Comparative physical evaluation of adhesive properties in modified gluten

The development of eco-friendly adhesives is essential to reduce reliance on petroleum-based products in the wood industry. In this study, wheat gluten was modified through enzymatic hydrolysis, heat treatment, and chemical reactions, including deamidation and acetylation, to improve its adhesive properties. The modified formulations were applied to bond Russian birch plywood (Betula pendula), and the tensile shear strength was evaluated under dry and wet conditions. Results showed that enzymatic hydrolysis provided the highest performance, with shear strength reaching about 6.4 MPa under dry conditions and 5.1 MPa under wet conditions, compared to other modifications. Heat treatment and deamidation with acetic acid or sodium hydroxide also improved properties, achieving values up to 3.5 MPa. In contrast, acetylation and deamidation with concentrated hydrochloric acid resulted in lower strength, around 2.0 MPa, particularly under wet conditions. These effects were attributed to structural alterations and new functional groups that enhance intermolecular interactions. Overall, targeted modifications of gluten can produce durable, eco-friendly adhesives suitable for wood applications.