Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 28, 2005
Publication Date: January 11, 2006
Citation: Sessa, D.J., Selling, G.W., Willett, J.L., Palmquist, D.E. Properties of zein processed with sodium dodecyl sulfate in semi-dry state. Industrial Crops and Products. 2006. p.111. Interpretive Summary: Corn is an abundant renewable resource that has been used to produce about 2.8 billion gallons of ethanol in 2003. Co-products of its manufacture must be better utilized to make ethanol production economically feasible with less reliance on government subsidy. About 1 million metric tons of zein, an aqueous alcohol soluble protein, have been generated annually from ethanol co-products. Zein can be used as an alternative to various bulk, petroleum-based, commerical plastics, a 50 billion pound per year industry. Extrusion is a standard for producing plastics. Unfortunately, zein when combined with plasticizers, needed to overcome its brittle nature, becomes very viscous with shear that needs to be controlled for extruding some formulations of zein. A surfactant, sodium dodecyl sulfate (SDS), was found to effectively control viscosity increases in zein when subjected to high shear. Despite the fact that extruded plastics with combinations of zein, plasticizers and SDS did not improve the strength of the plastic at the levels used, SDS blends can be used to develop formulations that can be processed within acceptable machine and end use requirement parameters. This finding should benefit scientists in academia, government and industry who are interested in finding new uses for co-products of the ethanol industry.
Technical Abstract: Zein, the predominant protein in corn, may be used as an alternative to various commercial plastics. To alleviate brittleness in plasticized zein, plasticizers such as triethylene glycol (TEG) and water have been used. When zein is blended with water and subjected to heat and shear in a torque rheometer, zein readily generates high molecular weight species giving rise to a rapid increase in torque which can be detrimental in industrial processes such as extrusion. Sodium dodecyl sulfate (SDS), a known protein denaturant, was investigated for use to control viscosity increases of zein when subjected to torque rheometry. Because extrusion is a standard method for processing plastics, our second objective was to assess the mechanical properties of extruded, SDS-modified zein. Our findings with torque rheometry showed that water alone allowed zein to generate high molecular weight species in approximately one minute. Varied combinations of TEG and water delayed the torque rise to 2 to 4 min. When SDS was added to zein, combined with water and TEG, it significantly delayed the viscosity rise in a linear relationship dependant on the amount of SDS added. For our second objective, zein was blended with fixed amount of water and TEG and varying amounts of SDS and subjected to extrusion processing on a single-screw extruder equipped with a 2mm round die. The resulting rope was pelletized. One half the weight of pellets was re-extruded through a 2cm ribbon die while the other half was freeze-ground and the resulting powder subjected to compression molding. Tensile bars from the compression mold and those cut from the ribbon die were stored at either 50 or 70% RH. Mechanical properties of these tensile bars were evaluated on an Instron with cross head speed of 50mm/min. Tensile strength diminished, elongation increased and Young's modulus diminished with increase in % SDS. Addition of SDS did not improve mechanical properties of the tensile bars. Addition of SDS to zein blends of water and TEG can be used to develop a formulation that can be processed within acceptable machine and end use requirement parameters.