In the thesis the effect of the temperature used for the thermal modification of wood on the curing of adhesive and on bond performance was investigated. Spruce wood, heat treated at temperatures of 150, 170, 190, 210 and 230 °C, and four different types of adhesives were used: one adhesive for hot pressing, phenol-formaldehyde (PF), and three adhesives for cold setting: polyvinyl acetate (PVAc), polyurethane (PU) and melamine-urea-formaldehyde (MUF). The curing of the adhesives was monitored by measuring their rheological properties with a rheometer. Wooden discs, prepared from wood that had been subjected to different degrees of thermal modification and having different moisture contents, were used, instead of standard aluminium discs. The oscillation test with the "multiwave" measurement technique was used. It was found that the PVAc, PU and MUF adhesives cured more slowly depending on the degree of thermal modification, but the reasons for the retardation of curing were different. PVAc and MUF curing was slower because of the lower degree of adsorption of water in the modified wood, whereas the PU cured slower because of the lower moisture content of the modified wood. Thermal modification had a significant influence on the shear strength of the adhesive bonds. The shear strength of the PF adhesive bonds decreased with an increasing temperature of thermal modification, because of the lower degree of adhesive cure and the lower strength of the modified wood. After soaking in water, the shear strength of the PF joints reduced by half, but the more strongly modified specimens retained a greater proportion of the initial shear strength. The average effective penetration of the PF adhesive slightly increased with the degree of thermal modification, but these differences were not statistically significant. Thermal modification reduced surface wetting with water, but improved wetting with the PF adhesive. The shear strength and wood failure of the PVAc adhesive bond (of dry specimens and after soaking in water) decreased with a higher degree of thermal modification. The shear strength of the PU adhesive bonds decreased with degree of thermal modification of the wood, but less than in the case of the PVAc adhesive bonds. After soaking in water the shear strength and wood failure of the PU adhesive bonds increased with the degree of thermal modification. The reason was probably water intake and swelling of the wood. The water intake after 24 h of soaking decreased with the degree of thermal modification of the wood. The shear strength of the MUF adhesive bonds decreased with the degree of thermal modification slightly more than that of the PU adhesive bonds, but much less than that of the PVAc adhesive bonds. After soaking in water the shear strength of the MUF adhesive bonds dropped to half the initial dry strength, and was observed to be independent of the degree of thermal modification. The average wood failure of the wood remained at 100 %. In the case of all the adhesives bonds is was noticeable that with a higher degree of thermal modification the deformation was smaller when failure of the bond occurred, and that the failure was more brittle. The total delamination of the PVAc adhesive bonds was quite high, and increased with the degree of thermal modification of the wood. Delamination of the PU and MUF adhesive bonds was not pronounced.
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