Enthalpy relaxation behavior of dry wood detected by temperature-modulated differential scanning calorimetry

Enthalpy relaxation of dry wood has been investigated by temperature-modulated differential scanning calorimetry. The reversing and non-reversing heat flow changes revealed that enthalpy relaxation occurred in dry wood, which did not exhibit any clear glass transitions. This enthalpy relaxation behavior seemed to differ significantly from those of previously reported isolated lignins, which implies that the microstructure of dry wood possesses a rigid amorphous state derived from interactions among wood components. The observed enthalpy relaxation is considered to be related to other components besides lignin, and the time-dependent physical properties due to unstable states or physical aging of wood originate not only from lignin but also from other components, such as cellulose and hemicellulose and the interactions between them.     

Determination of the fibre saturation point in whole wood using differential scanning calorimetry

Summary A new method for determining the fibre saturation point (FSP) of whole never-dried wood is described. Enthalpy of melting values from differential scanning calorimetry (DSC) experiments are used to calculate the proportion of non-freezing water. Two methods for calculating the FSP from the enthalpy data are described. FSP determinations were carried out on the commercially important West Australian eucalypt species, Eucalyptus marginata and Eucalyptus diversicolor and a plantation softwood, Pinus radiata. Results are reproducible and are corroborated by the traditional volumetric shrinkage method for determining the FSP. On all samples below 10 mg a low temperature endothermic peak is observed as a shoulder on the main peak. It is postulated that this is due to an intermediate layer of water between the freezing and non-freezing water.Use of the DSC at Curtin University of Technology, and the help of Mr. I. Sills is greatly appreciated. This and related work is supported by the Australian Govt. Department of Primary Industry and Energy (Forestry)     

Analysis of the pore-size distribution and fiber saturation point of native and thermally modified wood using differential scanning calorimetry

The aim of this paper was to investigate pore-size distributions in the nano-diameter range of wood and their alteration due to thermal modification of wood using thermoporosimetry, and to find out what consequences can be derived regarding the biological durability. Thermoporosimetry is a technique that is based on the measurement using differential scanning calorimetry (DSC). The method is based on the fact that frozen water contained within small pores is at elevated pressure and therefore has a depressed melting temperature as a function of the appropriate pore diameter. In addition, the fiber saturation points (FSP) were determined by DSC. The former were performed in an isothermal-step method and the latter using the continuous heating-up method. Native and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.), Sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelsior L.) were analyzed. The results clearly show that the pore shares of wood for the measurable diameter range between 4 and 400 nm decrease considerably in all studied wood species due to thermal modification of the wood. Furthermore, thermal modification of wood leads to a decreased FSP for all studied wood species. For evaluation as well as reproducibility of the results of pore-size distribution and FSP, the consideration of sensible heat and specific heat of fusion plays an important role. If this is not done, it can lead to misinterpretations.     

Differential scanning calorimetry characterization of the cure of phenol-formaldehyde adhesive in the presence of copper-based preservative treated wood

The interference of copper based preservative treated southern yellow pine (SYP) on the cure of phenol-formaldehyde adhesives was investigated by using differential scanning calorimetry (DSC). Copper preservatives used in this study include copper azole (NS), alkali copper quat (ACQ)-type C (NW). Three commercial phenol-formaldehyde (PF) adhesives used for oriented strand board (OSB) face area, core area and a plywood adhesive were studied. The curing peak temperature and peak time of OSB core and face PF resin shifted to higher temperature and duration in the presence of CCA, NS, and NW-treated SYP compared to that in untreated SYP. The above treatments interfere with the cure of OSB core and face PF resin. Untreated SYP showed a curing accelerating effect on the cure of plywood adhesive, but the accelerating effect of copper-treated SYP on the cure of plywood resin was not significant.     

Microfracture in wood monitored by confocal laser scanning microscopy

The paper deals with the experimental characterisation of damage evolution within the radial (R)–tangential (T) growth plane of softwood loaded in tension perpendicular to the grain. The reported investigations comprise in-situ monitoring of crack propagation by means of Confocal Laser Scanning Microscopy (CLSM) and evaluations of crack patterns of broken specimens. Three types of notched specimens, representing different crack propagation systems, were tested; for all configurations, both, loading and crack propagation direction were located within the RT plane of wood. The CLSM pictures of broken specimens show distinct differences among the regarded configurations with respect to crack paths. Two different damage mechanisms were identified being rupture of earlywood cell walls in the case of crack propagation in tangential direction and debonding of wood fibers, i.e. rupture of the interface zone between adjacent tracheids, in case of crack progression in radial direction. In the case of an intermediate crack system with an angle of 45° between initial notch direction and radial direction the crack evolution was monitored in-situ during the tension test, whereby the combined action of both basic fracture mechanisms was observed.     

Thermal conductivity and diffusivity of wood

Summary Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have been performed with the plane source technique on oven-dry hardwood (birch) samples at room temperature and at 100 °C. The influences of temperature, density, porosity and anisotropy on thermal conduction were investigated. The measurements were done in longitudinal (parallel to the grain) and transverse (intermediate between radial and tangential) directions. As the temperature increased from 20 to 100 °C, the thermal conductivity of each sample increased slightly for both longitudinal and transverse directions. The effect of density and porosity on the thermal conductivity may be related to the presence of other scattering mechanisms such as voids and cell boundaries. It seems that the dominant mechanism of heat transfer across the cell lumina in these types of wood is the heat conduction through the voids. An attempt was made to explain the behaviour of the effective thermal conductivity by adopting a model based on the ratio between heat conduction in parallel and serial layers of gas, liquid, and solid phases. Received 7 May 1997     

The fluorescence characteristics of furfurylated wood studied by fluorescence spectroscopy and confocal laser scanning microscopy

The fluorescence of furfurylated wood was studied. Furfurylation of wood introduced fluorescent curing products into the cell walls. Fluorescent products were also found in the lumina if high loadings were used and/or if the wood contained cells with small radii. More intense fluorescence was obtained from lignin-rich parts of the compound cell wall (i.e., the middle lamella and the cell corners) than from the secondary cell wall if the wood was impregnated using furfuryl alcohol (FA), while impregnation using small poly(FA) oligomers showed no or only minor differences between different regions. The study also showed that when higher amounts of catalyst were added to the impregnation liquid, a red-shift in the fluorescence from the furfurylated wood was seen, corresponding to an increased conjugation length of conjugated poly(FA) formed within the wood cell wall. Longer conjugation length than within the cell wall was observed for the poly(FA) formed within the lumina. This indicates that the cell wall polymers restrict poly(FA) formation.     

Thermal diffusion of bound water in wood

Summary There are few references in the wood science literature to nonisothermal moisture movement. Some experiments by Voight, Babbitt, and Choong indicate that thermal diffusion in wood may be very significant.Three equations are presented to represent nonisothermal moisture movement through wood in the transverse direction. The first, described in detail in a previous paper, is based upon two driving forces: Soret potential which results in thermal diffusion and chemical potential which results from a gradient of equilibrium relative humidity. All three equations include the same term for Soret potential and, in the second two equations, the thermal-diffusion term was derived by the application of activation theory. The isothermal term in these two equations utilizes moisture content gradient as the driving force and therefore a knowledge of the sorption isotherm is not necessary. The third equation contains an additional term for moisture-content activation to account for the increase in flux with an increased moisture content. All three equations give approximately the same result with the same input data at low moisture contents. The results diverge at high moisture contents and experimental data are required to determine which equation is most representative of the physical phenomenon of nonisothermal moisture movement.     

Load behaviors of a prefabricated wood framing house during lifting and transportation

Lifting for handling and flatbed truck transportation to the job site are important processes during manufacture of prefabri-cated wooden construction units like mini homes and building modules. Significant damage can occur to sections or components of units during these operations. Although damage usually will not impair its structural safety, it is costly to fix and causes the public to perceive prefabricated wooden buildings as low quality products. Field observations and preliminary numerical models for prefabri-cated units subject to lifting and transportation forces are summarized here. Once fully developed and verified, models will support the creation of damage mitigation strategies centered on structural details indicating how units are to be supported during lifting and transportation.     

阻燃处理木材的热分析

为研究阻燃处理对木材热解过程的影响,将未处理的和经过阻燃处理的木材进行热分析(包括TG、DTG、DSC),其结果表明:阻燃处理可改变木材发生剧烈热分解时的温度和重量损失速率,并使400℃时的残留物重量明显增加,在20～450℃范围内,未处理木材的DSC图谱有三个峰,相应于三个不同的热解阶段;不同阻燃剂的加入可明显地改变DSC图谱的峰形和峰位,即改变了木材的燃烧性能。此外本文还结合实验结果,对阻燃剂的作用机理提出了初步解释。     

Thermal and hydrophobic properties of glycerol stearate-modified Pinus radiata wood

Glycerol stearate was synthesized by esterification with non-toxic,inexpensive glycerol and stearic acid.The composite of glycerol stearate and Pinus radiata wood was prepared by vacuum impregnation.By Fourier transform infrared(FTIR)analysis,there was the generation of new C=O stretching vibration band of glycerol stearate in comparison with stearic acid.This confirms that glycerol stearate was successfully synthesized.The weight gain,FTIR spectrum and morphological analyses of the composite indicate that glycerol stearate was impregnated into the interior lumina of the cells.Thermal analysis showed that the maximal degradation temperature of the composite was 42℃higher than untreated wood.Contact angle images indicated that the value of the composite was134.2°.Hydrophobicity(the repulsion of water)of the composite was stronger than glycerol stearate,which a large number of hydroxyl of wood reacted with the oxygen-containing groups of glycerol stearate,improved hydrophobicity and thermal stability,thereby enhancing the potential application of P.radiata wood.     

Thermal treatment of wood: analysis of the obtained product

Summary Physicochemical analyses were performed on samples of torrefied wood obtained at various temperatures. The chemical structure of wood was strongly altered by this process; a reactional mechanism for this is proposed in this paper. The influence of temperature and the duration of heating were compared to find the more important factors in the process. We found that these two parameters widely affected the nature of the final product. The 3.D. surfaces enabled us to predict the operating conditions which were essential to obtain a definite product with the maximum efficiency.     

A scanning electron microscope study of cell wall degradation in elm wood by aggressive and non-aggressive isolates of Ophiostoma ulmi

Degradation of cell walls in elm wood tissue (Ulmus americand) by aggressive and non-aggressive isolates of Ophiostoma ulmi was studied by scanning electron microscopy. Xylem vessel walls were much more affected after infection with the aggressive isolate than after infection with the non-aggressive one.     

Assessment of standing wood and fiber quality using ground and airborne laser scanning: A review

Accurate information on the wood-quality characteristics of standing timber and logs is needed to optimize the forest production value chain and to assess the potential of forest resources to meet other services. Physical and chemical characteristics of wood vary with both tree and site characteristics. At the tree scale, crown development, stem shape and taper, branch size and branch location, knot size, type and placement, and age all influence wood properties. More broadly, at the stand level, stocking density, moisture, nutrient availability, climate, competition, disturbance, and stand age have also been identified as key determinants of wood quality. Such information is often captured in polygon based forest inventory data. Other terrain-related spatial information, such as elevation, slope and aspect, can improve assessments of site conditions and limitations upon plant growth which impact wood quality. Light Detection And Ranging (LiDAR) is an emerging technology, which directly measures the three-dimensional structure of forest canopies using ground or airborne laser instruments, and can provide highly accurate information on individual-tree and stand-level forest structure. In this paper, we explore the potential of LiDAR and other geospatial information sources to model and predict wood quality based on individual-tree and stand structural metrics. We identify a number of key wood quality attributes (i.e., basic wood density, cell perimeter, cell coarseness, fiber length, and microfibril angle) and demonstrate links between these properties and forest structure and site attributes. Finally, the potential for using LiDAR in combination with other geospatial information sources to predict wood quality in standing timber is discussed.     

Compression behaviors of acetylated wood in organic liquids. Part II. Drying-set and its recovery

Unmodified and acetylated cedar wood specimens were swollen in various liquids and dried under radial compression. Two stress relaxation processes were observed during drying, and the second process observed below the fiber saturation point was responsible for the drying-set and the temporary fixation of compressive deformation. The fixed shape of acetylated wood was partly recovered by soaking it in water and toluene and completely recovered in acetone. The effective shape fixation and recovery of toluene-swollen samples implied that the intermolecular hydrogen bonding was not necessary for the drying-set of acetylated wood. The degree of shape recovery was not explained by initial softening, while the acetylated wood always exhibited greater recoverability than unmodified wood. Although 85% stiffness was lost after large compression set and recovery of unmodified wood, such a stiffness loss was limited to 39% when the acetylated wood was processed with organic liquids. This indicated that the swelling of the hydrophobic region in the acetylated wood was effective in preventing mechanical damage due to large compressive deformation.