Submitted to: American Oil Chemists' Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 11, 2003
Publication Date: May 4, 2003
Citation: LAWTON JR, J.W., SESSA, D.J., BISWAS, A., WILLETT, J.L. IMPROVING ZEIN FILMS BY CROSS-LINKING. AMERICAN OIL CHEMIST SOCIETY MEETING. 2003. Abstract p. 115. Technical Abstract: Zein, the alcohol soluble protein found in corn, has been commercially available for the last 60 years. During this time, it has found uses in adhesives, varnishes, inks, and coatings all because of its film forming capabilities. However, zein films alone are very brittle. To resolve the brittleness of zein films, plasticizers are added to the films. These plasticizers solve the brittleness problem, but weaken the films. By cross-linking, the zein films can be strengthened. Most zein cross-linkers that have been tried are aldehydes of some type. These types of cross-linkers are great at increasing the tensile strength of the films, but have a detrimental effect on film flexibility. These substances probably cross-link along the length of the zein and create a cross-link network which would produce a film with greater strength but not much flexibility. We have started working with chemicals that can only cross-link zein at the terminal ends of the molecule. It is believed that this process will increase the size of the zein by chain extension and make zein act more like a traditional synethic polymer. Chain extension chemicals we are using are N-hydrosuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. Cast films made with these chain extenders, which also containing 30% triethylene glycol as the plasticizer showed the expected improvement in tensile strength over plasticized zein films containing no extenders. Tensile strengths improved from 9.2 MPa to 12.8 MPa. There was no difference in the percent elongation or young's moduli for plasticized films whether or not they contained extender when the films were stored at 50% relative humidity. However, plasticized films made with zein having been treated with extender showed a substantially lower young's modulus when stored at 20% relative humidity. At this humidity these films were much more flexible than films containing no extender. Plasticized films stored at 20% relative humidity had young's modulus of 626 MPa while plasticized films containing zein treated with extender had a modulus of 410 MPa.