Adhesive properties of wheat gluten after enzymatic hydrolysis or heat treatment – A comparative study

Wheat gluten, among other plant proteins, constitutes an attractive raw material for sustainable alternatives to today's petroleum-based wood adhesives. Nevertheless, the bonding performance, and especially the water resistance, of these plant proteins need to be improved to turn them into competitors equal in merit to today's petroleum-based products. The aim of this study was to investigate if mild hydrolysis or heat treatment of wheat gluten will improve its adhesive properties. Wheat gluten was hydrolyzed with the enzyme Alcalase (degree of hydrolysis 0.3–5.5%), or heat treated at different temperatures (50, 70, and 90 °C) and varying time intervals (15 min to 24 h). Alkaline water dispersions of these modified wheat gluten samples were used as adhesives to bond together wood substrates of beech at a press temperature of 110 °C and a press time of 15 min. The tensile shear strengths of the substrates were measured for comparison of bond strength and resistance to cold water. The substrates were evaluated according to a slightly modified version of the European Standard EN 204.Lower levels of hydrolysis (0.3–0.6%) and most of the heat treatments at 90 °C resulted in improved bond strength and water resistance. Nevertheless, the adhesive properties, especially the water resistance, need to be further improved to fulfill today's requirements for wood adhesives.

Figure optionsDownload as PowerPoint slideHighlights
► Enzymatic hydrolysis or heat treatment of wheat gluten for improvements of adhesive properties.
► Tensile shear strength measurements and optical microscopy analysis of wood substrates.
► Mild hydrolysis or heat treatment improves bond strength.