found that by heating the fibers at temperatures above 100 deg C solubility of fibers can be dramatically reduced. Results from this work will be helpful in developing new zein products, and therefore improving the economics of the bio-ethanol industry.
Technical Abstract: In order to develop zein fibers with improved physical properties and solvent resistance, glutaraldehyde was used as a cross-linking reagent. By weight of zein, glutaraldehyde was incorporated at levels between 2 and 8% where the reaction was carried out in acetic acid for twenty hours at room temperature. Fibers were produced using the electrospinning technique. When using 8% GDA, depending on % protein in the spinning solution, round and ribbon fibers were produced having diameters between 1 and 70 microns. The fibers readily dissolved in acetic acid after production. However, heating the fibers at temperatures from 80 – 180 deg C for different times provided various degrees of insolubility to the fibers. The time and temperature needed to deliver insolubility was dependent on the amount of glutaraldehyde used. A model was developed relating the extent of dissolution with the amount of glutaraldehyde used and the temperature/time at which the fiber was exposed. The material that was found to extract into AcOH was determined to be zein protein and corn oil. The tensile strength of the 8% glutaraldehyde zein fiber mat was increased by 200%. The fibers were found to be birefringent and had higher amounts of alpha-helix relative to starting material. With heating, the amount of alpha-helix in the fibers was reduced.