Thermo-hydro-mechanical (THM) densification is an effective method for improving the mechanical performance of low-density, fast-growing hardwoods such as poplar. This study examined the bending performance of THM-densified poplar wood at different compression ratios (CR = 0%, 50%, 60%, and 65%), with emphasis on the effects of ultrasonic pretreatment (US) and thermal modification posttreatment (TM), applied individually and in combination. A paired sampling design was used to reduce material variability, and modulus of rupture (MOR) and modulus of elasticity (MOE) were evaluated using linear mixed-effects models (LMM). Bending tests were performed in accordance with EN 310:1993. Increasing the compression ratio led to substantial increases in MOR and MOE; compared with non-densified specimens, MOR increased by approximately 240% and MOE by about 140% at CR = 65%, confirming densification as the dominant factor controlling bending performance. US did not affect non-densified wood but significantly enhanced MOR and MOE after densification, particularly at CR = 50%. In contrast, TM consistently reduced MOR and, to a lesser extent, MOE across all compression ratios. The results demonstrate that the bending performance of densified poplar wood is governed by both compression ratio and compression-dependent treatment effects.

Industrial beech timber steaming generates a process condensate that is typically treated as wastewater, despite its potential biological activity. This study explored the chemistry of beech steaming condensate (BSC) produced during an indirect industrial process and quantified its in-vitro effects on seed germination and early seedling growth in two model weeds, with maize as a crop reference. BSC was collected after two consecutive 12 h indirect-steaming cycles at 95 °C (25 mm beech timber). Chemical characterisation used UHPLC–QToF–MS (targeted identification/quantification of phenolics). Bioassays (0.25–4

This study explores the potential of using condensate generated during beech wood steaming (BSC) as an eco-friendly additive in urea-formaldehyde (UF) adhesives for wood-based panel (WBP) production. The research aimed to assess the hardening behavior of pure commercial UF resin and UF with added condensate (UF-BSC), investigating the potential catalytic effect of BSC on the hardening characteristics of UF adhesives. Changes in chemical structure after the curing process were observed with Fourier transform infrared spectroscopy (FTIR). The curing kinetics was studied by differential scanning calorimetry (DSC) under a dynamic scanning regime with heating rates of 5, 10, and 20 °C/min. Obtained data were analyzed using Kissinger-Akahira-Sunose (KAS) and Friedman (FR) kinetic iso-conversional methods to estimate the activation energy (Ea) of the curing reaction in the investigated UF adhesive systems. The results of DSC analysis imply that BSC lowers the temperature of the curing reaction of UF adhesive along with the prolongation of the curing reaction. The obtained kinetic data supported by FTIR and chemical analysis suggest that phenolic compounds present in BSC interfere with the main curing reactions leading to lower peak temperatures but higher activation energy. Тhis suggests that BSC increased the number of active sites involved in the reaction and, consequently, the number of collisions. BSC, as wastewater of the wood processing industry, can be efficiently utilized as an environmentally friendly, inexpensive substitute for deionized water in UF adhesive formulations for WBP manufacturing.

Steaming of green timber, a common industrial process for various hardwood species, significantly influences wood properties, including coloration and drying characteristics. However, the environmental implications of substantial volumes of condensate generated during wood steaming underscore the urgency for its sustainable management. This study explores the chemical composition of the condensate obtained during the 90-hour indirect steaming of walnut timber (WTSC), aiming to identify potential applications for this wastewater while addressing environmental risks. Chemical characterization of WTSC included qualitative LC-MS/MS analysis, determination of the total phenolic content (TPC), total flavonoid content (TFC) and the content of selected phenolics. WTSC exhibited high TPC (188 mg gallic acid equivalents per L) and TFC (9.74 mg quercetin equivalents per L) values. Additionally, WTSC showed significant antioxidant activity (IC50 (DPPH) = 61.4 µg/mL and 103 µg ascorbic acid equivalents per mL in FRAP assay). Specific phenolic compounds detected in the WTSC distinguish it from other wood industry effluents and are a consequence of the unique characteristics of walnut wood and conditions during steaming process. A variety of acids (p-hydroxybenzoic, protocatechuic, syringic, gallic, cinnamic, cinnamic, p-coumaric, o-coumaric, vanillic) and flavonoids (apigenin, genistein, naringenin, luteolin, kaempferol, chrysoeriol, isorhamnetin, apigenin 7-O-glucoside, vitexin, kaempferol 3-O-glucoside, catechin, epicatechin, and quercitrin) were identified and quantified. The condensate exhibited higher TPC value and antioxidant activity than other wood industry effluents, positioning it as a promising natural antioxidant with potential applications in pharmaceutical and food industries. However, our short-term goal is to explore the potential use of WTSC as received – without isolating individual compounds – in studies focused on plant protection, textile dyeing, and wood-based panel production.

This study aimed to compare two thermal modification (TM) schedules—with short and long heating phases—and their influence on the properties of maple (Acer pseudoplatanus L.) and ash (Fraxinus excelsior L.) wood. Two TM runs were conducted in industrial conditions (open system, steam atmosphere; substantially longer method compared to the processes usually described in the literature), with the same peak phase (200 °C, 3 h), but with different heating rates—slow (1.1 °C/h) and fast (2.5 °C/h). The results revealed that both TMs significantly reduced hygroscopicity and swelling of wood, but the influence of slow heating rate—through prolonged exposure of wood to relatively high temperatures—on dimensional stability was more pronounced. The modulus of elasticity, compressive strength and Brinell hardness remained mostly unchanged after TM (except for fast-modified maple), while the modulus of rupture was strongly reduced by TM in both species. It is assumed—at least in the case of maple wood—that a combination of initial moisture content above 8% and fast heating rate during TM can cause more intensive degradation of wood polymers. Relatively small differences in colour between slow- and fast-modified wood were found. The results confirmed the hypothesis that the heating phase is an important part of the TM schedule, and it can directly affect (together with peak temperature and time) certain wood properties.

In this study, the development of non-homogeneous color changes in oak timber during conventional drying and their relationship with the moisture gradient across the wood thickness were analyzed. The research was conducted on radial and tangential boards with a thickness of 38 mm, cut from two oak logs, one of sessile oak (Quercus petraea L.) and one of pedunculate oak (Quercus robur L.). A conventional drying schedule commonly used in enterprises was applied, and at specified time intervals samples were taken to determine the moisture content profile and monitor color changes on the cross sections of the samples. The findings reveal a complex relationship between the wood moisture content, the moisture content profile across the thickness, and the occurrence of color changes. Additionally, it was found that the wood of sessile oak dries slower and with less intense color changes compared to the wood of pedunculate oak. It was demonstrated that quarter-sawn boards dry slower compared to flat-sawn boards for both wood species. No differences in the appearance of non-homogeneous color between quarter-sawn and flat-sawn boards were identified.

Abstract In this research, the antifungal efficacy of dry plant extracts of Chinese cinnamon bark (Cinnamomum cassia L.), Rtanjski tea herb (Satureja montana L.) obtained by water extraction and extract of Thyme herb (Thymus serpyllum L.) obtained by ethanol-water extraction was investigated against the fungi Coniophora puteana and Serpula lacrymans, which cause brown rot, and the fungus Trametes versicolor, which causes white rot of hardwood and conifers. Five different concentrations of plant extracts were tested, and water was used as a solvent. Samples of beech wood (Fagus sylvatica ssp. moesiaca (Maly) Czeczott.) were treated by the immersion method with solutions of plant extracts and exposed for 60 days to the action of the test fungi. The smallest mass loss (%) of beech wood when affected by each of the test fungi was in samples treated with Thymus serpyllum extract at a concentration of 25%, followed by Satureja montana at the same concentration. Cinnamomum cassia bark extract did not show significant antifungal activity against the test fungi at any concentration. The obtained results can affirm the use of dry plant extracts as ecologically acceptable agents in the preventive protection of non-resistant wood species against rotting fungi.

The paper examined the strength of rotationally welded joints between untreated beech dowels and samples of thermally modified and unmodified oak wood (used as substrates). The results were compared with the control group where beech dowels were glued using PVAc (polyvinyl acetate) glue for the same types of samples. Maximum dowel pull-out force was significantly higher for the glued connection compared to the welded connection in both groups - thermally treated and untreated oak wood. Welded joint strength was higher for unmodified group, compared to thermally treated group, which was expected due to negative effects of thermal modification on mechanical properties of wood.

The prediction of physical (wood density, mass loss) and mechanical (bending properties, compressive strength parallel to grain, and Brinell hardness) properties of heat-treated sessile oak (Quercus petraea L.) by FT-NIR spectroscopy, colour change, and partial least squares regression (PLS) was studied. Samples of oak sapwood and heartwood were treated for 4 h at temperatures at 170, 190, and 210 degrees C. FT-NIR spectra (100 scans and 4 cm(-1)) and colour parameters (CIE L*a*b* system) were collected on the radial surface before and after heat treatment. The applied heat treatment changed wood properties, darkened the colour and reduced the colour difference between heartwood and sapwood. According to the residual prediction deviation (RPD), most models obtained could be used for preliminary wood quality screening (1.5 < RPD < 2.0) and the properties of heartwood were better predicted than those of sapwood. Mass loss prediction by colour change can be used for quality control while for the other properties FT-NIR provided a more clear picture of the heat-treated oak wood and can serve as a quality indicator.

Wood density and fibre length are two wood properties that are important in determining the quality of wood for commercial use. The fibre length of red oak has not been studied to the same extent as in other oak species. The aim of this paper is to explore the anatomical variation and wood density of red oak wood, as valuable information for researchers in other fields. Samples were taken in a 60-year-old red oak stand in the south part of Belgrade on the site of Stepin Lug. Along the south radius, the disc samples of 20 x 20 mm were cut from the sapwood, mature and juvenile wood. Ovendry density and fibre length were measured from the pith to the bark. According to the obtained data, the average oven-dry density of wood per radius is 0.694 g/cm3 . The lowest is in the juvenile wood and ranges from 0.628 to 0.681 g/cm3 , then in the part of sapwood - 0.662 g/cm3 , and the highest is in the mature wood where the density ranges from 0.707 to 0.740 g/cm3 . The presented values show certain differences, but also conform to literature data on the density of some industrial species from the genus Quercus L. The obtained results of the wood fibre length show that it varies from 0.99 to 1.33 mm which was measured in mature wood. The average length in a mature zone is 1.26 (1.16-1.33) mm, while in a juvenile area the average length is 1.02 (0.85-1.23) mm. Based on the known wood fibre length, it is possible to determine the density of red oak wood. In this research, a positive influence was determined in both parts of the tree, juvenile and mature, but a better mathematical dependence was obtained in the mature zone.

The subject of this paper is the analysis of the influence of higher initial temperatures during the drying of oak lamellas on the final quality and wood colour. Two different drying schedules (initial temperature: 45?C and 50?C; final temperature: 55?C) were used and then the drying quality and wood colour were determined. The colour change was expressed by parameter ?E but also by the corrected parameter ?E00. It was shown that the drying quality was very high in both cases, and that the colour change that occurred during drying was invisible to the naked eye. The application of higher temperatures does not pose a risk to the drying quality due to the small thickness of the wood and the short drying process. In industry, a higher initial temperature is justified in situations where sufficient quantities of (cheap) thermal energy are available. The results confirmed that the percentage of lamellas? deformation was reduced when the load was applied while drying.

This study presents preliminary results of the basic properties of the northern red oak wood as well as the relationship between the properties of the core samples obtained on the live tree and the tested properties. The core samples 5 mm in diameter were extracted from the tree and used for determining the fractometer properties: compressive strength parallel to grain, radial bending strength and braking angle. Using descriptive statistics and multiple regression, the relationship between fractometric parameters and basic physical and mechanical properties of wood determined by destructive methods (wood density, compressive strength in parallel with fibers and bending properties (bending strength and modulus of elasticity). The obtained values of the examined properties of northern red oak are within the limits of the literature data. Statistical analysis has shown that radial bending strength cannot be used as a reliable fractometric parameter in assessing wood quality. On the other hand, the obtained results suggest that the relationship between the other two parameters (compressive strength parallel to grain and fracture angle) and the properties of the northern red oak wood can be successfully described using the multiple regression models (coefficient of determination ranged from 0.945 to 0.990).

The subject of this paper is the analysis of moisture content (MC) changes of beech and ash wood during two years in room conditions (heating during winter; no air conditioning during summer). The registered MC changes are primarily the result of changes in relative humidity of the air (measured by capacitive probes). The average relative humidity of the air in the interior is lower today than in the past, as also shown in this experiment (the average relative humidity of air during two years was 44%). The lowest wood MC was reached on very cold winter days when the heating was on even during the night - between 5% and 6%, and the highest one at the beginning of June: 10.4-10.9%. As expected, the wood did not reach equilibrium moisture content - during winter, MC is by about 1% higher, and in summer it is lower by up to 2.5% than the equilibrium. The recommendation that the sawn timber from which the interior products will be made should be dried at 7-8% MC was confirmed.

The subject of this paper is to analyse the drying process of oak lamellas, which are the solid wood top layer of engineered wood flooring. The focus of the first part of the paper is on dehumidification kilns. Drying in a dehumidification kiln is an interesting alternative to conventional drying of thin solid oak wood with the aim of reaching high drying quality in a reasonable time. Drying tests were done in an industrial dehumidification kiln, and drying parameters were compared with the drying in the conventional kiln. Simultaneously, a drying test at a higher temperature was done in the programmable climate chamber. It was demonstrated that thin oak lamellas (approx. 5 mm thick) could be successfully dried in a dehumidification kiln in a relatively short time and with high drying quality. With the applied drying schedule (initial temperature of 36?C, final temperature of 46?C), the drying cycle will last 2 to 5 days, depending on the amount of wood and the initial MC. Due to the high rate of water evaporation and the inability of the kilns to remove it fast enough, the drying of lamellas in both dehumidification and conventional kilns takes place at a higher equilibrium moisture content than the set values.

This study aimed to determine the influence of equilibrium moisture content (EMC) oscillations on MC profiles of beech timber (38 x 120 x 500 mm) during drying in the climatic chamber. Two test runs with EMC oscillations (along with constant temperature) were followed by the equivalent test runs in constant climate: altogether, 4 drying runs were carried out. The amplitudes of EMC oscillations were ca. +/- 1.5% (absolute value) compared to the value in constant climate test, while the temperature in all cases was 35 degrees C. Among others, MC profile across thickness was periodically determined by slicing five lamellae and using the oven-dry method to determine their MC. Drying curves produced during constant and oscillation climate drying were similar and no statistical difference was found between average MC determined on the same day during constant and oscillation drying. In all cases it was found that MC difference between core and surface is lower (or at least not higher) in oscillating compared to constant climate conditions. This indicates that, if the positive influence of additional mechanosorptive creep (caused by EMC oscillations) on stresses in wood is taken into account, lower stresses in surface layers can be expected during oscillation drying. Further tests will be done to reveal the exact MC changes within surface layers of the boards. It is demonstrated that the climatic chamber is very stable in reaching and maintenance of air parameters during oscillation drying; it has practically no uncontrolled oscillations and will be used in further testing, along with the tests in semi-industrial and industrial kilns.

The subject of this paper is the analysis of the possibility of drying oak and ash elements with the presence of tree bark on one side of the element (bark edge). One batch was dried per species, and the process was controlled by moisture content (MC) probes in the kiln, but also determined by the oven-dry method. Drying defects and their causes were also analyzed. The results showed that conventional drying can be used for this purpose - the duration is relatively short (up to 7 days), and the variation of the final MC is relatively small. The main problem is a relatively large number of crooked elements at the end of drying, particularly those where the share of wood in relation to the bark was small. Very high axial shrinkage coefficients of the bark (4.5 times higher than wood) are the cause of these deformations.

The influence of log diameter and log quality were studied relative to the potential heat energy produced from wood residue. Research was conducted on beech sawmill logs (30 cm to 49 cm in diameter and 4 m in length) of different qualities. Logs with greater diameters and of better quality increased the amount of products and decreased the amount of residue. A decrease in the diameter and quality of beech logs increased the total energy capacity, ranging between 840 kWh/m3 (highest quality logs, 40 cm to 49 cm in diameter) and 1,350 kWh/m3 (lower quality logs, 30 cm to 34 cm in diameter). Drying the lumber produced from logs of small diameters used less than 10% of the potential heating energy. However, logs of 40 cm to 49 cm in diameter increased this usage to 33%. When burner losses and drying energy losses were calculated, there was approximately 430 kWh/m3 to 960 kWh/m3 of leftover energy. This could be used for various purposes or it could be sold. The amount of obtained energy was influenced more by log diameter than by the log quality.

The subject of this paper is the analysis of the quality of natural and conventional drying of subfossil oak wood. In addition to the drying quality, the colour of this material, as well as the effect of the drying process on colour change have been tested. The subfossil oak logs that were used in this experiment originate from the Morava River in Central Serbia. After sawing, timber was air-dried to about 20% moisture content (MC) followed by kiln-drying to 9.5% MC. By examining the quality of air-drying of the subfossil oak wood, a high presence of cracks was found, as well as the inaccuracy of humidity measurement using electric moisture meters. The stack for kiln-drying consisted of 24 boards, of which 4 were used for the monitoring of MC and MC distribution across the thickness of plank during drying. Drying quality was evaluated after the kiln-drying process. Although mild drying conditions during kiln-drying were applied, the gap as a measure of case-hardening had a value greater than usual for oak of same thickness. It was found that the drying process has no significant effect on the change in the colour of subfossil wood. The colour of the subfossil oak wood was significantly darker than the usual oak wood, and the colour difference between the central and the outer parts of the trunk of the subfossil oak was determined.

Possibilities for use of thermally modified poplar veneer were evaluated for the production of plywood boards in industrial conditions. Formats of poplar veneer were treated at temperatures of 190 °C, 200 °C, 210 °C, and 215 °C for 1 h. By combining the treated and non-treated formats of veneer, thirteen different types of board were made. Analyses showed that the examined physical and mechanical properties were influenced by both the type of construction and the applied thermal treatment. Boards composed only of thermally modified veneer achieved the best results regarding moisture absorption and dimensional stability, and boards composed of the combined veneers had better mechanical properties. Treatments at 200 °C and 210 °C proved to be optimal, while the treatment at 215 °C was too harsh and should not be used for the thermal modification of poplar veneer.