Veikko Möttönen

This article reports the variations in volatile organic compound (VOC) emission rates from Scots pine wood under varying relative humidity (RH) conditions. The experiment encompassed both heartwood and sapwood, involving recently sawn (“new”) wood, and aged (“old”) wood that had been stored indoors for 15 years. Individual specimens were placed in climate chambers, wherein specific RH levels were maintained in the following sequence: 20%, 40%, 60%, 80%, 60%, 40%, and 20%, 1 month each. VOC samples were systematically collected at the end of each RH period and analyzed using TD-GC-MS system. The results demonstrate a direct relationship between RH levels and VOC emission rates in all specimen categories. Old wood indicated significantly lower emission rates compared to new wood, with distinct differences in emitted compound composition. As the experiment progressed, the initial differences between old and new specimens diminished, reaching minimum difference by the last measurement. Aldehydes were among the two most prevalent compound groups in all sample types. Terpenes were the most abundantly emitted group during the first VOC collection. However, their emissions subsequently declined, followed by an increase in all main chemical groups at 80% RH. Additionally, more polar compounds were emitted as RH increased. This study contributes to the discussion regarding the suitability of standard emission tests performed in fixed 50 ± 5% RH for hygroscopic materials. More attention should be given to the influence of RH on VOC emissions to ensure a comprehensive understanding of wood material’s emission behavior.

Natural weathering gradually turns wood light grey over years, driven by exposure to sunlight, precipitation, and biological agents. Nontoxic chemicals have been used to accelerate artificial weathering-induced colour changes in wood. This study aimed to evaluate the effectiveness and underlying mechanisms of various surface treatment chemicals and a commercial silicon-based product in accelerating UV-induced colour changes in birch and aspen under artificial weathering conditions. Weathering was conducted by using an artificial weathering testing instrument with or without spraying the samples with water. Colour changes were measured with a portable spectrophotometer. Hyperspectral imaging data were included to visualise spatial variations of colour in wood samples. The use of water was a significant factor in determining the colour change in wood. Mostly photodegraded lignin constituents leached out of the wood with water spraying but remained if it was not used. The treatment chemicals caused distinct colour changes: Iron (II) sulphate caused dark grey staining, citric acid a unique red colour, sodium hydroxide darkening and brown hue, and hydrogen peroxide the most uniform colour. Commercial silicon-based product caused either little or no noticeable colour change over control samples. The greatest potential for colour change occurred during the first hours of artificial weathering. Spatial data of hyperspectral images allowed for more accurate estimation of variability over spectrophotometer data, and use of hyperspectral imaging in further research is therefore suggested.

Due to climate change, the risk of forest fires has increased in Europe, resulting in challenges in the allocation of salvaged wood. We studied the raw material potential for wood products of Norway spruce and Scots pine sawn log trees that remained standing after a large forest fire in Kalajoki, Finland, in July 2021. Eight burned trees, with four reference trees per species, were sampled as standard specimens, and measurements were analyzed with linear mixed models. The effects of fire on the modulus of elasticity and rupture, Brinell hardness, moisture gradient, and color were measured on clear wood specimens of sapwood and heartwood. The wood density, level of fire damage, and height location of a tree were used as additional predictors. The results show some changes in the sapwood material. Spruce wood underwent stronger changes after the fire than pine wood, probably due to spruce wood having a thinner bark and a longer crown. The moisture content decreased in spruce, and the color darkened in both spruce and pine. Changes in the mechanical properties were mostly negligible, but a small increase in the Brinell hardness in spruce and a small decrease in the modulus of rupture in pine were observed. Fresh salvaged wood can be a suitable material for middle-quality and lower-quality wood products. The spread of char and soot into wood and wood processing machinery still limits its usage, especially for spruce.

The aim of the study was to quantify total extractive contents and lipophilic compounds, stilbenes, and lignans in Scots pine stem wood, stem bark, branch biomass, and sawmill residues in four climatic regions of Finland to evaluate the most optimal sources of extractives for bio-based chemical biorefining and bioenergy products. Data were derived from 78 chip samples from the before-mentioned raw materials, the samples being pooled by tree height position from the sample trees of 42 experimental forest stands, and sawdust lots from 10 log stands. Accelerated solvent extraction (ASE) was employed to determine total extractive contents, followed by gas chromatography with flame ionization detection (GC–FID) to quantify extractive groups and gas chromatography-mass spectrometry (GC–MS) to analyse individual extractive compounds. Resin acids and triglycerides followed by fatty acids were the dominant extractive groups. Resin acids were most abundant in stem wood from final fellings and in sawdust, fatty acids in bark and branch biomass, and triglycerides also in stem wood from thinnings and the top parts of trees. Of the minor extractive groups, stilbenes were the most abundant in stem wood from final fellings and in sawdust, and steryl esters, sterols, and lignans in bark and branch biomass, the two last groups almost missing from other biomass components. Regional differences in the contents of extractive groups were generally small, 1.0−1.5 percentage points at the maximum, but factor analysis distinguished northern and southern regions into their own groups. Bark was the most potential source of fatty acids and sterols in southern Finland, and triglycerides and steryl esters in northern Finland. In stem wood, steryl esters, triglycerides, and lignans decreased and stilbenes increased from north to south. Certain fatty acids and resin acids were more frequent in the north. The results highlighted the importance of focused procurement and efficient sorting of raw materials, purity, unique properties, and feasible isolation techniques for competitive ability as well as large raw material volumes or well-defined value-added products.

The physical, mechanical, and chemical properties of both stem wood and knot wood were investigated from two subfossil Scots pine (Pinus sylvestris L.) trunks retrieved from a lake in Finnish Lapland, dated to 404–486 CE and to 1318–1444 CE. Both the stem wood and the knot wood of the younger trunk had higher moisture content, lower density, and lower strength properties in comparison to the older trunk. The ash content of the stem wood of the younger trunk was lower, but the ash content of the knot wood was higher than that of the older trunk. Due to the degradation that occurred over time, all the values of physical and mechanical properties were lower compared to typical values of recently grown Scots pine wood. The chemical composition of both stem wood samples was close to the composition of the recently grown wood, and the only exception was the small decrease of the cellulose and hemicellulose in the subfossil samples. The bulk extractives were well-preserved, but terpenes and fatty acids underwent transformation, resulting in more stable compounds. The SWOT analysis (strengths, weaknesses, opportunities, and threats) showed pros and cons for the productization of subfossil wood, with the branding value of an ancient material being the potential enabler in developing commercial niche uses.

Bark extracts are sustainable sources of biopolymers and have great potential to replace fossil-based polymers in wood coating applications. The present study investigated the applicability of suberin fatty acids hydrolysate (SFA) extracted from the outer bark of silver birch (Betula pendula Roth.) for coating of aspen wood (Populus tremula L.). The SFA combined with maleic anhydride (MA) and octadecyltrichlorosilane (OTS) as a curing agent was prepared in ethanol and used in surface coating. The water contact angle, surface reflectance spectra, FTIR, and SEM-EDS were used to characterize the physical and chemical properties of the coated wood samples. Further, the long-term stability of the SFA coating was analyzed via artificial aging. The wood surface became hydrophobic, as the contact angle for the water droplet (WCA) was over ~120°, and was stable for all of the prepared combinations of SFA, MA, and OTS.

This study aimed to identify and quantify phenolic and resin acid extractive compounds in Scots pine stemwood and sawmill residues in four climatic regions of Finland to evaluate their most optimal sources for bio-based chemical biorefining and bioenergy products. The sample consisted of 140 trees from 28 stands, and sawdust lots from 11 log stands. NMR for the overall extractive analysis and HPLC for the quantitative estimation of phenolic and resin acid compounds were employed. Correlation analysis, multivariate factor analysis, principle component analysis and multiple linear regression modelling were applied for statistical analysis. HPLC identified 12 extractive compounds and NMR five more resin acids. Pinosylvin (PS), pinosylvin monomethyl ether (PSMME), and partly neolignans/lignans occurred in the largest concentrations. Wood type caused the most variation, heartwood having larger concentrations than sapwood (sawdust between them). Regional differences in the concentrations were smaller, but factor analysis distinguished the northern and the southern regions into their own groups. The results indicated higher concentrations of PS, PSMME, and vanillic acid in southern regions and those of, e.g., PSMME glycoside, lignan 2, and neolignan 1 in northern regions. The rather low concentrations of extractives in stemwood and sawdust imply value-added products, efficient sorting and/or large raw material volumes.

Mozambique’s large pool of tropical hardwoods is hampered by the prevalence of low-grade tree species along with a lack of cost-effective processing technologies to improve timber properties.Brachystegia spiciformisandJulbernadia globifloraare the most abundant tree species in terms of volume in the country, but with limited use due to their low timber quality. In this study, thermal modification at three different temperatures (215 °C; 230 °C; 245 °C) was applied for 2 h to the timber of both species, followed by measurement of a set of physical and mechanical wood properties. The results show that the originally light-coloured sapwood of both tree species darkened gradually as the intensity of thermal modification increased. Additionally, from untreated samples to the highest thermal treatment level, timber ofB. spiciformisincurred a maximum mass loss of 27%, while oven-dry density was reduced from 0.65 to 0.56 g/cm³and equilibrium moisture content (EMC) changed from 7 to 3%. Timber ofJ. globiflorahad a mass loss of 23% after the highest treatment level, an oven-dry density reduction of 0.81 to 0.74 g/cm³and an EMC decrease from 8 to 3%. The changes in mechanical properties from reference samples to the highest thermal treatment level were also significant. ForB. spiciformis, MOE decreased by 10.2%, MOR by 50.8%, compression strength parallel to the grain by 29.2% and Brinell hardness by 23.5%. Timber ofJ. globiflorafollowed the same trend with an MOE decrease by 6.9%, an MOR decrease by 53.2% and a decrease in compression strength parallel to the grain by 21.9%. All tested wood properties showed significant responses to thermal modification after the most intensive treatment level had been applied. Despite the degradation of mechanical properties in both species, an optimal combination of temperature and treatment time could be achieved. The recorded changes of the tested wood properties in both species could increase the range of applications; the new colour resembled that of highly sought-after tropical hardwoods.