Protein adhesives: effect of high-pressure homogenization of plant proteins on wood bonding performance

Protein-based adhesives are emerging as sustainable, biodegradable alternatives to synthetic adhesives. However, their industrial use is limited by high viscosity and low moisture resistance, despite high water content. High-pressure homogenization (HPH) shows potential to improve these materials by altering mechanical and adhesive behavior. This study examined the effects of HPH on physical and bonding properties of adhesives produced from potato, soy, pea and maize flours and protein concentrates. Potato and maize dispersions were first ground, and then all samples were homogenized at 80 MPa for five cycles. Dispersion behavior, particle size, viscosity and tensile shear strength were evaluated. Grinding and HPH reduced particle size and prevented phase separation and sedimentation, improving suspension stability and application consistency. All formulations showed thixotropic behavior except soy flour, which maintained constant viscosity. For maize flour and potato concentrate, pre-treatment increased dry and wet bond strength. In contrast, pea concentrate showed reduced strength after HPH, but still higher than other proteins, while soy flour remained unchanged. Overall, HPH proved an effective pre-treatment for improving the physical and adhesive properties of plant-protein dispersions. By reducing particle size and exposing active groups, HPH enhances adhesive uniformity and reactivity, supporting development of protein-based wood adhesives from European crops.