Properties of films from corn zein reacted with glutaraldehyde

Abstract

To improve the mechanical properties of zein films, a commercial white zein was reacted in glacial acetic acid (HAc) with glutaraldehyde (GDA) from 0.5 to 16% by weight based on the weight of zein. Amounts of 4% or higher GDA-modified zein, when cured in a closed system, generated a gel. That gel was insoluble in organic solvents known to solubilize zein. Zein solutions cast within a silicon rubber gasket sealed onto Teflon-coated plates, when air dried, generated 0.7-0.9-mm thick films. Those films from 8% GDA-modified zein had a water vapor permeability of 5.9 Â 10 À8 g cm/Pa s m 2 . Overall, results indicate that our thicker films gave higher water vapor permeability than values reported in the literature. To achieve consistent and comparable results with differential scanning calorimetry (DSC) and dynamic mechanical analyses (DMA), film samples had to be heated to remove residual HAc. An increase in the glass transition temperatures for those films from GDA-modification of zein, observed with both DSC and DMA, was attributed to the crosslinking of zein. Physical testing of tensile bars cut from GDA-modified zein films showed minor enhancement of tensile strength, percent elongation, and Young's modulus in the 0.5% GDA-modified zein films, which increased and leveled off with 4% or higher amounts of GDA for the modifications. When the 4 to 16% GDA results are averaged, the tensile strength for the modified zein films increased 1.8-fold when compared with unmodified zein control films. On the same note, percent elongation showed a 1.8-fold increase and Young's modulus showed a 1.5-fold increase. GDA reaction with zein generated films with improved tensile strength, ductility, and stiffness when compared with respective zein control films that retained their integrity when subjected to either boiling water or extensive soaking.

REVIEW: Zein Extraction from Corn, Corn Products, and Coproducts and Modifications for Various Applications: A Review

“…Many different compounds such as formaldehyde, glutaraldehyde, and epichlorohydrin are used to cross-link zein proteins (Parris and Coffin 1997). Sessa et al (2007) studied the effects of cross-linking zein with glutaraldehyde in acetic acid. The opposite was true with films produced in aqueous acetone.…”

Effect of glycerol on solution properties governing morphology, glass transition temperature, and tensile properties of electrospun zein film

“…These films are nontoxic15 (or biocompatible) to bioenvironment, which cells can adhere and proliferate 6. However, single component zein films produced are generally very brittle and difficult to handle 16–19. As tensile strength and elongation at break are strongly relevant to such applications, attempts have been made to improve zein film properties by adding plasticizers.…”

Reactive extrusion of zein with glyoxal

“…Citric acid and 1,2,3,4‐butane tetracarboxylic acid have been used to modify zein in the melt state, however, either physical properties were not measured or the carboxylic acids were not incorporated into the zein structure 12, 13. Other methodologies are being explored to improve the properties of zein; however, these processes were performed in solution 14–19. Recently, zein has been cross‐linked using glyoxal (GLY), where GLY is capable of reacting with functional groups present on arginine, lysine (this residue is not present in zein) and the N‐terminal amine, in both solution20 and in the melt state 21.…”