Effect of zein subunit and plasticizer on rheology and adhesion properties of zein-based adhesives

Protein-based adhesives have received widespread attention due to their low-cost, resourcefulness, ecofriendliness. Here, an easy and quick preparation of zein adhesive was introduced. Under the plasticizing action of the plasticizer (acetic acid or ethanol), amorphous zein powder changed from solid particles to sticky and flowing state, and then formed zein-plasticizer adhesive with great adherence. During this transition, the aggregates of zein molecules were destroyed by the lubricative effect of plasticizer, and alpha-helix structures of zein increased by the protonation of zein in acetic acid, but decreased due to the hydrophobic interaction caused by ethanol. Zeinplasticizer adhesive was mainly composed of non-covalent `physical' cross-links. The zein-plasticizer adhesive containing stronger plasticizer got higher flowability and longer solidifying time. And stronger plasticizer also led to greater thermal stability, more stable structure and smoother surface for solidified zein-plasticizer adhesive, which resulted in stronger adhesion strength and greater water resistance. The alpha-zein was easier to be plasticized than beta- and gamma-zein, and the plasticizing ability of acetic acid was stronger than that of ethanol. The alpha-zein-acetic acid adhesive therefore showed outstanding performance in adhesion strength (600 kPa) and water resistance (300 kPa) among all zein-plasticizer adhesives, and has wide application as a promising waterproof adhesive.

Automated summary

Protein-based adhesives have gained attention for their affordability, availability, and environmental friendliness. This article presents a simple and fast method for preparing zein adhesive, and investigates the effects of different plasticizers on its properties.