1 WOOD RESEARCH 61 (1): 2016 01-12 THE EFFECT OF COMBINED MELAMINE- RESIN- COLOURING-AGENT MODIFICATION ON WATER RELATED PROPERTIES OF BEECH WOOD Bodo Caspar Kielmann, Holger Militz, Carsten Mai Georg August University of Göttingen , Wood Biology and Wood Products Göttingen, Germany (Received August 2015) ABSTRACT Beech wood (Fagus sylvatica L.) was modified with aqueous solutions of methylated N-methylol melamine (NMM) and a metal-complex dye and the water related properties were determined. Wood blocks, treated to the highest weight percent gain (WPG), attained approximately 5 % cell wall bulking and 30 % anti-swelling efficiency (ASE) after ten cycles of water saturation and drying. The metal-complex dye was stably fixed in the resin matrix and was hardly washed out. The equilibrium moisture content of the modified samples related to the dry mass of untreated beech wood (EMC R ) was not considerably reduced compared to the EMC of the control. The maximum swelling of the modified samples as a result of vapour sorption was only reduced above 65 % relative humidity compared to the control. Capillary water uptake of wood was significantly reduced by the resin modification. The results indicate the potential of the combined modification to improve the water related properties of wood. KEYWORDS: Wood modification, melamine resin, colouring agent, dimensional stability, water uptake, moisture sorption. INTRODUCTION In the modern society, wood cannot only be appreciated for its functional properties but also for its aesthetic appearance, i.e. homogeneity, texture, figure and coloration (Janin et al. 2001). Various paints, varnishes and other coatings are available on the market to enhance or maintain the aesthetic appearance of wood surfaces, and contribute to better performance and prolong the service life of wood. Coating problems due to defects in varnish materials and their application, as well as failure of the wood substrate at the wood-coating interface (e.g through high moisture content, dimensional changes, photo-degradation, colonisation by staining fungi), however, bring about additional maintenance costs during service life (Miller and Boxall 1984).