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The deterioration of the properties of wood-glued joints exposed to different environments with variable parameters, such as humidity and temperature, is caused by structural changes. The aim of this study was to evaluate the influence of cold (A3) and boiling (A5) water on the structure of a commercial-type one-component polyurethane adhesive filled with milled carbon fibres (MCF) in the form of thin films and wood bondline. The structure and stiffness of the films, neat and filled with 1, 3, 5, and 7% MCF, was studied by attenuated total reflectance infrared spectroscopy (ATR), temperature-modulated differential scanning calorimetry, wide-angle X-ray scattering, and dynamic mechanical analysis. The adhesive structure of the bondline (neat and filled with 5% MCF) was measured on the shear fracture surfaces of beech-glued joints using ATR. The adhesive structure was a mixed phase and largely amorphous. The adhesive was not cured completely in either thin films or wood bondline. After A3, slight post-curing of adhesive occurred. Hard domains of adhesive were degraded after A5 and dissociated structure improved the adhesive film stiffness above 70 °C. Compared with the films, the bondline structure differed in a higher degree of original curing and a much lower degree of degradation after A5.
Bálková et al. (Fri,) studied this question.