Tunable Tannic Acid-Zein Adhesives for Bonding Different Substrates

Plant-based, nontoxic and strong adhesives that can work on different substrates allow for better product recycling. Replacing synthetic adhesives with plant based ones that perform equally well may lead to a more sustainable ecosystem. Adhesives based on zein protein, derived from corn, can be made as strong as Super Glue. Unlike petroleum-based adhesives, this plant protein is removable and degradable. Here, adhesives from the components zein and tannic acid function well on different substrates such as metals, plastics, and wood. This work presents the properties of selected adhesive formulations including bond strengths when the substrates are changed. To achieve near Super Glue strength, each substrate requires a different adhesive formulation. Temperature-dependent curing, (potential of hydrogen) changes, and additional variables influence adhesion. Tack testing at room temperature is measured to provide comparisons between initial bonding and that achieved after curing. Adhesion to plastic substrates is less than wood or metal, but still plenty strong to measure. Aging of adhesive solutions as well as water resistance after curing is investigated. Infrared spectroscopy data are correlated with changes in color, age, and pH of adhesives. These new adhesives may lead to a sustainable and cleaner environment.