Wood is not very durable in long terms when is exploited outdoors. Its exposure to moisture and UV radiation leads to changes in measurements, shape and colour as well as to the deterioration of adhesive properties, photodegradation or the development of cracks. Moreover, it is gradually destroyed by nematodes, fungi and bacteria. In order to enhance the durability of wood, it undergoes various modifications (chemical, thermal) or is covered with different polymeric materials. Due to the low compatibility of wood surface and polymer, extremely high hygroscopicity, porosity, anisotropy and surface properties of wood, when exploiting outdoors, adhesion between wood substrate and polymer rapidly and intensively decreases and wood finishing material ceases to function as protective element. When modified thermally or chemically, wood chemical structure changes and wood becomes more hydrophobic, therefore poorly absorbs water. This advantage becomes limitation when modified wood is glued or finished with synthetic polymers: surface wetting, coating spreading on the wood substrate and bonding between wood surface and polymer are poor. Consequently, during the exploitation time, wood coating flakes off. Still it is a big problem in the market although the demand for modified wood is high and will only increase in the future. It is not yet fully understood, how changes the adhesion mechanism when modifying wood. Also it is important to understand the wetting processes. Therefore in this research the wetting and adhesion properties of thermally and chemically modified wood finished with water-based acrylic coatings were studied. For this research defectless oak wood samples with dimensions of 50 x 50 x 15 mm were used. All samples were distributed into 4 groups – heat treated (160oC and 220oC), ammonia modified and unmodified as a reference. Wood surface roughness, pH, wetting angle using sessile drop method and adhesion strength (according standard EN ISO 4624:2000) were evaluated.
Keywords: heat treatment, adhesion, chemical treatment, contact angle
Authors
Vitosytė J.
Department of Wood Technology, Kaunas University of Technology, Kaunas
Grigaliauskienė I.
Department of Wood Technology, Kaunas University of Technology, Kaunas
Ukvalbergienė K.
Department of Wood Technology, Kaunas University of Technology, Kaunas
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