In this thesis, we optimized the standard method SIST EN 927-7:2020 that determines the assessment of the knot-staining resistance of wood coatings. Since this method has never been performed in the laboratory for surface finishing, we decided to check whether the mentioned method is at all feasible with the existing equipment and to get as close as possible to the standardized procedure with appropriate adaptations. In addition, we wanted to test how some of the basic types of white pigmented coatings are evaluated. For the substrate we used various knotty specimens of red pine wood (Pinus sylvestris L.). The aim of the study was not so much to identify differences between the different types of coatings, but rather to make appropriate adjustments, optimizations and critical assessments to improve the standard. By applying the method, we found that by evaluating the coating before and after exposure and accounting for this colour difference we could classify coating systems much more legitimately or objectively according to their effectiveness against staining due to wood knots. We found that there are not many coatings that completely prevent yellowing of knots, but opaque coating systems are more effective at preventing resin breakthrough than semi-transparent coating systems. We also found that solvent-borne coating systems are better at preventing the appearance of knot yellowing than water-borne ones.
|
