The chemical composition of extractives in the sapwood (SW), heartwood (HW), knotwood (KW), and branchwood (BW of silver fir (Abies alba Mill.) was analyzed, and their antifungal and antioxidant properties were studied. In addition, the variability of extractives content in a centripetal direction, i.e., from the periphery of the stem towards the pith, was investigated. The extracts were analyzed chemically with gravimetry, spectrophotometry, and chromatography. The antifungal and antioxidative properties of the extracts were evaluated by the agar well diffusion method and the diphenyl picrylhydrazyl radical scavenging method. Average amounts of hydrophilic extractives were higher in KW (up to 210.4 mg/g) and BW (148.6 mg/g) than in HW (34.1 mg/g) and SW (14.8 mg/g). Extractives identified included lignans (isolariciresinol, lariciresinol, secoisolariciresinol, pinoresinol, matairesinol) phenolic acids (homovanillic acid, coumaric acid, ferulic acid), and flavonoids epicatechin, taxifolin, quercetin). Secoisolariciresinol was confirmed to be the predominant compound in the KW (29.8 mg/g) and BW (37.6 mg/g) extracts. The largest amount of phenolic compounds was extracted from parts of knots (281.7 mg/g) embedded in the sapwood and from parts of branches (258.9 mg/g) adjacent to the stem. HW contained more lignans in its older sections. Hydrophilic extracts from knots and branches inhibited the growth of wood-decaying fungi and molds. KW and BW extracts were better free radical scavengers than HW extracts. The results of the biological activity tests suggest that the protective function of phenolic extracts in silver fir wood can also be explained by their antioxidative properties. The results of this study describe BW as a potential source of phenolic extractives in silver fir.

Wood is one of the most important building materials. During the service life of wood and derived materials, various degradation factors affect performance. To assess how weathering influenced the material resistance and moisture dynamics of wood, 11 different materials were exposed to natural weathering for 9, 18 and 27 months or artificial accelerated weathering. Afterwards, the moisture performance of wood was determined in line with the Meyer-Veltrup procedure. Weathered samples were also exposed to the brown-rot fungus Gloeophyllum trabeum for 16 weeks. Respective materials were classified into durability classes according to EN 350, and relative resistance dose (D rd rel ) was calculated. Weathering resulted in leaching of biologically active extractives, changed surface morphology and increased permeability. All these changes were reflected in decreased relative resistance dose for all tested materials. The largest deceases were determined for thermally modified wood, Scots pine, European larch and sweet chestnut heartwood.

Wood in outdoor applications is subject to various decomposition factors. Wood degradation can be prevented by construction details, biocide protection of wood, wood modification or selection of naturally durable species. Unfortunately, most species in Europe do not have naturally durable wood. Imported tree species represent a new pool from which we can draw wood species with better natural durability and better resilience towards climate change. The performance of wood when used outdoors depends on the biologically active compounds (extractives) and the water exclusion efficacy. Considering decay, presence of biologically active compounds and water exclusion efficacy, we can estimate the density, modulus of elasticity, extractive content and resistance dose, which reflects the material properties of wood. Recently, the most commonly used model for this purpose is Meyer-Veltrup. Literature data indicate that the durability of the wood from native and new sites is not always comparable, so it is necessary to determine the resistance of non-native wood species from new sites. This paper presents original data on the wood’s overall durability from American Douglas fir (Pseudotsuga menziesii) grown in Slovenia. Experimental data show that the mature heartwood of Douglas fir is more durable than the wood of European larch (Larix decidua). Durability can be attributed to good water exclusion efficacy and inherent durability. Inherent durability is primarily the result of the high content of extractives. Based on the results, it can be concluded that American Douglas fir grown in Central Europe has a high potential for outdoor use.

This study aimed to evaluate the impact of thermal modification on the physical and mechanical properties of three different wood species from Bosnia and Herzegovina, namely beech wood (Fagus sylvatica L.), linden wood (Tilia cordata), and silver fir wood (Abies alba). The samples underwent thermal modification at five different temperatures (170 °C, 180 °C, 195 °C, 210 °C, and 220 °C) for varying durations (ranging from 78 to 276 min). After treatment, they were exposed to outdoor conditions for twelve months. The study examined the four-point bending strength, tensile force, color change, and surface quality of the modified and unmodified samples. The results showed that outdoor exposure negatively impacted the mechanical properties of the unmodified samples, especially in the linden wood which was 41% and the beech wood which was 42%. Additionally, outdoor exposure caused significant surface cracks in the thermally modified linden and beech wood. The study also found prominent color changes in the modified and unmodified samples during twelve months of exposure. The roughness of the samples was determined with a confocal laser scanning microscope, which showed that the roughness increased on both the axial and the longitudinal surfaces after weathering. The highest roughness for the fir wood was determined to be 15.6 µm. Overall, this study demonstrates the importance of wood modification and its impact on the use-value of wood products.

Wood is one of the most important building materials. Thermally modified wood is entering the market and replacing wood preservatives and tropical wood species in some applications. Thermally modified wood is exposed to weathering similarly as other wood-based building materials. It has been reported that if thermally modified wood is exposed to weathering, its moisture performance might decrease fairly fast. Moisture performance reflects the material’s ability to remain dry and dry out fast when wet. The aim of this study was to determine whether this phenomenon is associated with crack formation or roughness. Norway spruce, thermally modified spruce, wax-treated thermally modified spruce, and European larch heartwood samples were exposed to artificial accelerated weathering and natural weathering for 9, 18, and 27 months. Samples were subsequently isolated, and their roughness was determined with a confocal laser scanning microscope on axial and longitudinal surfaces at 10× and 50× magnification. After weathering, roughness increased on both axial and longitudinal surfaces. This was evident from the profile 2D measurements (Ra) and surface 3D measurements (Sa). The effect of natural weathering on roughness was higher than artificial accelerated weathering, presumably due to synergistic effects of abiotic and biotic factors. This may be associated with Wenzel’s theory on the influence of roughness on the contact angles of water on the surface; namely, increased roughness will decrease the contact angle on hydrophilic surfaces.