This paper analyzes the usability of different dynamic moduli of elasticity and wood density for the prediction of mechanical properties -static modulus of elasticity and modulus of rupture -in samples with grain deflection from the longitudinal direction. Five tropical hardwoods (Afzelia bipindensis, Intsia bijuga, Millettia laurentii, Astronium graveolens and Microberlinia brazzavillensis) with different grain characteristics were used for this purpose. The fiber deflection was caused by the presence of interlocked grain or the working process. The three nondestructive techniques used in this study -longitudinal and flexural resonance method and ultrasound method -provided higher values of modulus of elasticity than the static bending test, but close correlation was observed between these variables. The weakest correlation was found for the ultrasound method which is probably caused by its measuring mechanism. The prediction of the modulus of rupture is less accurate when the dynamic modulus of elasticity is compared with the static modulus of elasticity; on the other hand, it was still good in comparison with the density model, which is inapplicable when grain deflection occurs in wood. In the wood of Zebrano where the interlocked grain was strongly developed, almost all of the correlation coefficients showed the lowest values and the prediction of modulus of rupture by nondestructive techniques was unsatisfactory.

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In recent years, subfossil oak has become increasingly popular, particularly in the manufacture of small wooden products. Due to the long period of its underground preservation, detailed knowledge of its properties is essential to properly use this material. In this study, subfossil oak samples dated to approximately 1000, 2000 and 3000 years BP and recent oak samples were chemically analyzed to determine the contents of extractives, the main wood components, and inorganic elements. The results were then evaluated in light of their natural durability. The mass loss of subfossil oak was 2–3 times lower than that of the recent sample, but the age of the subfossil oak itself had no influence on its durability. The long-term leaching process of water-soluble ellagitannins, together with their hydrolysis and bonding in ferric tannate complexes, were responsible for the decreased durability. The oldest subfossil oak had the lowest amount of phenolic compounds and the highest content of inorganic elements. Optical emission spectrometry proved an increase in inorganic elements 5–7 times higher than recent oak content, with the highest increase found for calcium and iron. Compared to recent oaks, subfossil oaks manifested decreased content of carbohydrates and correspondingly increased lignin content. Our results revealed that subfossil oak cannot be considered a suitable material for exterior use under aerobic conditions.

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The wood-water interactions of modified beech wood (Fagus sylvatica L.) were studied. Specimens were thermally modified at 180 (TM1), 200 (TM2) and 220 °C (TM3), acetylated (Acet), and melamine formaldehyde (MF) resin (Mel) modified. Afterwards, the water vapour characteristics, i.e. water vapour sorption isotherms, equilibrium moisture content (EMC), dimensional stability of specimens conditioned at 30, 65 and 90% RH and liquid water characteristics, i.e. water absorption, maximum moisture content (MC), leachability and swelling kinetics, were determined and the results compared with reference (Ref) specimens. From the results, it is evident that the scale of wood-water interactions was highly dependent on the thermal modification temperature and type of chemical modification. The water vapour isotherms of thermally modified wood decreased, whereas more severe treatment exhibited more distinct reduction. The EMC values of the Mel and TM1 specimens decreased only at high RH, whereas the most significant decrease, within the whole range of observation, was found in the Acet group. The maximum MC reduction was achieved by acetylation. As a consequence of swelling reduction, dimensional stability expressed as anti-swelling efficiency (ASE) was considerably improved. A relatively high initial linear-phase swelling rate was found for the Ref specimens, whereas modified wood exhibited comparatively slow and gradual swelling.

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