Underwater Bonding with a Biobased Adhesive from Tannic Acid and Zein Protein

Abstract

Herein are presented several adhesive formulations made from zein protein and tannic acid that can bind to a wide range of surfaces underwater. Higher performance comes from more tannic acid than zein, whereas dry bonding required the opposite case of more zein than tannic acid. Each adhesive works best in the environment that it was designed and optimized for. We show underwater adhesion experiments done on different substrates and in different waters (sea water, saline solution, tap water, deionized water). Surprisingly, the water type does not influence the performance to a great deal but the substrate type does. An additional unexpected result was bond strength increasing over time when exposed to water, contradicting general experiments of working with glues. Initial adhesion underwater was stronger compared to benchtop adhesion, suggesting that water helps to make the glue stick. Temperature effects were determined, indicating maximum bonding at about 30 °C and then another increase at higher temperatures. Once the adhesive was placed underwater, a protective skin formed on the surface, keeping water from entering the rest of the material immediately. The shape of the adhesive could be manipulated easily and, once in place, the skin could be broken to induce faster bond formation. Data indicated that underwater adhesion was predominantly induced by tannic acid, cross-linking within the bulk for adhesion and to the substrate surfaces. The zein protein provided a less polar matrix that helped to keep the tannic acid molecules in place. These studies provide new plant-based adhesives for working underwater and for creating a more sustainable environment.

Zein-Based Nanoparticles as Active Platforms for Sustainable Applications: Recent Advances and Perspectives

“…Thanks to their peculiarities, like availability, biodegradability, low-toxicity, and their different shape versatility (particles, membranes, films, and scaffolds), protein-based nanocomposites, particularly zein-based ones, are used in applications in fields or industries that are different to those previously discussed. For example, they can be used in the production of bio-based adhesives [ 132 ] or in the textiles industry to impart hydrophobicity and antimicrobial activity [ 133 ]. However, their most common applications are in the biomedical field and the pharmaceutical industry [ 86 ]; their use is in the pursuit of developing systems that can be used for targeted drug delivery, bioimaging, or soft tissue engineering.…”