Submitted to: Journal of Biobased Materials and Bioenergy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/28/2007
Publication Date: 8/27/2007
Citation: Woods, K.K., Selling, G.W. 2007. Improved Physical Properties of Zein Using Glyoxal as a Crosslinker. Journal of Biobased Materials and Bioenergy. 1(2)282-288. Interpretive Summary: Zein is the predominant prolamine found in corn. As such it is one of the main co-products of the bioethanol industry. As the volume of bioethanol is increased, finding a technology that can fully utilize this co-product will become increasingly more important. Historically, zein was used in the textile and coatings industries. In order to have suitable physical properties for these markets, the zein was crosslinked with formaldehyde. This formaldehyde treatment delivered improved tensile strength, improved solvent resistance and improved resistance to fabric treatments such as dyeing. Formaldehyde is quite toxic, though, and commerical use of formaldehyde requires significant investment to be performed safely. Therefore, other chemistries to improve the properties of zein-based materials are being explored as an alternative to formaldehyde. We chose to evaluate glyoxal and methylglyoxal as potential crosslinkers to improve the physical properties of zein. Using glyoxal we were able to significantly improve the tensile strength of zein, while treatment with methyglyoxal gave no such improvement. This research will benefit the bioethanol industry by improving the marketability of a major co-product of this industry and therefore making the entire process more profitable.
Technical Abstract: The effect of crosslinkers glyoxal, methylglyoxal and formaldehyde on physical properties of zein films was studied. Zein was solubilized in 90%(v/v) aqueous ethanol and the pH was adjusted with either hydrochloric acid or sodium hydroxide. Crosslinkers were added to 0.3, 1, 3 and 6%(w/w by zein weight), with the reactions carried out at 60 deg C. Triethylene glycol was added as a plasticizer. Films were cast and dried at room temperature, with cut bars stored at 50% and 70% relative humidity before testing. Films crosslinked with glyoxal and formaldehyde showed a significant increase in tensile strength under certain pH conditions. Films of glyoxal reactions conducted at basic pH gave the highest overall tensile strength, with a 52% increase compared to the control film. Formaldehyde films had improved tensile strength when reacted at acidic or neutral pH. Methyglyoxal had no effect on the tensile strength of zein films. Zein films crosslinked with glyoxal or formaldehyde were found to swell, rather than degrade, when placed in three compatible solvents. Films crosslinked with glyoxal were resistant to boiling water. Denaturing gel electrophoresis of glyoxal and formaldehyde reactions showed presence of high molecular weight moieties when compared to control reactions.