Research Articles

The objective of the study was to investigate the influence of heat treatment on air-dried density, equilibrium moisture content (EMC), porosity, average surface roughness (R_a), sound transmission loss, and sound absorption coefficient of poplar (Populus nigra L.) and beech (Fagus orientalis Lipsky) woods. Specimens were exposed to four different temperature levels, namely 150 °C, 170 °C, 190 °C, and 210 °C, for 3 h. The sound absorption coefficient and sound transmission loss of test samples were determined in the frequency range of 63 Hz to 6300 Hz using an impedance tube. It was found that the density, EMC, and average surface roughness values of samples decreased with the heat treatment temperature. In contrast, as the heat treatment temperature increased, porosity of samples increased. The sound absorption coefficient and sound transmission loss of both wood species increased with the heat treatment temperature. The average sound absorption coefficients of untreated and heat-treated poplar samples were approximately 0.16 and 0.18; whereas for beech wood the corresponding values were approximately 0.15 and 0.16. The average sound transmission losses of untreated and treated poplar were approximately 22.7 and 24.0 dB, for the untreated and treated beech samples were 17.3 and 20.7 dB respectively.

Olive tree pruning waste represents a significant agricultural byproduct in Mediterranean regions. It can be regarded as a sustainable and cost-effective alternative resource to other traditional materials for buildings. It is necessary to evaluate the flammability of these materials, according to building regulations. In this preliminary study, several fire-retardant coatings were applied to the materials obtained from olive leaves mixed with a natural adhesive. The coatings included cement-based layers, hydraulic lime, gypsum plaster, intumescent varnishes containing phosphate-based compounds, and graphene-based paints. Treated samples were subjected to flame spread tests to determine their fire resistance properties according to Standard EN ISO 11925-2. The potential of using olive leaves waste as a building material when combined with appropriate fire-retardant coatings is highlighted. The findings suggest that such treatments contribute to mitigating fires and promote the sustainable use of agricultural byproducts in buildings. By applying the coatings, the fire resistance increases significantly compared to untreated samples. The ceramic coatings provided the highest level of protection by reducing the flame spread rate and increasing the time to ignition. Additionally, the treated samples exhibited increased char formation, reducing heat transfer, and delaying combustion. Further research is recommended to optimize the formulations and application methods for large-scale implementation.

Tensile, edgewise, and flatwise bending behaviors of visually graded fir (Abies nordmanniana subsp. bornmuelleriana) boards were investigated through destructive and non-destructive testing to evaluate their mechanical performance and grading accuracy. A total of 724 specimens were prepared and tested in accordance with EN 408 standards. Knot diameter ratios (narrow, mean, and parallel) were used to establish three visual grading methods. Vibration-based (PLG, Hitman) and time of flight (ToF) (Microsecond Timer, Ultrasonic Timer, and Sylvatest Duo) techniques were used for non-destructive evaluation (NDE), along with screw withdrawal tests. The results showed that although the vibration method had lower dynamic modulus of elasticity (MOEd) values ​​than the ToF method, it provided stronger correlations with tensile and bending properties. The mean and parallel knot diameter ratios provided more reliable grading results than the narrow ratio. Tensile strength was more affected by defects than bending strength, and the flatwise bending method consistently produced the highest strength values. The adjustment from global to local MOE reduced modulus values below 9000 MPa, resulting in lower strength class assignments. Overall, the vibration-based NDE method proved the most effective for predicting lumber quality, and the flatwise bending test emerged as a viable alternative to tension and edge bending methods for structural grading.

To address the loosening of mortise and tenon joints in solid wood chairs caused by prolonged use and wood expansion and contraction, this study proposes a reinforcement method using 3D-printed connectors based on polyethylene terephthalate-1,4-cyclohexanedimethanol (PETG) filament. First, the influence of key process parameters (extrusion extent, nozzle travel speed, and nozzle temperature) on the mechanical properties of PETG models was analyzed. Subsequently, based on the optimized process parameters, reinforcement connectors with rib structures were designed and 3D printed. The reinforcement effectiveness was evaluated by comparing the ultimate load of mortise and tenon joints with and without the reinforcement connectors. Results indicated that with the increase of extrusion extent and nozzle temperature, and the decrease of nozzle travel speed, the ultimate strength and Young’s modulus of PETG models increased, improving their mechanical properties. The optimal process parameters were determined as follows: extrusion extent of 105%, nozzle travel speed of 70 mm/s, and nozzle temperature of 250 °C. After installing the reinforcement connectors, the average ultimate load of the mortise and tenon joints reached 445.7 N, which was 34.9% higher than that of joints without reinforcement, demonstrating that the 3D-printed connectors effectively reinforced and protected the mortise and tenon joints.

Flowability is an essential property that must be evaluated to ensure smooth and consistent feeding of powder materials into hoppers. It can be influenced by particle shape, size and its distribution, and surface chemical characteristics. In the case of cellulose powders, their physical and chemical properties are not uniform and can vary depending on the cellulose source and powder preparation method. In this study, the flowability of cellulose powders was evaluated through static and dynamic analyses. The angle of repose was measured to assess static flow characteristics, while avalanche behavior was analyzed using a revolution powder analyzer. Cellulose nanofiber, microcrystalline cellulose, and milled kenaf pulp were classified by particle size to investigate the effects of morphology. Larger and more spherical particles exhibited superior flowability, whereas particles smaller than 70 µm showed a sharp decline in flowability. Particle size had a stronger influence than size distribution. Increasing moisture content improved the flowability of fine particles but reduced that of coarse ones. Moderate hydrophobization enhanced flowability by reducing surface energy, whereas excessive treatment caused deterioration due to aggregation. These results identified the key parameters governing cellulose powder flow and clarified the characteristics advantageous for stable feeding and uniform product quality.

To reduce the energy consumption of biomass densification, this study proposes a method of constructing solid bridges through pressurized binder spraying. The feasibility of this method for producing high-quality biomass molding was studied under ambient temperatures and lower pressures. Four-factor mixed-level orthogonal tests were designed to evaluate the relaxation ratio and durability of density pellets, in which the molasses served as the binder. Pressurized spraying of the binder resulted in a 27.0% increase of relaxation density, 8.21% decrease in relaxation ratio, and significantly enhanced durability compared to stirring method at pressure 40 MPa, which was determined in preliminary testing to conform to at least 95% durability. A multivariate quadratic regression equation through response surface analysis was established by selecting a 2FI model for the 100% importance in binder addition method. The relaxation ratio was normalized to the weights of the influencing factors obtained from model of multi-layer perceptron neural network. The test factors had a significant impact of on the relaxation ratio, and thus, the optimal combination condition for test was determined as 50 (MPa) densification pressure, 14% moisture content, 4% binder ratio, and pressurized spraying at 2 (MPa). These conditions reduced the minimum densification pressure required for biomass densification.

The biosynthesis of Reduced Graphene Oxide (RGO) was shown using an aqueous leaf extract of Rhododendron micranthum Turcz. as a reductant by deoxygenation of Graphene Oxide (GO). The reduction of GO to RGO was shown as a shift in UV-Vis peak from 230 nm to 270 nm. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Raman spectroscopy confirmed the GO reduction. Thermal gravimetry and zeta potential measurements exhibited the good stability of RGO. Transmission Electron Microscopy (TEM) results showed thin and transparent RGO sheets. Cell viability results showed that the mesenchymal stem cells (MSCs) of adult goats were viable in the presence of RGO at a concentration of 0.1 mg/mL, and their properties were retained. The analgesic effect of RGO was assessed in mice through the oral administration of different doses of RGO. Writhing episodes induced by acetic acid were decreased dose-dependently. Also, the inflammatory effect of RGO was shown by measuring the hind paw volume of rat exhibited the decreased inflammation with increased RGO concentration. The local anesthetic activity was assessed in guinea pig models and frog, revealing that the RGO exhibited a substantial local anesthetic effect in both the animals with decreased response in dose dependent manner.

Anaerobic co-digestion was evaluated for lignocellulosic materials and paper plant sludge cakes (PSL). The methane production, crystallinity, residual cellulose, and next-generation sequencing (NGS) were analyzed and compared. It was found that microcrystalline cellulose (MCC) had the highest accumulated methane production among the different materials in the anaerobic digestion system. The residual content and crystallinity of cellulose both decreased to a much larger extent, and the accumulated methane production was higher than that of the anaerobic digestion system with the added anaerobic sludge cake. NGS showed that the domain bacteria in the anaerobic digestion system with the added anaerobic sludge cake were Methanosaeta, which can convert organic sugars into methane. This substantially reduced the number of bacteria that can degrade cellulose. As the ability to degrade cellulose decreased, the residual cellulose content and crystallinity of cellulose became higher than those of the anaerobic digestion system without adding anaerobic sludge cake.

The hyper-cellulase producing bacterium Bacillus paramycoides strain BTH was isolated and characterized by 16S rRNA sequencing. Its potential for saccharification of Brachiaria mutica (para grass), a lignocellulosic aquatic weed, was examined. Cellulase production from strain BTH was enhanced by optimizing various parameters in the presence of goat dung as feedstock using One factor at a time (OFAT) and Response Surface Methodology (RSM) methods. The OFAT-based non-statistical method improved cellulase activity up to 1280.32±27.3 U/g. Box-Behnken Design of RSM-based optimization exhibited 1.3-fold enhancement in cellulase activity (1725.54±32.63 U/g) as compared to OFAT technique in the presence of goat dung medium (pH 8.0), incorporated with 1.5% (w/w) CMC and incubated at 37°C. Para grass biomass was further pre-treated via hydrothermal, alkali, acid, hydrogen peroxide, and microwave heating methods and subjected to strain BTH-associated cellulase-based hydrolysis. The alkali pre-treated biomass exhibited maximum total reducing sugar production of 6.73±0.2, 9.25±0.16, 11.6±0.17, 14.11±0.16, and 11.54±0.16 mg/g in the presence of 4% (w/v) NaOH from 12 to 96 h. Likewise, 4% (w/v) NaOH pre-treated biomass showed maximum saccharification efficiency of 30.28±0.8, 41.62±0.6, 52.2±0.7, 63.49±0.6, and 51.93±0.8% from 12 to 96 h. The findings validated the role of B. paramycoides-associated cellulase in the saccharification of para grass.

Esterified wood was produced from beech (Fagus orientalis Lipsky) using acetic anhydride via a soaking-impregnation process with varying impregnation (Im) and reaction (Re) durations. Oven-dried beech wood samples were immersed in acetic anhydride for either 60 or 180 minutes.The samples were then wrapped in foil and placed in an oven at 103 ± 2 °C for 60 or 120 minutes to facilitate the acetylation reaction. The weight percent gain (WPG) was determined to assess the extent of the chemical modification. Flexural strength (FS), flexural modulus (FM), impact strength (IS), and compression strength (CS), along with water absorption (WA), thickness swelling (TS), and anti-swelling and anti-shrinkage efficiencies were evaluated. The WPG increased with increasing reaction, reaching 9.1% for Im60-Re60 and 13.6% for Im180-Re120 treatments. Acetylation significantly reduced water absorption and dimensional changes compared with untreated wood. Higher WPG levels resulted in reductions in FS and IS, whereas FM and CS were not significantly affected. Among the tested conditions, the Im60-Re60 treatment provided the most balanced performance, achieving improved dimensional stability with minimal reduction in mechanical properties. These results demonstrate that controlled acetylation can enhance the moisture resistance and dimensional stability of beech wood while maintaining acceptable mechanical performance.