Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2013
Publication Date: 6/1/2013
Citation: Selling, G.W., Maness, A.N., Bean, S., Smith, B.M. 2013. Impact of thiocyanate salts on zein properties. Cereal Chemistry. 90(3):204-210.
Interpretive Summary: This research examines a new type of additive to develop improved products that use corn protein. Corn protein (zein) is a major component in the co-products of bioethanol production. Developing higher valued uses for this material will help improve the economics of this industry. We have a new type of plasticizer (a type of compound that increases a material elongation to break and reduces the force needed to stretch it). These compounds are a special type of salt that contain a thiocyanate group. These salts provide higher elongation and lower force to stretch zein films. However, they require the presence of a more standard plasticizer in order to deliver these attributes. It was also found that the degree of improve varied tremendously with the relative humidity in which the samples were stored. In certain applications, such as sensors, this attribute may have value. This information will be beneficial to manufacturers involved in the production of ethanol from corn as well as those companies interested in producing biobased (zein) articles.
Technical Abstract: A new class of zein plasticizer was investigated, thiocyanate salts. Ammonium (ATC), potassium (KTC), guanidine (GTC) and magnesium thiocyanate (MTC) salts were added to solutions of zein in 90% ethanol/10% water with various amounts of tri(ethylene glycol) (TEG), cast as films and then tested to determine the impact that each salt had on properties. The presence of these salts affected solution rheology and intrinsic viscosity, demonstrating that the salts interact with the protein. In film studies, it was found that these salts act as plasticizers as they lower the glass transition temperature of zein when evaluated using differential scanning calorimetry. The presence of higher amounts of ATC led to failure as the temperature was increased past 60 °C when evaluated using dynamic mechanical analysis. In zein films where TEG is present, these salts increase elongation and reduce tensile strength. However, unlike TEG, when the salts are used as the only plasticizer, elongation is not increased and the reduction in tensile strength is decreased. Of the salts tested, GTC was found to increase elongation the most, while MTC had the lowest impact on elongation. When these salts were compared on an equal molar basis versus TEG, only GTC was found to be more effective at increasing elongation. The impact of salts on the elongation of the films was greatly affected by the % relative humidity (RH) in which the samples were stored. Humidity had a large affect on properties, with little additional elongation being observed when samples were stored at 15% RH and the highest elongations were observed at 50% RH.