Gluing of Urea-Modified Aspen Wood with Polyvinyl-Acetate-Dispersion-Based Adhesives

There are many ways to improve the quality of wood (including little-used wood, in particular aspen), one of which is thermochemical modification. Modification of wood with a urea solution is associated with the polycondensation of urea, lignin, and readily available fractions of hemicelluloses. Urea reacts with the hydroxyl groups of wood components to form hydrogen bonds. When treating wood with urea solutions, chemical interaction of urea with wood occurs, lignin condenses with amides at hydroxyl groups, both aliphatic and phenolic. The aim of the work is to study the strength and water resistance of adhesive joints (made from thermochemically modified aspen wood) based on polyvinyl-acetate dispersions for further use in joinery and construction production, corresponding to DIN EN 204 and DIN EN 205 standards. These standards describe the test methodology and the required values for determining the shear strength of wood along the fibers. To determine the strength and water resistance of adhesive joints, glue based on polyvinyl-acetate dispersion was used. The formation of an adhesive joint based on PVA glue with modified wood occurs due to the chemical interaction between the hydroxyl groups of cellulose macromolecules and the methoxyl groups of urea with the formation of esters. As a result of the tests, the strength and water resistance of adhesive joints of aspen wood (modified with urea) were determined; Rhenocoll Super W/DW glue complies with the DIN EN 204–2003 class D3 standard in terms of average strength and water resistance.