Wood is a porous, anisotropic material characterized by a variety of natural anatomical features. In softwoods, the main structural components are longitudinal tracheids, while in hardwoods, these consist of vessel elements and longitudinal fibers. The lumens of these cells are typically large enough to allow the infiltration of liquid adhesives, which is essential for achieving strong and durable bonds. However, adhesive joints are often considered the weakest links in assembled wooden structures, as they are critical for transferring loads across the bonding interface. This highlights the importance of studying adhesive performance and behavior in such systems.
This study utilized beech wood with two different grain orientations (radial and tangential) and bonded the specimens using two types of adhesives: polyurethane (PUR) and fish glue (RK). The samples were prepared following the EN 302-1 standard and subjected to natural weathering for three months in Lisbon, Portugal. Due to the high solubility in water, we were unable to analyze the samples glued with RK, so this research is based on a study of the beech wood-PUR-beech wood system.
The investigation focused on assessing both the depth and distribution of adhesive penetration in to plates with various combinations of fiber/growth rings orientations. Additionally, the impact of aging was analyzed by observing mechanical, physical, and chemical changes in the bonded joints over time.
A wide range of analytical techniques was applied, including tensile-shear testing, Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), epi-fluorescence microscopy, Fourier-transform infrared spectroscopy (FTIR, μFTIR), Raman microscopy, and micro-computed tomography (μCT). The study also evaluated the precision and reliability of these methods in characterizing the bonded interfaces.
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