Submitted to: Journal of Applied Polymer Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/2/2008
Publication Date: 8/15/2008
Citation: Woods, K.K., Selling, G.W. 2008. Melt reaction of zein with glyoxal to improve tensile strength and reduce solubility. Journal of Applied Polymer Science. 109(4):2375-2383. Interpretive Summary: Zein is the main protein present in corn and is a potentially significant co-product of the bio-ethanol industry. Considerable effort has been put forth by many researchers to develop new technologies to improve the market suitability of zein. The research presented here describes the use of a crosslinking reagent, glyoxal, to improve the tensile strength and solvent resistance of melt processed zein. Zein, along with glyoxal and sodium hydroxide, was processed in a torque rheometer to produce a dough. This dough was then ground to a powder and compression molded into bars. Specific concentrations of glyoxal and base gave bars with increased tensile strength and improved solvent resistance when compared to control. Base composition, melt temperature and processing time had little effect on the solubility of molded bars. By performing this chemistry in a melt process, it may then be scaled up to use extrusion technology and take advantage of the economic advantages of extrusion processing. Results from this work will be helpful in developing new zein products, therefore improving the economics of the bio-ethanol industry.
Technical Abstract: Glyoxal, in the presence of base, has been used to crosslink zein in a melt process, involving reaction in a melt state combined with compression molding. The resulting zein articles had improved tensile strength, increasing from 34.3 to 40.6 MPa, when the amount of glyoxal was 6% by zein weight. Reduced solubility in solvents, such as acetic acid, was achieved with glyoxal amounts as low as 1%. Glyoxal derivitization required the presence of base. As little as 0.00019 mmoles of NaOH per gram of zein when using 6% glyoxal gave reduced solubility. Other bases, such as KOH and Ca(OH)2 also gave reduced solubility. However, these bases did not yield improvements in tensile strength. Decreases in melt temperature and processing time caused a corresponding decrease in tensile strength, but had little effect on solubility.