Effect of wetting/drying on the properties of OSB/3 and birch plywood

In this study the thickness swelling (TS), restore dimensions (RD), density (D) and modulus of rupture (MOR), after ten cycles of wetting over/drying, of commercial boards, i.e. 3-layered OSB/3 ("SWISS KRONO", thickness 12mm) and 9-layered birch (betula sp) plywood with phenol-formaldehyde (UPM-Kymmene, Otepää, Estonia), were investigated according to EN standards. Test samples (dimensions of 290×50×12 mm³) for determination of a change in the investigated parameters, according to the standard EVS EN 326-1:2002, were cut from the boards in the parallel (ǁ - major axis) direction to the face (outer layer) strand. The cutting forehead and the facet edges of the test samples were coated with the water repellent mastic Kiilto Fibergum ("KIILTO OY"). The specimens were altered by soaking in a tank with water (22±1°C) for 24 hours and dried for 48 hours in a ventilated drying box at 65 ± 1°C. Before testing, the samples were conditioned in a climatic chamber at a relative humidity of 65% at 21°C. The surfaces and cross-sections of the initial dry samples after the first wetting/oven-drying cycles were studied using the X-ray technique. The analytical exponent- and linear-fractional equations were used to approximate the obtained experimental data depending on the number of cycles. (paper)