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Highlights: [•] Used X-ray to visualize, quantify thermo-physical behaviour of wood for first time. [•] Visualization of intra-particle conversion during devolatilization for first time. [•] Visualization of propagation of char front and anisotropic effect for first time. [•] Determined “char formation time” and “shrinkage” during devolatilization. [•] 3-D model used to predict the intra-particle propagation of conversion fronts. [Copyright &y& Elsevier]

Ionic liquids (ILs) have been investigated for their potential as reagents for enhancing the fire resistance of wood. The following ILs were in focus: 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-ethyl-3-methylimidazolium hexafluorophosphate ([C2mim][PF6]). Supposedly, these ILs do not dissolve or degrade wood components to a large extent. No morphologic changes were observed in any ILtreated wood samples, but they showed an enhanced fire resistance compared with that of untreated wood. Scanning electron microscopy and energy-dispersive X-ray analysis demonstrated that the ILs are penetrated into the cell walls. The wood treated with [C2mim][PF6] exhibited the highest fire resistance based on thermogravimetric and differential thermal analyzer studies: it was more resistant against flaming at approximately 350°C and the subsequent glowing at higher temperatures. This enhanced fire resistance was interpreted by dehydration in the presence of the ILs under observation. In general, ILs are promising reagents for improving the thermal properties of wood. [ABSTRACT FROM AUTHOR]

The thermal and dielectric properties of medium density fiberboard (MDF) with different moisture contents were measured by light flash and the parallel-plane capacitor method, respectively. The results show that increasing moisture content has a positive effect on both thermal properties and dielectric properties. The higher the moisture content, the higher the thermal conductivity and dielectric properties were. The thermal conductivity of MDF with different moisture contents varies in the temperature range of 25 to 150 ºC in a double-hump pattern rather than a proportional pattern. The dielectric constant decreases with increasing frequency up to 1000 MHz. The dielectric loss factor undulates within the frequency range of 1 to 100 MHz, and the peak value occurs at around 10 MHz. The results presented in this study can be used for radio frequency heating, wood building energy, material design, and radio frequency evaluation. [ABSTRACT FROM AUTHOR]

Abstract: This study aims to investigate the change in chemical composition, surface characteristic and mechanical properties of heat treated four wood species (ash, iroko, Scots pine and spruce) during artificial weathering from 400 h to 1600 h in relation to their color changes, surface roughness, compression strength, modulus of elasticity, modulus of rupture and surface composition. Original color of wood species was significantly changed by heat treatment and artificial weathering. Artificial weathering decreased color change of heat treated wood samples except for iroko. Color change significantly increased with longer weathering exposure for heat treated wood samples however similar trend was not observed for control samples exposed to weathering factors. In general, heat treatment alone did not have a considerable effect on surface roughness of wood. Heat treatment seemed to protect wood surface to become rougher after weathering for softwoods. Compression strength and MOR of samples decreased while MOE increased during heat treatment. Compression strength, MOR and MOE of samples decreased considerably with longer weathering exposure both for heat treated and control samples. Softwood species seemed to be more affected by heat and weathering than hardwood species did with respect of loss on the strength properties. Severe delignification and hemicellulose degradation occurred in heat treated and control samples for all wood species during weathering from 400 h to 1600 h evident from rapid decrease at 1504/1508 cm−1 and 1730 cm−1, respectively. Heat treatment did not fully protect hemicellulose degradation and delignification occurred by weathering with longer exposure periods. [Copyright &y& Elsevier]

The work presented in this paper reports on the water sorption properties of thermally modified wood, densified wood and wood modified using a combination of the two methods. The paper presents new findings concerning the sorption isotherms and sorption kinetics behaviour. The sorption kinetics is analysed in terms of the parallel exponential kinetics (PEK) model which has recently been introduced to the wood science community as a better alternative to the often used Fickian models, at least where cell wall sorption behaviour is considered. The PEK model comprises two exponential sorption kinetic terms which are termed fast and slow sorption processes. The PEK model is then interpreted by using a relaxation-limited kinetics model consisting of two series-coupled Kelvin-Voigt elements. [ABSTRACT FROM AUTHOR]

Birch wood ( Betula pendula) samples were treated in a thermal regime (140, 160, 180 °C) for 1 h and investigated by means of scanning electron microscopy (SEM). SEM microimages of the wood cross-section were taken from one and the same place before and after the thermal treatment (magnification 100-2,000×). The results of measurements of areas and linear sizes of the birch wood cells show significant changes, which depend on the thermal treatment conditions and the type of the cell: libriform, tracheid, vessel and ray. After the treatment at 180 °C, the integrity of wood morphological structure begins to break up. Voids and cracks are formed between fibres, thus leading to a decline in the mechanical properties of the wood. [ABSTRACT FROM AUTHOR]

The thermal properties of wood in the green state have been determined by the transient plane source (TPS) technique. Data are presented on thermal conductivity ( λ), heat capacity ( C), and thermal diffusivity ( κ) at moisture contents (MCs) above the fiber saturation point, which are based on measurements using the HotDisk® apparatus. Four wood species (Douglas fir, beech, birch, and spruce) were tested, and the results are compared with literature data and those obtained by the flash method. A linear relationship was found between the thermal properties λ, C, and κ on the one hand and MC on the other. Equations predicting the thermal values as a function of MC and wood anisotropy are presented. Wood C and λ increase with MC, but wet wood diffuses heat more rapidly than dry wood. [ABSTRACT FROM AUTHOR]

The effects of laser incising on the surface of heat-affected zones (HAZs) and liquid uptake of wood were examined. Deep pin holes were incised on the tangential section of the wood with a laser beam of 1 kW in power with varied pulse widths, and the HAZs of the holes were investigated using scanning electron microscopy. The length of liquid uptake passing through HAZs surfaces was then measured. It was observed that the HAZs were unable to maintain normal porous structure, and smooth surfaces such as that of wood charcoal were also not observed. This is because the composite of the middle lamella completely melted, which led to a decrease in the length of liquid uptake. In addition, the release of high gas-pressure and thermal energy during the laser-incising process did not damage the tylose and the aspirated pit in the longitudinal direction. Because of this, the liquid movement remained blocked. However, the incising holes provided additional liquid-intake points, resulting in greater intake capacity. Moreover, it was observed that improvement of liquid impregnation is related to hole diameter. [ABSTRACT FROM AUTHOR]

The present study investigates the effect of heat treatment of untreated and nano-silver-impregnated Populus nigra, Populus deltoides and Fagus orientalis on the physical and mechanical properties. Specimens were impregnated with a 200-ppm aqueous silver nanoparticles suspension. Heat treatment was carried out at temperatures of 135 ± 3 °C and 185 ± 3 °C. Nano-silver impregnation aggravated the effects of heat treatment. Although significant in some cases, nano-silver impregnation did not seem to have great effect on physical properties. It may be concluded that although NS impregnation aggravated the effects of heat treatment on solid woods, other factors may also be involved such as the species and density of the wood. [ABSTRACT FROM AUTHOR]

Studying the impregnation and distribution of oil-based preservative in dried wood is complicated as wood is a nonhomogeneous, hygroscopic and porous material, and especially of anisotropic nature. However, this study is important since it has influence on the durability of wood. To enhance the durability of thermally modified wood, a new method for preservative impregnation is introduced, avoiding the need for external pressure or vacuum. This article presents a study on preservative distribution in thermally treated Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies (L.) Karst.) sapwood using computed tomography scanning, light microscopy, and scanning electron microscopy. Secondary treatment of thermally modified wood was performed on a laboratory scale by impregnation with two types of preservatives, viz. Elit Träskydd (Beckers) and pine tar (tar), to evaluate their distribution in the wood cells. Preservative solutions were impregnated in the wood using a simple and effective method. Samples were preheated to 170 °C in a drying oven and immediately submerged in preservative solutions for simultaneous impregnation and cooling. Tar penetration was found higher than Beckers, and their distribution decreased with increasing sample length. Owing to some anatomical properties, uptake of preservatives was low in spruce. Besides, dry-induced interstitial spaces, which are proven important flow paths for seasoned wood, were not observed in this species. [ABSTRACT FROM AUTHOR]

Scots pine ( Pinus sylvestris L.) sapwood was impregnated with aqueous solutions of phenol formaldehyde and methylated melamine formaldehyde resins and subsequently cured in an oven. One set of specimens was cured in plastic bags to avoid drying (wet curing) while another set of samples was heated and water was allowed to freely evaporate (dry curing). Macroscopic resin distribution was investigated using X-ray densitometry and infrared spectroscopy (FTIR-ATR). During dry curing, the resins migrated to the wood surface resulting in a gradient. Wet curing resulted in even distribution of the resins because it was immobilized due to condensation and precipitation in the wood. Neither densitometry nor FTIR-ATR was found to be generally applicable for investigating resin distribution in modified wood. Wet curing resulted in low cell wall bulking as compared to dry curing, probably because resin precipitated before drying. Storing impregnated wood prior to curing under non-drying conditions ('diffusion phase') also reduced cell wall penetration and bulking. [ABSTRACT FROM AUTHOR]

Wood-polymer nanocomposite (WPNC) based on styrene-acrylonitrile copolymer (SAN), γ-trimethoxy silyl propyl methacrylate-modified TiO nanoparticles, and nanoclay was prepared by impregnation. The flexural, tensile, and flame-retardant properties were improved. UV stability was evaluated by photo-induced weight loss, FTIR, loss in mechanical properties, and scanning electron microscopy. The results showed that UV stability was maximum for wood sample treated with SAN/TiO (0.5 %)/nanoclay (0.5 %). The presence of TiO nanoparticles in WPNC-exhibited antibacterial activity. [ABSTRACT FROM AUTHOR]

An overview on the mechanical and physical properties of cross laminated timber (solid wood panels) in the building industry and its use in timber construction is presented. Structure-property relations for solid wood based materials are discussed. Important properties, such as strength, sorption, diffusion, thermal conductivity in relation to the board structure are presented. By varying the structure, the properties can be optimized over a wide range. The focus of this publication lies on experimental works performed by Swiss researchers at the ETH Zürich. [ABSTRACT FROM AUTHOR]

The effect of zinc borate (ZB) treatment on the mechanical and morphological properties of wood flour/polypropylene composites was investigated. Wood flour was first treated with ZB solution (1% w/w in ethanol-distilled water), followed by 24 hours of soaking on an unheated magnetic stirrer hot plate until relatively complete saturation was reached. Then, composites based on ZB-pretreated, ZB-treated-during-manufacturing, and untreated wood flour, polypropylene and coupling agent were made by melt compounding and then injection molding. The ZB treatment had no significant influence on mechanical properties of the composite with the exception of tensile strength. The composite made with ZB-pretreated wood flour exhibited the same mechanical properties as the composites made with ZB-in-process-treated wood flour; however there were statistically significant differences between flexural modulus and tensile strength of ZB-pretreated composites and ZB-in-process treated ones. Specimens containing the ZB showed lower flexural, tensile, and impact strength compared with the untreated specimens. However, the zinc borate treatments produced modest improvements in hardness performance. The SEM micrographs revealed that the outer surface of the wood fibers was coated by some crystalline deposits of zinc borate. [ABSTRACT FROM AUTHOR]

The longitudinal compressive and multi-directional bending properties after hydrothermal treatment of juvenile and mature elm wood were analyzed. Wood chemical composition and X-ray diffraction analyses were conducted in order to investigate the different properties of the juvenile and mature wood. Scanning electron microscopy was used to observe the wood's microstructure during longitudinal compression. The results indicated that both juvenile and mature wood could bend multi- directionally and that their relative cellulose crystallinities increased after hydrothermal treatment. The hydrothermal-treated juvenile wood contained more hemicellulose with unstable net-linked polysaccharide and condensed lignin, higher relative crystallinities degree than did mature wood, and more spaces formed by the extractive separation of mature wood. The longitudinal compressive and bending performances of the juvenile wood were worse than those of mature wood. The relationship between variations of stress and strain was separated into two stages, both of which displayed linear increases. However, the stage after the proportional ultimate stress increased slowly and smoothly, confirming the formation of some folds in the wood cells. [ABSTRACT FROM AUTHOR]

The effect of hydrothermal treatment at various temperatures (100 to 160 °C) and treatment times (30 to 720 minutes) on color changes (ΔE*), equilibrium moisture content (EMC), tensile strength (TS), shear strength (SS), brown-rot fungal decay mass loss (FML), and termite attack score (TAS) of rubberwood was examined. Response surface methodology (RSM) with a two-factor, four level (42 ) full factorial was employed. The mathematical models describing those properties as functions of treatment temperature and logarithm of treatment time were obtained. Hydrothermal treatment adversely and positively influenced mechanical properties (TS and SS) and durability (FML and TAS), respectively, of rubberwood. Strong correlations between ΔE*, TS, SS, and FML of hydrothermally treated rubberwood, proposed to be a consequence of degradation of hemicelluloses, were observed. Finally, ΔE* proved to be a good indicator of TS, SS, and FML but not that of EMC and TAS of hydrothermally treated rubberwood. [ABSTRACT FROM AUTHOR]

A study was carried out to investigate the effect of thermal treatment on biological resistance of Populus tremuloides wood against four decay fungi, including T. versicolor, P. placenta, G. trabeum and C. puteana. The weight loss data showed that degradation of untreated wood by the white rot fungus T. versicolor resulted in higher weight loss (571%) compared to those by brown rot fungi G. trabeum (21•9%), P. placenta (36•7%) and C. puteana (7 1%). When this species was heat treated at 220°C, the weight loss was reduced to <10%. Increasing temperature and the holding time appeared to affect the resistance against I versicolor, P. placenta and G. trabeum attacks, but the effect on the resistance against C. puteana was not significant. The humidity during thermal modification affected the degradation of wood against I versicolor attack, but it did not have a significant effect on the other fungi. [ABSTRACT FROM AUTHOR]

Radio-frequency (RF) heating has been widely used in the wood industriesand it is essential to understand the factors affecting the heating rates. In this article, Chinese fir (Cunning hamialanceolata) was heated with RF energy intermittently at 2 min per cycle to study the effect of wood moisture content (MC), sample thickness, and RF power level on heating rates. The study revealed that wood MC significantly affected the RF heating rate (p < 0.01). The heating rate was the highest (5.0°C/cycle) at an MC around the wood fiber saturation point (FSP). The heating rates were lower with a lower MC of 15% (0.89°C/cycle) and a higher MC of 70% (1.2°C/cycle). Lumber thickness did not have a significant effect on the RF heating rate at the center of the lumber; however, the heating rates at various locations along the thickness direction were significantly different. The temperature at the lumber center was 20°C higher than the temperature at 10 mm below the surface during heating. The heating rate for lower RF power level was initially greater than the rate at higher power RF level and then rapidly decreased. However, the heating rate at the higher RF power level remained constant during the whole heating process. RF power levels had a significant effect on the internal heating rate of wood (p < 0.01). [ABSTRACT FROM AUTHOR]

The influence of thermal treatment on moisture exchange between wood and natural environment with variable air parameters as well as on dimensional stability of wood samples was investigated. The experiments were carried out with oak wood samples indoors and outside. The thickness of samples was 30 mm, width was 30 mm and length was 20 mm; conventional density varied from 500 kg/m³ to 580 kg/m³. Initially, the wood was air-dried down to 7%-9% of moisture content. In order to decrease possibility of the both moisture absorption and evaporation during wood application thermal treatment must be applied. Due to that the samples were heated at temperature of 60, 80, 100 and 120 °C for 24, 48, 72 and 96 hours. The moisture content of wood and its variations after thermal treatment depends on the both heating temperature and duration. The higher temperature and the longer heating duration, the lower wood hygroscopicity can be achieved. The effect of thermal treatment on the moisture content and its changes were observed for wood samples stored indoor and outside. In dependence of thermal treatment conditions moisture content in wood samples independently on storing conditions (indoor or outside) can decrease down to 30 % compare to the untreated ones. The change of moisture content during various seasons after 24 hours of storing indoor decreases down to 60 %, while outside that is only 39 %. Dimensional stability of wood samples also depends on the both thermal treatment temperature and duration. The higher treatment temperature and the longer duration, the higher dimensional stability can be obtained. The heat treatment of oak wood samples at selected regimes allows to decrease values of shrinkage and swelling coefficients down to 40 %. [ABSTRACT FROM AUTHOR]

Wood is still widely used as a construction material but in spite of great assortment of antifungal chemicals, incidents of treated-wood damage still happen. The objective of the present investigation was to identify the fungal species that survived after wood treatment and make a primary screening of some physiological properties important for fungi in wood colonization. Fungal strains from Alternaria, Cladosporium, Fusarium, Penicillium, Phoma, Trichoderma and Ulocladium genera were isolated and identified. The primary endoglucanase and phenoloxidase activity discoloration assays showed that wood colonization ability of fungi isolated from treated wood differed among the strains and some of them had not only cellulolytic but even ligninolytic activity as well. The spectrophothometric analysis of fungal enzymatic activity on wood showed that Alternaria alternata 8/15-2 was most active tyrosinase producer and Cladosporium herbaram 8/15-1 -- laccase producer whereas peroxidase activity level and variation tendency of all strains was alike. Among studied strains only Penicillium genus representatives had medium acidification ability. Alternaria alternata 8/15-2 was the hardiest to wood preservatives fungal strain. The study of fungal physiological properties could help in selecting wood preservatives, in elucidation of reasons of their inefficiency and creating of new ones. [ABSTRACT FROM AUTHOR]

The influence of wood components and cellulose crystallinity on the kinetic degradation of different wood species has been investigated using thermogravimetry. Four wood species were studied: Pinus elliottii (PIE), Eucalyptus grandis (EUG), Mezilaurus itauba (ITA) and Dipteryx odorata (DIP). Thermogravimetric results showed that higher extractive contents in the wood accelerate the degradation process and promote an increase in the conversion values at low temperatures. Alternatively, the results indicated that the cellulose crystallinity inhibits wood degradation; organized cellulose regions slow the degradation process because the well-packed cellulose chains impede heat diffusion, which improves the wood’s thermal stability. The wood degradation mechanism occurs by diffusion processes when the conversion values are below 0.4. When the conversion values are above 0.5, the degradation is a result of random nucleation with one nucleus in each particle. [ABSTRACT FROM AUTHOR]

Abstract: Natural wood, being biological material, undergoes rapid degradation by ultraviolet (UV) radiations and other environmental factors under outdoor exposure. In order to protect wood from such degradation, the chemical structure of wood is altered by chemical modification or heat treatment. In the present study, heat treated specimens of rubberwood (Hevea brasiliensis) were exposed to xenon light source in a weather-o-meter for different periods up to 300h. Photostability of modified and unmodified wood was evaluated in terms of colour and chemical changes. Light coloured untreated wood became dark upon UV irradiation whereas, dark colour of heat treated wood lightened on UV exposure. CIE lightness parameter (L *) decreased for untreated wood whereas its value increased for heat treated wood upon irradiation. Other colour coordinates a * and b * increased with exposure duration for both untreated and heat treated wood. The overall colour change (ΔE *) increased for both untreated and heat treated wood. The Fourier Transform Infrared (FTIR) spectroscopic studies revealed severe lignin degradation of heat treated wood due to UV light exposure. Colour changes and FTIR measurements indicate that thermal modification of wood was ineffective in restricting light induced colour changes and photodegradation of wood polymers. [Copyright &y& Elsevier]

The time-dependent mechanical behaviour (TDMB) of wood is important when using the material for structural purposes. Recently, a new method for predicting the TDMB by numerical modelling was established based on the assumption that TDMB is caused by the sliding of the microfibrils past each other. In this study, the TDMB is examined via creep experiments on small specimens of Norway spruce latewood. The results of these are compared with results from numerical modelling. The experiments include results at two levels of moisture content and three levels of temperature, enabling an investigation of these two climatic factors on TDMB of wood. It was found that the mechanical response of wood tissue is the sum of responses from both tracheids and middle lamella, with only the previous being reversible. The effect of moisture and temperature differed in that the latter affected the elastic and time-dependent responses equally. Moisture, on the other hand, reduced both the elastic properties and the activation energy barrier for sliding of the microfibrils, but furthermore changed the microfibril angle of the sample as a result of swelling. Hereby, moisture had a larger effect on the time-dependent response than the elastic. All of these effects were predicted by numerical modelling. [ABSTRACT FROM AUTHOR]

The moisture content of wood is known to have a significant influence on the wood's mechanical properties. Using wood as an energy absorber in impact limiters of packages for the transport of radioactive material, it is of particular importance to ensure the moisture content and thus relevant mechanical properties to be in specified limits. The paper surveys the influence of wood moisture content on the mechanical properties of wood. Different measuring methods are discussed with respect to in situ applicability, accuracy and effort. The results of an experimental analysis of the accuracy of hand held moisture metres using the electrical resistance method are discussed. Conclusions are drawn regarding the measurement of moisture content of wood upon delivery as well as of complete impact limiter assemblies. Requirements for quality surveillance during manufacturing of wood filled impact limiters are derived and it is exemplified how to meet them. Construction, manufacturing and inspection of impact limiter encapsulation with regard to leak tightness are addressed. [ABSTRACT FROM AUTHOR]

Fracture toughness of wood and wood composites has traditionally been characterized by a stress intensity factor, an initiation strain energy release rate ( G) or a total energy to fracture ( G). These parameters provide incomplete fracture characterization for these materials because the toughness changes as the crack propagates. Thus, for materials such as wood, oriented strand board (OSB), plywood and laminated veneer lumber (LVL), it is essential to characterize the fracture properties during crack propagation by measuring a full crack resistant or R curve. This study used energy methods during crack propagation to measure full R curves and then compared the fracture properties of wood and various wood-based composites such as, OSB, LVL and plywood. The effect of exposure to elevated temperature on fracture properties of these materials was also studied. The steady-state energy release rate ( G) of wood was lower than that of wood composites such as LVL, plywood and OSB. The resin in wood composites provides them with a higher fracture toughness compared to solid lumber. Depending upon the internal structure of the material, the mode of failure also varied. With exposure to elevated temperatures, G for all materials decreased while the failure mode remained the same. The scatter associated with conventional bond strength tests, such as internal bond and bond classification tests, renders any statistical comparison using those tests difficult. In contrast, fracture tests with R curve analysis may provide an improved tool for characterization of bond quality in wood composites. [ABSTRACT FROM AUTHOR]

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/CH 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Context: Recent works have showed the possibility of measuring sap flow density ( u) by a single heated probe using the transient regime just after the heating current is switched off. The method (SP-T) is based on a thermal index ( I) which involves the temperature of the probe at three different times of the cooling kinetics (beginning, intermediate time, and end), the latter representing wood temperature at equilibrium. Aims: The present paper re-examines the method to better estimate wood temperature and to account for possible variations in probe-wood thermal properties. Methods: After a recalibration of the method on an olive branch with a hydraulic bench, the SP-T method is used to measure sap flow on two olive trees under field conditions. Results: Estimated flow densities are compared to those obtained with the transient thermal dissipation-dual probe method (TTD-DP) of Do and Rocheteau. Conclusions: Obtained results show that: (1) wood reference temperature is better estimated when using the probe temperatures just before heating and at the end of the cooling phase; (2) calibration relationships based on a 'normalized' thermal index K = (I − I )/I, where I represents the value of I under zero flow conditions, better account for differences in the wood-probe thermal properties; (3) I, taken as the lowest I over a 24-h span, has shown consistent stability for a given probe-tree complex; (4) the SP-T method used in its normalized form appears to be in good agreement with the TTD-DP method. [ABSTRACT FROM AUTHOR]

In this paper, anisotropic wood is thermally characterized using the transient hot-bridge method recently developed at PTB Germany. The main element of this method is the THB sensor which is composed of four tandem strips forming a Wheatstone bridge and which has the specificity of measuring in the same experiment both thermal conductivity and thermal diffusitnty. The adoption of special configurations allows us to characterize anisotropic materials. In this context, the axial, radial, and tangential thermal conductivities as well as the thermal diffusivities of three wood species are measured and analyzed for different moisture contents. Due to the difficulty of measuring thermal diffusivity using the conventional electrothermal methods, particular care will be given to this task. Thus, the paper will focus on the analysis of thermal diffusivity versus moisture content, as well as on its relation to thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Eucalyptus globulus Labill. is managed in commercial plantations for the pulp and paper industry as a coppice system. For stand reforestation the stumps are uprooted and at present used as biofuel. In this study, the biomass of stumps collected in six eucalypt stands in Portugal was evaluated in terms of physical, chemical and fuel properties. Stumps had basic density between 0.55gcm−3 and 0.71gcm−3, and the chemical composition showed 15.1% total extractives (mainly ethanol soluble extractives, 10.5%), 24.8% lignin and 67.0% holocellulose. In terms of thermal properties the stumps presented 18.9MJkg−1 for higher heating value (HHV) and 0.6%, 81.1% and 18.3% respectively for ash, volatile matter and fixed carbon. The elemental composition (C=51.0%; H=5.8%; O=45.3%; Cl=0.04%) has adequate values for use as woodfuel. [Copyright &y& Elsevier]

With thermal modification, changes in properties of wood, such as the presence of VOC and water-soluble carbohydrates, may occur. Thermal modifications under saturated steam conditions (160°C or 170°C) and superheated steam conditions (170, 185, and 212°C) were investigated by analysing the presence of water-soluble 5-(hydroxymethyl)furfural (HMF), furfural, and carbohydrates in heat-treated wood. The influence of thermal modifications on Scots pine, Norway spruce, and silver birch was also studied. Furfurals were analysed using HPLC at 280 nm, while monosaccharides and water-soluble carbohydrates were determined by GC-FID as their acetylated alditiols and, after methanolysis, as their trimethylsilylated methyl-glycosides, respectively. The amount of furfurals was larger in boards thermally modified under saturated steam conditions than those treated under superheated steam conditions. Generally, more of HMF than furfural was found in the thermally modified boards. In process water, in which saturated steam conditions had been used, furfural and only traces of HMF were found. Higher content of water-soluble carbohydrates was found in boards treated in saturated steam rather than in superheated steam. After modification in saturated steam, substantial parts of the water-soluble carbohydrates were due to monosaccharides, but only traces of monosaccharides were found in boards treated under superheated steam conditions. [ABSTRACT FROM AUTHOR]

This work deals with pyrolysis decomposition of wood chips and the main components of wood by thermogravimetric analysis (TGA). Experiments were carried out in the inert atmosphere of nitrogen. The pyrolysis temperature range was varied linearly from 20 °C to 900 °C with the heating rate equal to 5 K min1 to detect all the changes without overlapping. Samples of cellulose, hemicellulose and lignin were used as main components of wood. Thermogravimetric (TG) and differential thermogravimetric (DTG) curves were obtained from experimental data. These records were compared with those obtained by mathematical modeling. The distribution activation energy model (DAEM) was used for mathematical description of experimental data and the prediction of kinetic parameters. According to the DAEM approach, every possible decomposition reaction with various values of activation energies is in progress at each time and temperature. Preexponential factors, mean activation energy and variance were obtained as kinetic parameters. This model is able to describe the integral decomposition curve of biomass, however, a problem occurs when describing the differential curve of biomass thermal decomposition. In general, this model does not accurately describe the decomposition of materials, which are a mixture of several compounds. [ABSTRACT FROM AUTHOR]

Changes in color (CIE L*a*b*) and properties (density, mass loss, density loss, and bending properties) of heat-treated beechwood were researched, as well as the possibilities of predicting these properties based on color. Considering the different market values of sapwood and red heartwood, the aim of this study was to establish whether these parts of beechwood differ after a heat treatment. Samples were exposed to temperatures of 170°C, 190°C, and 210°C, respectively, for 4 hours. In order to predict the properties, a linear regression with color change (ΔE) and ΔL predictors was used, as well as the partial least squares (PLS) regression with 12 color variables. It has been shown that heat treatment reduces the properties of sapwood and red heartwood in the same manner, and equalizes the colors. The PLS-R showed the best results of prediction and presented the very high coefficients of determination for the mass loss, density loss, and modulus of rupture (MOR) in both sapwood and red heartwood. The equalized colors of heat-treated red heartwood and sapwood can significantly increase the use of products made out of red heartwood. Color can be an important indicator of the quality of such beechwood. [ABSTRACT FROM AUTHOR]

Wood-TiO2 (titania) composites were prepared by a sol-gel process, in which wood was impregnated with the precursor solutions prepared from tetrabutyl titanate (TBT), followed by a curing step. The surface morphology and moisture absorption behavior of the wood composites, as well as their thermal and mechanical performances, were examined. Environmental scanning electron microscopy (ESEM) analysis revealed that TiO2 gels were deposited principally in the cell lumens and partly in the cell walls, as confirmed by the energy dispersive X-ray (EDX) analysis. By this inorganic modification, the hygroscopicity of wood was significantly reduced and its dimensional stability was improved consequently. Greater amounts of TiO2 gel deposited in the cell lumens were not helpful in enhancing the hygroscopicity of wood. Thermal analysis (TG-DTA) showed that the incorporation of TiO2 gel retarded the thermal decomposition of wood matrix and improved the thermal stability of wood. The incorporated inorganic gel seemed to stiffen the wood cell walls, as indicated by the increased resistance of the wood composites to deformation and collapse in compression. [ABSTRACT FROM AUTHOR]

The second part of a comprehensive review of the literature on wood published in the Journal of Materials Science since its inception in 1966 is presented. The topics reviewed include wood modification and surface treatment, the thermal stability of wood and resistance to fire, the physical properties of wood chars and wood-based carbon materials, and the structure-related properties of wood-cement and wood-polymer composites. The articles reflect the wide range of techniques utilised to improve wood properties, the role of wood as a precursor for carbon-based materials and cellular ceramics and the application of wood as a composite reinforcement. JMS is in the vanguard of the latest developments in all these disciplines. [ABSTRACT FROM AUTHOR]

In this study the thermal conductivity of different wood materials was determined. For this purpose, Scots pine (Pinus sylvestris L.), Uludag fir (Abies Bornmülleriana Matff), Oriental beech (Fagus orientalis L), Oak (Quercus robur L.), and Chestnut of Anatolia (Castanea sativa Mill.) woods were used. In the test, the thermal conductivity of the woods was measured according to procedure of ASTM C 1113-99 standards. The lowest thermal conductivity was obtained in the perpendicular direction of Scots pine samples as 0.156 Kcal/mh°C. The highest thermal conductivity was obtained from perpendicular direction of samples in Oriental beech as 0.331 Kcal/mh°C. [ABSTRACT FROM AUTHOR]

A variety of thermal approaches are used to estimate sap flux density in stems of woody plants. Models have proved valuable tools for interpreting the behavior of heat pulse, heat balance and heat field deformation techniques, but have seldom been used to describe heat transfer dynamics for the heat dissipation method. Therefore, to better understand the behavior of heat dissipation probes, a model was developed that takes into account the thermal properties of wood, the physical dimensions and thermal characteristics of the probes, and the conductive and convective heat transfer that occurs due to water flow in the sapwood. Probes were simulated as aluminum tubes 20 mm in length and 2 mm in diameter, whereas sapwood, heartwood and bark each had a density and water fraction that determined their thermal properties. Base simulations assumed a constant sap flux density with sapwood depth and no wounding or physical disruption of xylem beyond the 2 mm diameter hole drilled for probe installation. Simulations across a range of sap flux densities showed that the dimensionless quantity k [defined as (ΔTm −ΔT)/ΔT, where ΔTm is the temperature differential (ΔT) between the heated and unheated probe under zero-flow conditions] was dependent on the thermal conductivity of the sapwood. The relationship between sap flux density and k was also sensitive to radial gradients in sap flux density and to xylem disruption near the probe. Monte Carlo analysis in which 1000 simulations were conducted while simultaneously varying thermal conductivity and wound diameter revealed that sap flux density and k showed considerable departure from the original calibration equation used with this technique. The departure was greatest for variation in sap flux density typical of ring-porous species. Depending on the specific combination of thermal conductivity and wound diameter, use of the original calibration equation resulted in an 81% under- to 48% overestimation of sap flux density at modest flux rates. Future studies should verify these simulations and assess their utility in estimating sap flux density for this widely used technique. [ABSTRACT FROM AUTHOR]

Abstract: In order to promote the use of Pinus pinea L. wood within the Migliarino-San Rossore Nature Reserve (Pisa, central Italy), three low-environmental-impact wood treatments, supposed to enhance natural durability, were compared. Impregnations with an oil-based preservative and natural waxes and a wood thermal treatment were tested in the field in accordance with standards ENV 12037 and EN 252. The above-ground test revealed that: P. pinea sapwood is more durable than Pinus sylvestris sapwood; all the alternative treatments showed a low mean decay level; wax and oil treatments performed as well as the traditional copper-based preservative; the natural durability class of P. pinea will only be calculated upon the complete failure of all reference lap-joints. The main outcomes from the in-ground test were: All the tested treatments increased the durability of wood, and the protective effectiveness of alternative treatments was comparable to traditional copper-based ones, or even superior in the case of heated oil. Taking certain mechanical and aesthetic limitations into account, all the treatments were suitable for the promotion of the P. pinea wood commodity in use classes 3 and 4. [Copyright &y& Elsevier]

Abstract: The purpose of this study is to investigate the torrefaction behavior of woody biomass (Lauan) blocks and its influence on the properties of the wood. Three different torrefaction temperatures of 220, 250 and 280 °C, corresponding to light, mild and severe torrefactions, and four torrefaction times of 0.5, 1, 1.5 and 2 h were considered. After analyzing the torrefied woods, it was found that the torrefaction temperature of 280 °C was able to increase the calorific value of the wood up to 40%. However, over 50% of weight was lost from the wood. The grindability of the torrefied wood could be improved in a significant way if the torrefaction temperature was as high as 250 °C and the torrefaction time longer than 1 h. Therefore, the torrefaction temperature of 250 °C along with the torrefaction time longer than 1 h was the recommended operation to intensify the heating value and grindability as well as to avoid too much mass loss of the wood. This study also suggested that over 50% of the reacted wood was converted into condensed liquid. The main components in the liquid were monoaromatics; little amount of heterocyclic hydrocarbons were also obtained from the torrefactions, especially at the torrefaction temperature of 280 °C. [Copyright &y& Elsevier]

Abstract: The Higher Heating Value (HHV) of 17 wood fuels was correlated with their Klason lignin (L) and extractive contents (Ext). There was a highly significant correlation between higher heating value, Klason lignin and extractive contents. The HHV (MJ/kg) of wood fuels as a function of lignin and extractive contents can be calculated using the following equation: qv,gr,d = 14.3377 + 0.1228 (L) + 0.1353 (Ext). The correlation coefficient (r) was 0.915. The standard error for Klason lignin was 0.017 and to extractive contents of 0.024. The proportion explained by Klason lignin was 56.4% and explained by extractive contents was 43.6%. [Copyright &y& Elsevier]

The ignition of various wood species by exposure to the radiation of a DKsR-10000 xenon lamp was investigated. Time dependences of ignition delay on the radiant energy intensity were obtained for various wood species: cedar, larch, pine, birch, and aspen. The effect of the initial temperature and moisture content of wood on the ignition time was studied. The ignition temperature of pine and birch wood for various radiant energy intensities was determined by an optical method. It is shown that the ignition time of pine wood decreased by a factor of 1.5-2 as the initial temperature of samples was increased by 100 degrees. It was found that the ignition temperature of wood increased with increasing radiant flux density and depended on the wood species. Increasing the wood moisture content by a factor of 10 increased its ignition time by more than 50%. [ABSTRACT FROM AUTHOR]

Two Malaysian hardwoods, acacia (Acacia mangium) and sesendok (Endospermum malaccense), that had been subjected to oleo-thermal modification were studied to determine their sorption isotherm behaviour using a dynamic vapour sorption apparatus. All the specimens were thermally modified using palm oil at three different temperatures (180, 200 and 220°C) and three different times (1, 2 and 3 h). The results showed that there was a reduction in equilibrium moisture content at each target relative humidity due to the heat treatment, but that the two wood species showed different behaviour in this respect. The adsorption isotherms were analysed using the Hailwood and Horrobin model, with excellent fits to the experimental data. The monolayer water and polylayer water were both reduced at a range of relative humidity values of the treated samples, although behaviour between the two wood species differed. Heat treatment resulted in an increase in hysteresis ratio, which was probably due to the increase in matrix stiffness of the cell walls. [ABSTRACT FROM AUTHOR]

In this study, thermal properties of wood/HDPE composites were measured by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The composites comprised of different wood (45%, 55%, and 65%) and maleic anhydride grafted polypropylene (MAPP) contents (0%, 1.5%, and 3%), and particle size (20, 40, and 80 mesh) were produced by extrusion method. TGA measurements showed that wood content is the most important factor affecting the thermal stability, initial mass loss, and ash content of the composites. Any increase in wood content led to increase in ash content and less thermally stable composites. MAPP and particle size were found to have less impact on thermal stability. By retarding the formation of charcoal MAPP influenced thermal stability of composites adversely in composites consisting of bigger particle. Composites made of 65% wood content with 20 mesh size and 0% MAPP were more thermally stable than composites made of 65% wood content with 80 mesh size and 3% MAPP, in the temperature range of 270-500°C. Melting point measurements by DSC showed that melting point had no relationship with wood and MAPP contents, and particle size. [ABSTRACT FROM AUTHOR]

Abstract: This research aims at developing a new approach able to simulate 3-D heat and moisture transfer coupled with the mechanical behaviour of a wood during drying process. From the moisture content and temperature profiles, a 3-D formulation and a relevant constitutive model are used to calculate the stress/strain evolution within the board due to shrinkage and external mechanical loading. This allows a fast, comprehensive and realistic model to be implemented. The mechanical model takes into account the hydrous, thermal, mechano-sorptive and elastic deformations, as well as the changes of wood properties, caused by these processes, e.g. porosity, permeability, stress–strain relation, etc. The mathematical model describing simultaneous unsteady heat and moisture transfer between a gas phase and a solid phase during heat treatment has been developed. The conservation equations for the wood sample are obtained using diffusion equation and the 3-D incompressible Navier–Stokes equations have been solved for the flow field. The constitutive equations are discussed in some detail. ANSYS-CFX10 commercial code was used to solve the hygro-thermal problem and FESh++ for the mechanical behaviour. Experimental results obtained regarding temperature, moisture content and deformation profiles during industrial drying of black spruce wood are compared with the numerical results. Satisfactory agreement is obtained over a range of drying air temperatures. [ABSTRACT FROM AUTHOR]

In this study the thermoplastic flow behavior of steamed wood flour was investigated. First it was demonstrated that steamed Japanese beech flour flowed out of the nozzle under compression at high temperature in a thermal flow test with a capillary rheometer. The effects of the steaming temperature, steaming time, compressive pressure, and moisture content of wood flour on the thermal flow temperature were examined. It was shown that the higher the steaming temperature and compressive pressure, the lower the thermal flow temperature. Also, the thermal flow temperature of the sample steamed at 200°C for 20 min became lowest and increasingly higher over time. Furthermore, the thermal flow temperature became linearly low with increasing moisture content of the sample under 15%, whereas it became essentially constant over 15%. It is clarified that compressive pressure and moisture content as well as the steaming conditions profoundly affect the thermoplastic flow behavior of steamed wood flour. [ABSTRACT FROM AUTHOR]

Abstract: The present study is devoted to a numerical study with experimental validation of the high-temperature thermal treatment of three-dimensional wood pole. During the heat treatment process, the heat and mass transfer takes place between the solid and the drying medium, and the moisture evaporation occurs within the solid due to the capillarity action and diffusion. The development of the model equations, taking into account both bulk phases and interfaces of the multiphase system is described, starting from the microscopic scale. Fundamental to this model is the ability to quantify the effects of key material and geometric properties of the pole. The three-dimensional and unsteady-state mathematical model equations are solved numerically by the commercial package FEMLAB for the temperature and moisture content histories under different treatment conditions. A detailed discussion of the computational model and the solution algorithm is given. Heat treatment was applied on the test samples in an oven for three final temperatures (180, 200 and 220°C). A series of experimental tests aimed at determination of heat treatment schedules kinetics curves and the temperature and moisture profiles and there time evolution were carried out. A very good agreement between the experimental and predicted results was obtained, implying that the proposed numerical algorithm can be used as a useful tool in designing high-temperature wood pole treatment processes. [Copyright &y& Elsevier]

In this study, the qualities of dimensional change and adhesion resistance of moulded concave plywood material after being exposed to water vapour have been investigated. To this end, for the production of moulded concave plywood material, Oriental Beech (Fagus orientalis) was used as the wood material; and Urea formaldehyde was used as the adhesive. The moulded plywoods were exposed to water vapour for 2, 6, 12, 24, 48 and 96 according to TS 3639 standards and their dimensional stabilisations according to TS 318 standards and adhesion resistances according to BS EN 205 standards were determined. As a result; average exact dry density has been established as 0,708g/cm³ and air dry density has been established as 0,814g/cm³. The dimensional increases are found to be % 1,03 in wideness, % 8,08 in thickness, % 5,08 in arc openness, % 3,21 in arc and environment longitude. In the adherence resistance, the highest value is stated in the control group paralel to the fibres with 4.07 N/mm²; the lowest one is stated as 1.19 N/mm² in the examples which are vertical to the fibres and were exposed to hot water vapour for 96 hours. According to this: moulded concave plywood can be used in the areas prone to be exposed to water vapour for 48 hours or less. [ABSTRACT FROM AUTHOR]

The main objective of this work was to study the chemical composition of surfaces and ageing effects on acetylated pine ( Pinus sylvestris), heat treated spruce ( Picea abies), and furfurylated radiata pine ( Pinus radiata) in comparison to unmodified wood. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were the instruments of choice. Observation with a low-vacuum scanning electron microscope (LV-SEM) complemented the study. The spectroscopic information was also linked to a parallel wettability study on matched wood samples by the Wilhelmy method. The results show that XPS and ToF-SIMS are two powerful tools that in combination give complementary information, both quantitative and qualitative, and are well suited for observation of the ageing process of different wood surfaces. The hydrophobization process as a result of migration of extractives during ageing was well quantified by the XPS measurements and the results correlated well with wetting results. Several specific hydrophobic substances could be identified by ToF-SIMS measurements. [ABSTRACT FROM AUTHOR]