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 α-helix structures of zein increased by the protonation of zein in acetic acid, but decreased due to the hydrophobic interaction caused by ethanol. Zein-plasticizer 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 ɑ-zein was easier to be plasticized than β- and γ-zein, and the plasticizing ability of acetic acid was stronger than that of ethanol. The α-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. • Zein can form adhesive with great adherence under the action of plasticizer. • Zein-plasticizer adhesive was composed of non-covalent ‘physical’ cross-links. • The degree to which the zein was plasticized determined its adherence. • The adhesion of α-zein-acetic acid adhesive was 600 kPa in dry and 300 in wet.