High Strength Adhesives from Catechol Cross-Linking of Zein Protein and Plant Phenolics

Corn zein is a nontoxic protein that has found use in adhesive and coating materials for pharmaceutical, biomedical, and food applications. The degradability and amphiphilic properties of zein are attractive for materials design. Unmodified zein polymers, however, have drawbacks when it comes to adhesive strength, water resistance, and wet adhesion. Here, compositions of zein plus plant-based phenolics including catechol, tannic acid, juglone, caffeic acid, quercetin, and gallic acid are examined. Combinations of zein with phenolic components from plants provide high strength adhesive bonding. These catechol-containing phenolics may present an analogy to the cross-linking chemistry of catechol found in mussel-mimetic adhesives. Bonding is tested on dry and wet aluminum substrates using lap shear configurations. In each case, bond strengths are substantial and exceed the minimal bonding of zein only controls. Maximum adhesion for zein + catechol is 8 +/- 1 MPa. Under similar conditions, commercial Super Glue bonds at 8 +/- 2 MPa. Further results involve examinations of bond persistence on substrates submerged under water. Such results indicate that proper formulation efforts yield strong adhesives with some water resistance. These studies show that benign components from food can provide performance comparable to the petroleum-based materials in current wide spread use.