In this bachelor’s thesis, the influence of adhesive type and thermal modification of wood on adhesive penetration in bonded beech wood was investigated. The aim of the study was to determine the maximum and effective penetration, as well as the bondline thickness, using four different adhesives (MUF, 1K-PUR, 1K-PUR+P, and EPI) on thermally modified and unmodified beech wood. Microscopic specimens were prepared from bonded samples and analysed using light microscopy combined with image analysis. The results showed that the type of adhesive significantly affects penetration. Polyurethane adhesives (1K-PUR and 1K-PUR+P) achieved the highest and most consistent maximum penetration, while the EPI adhesive exhibited the lowest penetration and the greatest bondline thickness. The MUF adhesive showed high maximum penetration in unmodified beech wood, whereas its effectiveness was reduced in thermally modified wood. The effect of thermal modification on penetration varied depending on the adhesive type. In all cases, penetration was greater in earlywood than in latewood due to differences in wood structure. The results confirm that adhesive penetration is strongly influenced by adhesive type, while the influence of wood thermal modification is not uniform. The penetration of the adhesive was sufficient in all cases to ensure adequate shear strength of the bonded joints. We also found that the use of a primer influences the penetration of the 1K-PUR adhesive, and that the resistance of bonded joints to delamination depends on the type of adhesive and the use of a primer. The findings contribute to a better understanding of bonding in beech wood and support the selection of suitable adhesives according to wood properties.
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