Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2006
Publication Date: 1/1/2007
Citation: Selling, G.W., Sessa, D.J. 2006. Multivalent carboxylic acids to modify the properties of zein. Industrial Crops and Products. 25:(1)63-69.
Interpretive Summary: With the passage of the energy bill, the amount of ethanol produced from renewable resources will increase dramatically. This will also generate much larger quantities of co-products that could be used in higher value markets. One of these co-products is the predominant corn protein zein. Zein was utilized in the 1940's and 50's in textile fibers and coatings industries. Due to the development of cheaper competitive products based on fossil fuels, which unlike zein based materials did not lose strength at high humidity, the use of zein rapidly declined. Currently zein is used predominantly in the pharmaceutical business as a coating for pills. In order to re-enter the larger textile market, research must be performed to improve the physical properties of zein based articles, especially on exposure to high humidity. Historically this was accomplished using formaldehyde which is known today to be a possible carcinogen. Formaldehyde can be handled safely, however, alternative routes utilizing inherently safer materials will be significantly less costly to commericialize. Carboxylic acids having more than one reactive site have been used to cross-link cotton. They have also been used to cross-link zein in solution. Developing a process where the zein is modified in the melt state, no solvent has significant economic advantages. We have used two types of carboxylic acids to modify zein. These materials were found to improve the processability of zein. However, at higher levels of incorporation they did reduce the overall strength of the zein. Surprisingly, the samples having higher levels of these acids had higher strength at high humidity versus low humidity. This result is very surprising and if it could be understood on a molecular level, it may be employed in other technologies that do not alter overall strength. This basic study has revealed that relatively simple safe materials can improve properties of zein in a critical area which will help in the development of zein based articles for much larger markets.
Technical Abstract: Carboxylic acids having more than one carboxylic acid moiety have been evaluated in zein melt formulations produced in a torque rheometer. These reagents are effective plasticizers for zein, lowering zein viscosity and delaying the onset of rapid viscosity increase. These reagents have been shown to alter viscosity in a different fashion than traditional plasticizers such as triethylene glycol. These additives lowered the tensile strength (TS) of zein formulations at 50% RH. Surprisingly at elevated levels of these additives, TS at 70% RH was higher than that at 50% RH. NMR analysis of soxhlet extracted samples showed that these reagents do not cross-link the zein under the reaction conditions employed.