Showing papers in "European Journal of Wood and Wood Products in 2019"

Stress wave evaluation by accelerometer and acoustic emission sensor for thermally modified wood classification using three types of neural networks

Abstract: Classification of thermally modified wood (TMW) allowing the distinction between different processing temperatures and the corresponding changes in wood properties is a crucial task in TMW grading. In this study, stress wave evaluation technique was used to classify the heat treatment level. Accordingly, an acoustic emission (AE) sensor and a pair of accelerometers captured stress waves generated by pendulum impact, and the data was used to classify the heat treatment level of thermally modified Western hemlock wood samples. Sensory features were extracted from time, frequency, and wavelet domain analysis. The extracted features were then used to train multilayer perceptron (MLP), group method of data handling (GMDH), and linear vector quantization (LVQ) neural networks for TMW classification. The results showed that while the features extracted from the accelerometers such as stress wave velocity and wood dynamic modulus of elasticity showed poor classification performance, acoustic emission sensory features were effective for classification of TMW. Wavelet domain features lead to better classification than those extracted from time and frequency domains. Feature fusion approach comprising the features from all the signal domains showed the best classification performance that was further improved by using a dimensionality reduction approach. The linear discriminant analysis was conducted on all acoustic emission features and resulted in 91.1% and 89.1% accuracy obtained from the LVQ and GMDH network, respectively. This performance was further increased to 98% and 97% using the LVQ and GMDH models when the input was combined with wood moisture content. The MLP neural network did not seem as suitable as the other two models. Neural network modeling using the captured stress wave data from an AE sensor could therefore be a promising nondestructive evaluation method for TMW classification.

Lignocellulosic waste fibers and their application as a component of urea-formaldehyde adhesive composition in the manufacture of plywood

Abstract: This research uses lignocellulosic waste fibers from the fiberboard industry, pulp and paper mills for their effective processing to reduce waste discharge, preserve the ecological environment, and produce innovative and sustainable solutions. The effects of using waste fibers obtained from fiberboard wet process, recycled paper process, and cellulose process as adhesive additives on some physical and mechanical properties and formaldehyde emission of adhesives and plywood panels were examined. Three major types of fibers, primary fibrous sludge (PFS), primary cellulose sludge (PCS), and deinked paper sludge (DPS) were characterized and evaluated as adhesive fillers in plywood manufacturing. UF adhesive filled with 15 wt% wheat flour (WF) was used as a reference sample. Plywood panels were made of formulations with urea-formaldehyde (UF) resin filled with three different concentrations of fibers, 1 wt%, 3 wt%, and 5 wt%. Compared with DPS and PCS, PFS had a higher lignin and extractives content, and lower pH. These characteristics make PFS a better adhesive filler for plywood than DPS or PCS. Panels with UF/PFS, UF/DPS and UF/PCS formulations at a sludge content of 1–5 wt%, 1 wt% and 3 wt%, respectively had higher wet shear strengths than those made with the control sample. It was also found that the use of fibers obtained from different processes in the UF adhesive composition decreased the formaldehyde emission of panels. The PFS, PCS, and DPS reduced formaldehyde emissions by up to 27.8, 24.9, and 19.4%, respectively compared with control panels, without compromising the shear strength. The shear strength of plywood panels with all investigated sludges met the requirements of the EN 314-2 standard.

Comparative study on radical scavenging activity and phenolic compounds content in water bark extracts of alder (Alnus glutinosa (L.) Gaertn.), oak (Quercus robur L.) and pine (Pinus sylvestris L.)

Abstract: The radical scavenging activity and the content of proanthocyanidins, tannins, flavonoids, and total phenolic compounds in water extracts from whole bark and outer bark of alder (Alnus glutinosa (L.) Gaertn.), oak (Quercus robur L.) and pine (Pinus sylvestris L.) trees growing in the coastal and continental zones in Kaliningrad region (Russia) were evaluated. The content of proanthocyanidins was highest in extracts from whole alder bark collected in continental zone (3.8 ± 1.2 mg g−1), which was 34–38 times more than in outer part. No significant difference in tannin content in alder and oak bark extracts was revealed. Pine bark samples had less tannins. The whole alder bark showed higher content of flavonoids (9.7–21.5 mg g−1), compared to oak bark (7.2–8.4 mg g−1) and, in particular, pine bark (2.1–5.2 mg g−1). The maximal total phenolic content was found in whole alder bark from continental zone (29.0 ± 5.3 mg g−1). High content of phenolic compounds was determined in whole oak bark (about 18.1 ± 3.5 mg g−1). All investigated species showed approximately 1.3–2.5 times lower total phenolic content in outer bark in comparison to whole bark. Maximal radical scavenging activity of alder extracts (up to 276 ± 29 mg g−1) and minimal of pine extracts (up to 23.8 ± 4.0 mg g−1) was established. A higher level of radical scavenging activity for all samples from continental zone in comparison to samples from coastal zone was revealed. Based on the results of a cluster analysis, it was first demonstrated that the phenolic compounds content and radical scavenging of bark extracts are influenced by a complex of factors, such as tree species, part of the bark and the place of growth. The results of this study proved that whole bark of alder may be considered as a valuable source of phenolic compounds with radical scavenging properties.

Changes in chemical components of steam-treated betung bamboo strands and their effects on the physical and mechanical properties of bamboo-oriented strand boards

Abstract: The purpose of this study was to analyze the chemical component change in betung bamboo (Dendrocalamus asper (Schult. & Schult. F.) Backer ex K. Heyne) strands after different steam and washing treatments, and their influence on the physical and mechanical properties of bamboo-oriented strand boards (BOSB). Strands were prepared with three different treatments: (1) steam-only, (2) steam followed by washing with distilled water, and (3) steam followed by washing with 1% sodium hydroxide solution. The steaming process was performed at 126 °C for 1 h at a pressure of 0.14 MPa. Chemical components such as holocellulose, alpha-cellulose, lignin, and starch were analyzed. Phenol formaldehyde resin was used to manufacture BOSB, and the physical and mechanical properties were evaluated in the final products. Steam treatments resulted in changes in chemical components that affected the physical and mechanical properties of BOSB. These changes were mainly caused by the degradation of hemicellulose and extractives dissolved in hot water or 1% sodium hydroxide. These treatments increased the bonding between strands, resulting in higher dimensional stability and strength of BOSB. Considering all the performed experiments, the steam treatment followed by washing with 1% sodium hydroxide was the best treatment for manufacturing BOSB.

Length and orientation direction effect on static bending properties of laminated Moso bamboo

Abstract: Considering the influencing factors length and bending direction, 124 small size specimens and 12 beam specimens of laminated Moso bamboo were manufactured and tested under static loading. Detailed discussions on how the length influences the bending performance of laminated Moso bamboo are presented in this paper. The bending directions have an influence on the strength but not very significant as a whole. No matter how long and which bending direction, each specimen showed a similar tensile failure process with increasing loading. Comparison of the two orientations of the small specimens indicates that the strength and modulus of elasticity values for tangential bending direction had increased over the values for radial bending direction. The length has an influence on the static bending properties of laminated Moso bamboo but not very clear. In addition, the formulas for calculating the ultimate bending moment and ultimate bending deflection were discussed under nonlinear conditions.

Bending performance of nail-laminated timber constructed of fast-grown plantation eucalypt

Abstract: Australia’s hardwood plantation estate is predominantly comprised of Eucalyptus nitens and Eucalyptus globulus, which are mainly being managed to produce woodchips—a low-value commodity export. There is an increasing interest by the timber industry in developing higher-value structural products from the low-grade timber recovered from these plantation resources. In this experimental study, for the first time, the bending performance of nail-laminated timber (NLT) and NLT-concrete composite (NLTC) floor panels constructed of the low-grade, fibre-managed Eucalyptus nitens and Eucalyptus globulus timber was evaluated. The test panels were constructed with various span lengths and cross-sectional configurations and subjected to vibration and four-point bending tests. The results indicated that the modulus of elasticity of the Eucalyptus nitens NLT panels (11,074.6 MPa) was comparable to that of NLT panels made of Eucalyptus globulus (11,203.2 MPa). The modulus of rupture of the Eucalyptus globulus panels was 13.8% higher than that of the Eucalyptus nitens ones. The bending properties of the NLT panels constructed of the two plantation species were superior to those of some commercially important mass laminated timber products reported in the literature. Under the limit state design loads, all the NLT and NLTC panels were still in the linear-elastic range. The fundamental natural vibration frequency values of the test panels were above the recommended minimum range of 8–10 Hz for residential and office floors. The two plantation timber species therefore demonstrated sufficient short-term bending performances to be used in the construction of higher-value structural floor products.

Optimal power consumption and surface quality in the circular sawing process of Douglas-fir wood

Abstract: Optimal cutting conditions that result in high cutting accuracy and low power consumption are critical in lumber recovery and quality for sustainable wood manufacturing. Despite the many research on wood machining for secondary processing applications, less emphasis has been put on the challenges faced in primary sawing applications. These challenges are associated with online monitoring of surface quality through waviness measurement and conducting full-scale wood cutting experiments under extreme conditions. This paper investigated the effect of feed speed, rotation speed, depth of cut, and the average chip thickness on the power consumption and waviness during the sawing process of green Douglas-fir wood. Power consumption and waviness were measured to find the optimal cutting conditions for energy efficient cutting with high cutting accuracy. Waviness was monitored online using laser displacement sensors and the acquired signals were filtered using the wavelet denoising method. The results showed that cutting power and waviness increased with feed speed. While increasing the rotation speed accounted for higher cutting power, it resulted in less waviness. The impacts of rotation speed on cutting power and the waviness of the sawn lumber were discussed. The waviness is significantly greater at the board top as it is close to saw rim, which is characterized by higher blade deflection. For an identical chip thickness, energy efficient cutting was obtained under low-speed conditions, whereas high-speed conditions improved the waviness. There is a trade-off between productivity, cut quality, and power consumption.

The influence of veneer thickness and knot proportion on the mechanical properties of laminated veneer lumber (LVL) made from secondary quality hardwood

Abstract: The first objective of this work was to study the influence of veneer quality on the mechanical properties of laminated veneer lumber (LVL) made of secondary quality hardwood. The second objective was to propose an adapted veneer thickness that provides the optimum mechanical properties of LVL, taking the veneer properties into account. Forty-eight LVL panels glued together using polyvinyl acetate (PVAc) were prepared. The quality of fresh veneers was assessed by measuring veneer knot proportion, lathe check depth and lathe check interval. The static modulus of elasticity (MOE), dynamic MOE, modulus of rupture (MOR) and shear modulus were measured using destructive and non-destructive methods. The 3 mm thick veneer provided the optimum mechanical properties for LVL for both species. The test direction did not have any significant influence on the mechanical properties. In the flatwise direction, the average MOE values obtained were 13.2 GPa for beech LVL and 13.3 GPa for oak LVL, whereas the MOR was 72.0 MPa and 63.4 MPa, respectively. Increasing knot proportion in veneers results in a decrease in LVL MOE and MOR. Moreover, deeper lathe checks and higher lathe check intervals on veneer surfaces provide lower LVL shear modulus in the edgewise direction for both species. Internal veneer provides LVL with a higher density but weaker mechanical properties due to a higher knot proportion in the internal veneer.

Effects of saturated steam pretreatment on the drying quality of moso bamboo culms

Abstract: Bamboo (Phyllostachys heterocycla f. pubescens) culms were pretreated by the saturated steam with the temperature of 140, 160, and 180 °C and subsequently dried by the kiln drying method. Results indicated that steam pretreatment has a significantly positive effect on the drying quality of the bamboo culms. The steam treatments with a temperature of 160–180 °C and duration of 25–15 min are suggested for the rapid drying of bamboo culms.

Seismic protection technologies for timber structures: a review

Abstract: Timber structures traditionally provided satisfactory seismic performance due to multiple known features. However, the consequences of the last major earthquakes have clearly proofed that seismic timber design must further improve. In addition, nowadays timber structures target taller heights and so they face much larger seismic demands. All this together has made seismic protection technologies (SPTs) to emerge as a hotspot in timber engineering research, devoting more than 80 publications only in the last decade. All types of SPTs share the common principle that, rather than increase the lateral resistance of a structure, they are focused on reducing the seismic demands and such reduction has been reported as large as 90% and above. Although many distinct devices and techniques are intended to this end, SPTs applied to timber structures may be grouped into supplemental damping, seismic isolation, and rocking systems. Apart from the copious scientific production in the field, knowledge has been published in very distinct niches, which makes a linkage of state-of-the-art very difficult, as well as an analysis of current challenges and limitations. This review attempts to provide so after explaining first the basic principles of these technologies so that they are comprehensible for a timber engineer or researcher not necessarily familiar with all structural dynamics’ underlying concepts. An outlook for future research trends is expected towards cost-effectiveness, rate-effects, engagement of devices, and design guidelines which may expand these technologies bringing timber structures into higher levels of seismic performance.

Particleboard bonded with bio-hardeners of tannin adhesives

Abstract: A totally bio hardener acting with an unusual and new hardening mechanism derived from the exudate extract of the African trees Vachellia nilotica and Senegalia senegal was used to harden a maritime pine tannin resin without any aldehyde obtaining a completely bio adhesive for interior particleboard. For a density and pH given, the internal bond (IB) values increased simultaneously with the rate of bio-hardener. The optimal dry IB values (0.63 MPa) were obtained with 15% of bio-hardener solids. The low IB value (0.38 MPa) was obtained with 6% of bio-hardener solids. The IB of panels manufactured with UF as hardener are slightly higher than those using the above bio-hardeners.

Influence of high voltage electrostatic field (HVEF) on bonding characteristics of Masson (Pinus massoniana Lamb.) veneer composites

Abstract: For the first time, it was experimented with high voltage electrostatic field (HVEF) for the optimization of the bonding process of urea formaldehyde (UF) resin to wood. Varying HVEF treatment times (0–8 min) and intensities (5–20 kV) were applied. Wood surface characteristics, polymerization extent of UF, and bonding interphase of UF to wood were examined by electron spin resonance (ESR) spectroscopy, dynamic contact angle goniometers, Fourier transform infrared spectroscopy (FTIR), X-ray densitometer, fluorescence microscope and bonding strength measurement. The results indicated that HVEF treatments applied to wood veneer induced a decrease in contact angles and an increase in the free radicals of wood, and surface energy varied with treatment times and intensities. These varieties were because triggered free electrons, broken chemical bonds and new ions appeared on the wood surface with HVEF treatment. An aggregated performance was obviously obtained in micrographs and vertical density profiles (VPDs). It was explained that resin penetration into wood structure was significantly shallow, and resin concentration and density at bonding interphase were more enhanced than the control. This is due to the increment of surface energy and lower contact angles providing more chances for possible reactions of wood surface with the UF resin. Resin penetration depth and density varied with different treatment times and intensities. Increased cross-linking extent of UF was obtained under varied conditions of HVEF treatment. The bonding strength was measured as a function of treatment times and intensities respectively; it increased by 85% and the wood failure ratio significantly increased by 70% under HVEF treatment (20 kV, 8 min) due to the aggregation performance and more cross-linked UF resin. It was manifested that both treatment time and intensity play a significant role in HVEF treatment, and HVEF treatment has a significant influence on the characteristics of the wood surface and the bonding properties of wood composites.

Protection of Moso bamboo ( Phyllostachys pubescens ) materials against fungal decay and discolouration by treatment with wood preservatives

Abstract: The efficacy of wood preservatives in protecting lignocellulosic materials of the gramineous species Phyllostachys pubescens (Moso bamboo) against decay by brown-, white- and soft rot fungi and discolouration by mould fungi was investigated. Vacuum treatment with copper amine and metal-free preservatives protected the bamboo material from attack by decay fungi. Solution uptake of the bamboo material was lower than that of the woody reference materials and must be considered for the treatment process. Dipping treatment with the metal-free preservative inhibited growth of mould fungi and prevented discolouration of the material. Untreated bamboo material was more susceptible to decay by white- and soft rot fungi than to decay by brown rot fungi but was generally more resistant to decay than the untreated wooden reference materials.

Thermal, physical and mechanical properties of surface overlaid bark-based insulation panels

Abstract: In terms of reduced energy consumption and simultaneously promoting woody biomass sustainability, researchers are seeking energy-efficient materials, originating from forestry and agricultural residues, for application in the building sector. In this study, bark-based panels overlaid on both surfaces with three different fibreglass types and two types of paper sheets were evaluated for potential utilization as thermal insulation panels. The proposed panels were then characterized regarding their thermal conductivity, physical, and mechanical properties such as density, water absorption, thickness swelling, surface soundness, bending strength and modulus of elasticity. It was found that thermal conductivity values ranged from 0.067 to 0.074 W/(m K) for all the produced panels. As suggested from the results, fibreglass overlays exhibited improved performance compared to paper sheet overlaying. In addition, the fibreglass overlaid bark-based panels displayed promising characteristics as insulation materials. Finally, fibreglass woven fabric was found to be more beneficial than the mesh and mat fibreglass types.

Volatile organic compounds and odor emissions from veneered particleboards coated with water-based lacquer detected by gas chromatography-mass spectrometry/olfactometry

Abstract: To reduce the problem of volatile organic compounds (VOCs) and odor emissions from veneered particleboards coated with lacquer, this study focused on identifying odorant compounds and exploring the potential influence of environmental factors on VOCs and odor emissions. Veneered particleboards coated with water-based lacquer were studied via gas chromatography-mass spectroscopy/olfactometry, and, in total, 10 different odor types were identified, which were concentrated in 15 to 23 min. The predominant odor impressions were fragrant, leather, and soybean paste, and the main odorant compounds identified were aromatics and alcohols. The total VOCs (TVOC) concentration and total odor intensity increased as the temperature increased, but decreased as the ratio of relative humidity and the air exchange rate to the loading factor increased. The ratio of the air exchange rate to the loading factor had a greater impact on the VOCs released from the veneered particleboard than did either temperature or relative humidity, and, therefore, this ratio should be the primary factor considered during storage. The proportion of the odorant concentration to the TVOC concentration decreased with an increase in temperature and relative humidity, whereas the ratio of the air exchange rate to the loading factor had little effect. To accelerate the release of VOCs and odors from veneered particleboard coated with water-based lacquer before its indoor use and, thus, to reduce negative effects on humans, the following conditions were found to be optimal: 40 °C, 40% RH, and 1.0 m3 h−1 m−2 (ratio of air exchange rate to loading factor).

Revealing the impacts of recycled urea–formaldehyde wastes on the physical–mechanical properties of MDF

Abstract: Recycling of the urea–formaldehyde (UF) products mainly obtained from adhesive wastes of wood industries is vital and requires a high level of attention due to the environmental and human health impacts of formaldehyde and other chemicals. In this study, the complete polymerized resin, as undesired waste product of Chassbsaz company, has been recycled and reused in the manufacturing process of medium density fiberboards (MDF). The results demonstrated that by adding recycled polymerized powder in sub-micron size to urea–formaldehyde control resin and replacing 1 wt% of the 55% solid content resin, the curing time of the resin significantly decreased. Fourier transform infrared spectroscopy (FTIR) demonstrated the chemical stability of the UF resins after adding 1 wt% recycled polymerized resin. In addition, there were substantial improvements in physical–mechanical properties [i.e., modulus of elasticity (MOE), modulus of rupture (MOR), internal bond (IB) strength and thickness swelling (TS)] of the newly manufactured board compared to that of the control board. Analysis of variance (ANOVA) was employed to study the dependency and significance of the physical–mechanical properties of the MDF on the concentration of the recycled polymer. Moreover, the production capacity was expected to significantly increase as the curing time decreased while maintaining the outstanding mechanical characteristics of the boards.

Prediction of the color change of heat-treated wood during artificial weathering by artificial neural network

Abstract: The purpose of this study was to predict the color change of heat-treated wood during artificial weathering by an artificial neural network (ANN) model. Chemical component analysis was used to analyze the origin of color change of the heat-treated wood. The network included an input layer consisting of three input nodes, namely, the weathering exposure time, heat treatment temperature, and heat-treated wood species, a hidden layer using six neurons and an output layer consisting of one output node, namely heat-treated wood color. A hyperbolic tangent sigmoid transfer function was used in the hidden layer, and the training algorithm was the Levenberg–Marquardt backpropagation. According to the results, the mean absolute percentage errors (MAPE) were 8.17, 9.70, and 9.85% for the prediction of color change (ΔE) for training, validation and testing data sets, respectively. Determination coefficients (R2) above 0.92 were obtained with the proposed ANN model for all data sets. These results showed that the ANN model can be successfully used for predicting the color change of heat-treated wood during artificial weathering. FTIR results showed that the color change of heat-treated wood during artificial weathering is due to the change in the chemical composition, especially the photodegradation of lignin and wood extractives.

Chemical analysis and cellulose crystallinity of thermally modified Eucalyptus nitens wood from open and closed reactor systems using FTIR and X-ray crystallography

Abstract: Currently there is a growing market for high quality solid wood products in Chile made from Eucalyptus nitens. Thermal modifications have been used to obtain such products out of fast growing species. The chemical and crystallinity changes in the modified wood were investigated using diffuse reflectance FTIR spectroscopy and crystalline analysis by X-ray diffraction to analyze the difference between thermal modifications processes using pressure under wet conditions (closed system) and processes without pressure under drier conditions (open system). In general, the FTIR spectra showed differences in the degradation of the hemicelluloses in the peaks of the C=O linkages, but almost no differences in the peaks that identify the lignin structure of the wood, as it was difficult to separate the different chemical reactions due to the depolymerization of lignin only observing the bands. The degree of crystallinity showed a tendency to increase at high pressure in the closed system modifications and at temperatures above 200 °C in the open system modifications, but no significant differences at low modification pressure and temperatures. Nonetheless, there were differences in FTIR spectra and cellulose crystallinity when directly comparing modifications with the same corrected mass loss under different conditions.

Effects of moisture content on elastic constants of fir wood

Abstract: In this study, the effect of moisture on elastic properties of fir wood (Abies cilicica Carr.) was investigated. Three moduli of elasticity in principal directions (EL, ER, ET), six Poisson’s ratios (υLR, υLT, υRT, υTR, υRL, υTL) and three shear moduli (GLR, GRT, GLT) were determined using compression tests. Compression strength in principal directions was also determined. Clear and small wood specimens were conditioned at 20 °C and 45, 65 and 85% relative humidity. Stress–strain curves of the samples were obtained using bi-axial extensometer in order to calculate elastic constants. Test results indicated that moisture content significantly reduced the measured properties except for Poisson’s ratio. The elastic modulus in the three principal directions is significantly different. Well-known order of EL > ER > ET for elasticity, and L > T > R for compression strength is valid. Shear modulus obeys the GLR > GLT > GRT rule. The results of this study can provide sufficient data for modeling of the elements or system’s behavior under load using fir wood.

Selected physical, mechanical, and insulation properties of carbon fiber fabric-reinforced composite plywood for carriage floors

Abstract: Lightweight automobiles urgently need a kind of high strength lightweight structure carriage floor. In this study, a carbon fiber fabric/poplar/eucalyptus composite plywood for carriage floors was prepared by designing different structures of low-strength, fast-growing poplar veneer, eucalyptus veneer, and high-performance carbon fiber fabric. The mechanical properties, thermal insulation, and sound insulation of the composite plywood were evaluated. Results indicated that the composite plywood had a density of less than 0.7 g/cm3. In addition, the 24 h water absorption rate and the 24 h thickness swelling rate of the composite plywood were markedly reduced after the surface was reinforced with the carbon fiber fabric. The core-reinforced group showed large increases in bond strength, screw holding capability, and thermal insulation performance. The carbon fiber fabric-reinforced plywood showed improvement in stability and sound insulation performance in high-frequency bands. The carbon fiber fabric-reinforced plywood is a low-cost, high-strength, lightweight floor alternative.

Modelling and multi objective optimization of bamboo reinforced concrete beams using ANN and genetic algorithms

Abstract: In this research, the costs as well as flexural and tensile strength of bamboo reinforced concrete material were predicted and optimized using artificial neural network (ANN) and non-dominated sorting genetic algorithm-II (NSGA-II). The inputs to the ANN were curing days and percentage bamboo content in the bamboo reinforced concrete material, while the outputs were cost, flexural and tensile strength. The ANN predicted the experimentally determined values of the tensile strength, flexural strength and costs of the bamboo reinforced concrete material excellently with correlation coefficients of 0.99635, 0.99739 and 1, respectively. Subsequently, the ANN was used as the fitness function for NSGA-II for multi-objective optimization of the cost, flexural and tensile strength of bamboo reinforced concrete material. The Pareto optimal solution obtained could serve as a design guide for engineers for optimal design of structures using cost, flexural and tensile strength of bamboo reinforced concrete material.

Mechanical characteristics of pine biomass of different sizes and shapes

Abstract: In the present study, the mechanical properties of granular biomass of pine origin (sawdust, shavings, long shavings and pellets) were determined. The bulk and tapped densities were determined in a cylindrical chamber. The compacted density was measured, and the influence of the moisture content on this quantity was examined in a vane tester. The flowability and strength properties were determined using a direct shear tester (Jenike box) 210 mm in diameter and standard Schulze ring shear tester. The tests in the Jenike tester complied with the Eurocode 1 procedure for normal pressure (σn) of 15 and 30 kPa and speed of shearing of 0.17 mm s−1. Ring shear testing was conducted using a Schulze annular shear cell of 195 mm outer diameter. Tests were performed for 10 and 20 kPa pre-shear σn. A prototype vane tester was constructed for determining the torque, shear strength, and relaxation of a consolidated sample of granular biomass. σn was exerted by a pneumatic system with a rubber air spring and yoke. The torque and density were measured for moisture content in the range of 10–50% and for σn in the range of 5–30 kPa. The torque was observed to be affected by σn and the moisture content, whereas no relationship between the torque and the rotational speed was observed.

Prediction of modulus of elasticity in static bending and density of wood at different moisture contents and feed rates by drilling resistance measurements

Abstract: An IML-RESI PD 400 drilling tool and a standard spade drill bit were used to find the correlations of drilling and feeding resistance with the modulus of elasticity in static bending and density of wood. In total, 1575 drillings at 0.5, 1.0 and 1.5 m/min feed rates were made in specimens of Scots pine (Pinus sylvestris L.), European beech (Fagus sylvatica L.), English oak (Quercus robur L.) and common lime (Tilia europaea L.), which were oven-dried, conditioned at 20 °C/65% RH and 20 °C/95% RH and vacuum-impregnated with water. The feed rate (feed rate per major cutting edge or uncut chip thickness) had a significant impact on the prediction of density and modulus of elasticity through drilling resistance measurements and should be considered for comparison of properties and internal conditions of wood. Because of stronger correlation between drilling resistance and tested wood properties compared to feeding resistance, drilling resistance is recommended for density and MOE prediction of sound wood. Moisture content had no significant impact on the modulus of elasticity prediction by the drilling resistance measurements, while density can be predicted by linear models for two stages of moisture content variation, below and above fibre saturation.

Initial study on the use of support vector machine (SVM) in tool condition monitoring in chipboard drilling

Abstract: The paper presents the idea of using support vector machine algorithm in a tool wear identification system in chipboard drilling. The indirect sources of information about tool wear were: feed force, cutting torque, acceleration of jig vibration, audible noise, and ultrasonic acoustic emission signals. The drills were classified (analogous to traffic rules) as “Green” (able to work), “Yellow” (warning state) or “Red” (unable to work–replacement needed).

Development of plywood using geopolymer as binder: effect of silica fume on the plywood and binder characteristics

Abstract: Geopolymers show good potential to be used as free formaldehyde-based binder to produce wood-based panels. Hence, the objective of this research was to investigate the geopolymer composition as binder on the physical and mechanical properties of multi-layered plywood. The geopolymer binder was prepared based on kaolin and metakaolin as the major aluminosilicate powder that were substituted with different contents of silica fume. The results showed that the substitution of aluminosilicate with silica fume (up to 20% based on weight) in the geopolymer mixture modified the chemistry of the geopolymerisation, and hence, improved the amorphous structures of the geopolymer binder. In summary, the substitution of aluminosilicate with silica fume (up to 20% based on weight) in the geopolymer mixture improved the geopolymer binder cohesion, reduced the binder viscosity, reduced the binder curing time, increased the binder penetration into the superficial wood cells, increased the binder shear strength, increased the bending strength of plywood, and accordingly, reduced the plywood stiffness. Notably, none of the plywood samples did delaminate even after 672 h water immersion, implying that the geopolymer binder-based products have a better stability in water compared to some organic binders (e.g., adhesives based on tannin, soya and starch), which suffer from hydrolysis after immersion in water. All in all, the geopolymer binder based on metakaolin showed promising potential to be used as formaldehyde-free binder to produce plywood.

Moisture-dependent mechanical properties of longitudinally compressed wood

Abstract: Since the properties of wood significantly change with its moisture content, it is important to know the effect of different moisture conditions on wood. A brief summary is provided on this topic in the first part of this article. The compression along the wood grain is a modification resulting in better pliability. The moisture dependence of mechanical properties of longitudinally compressed wood is not known yet. For this purpose, the results in this article are considered as basic research results. Bending- and compression tests on beech specimens compressed longitudinally by 20% were carried out at different moisture contents. Changing moisture content has almost no significant effect on the modulus of rupture of wood that has been longitudinally compressed, compared to the sensitivity to changes in moisture content of untreated wood. However, the effect of moisture content on the change of bending modulus of elasticity, compressive strength parallel to the grain and bendability coefficient diverges significantly. As a result of these changes, there is a great difference in the pliability with different moisture contents of treated wood. For the best pliability during bending, the moisture content of longitudinally compressed wood must be close to its fiber saturation point.

Experimental and numerical evaluation of hold-down connections on radiata pine Cross-Laminated-Timber shear walls: a case study in Chile

Abstract: Cross-Laminated-Timber (CLT) structures have gained popularity in the field of medium-rise buildings due to the quick fabrication and assembly of the panels. However, connections in radiata pine CLT shear walls and the behavior of CLT structures under lateral loads is still not well understood. In this context, this paper studies the structural behavior of hold-down connections on radiata pine CLT walls by means of experimental tests and numerical simulations under static and dynamic conditions. The test response of connections was replicated by calibrating two hysteretic models on OpenSees. The main results showed that applied models can reproduce the hysteretic behavior of hold-down connections with high precision. It was observed that hold-down connections on radiata pine CLT walls reached a loading capacity similar to other wood species, but the strength and stiffness degradation was quicker, and no significant difference with the parallel to grain capacity of angle bracket connections was noticed. In addition, it was found that radiata pine CLT walls can achieve suitable cyclic loading performance with low damage level in connections and reach high levels of displacement ductility. Finally, the importance of friction in the load capacity of the wall was also shown.

Surface mould growth on wood: a comparison of laboratory screening tests and outdoor performance

Abstract: Laboratory screening tests are commonly used to indicate wood materials’ resistance or susceptibility to surface mould growth, but the results can deviate from what happens during outdoor exposure. In this study, the aim was to investigate how well agar plate screening tests and water uptake tests can predict mould growth on exterior wooden claddings. The tested wood materials included Norway spruce heartwood (Picea abies), sapwood and heartwood of Scots pine (Pinus sylvestris), aspen (Populus tremula), acetylated Radiata pine (Pinus radiata) and DMDHEU-modified Scots pine sapwood. The agar plate test included four inoculation methods (two monoculture spore suspensions of Aureobasidium species, one mixed-culture spore suspension, and inoculation from outdoor air) and three incubation temperatures (5, 16 and 27 °C). Inoculation method and incubation temperature had significant effects on the mould rating in the agar plate screening test, but none of the agar plate test combinations gave good indications of outdoor performance. Results from the agar plate test gave significantly negative correlations or no significant correlation with results from the outdoor test. However, the water uptake test gave significantly positive correlations with outdoor mould rating, and could be a useful indicator of susceptibility of uncoated wooden claddings to surface mould growth.

Cu thin films on wood surface for robust superhydrophobicity by magnetron sputtering treatment with perfluorocarboxylic acid

Abstract: Superhydrophobic wood was fabricated using a magnetron sputtering method, which can be applied to substrates with different shapes for its facile and controllable advantages. Copper was deposited on the cross-section surface of pristine wood followed by a treatment of perfluorocarboxylic acid. The results revealed that the deposition thickness played an important role in varying the surface morphology. In the optimized condition, water contract angle (CA) and sliding angle can reach 154° and 3.5°, respectively, when the deposition thickness was 50 nm. More importantly, the superhydrophobic surface can resist up to 100 times impingement of sand abrasion, and CA retained to be 151°. This method will have promising applications in wooden artifacts, such as clock frame, art, carvings and decorations.

Efficiency of three conventional methods for extraction of dihydrorobinetin and robinetin from wood of black locust

Abstract: The aim of the study was to examine the amounts of extractives in sapwood and heartwood of black locust recovered using three different conventional extraction techniques and three different solvent compositions. Heartwood contained larger amounts of total phenols, dihydrorobinetin and robinetin than sapwood, irrespective of the extraction technique and solvent used. Dihydrorobinetin and robinetin were the characteristic phenolic compounds of black locust wood, whereas the concentration of dihydrorobinetin was significantly higher. The highest concentrations of examined extractives were obtained by Soxhlet extraction. More than ninety percent of extractives were leached from wood in a Soxhlet apparatus in less than 2 hours. Maceration with stirring and ultrasonic extraction gave smaller yields of extractives. The amounts of total extractives, total phenols and robinetin leached with the three solvents were comparable. Extraction of heartwood with acetone yielded significantly larger amounts of dihydrorobinetin than extraction with methanol or ethanol. Four hours extraction of wood meal with aqueous acetone in a Soxhlet apparatus was found to be the optimal extraction procedure for the recovery of dihydrorobinetin.