Showing papers in "Wood Science and Technology in 2012"

A review on natural products as wood protectant

Abstract: Traditional wood protection methods employ chemicals that are considered toxic and can adversely affect human health and the environment. Fortunately, serious efforts are being made globally to develop alternative protection methods based on natural products with little or no toxicity, but the progress in implementation of the technologies has been slow because of certain limitations, including discrepancies between laboratory and field performance of natural products, variability in their efficacy related to exposure/environmental conditions, and legislation difficulties due to disagreements globally on setting standards defining the quality of their performance and use. The focus of this review is to present information on the natural compounds that have shown promise for wood protection, and the information is presented under defined interactive categories. In closing, some thoughts are presented on potential use of rapidly evolving technologies, such as nano- and gene-technologies that can lead to significant advances, particularly from the consideration of specificity of natural products and their economic value.

Nanofibers from bagasse and rice straw: process optimization and properties

Abstract: Nanofibers (NF) were isolated from bleached bagasse and rice straw pulps. The pulps were refined using high-shear ultrafine grinder and then homogenized using high-pressure homogenizer. The efficiency of the used isolation processes was studied by optical microscopy (OM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and testing the tensile properties (wet and dry) of nanopaper sheets made from the nanofibers. In addition, opacity and porosity of nanopaper sheets made after different processing steps were investigated. The microscopy studies showed that the processes used resulted in nanofibers with diameters ranging from 3.5 to 60 nm. The results indicated that main isolation of nanofibers took place during refining using the ultrafine grinding process, while high-pressure homogenization resulted in smaller and more homogeneous size of nanofibers. Nanopaper sheets made from bagasse showed better wet and dry tensile strength properties than those made of rice straw.

Adhesive penetration in beech wood: experiments

Abstract: A study with synchrotron radiation X-ray tomographic microscopy (SRXTM) of PUR, PVAc, and UF adhesive bond lines in beech wood, bonded under various growth ring angles, is presented. The bond line morphologies and the adhesive penetration into the wood structure were evaluated after determining the hardening characteristics of the adhesives. Distinct bond line imperfections were found for the different adhesive systems. To describe the adhesive distribution inside the bond line, the saturation of the pore space instead of the commonly used maximum penetration depth seems to be adequate.

Moisture-dependent orthotropic elasticity of beech wood

Abstract: Elastic material properties are one of the most important material characteristics in mechanical modelling. Wood with distinctively different properties in the longitudinal, radial and tangential directions exhibits a strong moisture-dependent material characteristic in the elastic range. In order to characterise beech wood as an orthotropic material, all of the independent elastic properties were determined at different moisture conditions. These characteristic properties have never been determined before as a function of moisture content yet are vital to the field of wood modelling. All elastic parameters, except for some Poisson’s ratios, show a decrease in stiffness with increasing moisture content. In comparison to available literature references at a moisture content of ω ≈ 12%, the identified values were of the same order of magnitude. The determined material properties can be used to investigate the mechanical behaviour of beech wood structures including different moisture conditions.

A common near infrared—based partial least squares regression model for the prediction of wood density of Pinus pinaster and Larix × eurolepis

Abstract: Wood density is defined as the ratio of mass to volume and therefore in principle it should be possible to calculate a unique partial least squares regression (PLS-R) model for several species. PLS-R models for wood density based on X-ray microdensity data were calculated for each species Pinus pinaster and Larix × eurolepis and for both species together. After cross-validation and test set validation the data sets were combined and final models were calculated. The common model gave a residual prediction deviation (RPD) of 3.1, a range error ratio (RER) of 11.7, and a SEP/SEC of 1.06. The single models for Pinus pinaster and Larix × eurolepis gave RPD’s of 3.5 and 3.2, RER’s of 13 and 11, and a SEP/SEC of 1.2. To the best knowledge of the authors all obtained PLS-R models are the first ones that fulfil the requirements according to AACC Method 39-00 (AACC in AACC Method, 39-00:15, 1999) to be used at least for screening (RPD ≥ 2.5). Although this method and the defined limits were developed for the analysis of grains they can be used as a rough rule of thumb until limits for wood are available. The improvement of the PLS-R models, compared to published results, might be due to three facts (1) the higher number of scans collected for a single spectrum, (2) that the samples were better represented by the NIR spectra and X-ray microdensity values, and (3) that the sites for the measurement of NIR spectra and X-ray microdensity were coincided as strictly as possibly.

Chemical modification of simul wood with styrene–acrylonitrile copolymer and organically modified nanoclay

Abstract: Simul wood (Salmalia malabarica) was chemically modified by treatment with styrene–acrylonitrile copolymer (SAN), glycidyl methacrylate (GMA), and organically modified nanoclay. The physical properties of wood polymer composites (WPC) were improved due to the addition of GMA and nanoclay. XRD analysis indicated a decrease in crystallinity in WPC. FTIR study confirmed the presence of clay in WPC. The presence of clay in cell lumen and cell wall was evidenced by SEM study. WPC containing lower percentage of clay showed better thermal stability compared to WPC loaded with higher percentage of clay.

Properties of oriented strand board made from Betung bamboo ( Dendrocalamus asper (Schultes.f) Backer ex Heyne)

Abstract: Bamboo has gained increasing attention as an alternative raw material for use in the manufacture of composite boards. Three-layer OSBs were made using Betung bamboo (Dendrocalamus asper (Schultes.f) Backer ex Heyne) strands to evaluate the effects of strand length and pre-treatment techniques on the physical, mechanical, and durability properties. Three different strand lengths, namely 50, 60, and 70 mm, were prepared. Prior to the manufacture into OSB, the strands were immersed in cold water for 24 h and in 6% acetic anhydrides solution for 48 h. The OSBs were fabricated using 5% MDI resin based on the strand dry weight. The results indicated that MOR and MOE values in perpendicular to the grain direction were much influenced by strand length. The dimensional stability of OSB was slightly improved by immersing the strands in acetic anhydride solution. Immersing strands in cold water and acetic anhydride solution improved the resistance of OSB against subterranean termite (Macrotermes gylvus) attack under the adopted experimental condition. All OSB parameters manufactured in this experiment were better than the minimum requirement of CSA 0437.0 (Grade O–2) standard.

Influence of temperature and steam environment on set recovery of compressive deformation of wood

Abstract: Low-density hybrid poplar wood (Populus deltoides × Populus trichocarpa) was densified by mechanical compression under saturated steam, superheated steam, and transient conditions at temperature levels of 150, 160, and 170°C. Furthermore, compression of wood under saturated steam conditions at 170°C, followed by post-heat-treatment at 200°C for 1, 2, and 3 min, was performed. To determine the influence of compression treatment on the set recovery, specimens were subjected to five cycles of water soaking and drying. Modulus of rupture (MOR) and modulus of elasticity (MOE) of specimens compressed under saturated steam conditions at 170°C and post-heat-treated at 200°C were determined in the dry condition and after five soak/dry cycles. Higher temperature of the compression treatment resulted in lower equilibrium moisture content, while the steam conditions during the treatment and the post-heat-treatment did not have significant effect. Furthermore, the highest degree of densification was obtained in specimens compressed under saturated steam conditions at 170°C and post-heat-treated at 200°C. The steam condition and temperature influenced the set recovery of compressive deformation. Reduced hygroscopicity does not necessarily imply reduced set recovery. The results established that considerable fixation of compressive deformation can be obtained by compressing the wood in a saturated steam environment and by post-heat-treatment at 200°C. The short heat-treatment had no influence on MOR or MOE, but soaking/drying treatments caused a decrease in the MOR and MOE.

Extraction of antioxidants from eucalyptus ( Eucalyptus globulus ) bark

Abstract: The extraction of phenolic compounds from eucalyptus (Eucalyptus globulus) bark was examined with the aim of analyzing the potential of the extracts as natural antioxidants. Experiments were planned according to a 23 factorial design to analyze the influence of temperature and Na2SO3 and NaOH concentrations in aqueous solutions on extraction yield, extract total phenols content, ferric reducing antioxidant power (FRAP), and number- and weight-average molecular weights. Extract total phenols content and FRAP antioxidant activity in the ranges 0.91–2.58 g gallic acid equivalent (GAE)/100 g oven-dried bark and 4.70–11.96 mmol ascorbic acid equivalent (AAE)/100 g oven-dried bark, respectively, demonstrated the potential of eucalyptus bark as a source of antioxidant compounds. Extraction at the highest temperature (100°C), the lowest Na2SO3 concentration (1.5% on oven-dried bark), and without NaOH provided the highest extract total phenols content and FRAP antioxidant activity. Those eucalyptus bark extracts with lower molecular weight showed higher antioxidant activity. Matrix-assisted laser desorption ionization time-of-flight and reverse-phase high-performance liquid chromatography electrospray ionization time-of-flight mass spectrometry revealed the presence of polygalloyl glucoses, catechin, epicatechin, ellagic acid, quercetin-3-o-rhamnoside, and isorhamnetin in eucalyptus bark aqueous extracts.

Changes in wettability of heat-treated wood due to artificial weathering

Abstract: Effect of artificial weathering on the wettability of three heat-treated North American wood species (jack pine, aspen, and birch) is studied from the point of view of the structural and chemical changes taking place on the wood surface. Weathering increases wettability of all three heat-treated woods by water. Changes in wettability during artificial weathering differ according to heat treatment procedure and wood species and are likely due to combination of structural and chemical changes of the surfaces. Scanning electron microscopic analysis indicates that cracks form due to degradation taking place during weathering. As a result, water has easier entry into the cell wall, which consequently increases wettability. IR spectra suggest that the OH/CH2 ratio for heat-treated specimens is inversely proportional to the contact angle regardless of the type of wood species. The presence of cellulose-rich layer on wood surface and increasing amount of amorphous cellulose transformed from crystallized cellulose due to weathering result in increase in hydroxyl; consequently, it increases heat-treated wood wettability.

Fire-retarding properties of nano-silver in solid woods

Abstract: Fire-retarding properties of 200 ppm nano-silver solution, with a size ranging from 20 to 80 nm, on five woody species were studied and compared with Borax and Celcune ® . Blocks of 150 × 130 × 9 mm³ were prepared and divided into four groups of control samples, nano-silver-, Borax-, and Celcune-impregnated specimens. A special apparatus was designed, and six fire-retarding properties of each specimen were measured, namely ignition, glowing, back-darkening and back-holing times, as well as length and width of burning. Results showed that all three kinds of treatments had improving effects on the fire-retarding properties. Celcune showed the best improvement on glowing time. Cluster analysis showed direct relation between density and fire-retardant properties; also, fire-retarding behaviors of the four hardwoods were quite different to those of the one softwood. Furthermore, there are improvements in some fire-retarding properties of nano-silver-impregnated specimens that are in connection with its heat-transfer property.

Variation of extractives content in heartwood and sapwood of Eucalyptus globulus trees

Abstract: The variation in extractives content in sapwood and heartwood was investigated among 12 trees in each of four commercial plantations of Eucalyptus globulus in central Portugal. The study was carried out at the 15% height level and extractions used successively dichloromethane, ethanol and water. At all sites, heartwood had significantly more extractives than sapwood, on average 3.8 and 2.4%, respectively. Most extractives consisted of ethanol soluble material (on average 52% of total extractives). Among the sites, there was a statistically significant difference in the content of extractives but the most important source of variation was the within-tree variation between sapwood and heartwood. Differences in the content of extractives were also observed among trees. A strong relation between extractives content and heartwood proportion was found. The potential loss of pulp yield and problems associated with accumulation of extractives are directly related to the heartwood proportion in the eucalypt stems. Forest management should take into account heartwood development and selection for minimising heartwood extractives.

Coloring characteristics of in situ lignin during heat treatment

Abstract: To investigate the effects of lignin on the discoloration of Black locust (Robinia pseudoacacia) wood during heat treatment, chromatic indexes of the extractive-free wood samples are examined at different moisture contents (MC) under oxygen and nitrogen environment, respectively. The organic acids are produced during heat treatment, resulting in pH decrease in the samples. Components absorbing visible light are formed during heat treatment, and oxygen and moisture contents have obvious effects on the decrease in L*, increase in a* value, yellowness (b*) and total color difference (ΔE) of the samples. It is found that the β-5, C α C β unsaturated bond, the conjugated carbonyl group, quinones structures, α, β-unsaturated ketone and α-C = O in lignin increased after heat treatment. The formation of condensation products, the low-molecular-weight phenolic substances and the oxidation products in lignin result in the increment of the light absorption within the entire visible region.

Surface functionalization of bamboo with nanostructured ZnO

Abstract: Imparting excellent preservative performances to bamboo is the key to expand the applications of this extraordinary non-wood forest resource. This study reports on the formation of ZnO-nanostructured network films on the surface of bamboo via a simple two-step process. This process consists of the generation of ZnO seeds on the bamboo surface followed by a solution treatment to promote the crystal growth. The morphology and chemical composition of the ZnO films were studied by field-emission scanning electron microscopy combined with energy-dispersive X-ray analysis and X-ray diffraction. Accelerated weathering was used to evaluate the photostability of the treated wood. The antifungal and antibacterial performances were also examined. The results indicate that the approach can simultaneously furnish bamboo with excellent photostability and antifungal and antibacterial performances. The growth mechanism of ZnO-nanostructured network films on the uneven and chemically complicated surface of bamboo was also discussed.

Compression of wood under saturated steam, superheated steam, and transient conditions at 150°C, 160°C, and 170°C

Abstract: In this paper, the compressive deformation of hybrid poplar wood (Populus deltoides × Populus trichocarpa) at high temperature (150, 160, and 170°C) and under various conditions of steam pressure was studied. Temperature and conditions of steam environment affected the relative density change and creep deformation during compression, as well as properties of the resulting densified material. While the temperature significantly affected the compression deformation of specimens compressed under transient and superheated steam conditions, temperature within the range studied had little effect on the compressive deformation in saturated steam. In all tested conditions, compression deformation was achieved without cell wall fractures. Higher temperature of compression, regardless of steam condition, resulted in lower equilibrium moisture content. In specimens compressed under saturated steam, the modulus of rupture (MOR) and modulus of elasticity (MOE) were increased proportionally to the increase in density, while the compression under superheated steam produced lower increase in the MOE and MOR than expected based on the increase in density. Compression in transient steam conditions at 170°C produced densified wood with higher MOE and MOR than expected based on the increase in density.

The Fracture Toughness and Properties of Thermally Modified Beech and Ash at Different Moisture Contents

Abstract: The fracture toughness of thermally modified beech (Fagus sylvatica L) and ash (Fraxinus excelsior L) wood under Mode I loading was quantified using Compact Tension (CT) specimens, loaded under steady-state crack propagation conditions. The influence of three heat-treatment levels and three moisture contents, as well as two crack propagation systems (RL and TL) was studied. Complete load–displacement records were analysed, and the initial slope, k init, critical stress intensity factor, K Ic, and specific fracture energy, G f, evaluated. In the case of both species, thermal modification was found to be significantly affect the material behaviour; the more severe the thermal treatment, the lower the values of K Ic and G f, with less difference being observed between the most severe treatments. Moisture content was also found to influence fracture toughness, but had a much less significant effect than the heat treatment.

Physical properties and termite durability of maritime pine Pinus pinaster Ait., heat-treated under vacuum pressure

Abstract: An original heat treatment performed under vacuum pressure was investigated. Maritime pine samples were treated at six different temperatures: 140, 160, 180, 200, 230 and 260°C. The physical and mechanical consequences, i.e. bending strength (MOR), modulus of elasticity (MOE), hygroscopic behaviour, equilibrium moisture contents and anti-swelling efficiency (ASE) were studied. A no-choice feeding test according to the NF EN 117 standard was achieved. Temperatures up to 200°C had no significant effect on wood properties. However, at 230 and 260°C, the decrease in MOR was severe, reaching 42.5 and 62.5%, respectively. Whatever the treatment conditions, wood samples were still highly degraded by termites, revealing no increase in their durability.

Roughness models for sanded wood surfaces

Abstract: The understanding of the effects of variables is crucial to achieve the desired sanded surface quality at optimum condition. In wood surface evaluation, it is known that anatomies on wood surface could distort the roughness value and cause a misinterpretation of the processing performance. In this study, statistical approaches were taken to characterize the influence of sanding variables as well as to analyze the anatomical noises that were inherited from intra- and inter-species of woods. Four available roughness parameters (R a , R q , R k and R ap) were used to examine the surface of three distinct wood species, viz. kembang semangkok, red oak and spruce in wide-belt sanding. Based on the mean values, analysis of variance showed that species (anatomy) was significant to all conventional parameters except R ap which was filtered by monitoring the second derivative of Abbott-curve. In spite of this, R ap recorded a more widely dispersed deviation of random measurement values than R k and R a . The effects of grit size and feed rate were found to be significant. Empirical roughness models were established using response surface methodology, and the errors were calculated by comparing the model values to all the randomly measured values. Although exhibiting slight species-dependant effect by nature, R k showed reliable consistency by recording the lowest error values (<10%) for both intra- and inter-species measurements. Experimental results also suggested that three random measurements at each run could be sufficient. The method of constructing machinability models can be readily applied in the industry as a quality control tool for wide-belt sander.

Nondestructive evaluation of heat-treated Eucalyptus grandis Hill ex Maiden wood using stress wave method

Abstract: The objectives of this study were to evaluate the effect of heat treatment of eucalypt wood (Eucalyptus grandis Hill ex Maiden) on the dynamic modulus of elasticity by using the stress wave nondestructive method and also to determine the air-dry density variation, weight loss and equilibrium moisture content following treatment. Heat treatments were performed at four different temperatures (180, 200, 215 and 230°C) and for three different durations (15 min, 2 and 4 h). The results revealed a significant reduction in air-dry density following heat treatment independent of temperature and time. A significant weight loss was observed between and within treatments. The treatment at 230°C for 2 and 4 h produced a weight loss of 20.5 and 26.5%, respectively, which was statistically different from other treatment conditions. The dynamic modulus of elasticity decreased by about 13% in the most severe treatment (230°C for 4 h). Depending on the temperature and time, the equilibrium moisture content was significantly reduced within the range of 40–74%.

Eucalyptus camaldulensis density and fiber length estimated by near-infrared spectroscopy

Abstract: Density and fiber length belong to the parameters that are used by the pulping industry as indicators of wood quality for different industrial processes and final paper products. The feasibility of Fourier transform near-infrared (FT-NIR) spectroscopy for the non-destructive evaluation of fiber length and air-dry density of fast-growing E.camaldulensis from Thailand was investigated using 50 samples. NIR spectra taken from solid wood and air-dry density as well as fiber length were used for partial least squares (PLS) regression analyses. It is the first time that the fiber length of E.camaldulensis solid wood could be predicted with high accuracy and precision and that the ratios of performance to deviation (RPD) obtained are the first that fully fulfill the requirements of AACC Method 39-00 (AACC 1999) for screening in breeding programs (RPD ≥ 2.5). The RPDs for cross-validation (test set validation) of the NIR-PLS-R models of 3.3 (3.8) for air-dry density and 3.5 (3.9) for fiber length allow drawing the conclusion that the models are at least applicable for screening in breeding programs as they lie in-between screening (RPD ≥ 2.5) and quality control (RPD ≥ 5). Even when 40% of the samples were removed in cross-validation of the air-dry density model, the RPD is 3.2, which confirms that the model is robust, stable, and well qualified for prediction. The good model statistics obtained in this study might be due to the fact that measurement sites for the measurement of NIR spectra, air-dry density, and fiber lengths were strictly coincided.

Liquid water absorption in dried Norway spruce timber measured with CT scanning and viewed as a percolation process

Abstract: Liquid flow in dried wood is complicated to study, since wood is a nonhomogeneous, hygroscopic-porous, anisotropic material. However, liquid flow is important to understand, since it has an influence on the durability of wood and on such processes like impregnation, drying, surface treatment, etc. In this study, simulations of liquid water absorption in wood as a fibre network, percolation, were compared with experimental water absorption in the longitudinal direction in spruce timber. With CT scanning, water distribution during liquid flow can be shown visually and measured by image processing. Liquid water absorption in end grain of spruce was measured with CT scanning after 1, 3, 7 and 14 days of liquid water absorption and shown as moisture content (MC) profiles in heartwood and sapwood. It was found that the amount of water absorbed could be expressed as a linear function of the square root of time. The slopes of the lines differed between sapwood and heartwood and also varied depending on the growth condition of the trees. The simulations according to the percolation method show generally good agreement with the measured results for sapwood.

Removal of cadmium (II) from aqueous solutions by adsorption using meranti wood

Abstract: Meranti wood, an inexpensive material, has been utilized as an adsorbent for the removal of cadmium (II) from aqueous solutions. Various physico-chemical parameters such as equilibrium contact time, solution pH, initial metal ion concentration, and adsorbent dosage level were studied. Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The experimental data fitted well with the Langmuir adsorption isotherm, indicating the monolayer adsorption of the cadmium (II). The monolayer adsorption capacity of meranti wood for cadmium (II) was found to be 175.43, 163.93 and 153.84 mg/g at 30, 40, and 50°C, respectively. The thermodynamics of cadmium (II) adsorption on meranti wood indicates its spontaneous and exothermic nature. Kinetic studies showed that the adsorption followed a pseudo-second-order kinetic model. The results indicated that the meranti wood could be an alternative for more costly adsorbents used for cadmium (II) removal.

Production of hemicellulosic sugars from Pinus pinaster wood by sequential steps of aqueous extraction and acid hydrolysis

Abstract: Pinus pinaster wood samples were subjected to aqueous extraction at 130°C to remove extractives and to a sequential stage of hydrothermal processing under selected operational conditions to obtain hemicelluloses-free solids and liquors containing hemicelluloses-derived products (mainly oligomeric saccharides and monosaccharides). Liquors were separated from the media, supplemented with sulfuric acid (4%), and heated to cause the posthydrolysis of oligomeric saccharides to yield hemicellulosic sugars. The effects of the major operational conditions on the yields of the target products were assessed in selected experiments. The considered process enabled the recovery of hemicellulosic sugars (mannose, glucose, xylose, and galactose) at almost quantitative yields.

Biosorption of Ce(III) onto modified Pinus brutia leaf powder using central composite design

Abstract: The biosorption of Ce(III) from aqueous solution by citric acid-modified Pinus brutia leaf powder was studied in a batch system as a function of initial pH, temperature, initial concentration of adsorbate, and contact time. Central composite design method was used in the experiments. Thermodynamic parameters such as standard enthalpy (ΔH0), entropy (ΔS0), and free energy (ΔG0) were calculated, and the results indicated that biosorption was exothermic. The biosorption of Ce(III) on modified Pinus brutia leaf powder was investigated by Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) isotherms. The results show that Ce(III) adsorption can be explained by Langmuir isotherm model, and monolayer capacity was found as 62.1 mg/g. The results suggested that the modification process enhances the biosorption capacity of the adsorbent, and modified Pinus brutia leaf powder may find promising applications for the recovery of Ce(III) from aqueous effluents.

Bamboo nanofiber preparation by HCW and grinding treatment and its application for nanocomposite

Abstract: A new approach to prepare cellulose nanofiber was attempted using the combined method of hot-compressed water (HCW) treatment and disk milling. The HCW treatment was effective in loosening the cell wall structure and enhancing fibrillation by disk milling. The fibrillated products showed fine fibrous morphology at the nanometer scale. Filtration time and specific surface area were measured as criteria of the degree of fibrillation, and both these values were increased in nanofibers obtained by disk milling after HCW treatment. The obtained nanofiber-reinforced polyurethane composite was prepared, and its tensile properties were drastically improved by the increased nanofiber content.

Acoustic tomography in relation to 2D ultrasonic velocity and hardness mappings

Abstract: Acoustic tomography is an emerging nondestructive testing (NDT) technology for tree decay detection in both urban community and production forest. Many field studies have been conducted to assess the applicability and reliability of the technique in such applications. Although investigations into urban trees showed great success using acoustic tomography to detect moderate to severe internal decay within the trunk, detection of early stage of decay using such technology still constitutes a challenge. This study was aimed to evaluate the capability of acoustic tomography by determining the relationships between acoustic tomograms and two-dimensional mappings of ultrasonic properties and end-hardness of the trunk cross sections. A freshly cut black cherry (Prunus serotina) log was used to simulate a tree trunk and tested in the laboratory. Time-of-flight (TOF) acoustic tomography measurements were conducted at three different heights (10, 30, and 50 cm). A disk was then cut from each height and subjected to ultrasonic and mechanical evaluations. The results indicated that the acoustic shadows in the tomograms revealed internal structural defects that were at the same locations and in similar magnitudes as the wood property mappings of the disks. However, no good correlations were found between apparent acoustic velocity of the tomograms and the measured ultrasonic velocity and end-hardness of small cubic samples. This analysis indicates that TOF acoustic tomography lacks the sensitivity to low-velocity features of decayed areas and thus has limited capability in detecting early stages of decay in trees.

Viscoelastic properties of wood materials characterized by nanoindentation experiments

Abstract: The viscoelastic properties of the cell wall of the tropic hardwood Carapa procera are investigated by means of nanoindentation tests. Three types of nanoindentation tests are undertaken: creep, continuous stiffness measurement (CSM) and nanoscale dynamic mechanical analysis (Nano-DMA), corresponding to the increased loading rate and so the response of wood cell wall to the loading in a relatively large time scale. It is found that the creep rate is dependent on the applied stress and the relation can be described by the rule of power law. Regarding the dynamic properties (i.e., storage modulus and damping coefficient) in the frequency range of 10–240 Hz, it is shown that the storage modulus increases monotonically, while the damping coefficient decreases. By using the traditional dynamic mechanical thermal analysis as a reference method, the phase transition behavior of wood cell wall can be successfully characterized by the Nano-DMA in a large frequency scale. A dependence of the storage modulus and damping coefficient on the penetration depth is quantified by the CSM tests.

Classification of thermally modified wood by FT-NIR spectroscopy and SIMCA

Abstract: Quality assessment of thermally modified wood has evolved as one of the major fields in the research on thermal modification of wood. This study investigates NIR spectroscopy in combination with the pattern recognition method of soft independent modeling of class analogies (SIMCA). Focus is put on identifying different treatment intensities of thermally modified samples of beech, ash, and Norway spruce. The results indicate that SIMCA classification based on NIR spectroscopy could be used for quality control of thermally modified wood. The method might be applicable for producers (pre-delivery checks) and customers (reception control). However, transfer from laboratory to industrial conditions needs further investigation.

Mechanical behaviour of finger joints at elevated temperatures

Abstract: Finger joints are commonly used to produce engineered wood products like glued laminated timber beams. Although comprehensive research has been conducted on the structural behaviour of finger joints at ambient temperature, there is very little information about the structural behaviour at elevated temperature. A comprehensive research project on the fire resistance of bonded timber elements is currently ongoing at the ETH Zurich. The aim of the research project is the development of simplified design models for the fire resistance of bonded structural timber elements taking into account the behaviour of the adhesive used at elevated temperature. The paper presents the results of a first series of tensile and bending tests on specimens with finger joints pre-heated in an oven. The tests were carried out with different adhesives that fulfil current approval criteria for the use in load-bearing timber components. The results showed substantial differences in temperature dependant strength reduction and failure between the different adhesives tested. Thus, the structural behaviour of finger joints at elevated temperature is strongly influenced by the behaviour of the adhesive used for bonding and may govern the fire design of engineered wood products like glued laminated timber beams.

Western red cedar extractives associated with durability in ground contact

Abstract: Western red cedar (WRC) is well known for its natural durability. However, the roles of all the extractives that may be associated with this durability are not fully understood. The literature primarily credits the thujaplicins, with a lesser role for the lignans; however, previous work has identified highly durable material with low thujaplicin content. To elucidate the relative importance of various extractives, the decay resistance of WRC stakes at four test sites was compared with data on the content of specific extractives to determine whether there was any detectable association. The concentration of plicatic acid, a lignan, was associated with the decay resistance of WRC lumber in ground contact. An unidentified, unquantified compound (B) appeared to be similarly associated with decay resistance. The thujaplicins were only weakly associated with the decay resistance of WRC in ground contact.