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Abstract. Gluing of wood with great moisture content has challenge of water interaction with glue to give unwanted changes in glue properties and formed bond-line. Rheological measurements of polyurethane glues are sufficiently effective method to understand the polymer curing process and viscoelastic properties. Gel formation point is important parameter for a glue from the point of its application. When glue reaches the gel formation point, its viscosity drastically increases so that it could not properly wet the wood and it can result in poor bonds. One-component moisture curing polyurethane glues require water molecules for the polyadditional reaction. When water is involved in the curing reaction, it reacts with the isocyanate groups of glue and can lead to the formation of excessive carbon dioxide and thus can lead to glue penetration out of bond-line, additional backpressure. The dynamic viscoelastic parameters such as complex dynamic viscosity (ή), phase angle (δ), elastic storage modulus (G`), the viscous loss modulus (G") of two kinds of polyurethane glues depending on added water amount (from 0.9% to 10.0%) at a constant frequency and deformation (oscillation mode) were determined using rheometer. The aim of the present study was to investigate impact of added water on rheological behavior of polyurethane glues. At the end of this study it was concluded that tested glues indicated various behavior depending on chemical composition and added water content. Gel formation point is higher in case of GlueI. However, gel formation time was higher in case of GlueII and was not dependent on added water content. Gel formation time was faster for GlueII. Nevertheless, faster formed gel is stronger than longer formed gel of GlueI.

Abstract. In recent years the popularity of ecological and renewable materials has grown. Aware of the limited resources as well as availability of local resources and economic grounds, the attention is paid to the development of new materials. Currently, there is a political as well as a societal demand for products that require less energy for the manufacturing process and are easy to recycle with less impact on environment. In comparison with concrete, wood-geopolymer emits less CO 2 , it is environmentally friendly and made from available local resources. Therefore, the geopolymer composites obtained from clay, sodium silicate and wood particles or fiber could be one of the solutions. Geopolymers are inorganic polymers that are formed by the polymerization reaction of silico-aluminate and silico-oxide. In this case, the geopolymer is formed from clay, which is mined in Latvia (silico-aluminate) and water glass (silico-oxide). The wood-geopolymer was made by mixing geopolymer with softwood particles. The aim of the research was to develop a wood-geopolymer composite material and to evaluate its optimal composition and properties. The study defined the impact of the compound on the mechanical and physical properties (bending strength, compressive strength, modulus of elasticity, swelling and thermal conductivity) of the wood-geopolymer composite. The current paper presents mechanical properties of different composition and treatment methods of wood-geopolymer. As a part of the research the geopolymer and wood geopolymer thermal conductivity was compared. The results have shown that there is a correlation between the wood-geopolymer density and the thermal conductivity. The same correlation was observed between the wood-geopolymer density and the mechanical strength.

Abstract. Wood is renewable stock that is used for shield, heating and defence since the times men emerged. Wood product dimensional alterations are a serious drawback in the wood practical applications. These alterations are caused by atmospheric moisture absorbance into wood and water interaction with hemicelluloses and cellulose amorphous part hydroxyl groups to entail wood swelling or shrinking in the case of wood drying that leads to wood products cracking and properties loss. It is assumed that the accessible to water hydroxyl group's hydrogen atom substitution with more voluminous and less polar organic radical arouse wood permanent swelling or hydroxyl group shielding. Modified wood has less water absorption and diminished water equilibrium content (EMC) that is considered as the main reason of biological resistance improvement. Wood furfurylation with furfuryl alcohol (FA) catalysed with maleic anhydride (MA) is one of the wood modification approaches. Wood dimensional stability and biological resistance to decay increase by modification with furfuryl alcohol FA is assumed as a result of FA polymers grafting to cell wall polymers. Sufficient amount of FA must be infused into wood cell walls, but FA diffusion into the wood cell wall might be hampered by formation of more voluminous π-complex between MA and FA that favour useless polymerisation in wood voids and increased FA and MA consumption. The objective of the given research was to attain maximal modification of the wood cell wall by saturation with FA and subsequent its polymerization by catalysis with formic acid vapour. Assessment of furfurylated and reference wood specimens durability in hot water -freezing -drying treatment was tested by the cyclic hydrothermal treatment (CHT) test. Wood furfurylation decreased water absorption by 80 % and swelling by 40 % during CHT in comparison with untreated wood.