With increasing competition for wood resources, the importance of using small-diameter timber, which consists predominantly of juvenile wood (JW), is growing. The manufacturing of glued products is one way to make rational use of small-diameter wood assortments. However, the properties of JW differ considerably from those of mature wood (MW) and can affect product performance. Radial profile analyses of anatomical structural elements were performed, and based on the fibre length results, the cambial ages of 17 years for silver birch (B. pendula Roth.) and 23 years for Scots pine (P. sylvestris L.) were determined to distinguish between JW and MW. The results showed that the JW of both species had a lower density and higher transverse swelling anisotropy. Lamellae of JW and MW were glued into beams using two one-component polyurethane adhesives and different assembly regimes. The glued beams were then used to prepare samples for delamination tests, performed according to the EN 302-2 standard method for Type I adhesive. Higher resistance to delamination was observed for the JW of both wood species, implying an advantage of laminated products from JW regarding bond-line stability under varying moisture conditions. For pine JW, shorter open assembly times resulted in significantly less delamination.

Most microplastics (MPs) are generated as a result of photodegradation during the life of plastic products and after the end-of-life as mismanaged waste. At present, it is impossible to avoid plastic-based materials altogether because of their unique properties, versatility, and price. An option is to set limits on how much MPs these materials can release over their lifetime, which would not only reduce MPs pollution, but also improve product quality. However, there is a lack of reliable methodologies for assessing the generation of MPs from these products during use or when they are left as unmanaged waste. The objective of this study was to develop a novel method to assess (collect and quantify) MPs formation from plastic-based materials during weathering. The developed process design is based on a well-established accelerated weathering tester that has been modified by incorporation of a sieve system and water recirculation. The case study is carried out on a recycled polypropylene (rPP) and wood plastic composite (WPC) made from wood particles and the same rPP. Despite the lower plastic content, WPC released significantly more MPs (up to 9.4 g/m2) than the rPP (up to 0.3 g/m2) in the same weathering conditions and duration. Examination of the degraded surfaces revealed that the wood particles facilitated the release of MPs most likely due to moisture fluctuations causing wood swelling induced internal stresses. The collected MPs were mainly below 500 μm and their properties were different comparing to MPs made by cryogenic milling. PY-GC-MS did not detect MPs smaller than 20 μm that could pass through the smallest sieve and end up in the effluent. The reproducibility of the measured MPs release using the process design was very good during the tested weathering period, with variations of less than 7

Accumulation of microplastics (MPs) and the potential risks that they bring causes justified concerns. Plastic-based materials are widely used in various applications. The materials are presumed to be inert and safe. However, the formation of potential MPs has introduced some doubts. Wood-plastic composites (WPCs) are among the materials suggested to be environmentally friendly. However, they may release MPs due to weathering as WPCs are widely used in outdoor applications. The objective of the study was to collect, quantify, and compare MPs' release during artificial weathering from WPCs and evaluate the effect of composition. In the study, four experimental and four commercial WPCs were analysed. Recycled polypropylene (rPP) was used as a reference. The results showed that WPCs can be a source of MPs, and that their composition significantly affects their formation. Wood particles in WPCs facilitate erosion, causing MPs to be released at a rate of 5.6 g/m2, whereas the release from rPP was 0.1 g/m2 after one month of accelerated weathering. For commercial products, MPs formation depends on the product type, with no MPs released for WPC decking but a significant release of up to 58.9 g/m2 for the flowerpot after 2 months of accelerated weathering.

The changes in the interaction of wood with liquid water caused by thermal modification (TM), which is a less studied effect of TM, was investigated. Birch (Betula spp.) wood and pine (Pinus sylvestris L.) sapwood were thermally modified and their properties compared with unmodified counterparts. The wettability was assessed by sessile drop contact angle measurements. The water permeability was measured by capillary absorption tests through the radial and tangential surfaces and indirectly evaluated from water distribution in cross-section of boards exposed on weathering rack to an intensive rain episode. The liability to rapid drying was evaluated by comparing the amount of the retained water in impregnated specimens after definite time period of drying in controlled environment. For both woods, TM caused not only a reduction in wettability, but also a reduction in drying rate, which could result in prolonged periods of high wetness during service. Lower liquid water permeability was observed for TM birch through both lateral surfaces which was supported by the results of water distribution in boards exposed to rain. Significant increase in water absorption was detected for TM pine through tangential surface in both tests used for evaluating water permeability of wood.

Microwave technology finds application in wood processing, particularly for improving drying and impregnation. A less explored application is the treatment of wood to reduce resin exudation. The aim of this research is to examine how microwave treatment of spruce wood specimens can change the physico-chemical properties of resin to retain it in the wood. The results demonstrated that microwave treatment can increase the glass transition temperature more rapidly than conventional heat treatment. Both the amount of volatile content and chemical composition of resin are affected. Further optimization of treatment parameters, such as duration and power density, could enhance the efficiency of this method.

Wood plastic composites (WPCs) have recently gained attention as alternatives to traditional wood materials for outdoor use, thanks to their enhanced moisture resistance and durability, which extends their service life. Discolouration as well as surface erosion has been observed during weathering for both WPCs with untreated and heat-treated wood. However, aspects such as changes in surface hydrophobicity, chemistry, and erosion in terms of microplastic formation have received less attention; this research aimed to evaluate these factors during natural weathering. Four types of WPC samples, consisting of 50% wood particles (untreated and heat-treated) and 50% polypropylene, were naturally weathered in Latvia for two years. The samples measured 240 mm × 240 mm × 5 mm. Results showed rapid colour changes, microcracks, and exposed wood particles, suggesting microplastic formation. ATR-FTIR analysis showed increased absorption at 1715 cm⁻¹ (carbonyl groups) and at 3410 cm−1 and 3460 cm−1, typical of wood, indicating chemical changes on the surface. These changes influenced surface hydrophobicity, roughness, and water penetration. In a relatively short exposure time, WPCs without proper additives undergo significant changes in their aesthetic and physical properties, leading to surface erosion and potential microplastic formation. This could challenge the perception of WPCs as environmentally friendly materials.

Although linseed oil (LO) has been used in wood protection for centuries, research continues to develop new and more effective formulations and treatment approaches. In the future, growing interest in LO use could be expected due to its cost and environmental friendliness. This review summarizes recent research (from 2000 onwards) on the use of LO in wood protection, published in peer-reviewed scientific journals and included in the online publication databases Scopus or Web of Science. The studies cover surface and impregnation treatments of various wood substrates using different LO formulations, including chemically modified LO and the use of LO as a base for the development of biofinish and as a medium for thermal modification of wood, as well as research into the mechanisms behind the changes in wood properties due to treatment methods and interaction with LO formulations. Although the improvement of wood hydrophobicity and biodurability dominates, other aspects such as weathering and color stability, adhesion, and environmental safety are included in these studies. In general, almost all of the studies show a greater or lesser potency of the proposed approaches to provide benefits in wood protection; however, the level of innovation and practical feasibility varies.

A major function of resin in trees is to provide defense against external attacks by releasing the resin flow in the attacked or damaged area. Nonetheless, leakage of resin on the surface can have negative aesthetic and economic impacts on wood materials. The aim of this study was to investigate how heat treatment affects the physico-chemical properties of the resin of Pinus sylvestris L. to hinder exudation on wood surfaces during service. To reduce the fluidity of the resin, it is necessary to remove the volatile fraction of resin, and several studies have been carried out in this direction, providing useful information about this process. The results from thermal analyses (DSC, TGA) confirmed that heat treatment at mild temperatures, 80 °C, 90 °C and 100 °C had a positive effect on increasing the glass transition temperature Tg and that the Tg and the residual volatile content were strongly correlated. FTIR spectroscopy, before and after heat treatment, did not reveal major changes in chemical structure, while UHPLC-DAD-MS analysis revealed significant differences in the ratios of compounds, which are the result of possible chemical reactions, such as dehydrogenation, oxidation and isomerization.

Plastics when exposed to UV radiation start to degrade via photooxidative aging including free radical formation, oxidation, chain scission and/or crosslinking reactions. These chemical changes can cause loss in mechanical strength, surface embrittlement, and eventually surface erosion. The eroded particles are microplastics (MPs), which have been identified as a potentially serious threat to the environment and its inhabitants. In general, photodegradation of virgin plastics has been studied extensively, but there is not much literature on the degradation of recycled plastics. The goal of the study was to investigate the changes caused by photodegradation in recycled plastics and assess the potential risks of MPs formation. And eventually, knowing the chemical and physical transformations occurring on the surface understand the mechanism behind surface microcracking, which is the first step of MPs formation. Pellets of five industrially recycled plastics (low-density polyethylene (rLDPE), linear low-density polyethylene (rLLDPE), high-density polyethylene (rHDPE), and two polypropylenes (rPP)) from different waste sources were analysed. UV irradiation was performed in an accelerated weathering chamber for milled (< 400 m) plastic powder to ensure homogeneous changes throughout the sample. The properties were investigated by ATR-FTIR, HT-SEC, XPS and DSC. Formation of microcracks was studied on plastic pellets by SEM. The results showed that the degradation significantly differed between the recycled plastics, and the waste source was more important than the plastic type. rLDPE and one of the rPP samples showed a significant increase in carbonyl index as well as decrease in molar mass during the first 500 h of UV exposure. The other rPP and rHDPE samples showed first considerable signs of degradation only after 1000 h of UV exposure. Minor changes were observed for the rLLDPE sample during the whole test. The SEM revealed microcracking on the surface of all samples, which also had noticeable degradation identified by other methods. These recycled plastics can be considered the ones with the highest potential of MPs formation. From the chemical and physical transformations identified on the surface, the mechanism leading to microcracking, which is the first step in the formation of MPs, is proposed.

During outdoor use, glued wood products are exposed to rather harsh conditions, which involve moisture and temperature fluctuations, attacks by microorganism, UV radiation etc. For some risks, the effect on glued wood products are already known, however less investigated are the risks concerning UV radiation. It has been established that weathering affects only the surface of the wood without influencing the mechanical properties. However, polyurethanes are known to undergo more significant degradation with structural changes, strength reduction and surface erosion. The objective of the study was to investigate whether photodegradation caused by UV irradiation can impair the bond quality of glued wood products bonded with one-component polyurethane adhesives. In the study, considerable attention was attributed to the investigation of the chemical changes by FTIR methods focusing on the differences as well as normalisation possibilities of the spectra. The results showed that UV significantly degraded the chemical structure and mechanical properties of the one-component polyurethane films as well as introduced a number of microcracks in the gluelines. Despite that, glued wood products after UV irradiation showed only minor or none at all reduction in the bond quality characterised by wood failure percentage. The only identified aspect that had some effect was the thickness of glueline, which should be kept at minimum. The chemical analysis revealed two stable bands, which could be used for normalisation of polyurethanes FTIR spectra during weathering investigations. The corresponding bands are attributed to the aromatic and isocyanurate ring structures.

The aim of the present research was to obtain a wood material with improved service properties, by combining two industrially used processes - namely a thermo-hydro treatment (THT) and an impregnation (Imp) with a commercial biocide - through the application of both a lower preservative retention and lower modification temperature, respectively. In the study, specimens from Scots pine (Pinus sylvestris L.) sapwood were used. The properties of the wood obtained with the sequence Imp-THT were extensively studied. Impregnation was performed in a pilot scale autoclave by a vacuum-pressure-vacuum process using a copper-azole type wood preservative, whilst THT was carried out in a WTT laboratory pilot device in a water vapour medium under elevated pressure. To improve physical properties while maintaining strength properties, the THT regime 160 degrees C/1 h was used. The properties (strength, swelling, water uptake, colour, biocide (Cu) fixation properties as well as bioresistance to rot fungus) of combined treated pine wood were compared with those of the wood obtained in the respective separate processes.

The wood photodegradation, including discolouration caused by exposure to UV and solar radiation, has been intensively studied, while the effect of artificial lighting on wood has been little investigated. In the present study, the effect of three types of artificial light sources (LED, incandescent, and fluorescent lamps) on the colour changes of wood was evaluated. LEDs with high (6500 K) and low (3000 K) correlated colour temperature were employed in the experiments. Wood colour was assessed by spectrophotometric measurements of reflectance spectra, which were converted into colour parameters of the CIELAB colour system. The total discolouration as well as the changes in colour lightness, chroma (saturation), and hue were evaluated for two hardwood species (birch, oak) and two softwood species (spruce, pine - sapwood and heartwood) depending on the irradiation dose. Visually perceivable changes in colour of all woods were observed already at relatively low irradiation doses, indicating a high sensitivity of the wood to radiation emitted by artificial light sources. Comparing the softwoods and hardwoods included in the study, the latter proved to be more resistant to discolouration caused by the tested light sources. Overall, greater colour changes in long-term exposure were caused by incandescent and fluorescent lamps, although more rapid discolouration developed in the early stage irradiation with LEDs. A substantial difference between the effect of the tested LEDs was only observed in the initial phase, when the cool LED (6500 K) caused more discolouration. The changes in the colour parameters were complex and varying in directions, including a reversal with the accumulation of the irradiation dose, indicating that the exposure to artificial light sources resulted in continuous alteration in the shade of the wood colour.

Modification can significantly improve the service life of wood products, however, from the environmental perspective, the process has its drawbacks causing excessive influence in some specific impact categories. To reduce the impact that is characteristic of each individual modification process and to gain benefits due to synergy, the potential of using a combined treatment (copper azole impregnation + thermal modification) is evaluated. The results show that a combined treatment can provide enhanced environmental performance over each individual modification.

Effective prevention of mould growth indoors is still an important topic considering that mould growth is frequently observed in buildings, it causes serious health hazards and can irreversibly damage infected objects. Several studies have been conducted and mould growth models developed. Despite that, some potentially important aspects such as water damage and spore contamination have received only little attention. The objective of the present study was to investigate the effect of the initial moisture content of wood and spore contamination on mould development indoors. The mould tests were performed in constant temperature (10, 20 and 30 °C) and relative humidity (91% and 97%) conditions. The results show that wetting of wood specimens prior to the test significantly accelerates mould growth at a temperature of 10 °C. For the other temperatures, the effect was insignificant. Similar results were obtained for the test involving dry (conditioned at RH 50%) and conditioned specimens (RH 91% or RH 97%). The results regarding initial spore contamination show that significantly longer periods are required for mould to develop without spore contamination at 10 °C and 20 °C, while at 30 °C the effect is relatively small.

The aim of this study was to characterize and evaluate the performance of two wood species, pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) used for wooden furniture in outdoor coated with a water based ecological paint and subjected to artificial weathering. Another task of this research was to investigate the potential of the application of paint using dipping method in alternative to traditional brush or spraying coating application methods, since, if wood samples are grouped in stacks, the processing time can be reduced, compared to samples painted singularly. From the analysis of the dipping parameters, such as time and paint concentrations, more practical and specific knowledge was obtained regarding this painting method.From the characterization of the painted samples and from the measurements of color changes during artificial weathering it was observed that coated wood surfaces have similar optical properties also in case of different dipping times, although the type of wood could affect the performance of final product during artificial weathering test as in case of spruce wood samples, specifically those prepared with the shortest dipping time: for these samples a lower resistance to weathering and higher color changes were observed.

Mostly the effect of solar and UV radiation on wood photodegradation has been researched. This paper discusses the effect of artificial light sources, which differ in the spectral composition of the emitted light, on the photodegradation of wood. Ash, birch, aspen, pine sapwood and heartwood, and spruce wood were exposed to two LEDs of different colour temperature (3000 and 6500 K), incandescent and fluorescent lamps. Changes in colour (ΔE) and colour parameters L*, a*, b* (CIELAB colour space) as well as reflectance and FTIR spectra were analysed to evaluate the photodegradation of wood depending on the light source. According to the results of changes in the chromaticity system of woods, the tested light sources can be divided into two groups: one group with similar results includes the two tested LEDs while the other group includes incandescent and fluorescent lamps. Lower irradiation dose was needed for the LEDs to impart visually perceptible discolouration, whereas colour changes of greater magnitude were caused by the incandescent and fluorescent lamps at higher irradiation doses. It was detected that depending on the light source, there are differences in the changes in the chromophores between hardwoods and softwoods, with more total discolouration observed for softwoods. The transformations in the chemical structure, which was analysed by FTIR, considerably differed for all tested light sources with a general trend of the greatest effect of the fluorescent lamps followed by the incandescent lamps and LEDs.

As a vast majority of glued wood products are intended for outdoor use or for building construction, impregnation with different agents is important for ensuring proper performance. It has been shown that the impregnation prior to gluing has several disadvantages, therefore the possibility of carrying out impregnation after gluing is analysed in the present research. Impregnation efficiency as well as the effect on the bond quality is evaluated for the one-component polyurethane glued wood specimens. The results showed that the impregnation with Cu preservative after gluing did not affect the shear strength of the glued wood specimens, but did significantly restrict Cu preservative penetration due to the adhesive bondlines. Considering the results, the possibility of improving the impregnation efficiency was also investigated. By using specific adhesive application designs, which cover the bondline only partially, it was possible to improve the impregnation efficiency. However, the Cu distribution was inhomogeneous and the improvement was noticeable only up to the second bondline. The partial adhesive application design also affected the bond strength of glued wood specimens, which resulted in a decrease both in dry and wet state. However, the reduction was not so sever as to cause delamination during three consecutive wetting and drying cycles.

Considering interior applications, sunlight, both direct through open window and through window glass, and artificial lighting are the main sources of radiation possessing sufficient energy to trigger photodegradation processes in wood. LED lamps, which emit mostly visible light, are becoming the dominant artificial light source in various interiors. In the present study, photodegradation of thermally modified (TM) and unmodified (UM) ash (Fraxinus excelsior), aspen (Populus tremula), and pine (Pinus sylvestris) due to exposure to UV radiation and LED lamps was evaluated and compared by analysing wood discolouration (CIELAB colour space), changes in reflectance and FTIR spectra, and formation of water-soluble components. The results show that, apart from UV radiation, LED lamps may cause considerable photodegradation of both TM and UM wood resulting in visually perceptible colour change, alteration in chemical structure and formation of water-soluble components. Improved photo-stability was observed for TM wood exposed to UV radiation, while even more changes in FTIR spectra were detected for TM than UM wood in the experiment with LED lamps. Comparing TM and UM wood, the changes due to photodegradation were quite similar for TM wood of all species while significant differences were observed in the case of UM wood.

When using binders in coatings, whose film formation process relays on the oxygen uptake to start the cross-linking reaction, the use of special metal salts, so called driers, can catalyze the process, accelerating the curing of the film and reducing the waiting time between the applications of the next layers of paint. In this work, three primary driers, based on cobalt, iron and manganese are compared, to determine which one is more efficient in drying of alkyd and boiled linseed oil based coating. The study has been done using FTIR spectroscopy to investigate the rate of drying for each drier. The obtained results confirm that using the cobalt drier, the film formation is faster than with the other two alternative driers.

Thermal modification of wood has gained its niche in the production of materials that are mainly used for outdoor applications, where the stability of aesthetic appearances is very important. In the present research, spectral sensitivity to discoloration of thermally modified (TM) aspen wood was assessed and, based on these results, the possibility to delay discoloration due to weathering by non-film forming coating containing transparent iron oxides in the formulation was studied. The effect of including organic light stabilizers (UVA and HALS) in coatings as well as pretreatment with lignin stabilizer (HALS) was evaluated. Artificial and outdoor weathering was used for testing the efficiency of different coating formulations on TM wood discoloration. For color measurements and discoloration assessment, the CIELAB color model was used. Significant differences between the spectral sensitivity of unmodified and TM wood was observed by implying that different strategies could be effective for their photostabilization. From the studied concepts, the inclusion of the transparent red iron oxide into the base formulation of the non-film forming coating was found to be the most effective approach for enhancing TM wood photostability against discoloration due to weathering.