engleski

Surface properties of Croatian heat treated wood floorings

Heat treated wood (HTW) can be successfully appllied for floorings due to its better moisture resistance, increased dimensional stability, and uniform colour change to darker, brownish colours. Material of ash (A), beech (B) and hornbeam (H) for parquet elements was treated at two temperature levels, 190 °C and 210 °C, and the properties were compared with native wood. The reduction in dimensional changes was expressed by volumetric shrinking and Anti Shrink Efficiency (ASE). Additionally, parquet elements, produced from HTW, were oil-impregnated and waxed, and subsequently tested for water vapor and liquid water permeability. Shrinking coefficients of HTW were not reduced in comparison with native beech wood. However, the significant reduction in absolute water uptake resulted in ca 50 % lower EMC values and up to ca 60 % improved ASE values of HTW. Heat treatment only slightly reduced the density of all species tested, but significantly improved their biological durability. This biological resistance was drastically influenced by treatment temperatures above 190 °C. Surface treatment with flooring oil and wax further improved the hygroscopic properties of HTW parquet elements. The effect of UV light through window glass on the changes in colour of surfaces of uncoated and clear-coated thermally modified wood, and on chemical changes of surfaces of uncoated thermally modified and unmodified wood was monitored using QUV accelerated exposures. Discoloration of the uncoated wood samples and those treated with three commercial transparent coatings (two-component polyurethane varnish (PU), water-borne varnish (AQ), and nano-impregnation (I)) was measured spectrophotometrically using CIELAB parameters (L*, a*, b* and ΔE*). FTIR spectroscopy was used to study chemical changes caused by UV irradiation. Colour change (ΔE*) was recorded in all tested wood samples after exposure to UV light, and the smallest discoloration was recorded in wood samples coated with two-component polyurethane varnish. FTIR spectroscopy results show that thermal treatment and exposure to UV light modify the chemical structure of wood surface and that the thermally modified samples exposed to UV light show similar changes as unmodified samples exposed to UV light, but less pronounced.

heat treated wood floorings; water and vapour permeability; light resistence; FTIR

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