Currently, wood remains a primary material for construction and finishing applications due to its inherent advantages, including accessibility, environmental sustainability, ease of processing, and renewability. However, the structural application of wood is constrained by several limitations: low resistance to mechanical, atmospheric, thermal, and biological stressors; susceptibility to degradation; and the aesthetic disparity between affordable and premium species. To mitigate these disadvantages while maintaining environmental integrity, thermal modification is employed. This process enhances biological durability and ensures the dimensional stability of wood products during operational cycles. The study utilized radial samples of spruce wood with a rectangular cross-section 35 × 12 × 0.6 mm. These samples underwent thermal modification at temperatures of 180°C and 210°C within a nitrogen-controlled environment. The viscoelastic behavior (creep) under constant loading was analyzed using a Gabo Eplexor 25N Dynamic Mechanical Analyzer (DMA). The experimental protocol was governed by a software module based on the Burgers model. Primary data acquisition and processing were conducted via the GABO software suite. Viscoelastic characteristics were evaluated in tensile mode using "Time Sweep" and "Temperature Sweep" modules at a quasi-static load frequency (f = 0...0.01Hz). The investigation established the correlation between thermal modification temperature in nitrogen, medium and the resulting changes in viscoelastic characteristics and creep modulus. Analysis of deformation kinetics under load indicates that thermal modification significantly alters the mechanical stability of the material. This effect demonstrates a distinct gradational dependence on the treatment temperature. The comparative analysis of deformation ranges between modified and unmodified spruce wood provides a quantitative basis for evaluating the impact of thermal treatment on the material's rheological properties. It has been demonstrated that modification at a moderate temperature of 180°C results in a relatively minor increase in the material's deformability, within the range of 13-15% compared to the control group. This indicates the initial stage of structural transformations, where the degradation of hemicelluloses does not lead to a substantial loss of stiffness. Increasing the treatment temperature to 210°C induces a sharp shift in rheological behavior and leads to a reduction in the mechanical stiffness of the thermally modified European spruce. Consequently, the deformation rate increases by 52-57%, and the difference in ultimate deformation values between the unmodified and high-temperature thermally modified wood reaches 45-47%. It has been established that the thermal modification of wood at 210°C, despite improving biological durability and dimensional stability, leads to a significant reduction in resistance to sustained loading. The intensification of creep processes and the increase in residual deformations restrict the application of such wood in load-bearing building structures. It is recommended to either optimize the thermal treatment parameters or account for the actual decrease in the modulus of elasticity when designing structural elements. The findings offer a quantitative assessment of how temperature influences the structural integrity of spruce wood. Based on the established viscoelastic profiles, practical recommendations are proposed for the industrial application of thermally modified spruce wood in environments requiring high dimensional and mechanical stability.
The increase in deforestation limits the availability of wood, raises its cost, and intensifies competition for raw materials, which complicates the sustainable development of the wood-based panel industry. This stimulates the search for alternative raw material sources for the partial or complete substitution of wood in the production of wood-based composite materials. The use of agricultural residues makes it possible to reduce dependence on wood, lower production costs, and decrease negative environmental impacts, while simultaneously creating additional economic value from agricultural waste. The increase in deforestation limits the availability of wood, raises its cost, and intensifies competition for raw materials, which complicates the sustainable development of the wood-based panel industry. This stimulates the search for alternative raw material sources for the partial or complete substitution of wood in the production of wood-based composite materials. The use of agricultural residues makes it possible to reduce dependence on wood, lower production costs, and decrease negative environmental impacts, while simultaneously creating additional economic value from agricultural waste. Moreover, the wood content in particleboards is approximately 90%; therefore, their properties largely depend on the type of lignocellulosic raw material used in production. The type of raw material affects not only the performance characteristics of the finished board but also the parameters of the manufacturing process and the final production cost. The cost of primary materials, adhesives and wood particles, constitutes the major share of particleboard manufacturing expenses. The share of wood particles in the overall cost structure is estimated at 30–40%. The cost of agricultural biomass is, on average, about 50% lower than that of wood particles. In this regard, replacing wood particles with alternative non-wood raw materials may result in a significant reduction in production costs. The aim of this study was to determine the effect of partial or complete replacement of wood particles with sugar beet pulp (SBP) on the mechanical properties of particleboards. Single-layer boards with target densities of 600 and 750 kg/m³ were manufactured using different volumetric ratios of wood and SBP: 100:0, 75:25, 50:50, 25:75, and 0:100%. Polymeric diphenylmethane diisocyanate (pMDI) adhesive was used to bond the particles. The vertical density profile, bending strength (MOR), modulus of elasticity (MOE), and internal bond (IB) strength of the boards, were investigated. It has been established that single-layer boards are characterized by a uniform, flat density profile without pronounced densification of the surface layers. This is attributed to the peculiarities of the raw material composition, in particular the lower proportion of wood particles and the particle size of SBP. With an increasing SBP content, a decreasing trend in MOR and MOE is observed, indicating limitations in its use at high concentrations to ensure the mechanical performance of the boards. At the same time, boards with a high SBP content, particularly 100%, demonstrate increased IB strength, which can be explained by effective adhesion between the components of the board. An important role in this is played by pMDI adhesive, as well as the natural constituents of SBP (pectins and sugars), which may act as additional binding agents. Boards containing 25–100% SBP comply with the requirements of EN 312 regarding the minimum IB strength for different board types (P1–P5), confirming their potential for practical application. An increase in board density from 600 to 700 kg/m³ leads to a 19% improvement in internal bond strength, demonstrating the feasibility of optimizing density as a key technological parameter. A promising direction is the production of three-layer boards using wood particles in the outer layers and SBP in the core layer (up to 50%), which would improve the performance properties of the material. The use of sugar beet pulp in particleboard production contributes to reducing dependence on primary wood resources and enhances the environmental and resource efficiency of the industry.
The study presents the results of investigating the effect of sunflower-stalk (Helianthus annuus L.) and miscanthus-stalk (Miscanthus × giganteus) particles (chips) on free formaldehyde emissions from lightweight three-layer particleboards glued with urea-formaldehyde (UF) adhesive. The relevance of this study is due to increasingly stringent environmental requirements for wood-based composite materials and the need to reduce the consumption of wood raw materials in the production of boards (panels). Formaldehyde is classified as a carcinogenic and substance, and current trends in the woodworking industry are focused on reducing its emissions while simultaneously reducing dependence on traditional wood raw materials. In this context, agricultural lignocellulosic residues are considered promising alternative resources for sustainable particleboard production. Among such materials, sunflower stalks and miscanthus biomass attract considerable attention due to their low density, porous structure, wide availability and potential for improving the environmental performance of composite panel materials. Therefore, the aim of the study was to determine the impact of partial and complete replacement of wood particles in the core layer of lightweight particleboards with sunflower stalk and miscanthus stalk particles on the level of formaldehyde emission. Three-layer particleboards with a density of 550 kg/m3 were manufactured in laboratory conditions. The outer layers consisted entirely of wood particles (chips), while the core layer contained different proportions of wood particles, sunflower stalks and miscanthus stalks. Agricultural raw material particles were included in the core layer with a substitution step of 50%, including mixtures of sunflower and miscanthus particles. An urea-formaldehyde resin-based adhesive was used for bonding. The emission of free formaldehyde was determined by gas analysis according to EN ISO 12460-3. The highest emission value was recorded for the control boards and was 3.05 mg/(m²·h). The lowest formaldehyde emission level was obtained for boards containing 100% sunflower stalk particles in the core layer amounting to 2.32 mg/(m²·h), which is 23.93% lower compared to the control samples. Boards made from 100% miscanthus stalk particles showed an average formaldehyde emission value of 2.76 mg/(m²·h), which is 9.51% lower than this indicator of the control boards. The combined use of sunflower and miscanthus particles also contributed to the reduction of formaldehyde emissions compared to the control lightweight particleboards. All tested specimens met the requirements for formaldehyde emission class E1 in accordance with EN ISO 12460-3. The reduction in formaldehyde emission can be attributed to the structural characteristics of lignocellulosic agricultural raw materials, their lower density and the formation of a denser internal structure of the board with improved adhesive bonding and reduced porosity. In particular, sunflower stalk particles demonstrated the best ability to bind and retain formaldehyde due to the presence of a porous parenchymal structure of the stem pith. The findings demonstrate the potential of sunflower stalk and miscanthus particles as environmentally friendly alternative raw materials for the production of lightweight particleboards. Their use enables the expansion of the raw material base for panel production, reduces wood consumption, enhances environmental sustainability, and facilitates the development of sustainable technologies aimed at reducing the use of wood in the manufacture of wood-based composite materials.
Wood is among the materials whose linear dimensions vary depending on the temperature and humidity conditions of the surrounding environment. These characteristics should be taken into account not only during wood machining processes, where allowances for shrinkage must be considered, but also during service under conditions of varying environmental parameters. The experimental studies were carried out on specimens (blanks) with nominal dimensions of 50×50×1,000 mm, sawn from pedunculate oak wood (Quercus robur L.). The magnitude of shrinkage was determined after drying the specimens in a batch-type convective kiln (KAD-1×6S, Katres) and in a Hildebrand-Brunner vacuum-convective drying kiln. Both kilns had a capacity of approximately 50 m³ of timber to be dried. Stacks measuring 1,200×1,200×1,000 mm were formed from the sawn oak specimens. Stickers with a thickness of 22 mm were used during stack formation. A total of 72 stacks were loaded into each kiln. The specimens were dried to a target final moisture content of 8%. Multi-stage drying schedules were employed for drying the specimens, comprising the following phases: initial heating, drying, final heat and moisture treatment (conditioning), and cooling. At the first stage of the drying schedule in the convective kiln, the drying agent temperature (tc) was 33°C and the equilibrium moisture content (Wᵣ) was 16%. At the final stage of the drying schedule, the drying agent temperature was maintained at 60°C, and the drying gradient (TG) was 2.4. In the vacuum-convective kiln, the drying agent temperature at the first stage of the schedule was 40°C and the equilibrium moisture content was 14%. At the final stage of the drying schedule, the drying agent temperature (tc) was 63°C and the equilibrium moisture content (Wᵣ) was 5.4%. After unloading from the drying kiln, the specimens were conditioned in a storage facility with a controlled microclimate for 48 hours, after which their moisture content was measured using a MERLIN HM9 WS-25 capacitive moisture meter. The linear dimensions of the specimens, specifically their thickness and width, were then remeasured at the previously marked locations. The sample size comprised 238 specimens dried in the convective kiln and 210 specimens dried in the vacuum-convective kiln. When the moisture content of wood decreases below 30%, a reduction in its linear dimensions occurs. The magnitude of this change is influenced by several factors, including wood species, moisture content, density, wood grain (orientation of wood fibres relative to longitudinal axes of the tree), dimensions of the timber assortment., drying schedule, proportion of latewood, anatomical and submicroscopic structure of the wood and the location of the wood specimen extraction with respect to the height and diameter of the log, etc. The change in the linear dimensions of the specimens was found to be 3.03 mm after vacuum-convective drying and 3.41 mm after convective drying. The corresponding wood shrinkage factors were 0.247 and 0.273 for the vacuum-convective and convective drying methods, respectively. The experimental results indicated that vacuum-convective drying is characterized by a higher drying intensity, which influences the shrinkage behavior of the wood, leading to lower shrinkage values than those observed in case of convective drying.
The paper presents the results of an experimental study on the influence of cutting tool diameter and feed rate on the time required to machine a lock mortise in a door leaf. The study also considers the influence of toolpath geometry, as well as the mortise length and depth. Particular attention is focused on investigating the nonlinear effect of the cutting tool feed rate on lock mortise milling time caused by the presence of acceleration and deceleration sections along the toolpath. A graphical representation of the relationship covering a feed rate range from 1 to 10 m/min is presented. The obtained experimental results were approximated using a second-order polynomial. A mathematical model was developed for calculating the machining time time required for lock mortise production, taking into account the geometrical parameters of the mortise, cutting tool diameter, and tool feed rate. As the feed rate increases, the machining time required to produce the lock mortise decreases nonlinearly. The value of the feed rate coefficient varies from 0.992 at a feed rate of 1 m/min to 0.756 at a feed rate of 10 m/min. This is explained by the fact that increasing the feed rate of the cutting tool increases the length of the toolpath sections where acceleration and deceleration occur. A significant influence of the cutting tool diameter on the feed rate coefficient was observed. In the case where the tool diameter matches the width of the mortise, the feed rate coefficient reaches its highest values. When the tool diameter is smaller than the mortise width, the coefficient values decrease but exhibit little dependence on the specific tool diameter used. This confirms the feasibility of using a cutting tool whose diameter is equal to the width of the lock mortise, provided that the CNC equipment is technologically capable of applying such a tool diameter. In addition, the influence of mortise length on the feed rate coefficient was established. The coefficient increases with increasing mortise length. This is attributed to the relative increase in the length of toolpath sections at the specified feed rate compared to the length of the acceleration and deceleration sections. The magnitude of this effect is insignificant at low feed rates but increases considerably as the feed rate rises. The influence of mortise depth on the feed rate coefficient is the smallest and does not allow clear patterns of variation to be identified due to its minor magnitude. This is explained by the fact that increasing mortise depth increases the number of repeated toolpath segments resembling spiral turns. However, the ratio between the length and number of constant-feed toolpath sections and acceleration/deceleration sections remains almost unchanged. The scientific novelty of the study lies in the development of a mathematical model for predicting the machining time required to produce a lock mortise in a door leaf, taking into account the feed rate coefficient, the values of which were obtained experimentally and approximated by a second-order polynomial. The practical significance of the study consists in the potential application of the developed mathematical model for planning the technological process of door leaf manufacturing and for analyzing the influence of the applied cutting tool, feed rate, as well as mortise depth and length on milling time. The obtained results may be applied under industrial production conditions for predicting and controlling the machining time required for producing lock mortises on CNC woodworking machines.
