Through the modification of wood, various properties can be altered by chemical, physical or mechanical processes that influence the bonding quality and workability of gluing systems. This is evident for adhesion, pressing time, curing and glue line properties. Further, testing methods need to be evaluated on their applicability for determining the bonding quality of modified woods. In this paper, laboratory test results of non-load-bearing-laminated acetylated products are presented. The results are evaluated and discussed in respect to chemical composition, ultra-structure and other properties altered by the acetylation process.

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In this study, the tensile shear strength of untreated, acetylated, and heat-treated beech (Fagus sylvatica L.) wood joints was investigated as a function of different surficial processing techniques. It was hypothesized that differentiating patterns of surface texture are induced by specific processing techniques directly affecting the bonding performance of adhered assemblies. Surface processing was implemented either by peripheral planing with sharp and dull knives, or by sanding (P100). Process-dependent surface textures were visualized by scanning electron microscopy and a digital light microscope was applied to display the structural integrity of surficial wood tissues. In dependence on wood modification techniques, process-related patterns of surface texture were observed. Laser scanning data of surface morphology was used to derive area-related functional roughness parameters defining complex surface textures quantitatively. For tensile shear testing, lamellae were bonded either with a two-component melamine-urea-formaldehyde adhesive or with a one-component moisture-curing polyurethane adhesive. Single lap-joint specimens were prepared following EN 302-1:2013 by the Deutsches Institut für Normung considering a material-adapted specimen geometry. Bonding strength was evaluated with respect to differentiating regimes of moisture. Specific dependences of modified beech wood properties on surface morphologies subsequent to surface processing and, therewith, on the associated bonding performance could be verified. As a result, universal relationships between bonding performance and surface processing technique could not be identified. Thus, individual studies of bonding performances in dependence on adherend- and processing-related surface textures are inevitable.