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

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.     

Color and surface chemistry changes of extracted wood flour after heating at 120 °C

To investigate the effect of heat on color and surface chemistry of wood flour (WF), unextracted, extracted and delignified samples of commercial WF were heated at 120 °C for 24 h and analyzed by colorimetry, diffuse reflectance visible (DRV), attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Fourier transform Raman (FT-Raman) spectroscopies. Unextracted samples showed a slight increase in CIEL^*a^*b^* color coordinates, a ^* and b ^*. Compared with unextracted samples, color changes of the extracted samples varied with composition of the extraction solvents with generally smaller increases in a ^* and larger decreases in b ^* values. Delignified samples were marked by even larger increases in both a ^* and b ^* values. The color changes could be explained by analysis of the respective DRV, FTIR and FT-Raman spectra of the samples before and after heating. Heating of the extracted WF at 120 °C resulted in a red shift of the absorption at 430 nm and increase in absorption in the violet-blue spectral region of visible light. Delignified samples showed even more pronounced absorption in this spectral region after heating.     

Behavior of piezoelectric, dielectric, and elastic constants of wood during about 40 repeated measurements between 100°C and 220°C

This study investigated the behavior of piezoelectric, dielectric, and elastic constants and the crystallinity in wood cellulose by repeated measurements (n = 42) between 100°C and 220°C. There was an insignificant change in the piezoelectric constant during repeated measurements in this temperature range. On the other hand, thermal decomposition of the amorphous region contributed to the decreasing trend of dielectric and elastic constants, although only a small increase in the elastic constant was found at the time of the initial measurements. The increase in the repeated measurements in this temperature range resulted in an increase in the piezoelectric loss modulus constantd ₂₅, which is closely related to energy loss. Thed ₂₅ peak shifted to a higher temperature with increasing measurements, which might be due not to the increase in rigidity of the wood specimen but to the increase in total peak area, which was observed during the later measurements. At the same time, variations of piezoelectric loss modulusd ₂₅ ande ₂₅ at advanced stages of the measurements suggested damage and structural changes in the wood.     

Influence of stress level on compression deformation of wood in 170°C transient steam conditions

Abstract

Compression creep experiments of hybrid poplar (Populus deltoides×Populus trichocarpa) were performed in a pressurized vessel equipped with a heated hydraulic press. The viscoelastic response at various stress levels (2–7 MPa), a temperature of 170°C and transient steam conditions was studied. Moisture content and oven-dry density of compressed specimens were determined. While some recovery of compression strain occurred, compression resulted in permanent deformation and increased wood density. The influence of stress level on the amount of set recovery of compressive deformation was evaluated after 24 h water soaking. Applied stress level had a significant effect on the compression deformation. The initial strain, as well as creep strain, varied depending on the applied stress level. The highest oven-dry density was obtained at a stress level of 6.9 MPa. Lower stress levels resulted in lower moisture content after the compression process, while the equilibrium moisture content of compressed specimens was not significantly affected by stress level. Set recovery increased from 20% to 65% with increased stress level from 1.7 MPa to 4.1 MPa, then decreased to 53% for specimens compressed at 6.9 MPa. Moisture content after the compression process significantly affected the set recovery.     

Intra-specific patterns of δ13C,growth and wood density variation at sites of contrasting precipitation with implications for modelling carbon sequestration of tropical tree species

Agroforestry Systems - Tropical agroforestry practices play a crucial role in mitigating global climate change by absorbing CO2 from the atmosphere through photosynthesis and storing carbon in...     

Time dependence of Poisson’s effect in wood IV: influence of grain angle

Off-axis tensile creep tests were conducted on woods taken from Japanese cypress and Kalopanax by changing the angle of load to the grain direction in the longitudinal–tangential (LT) plane. The dependence of the Poisson’s ratio and trend of the viscoelastic Poisson’s ratio on grain angle were investigated. The Poisson’s ratios were found to reach their extrema when the grain angle was around 30°. Moreover, the Poisson’s ratio in the LT plane was observed to be negative when the grain angle was in the range of 15°–45°. Comparing the experimental results with theoretical values obtained from the theory of orthotropic elasticity, it was revealed that, although the Poisson’s ratio reached an extremum in both cases, the specific values did not match, especially when the angle was between 15° and 45°. Furthermore, the temporal variation of the viscoelastic Poisson’s ratio was found to depend on the grain angle and the measurement plane. It also appeared to be affected by the Poisson’s ratio, showing an increasing tendency above a specific Poisson’s ratio (Japanese cypress: 0.196, Kalopanax: 0.102) and a decreasing tendency below it, regardless of the grain angle and measurement plane. Additionally, the increment in the viscoelastic Poisson’s ratio after 24 h of creep was observed to reach its extremum when the grain angle was around 30°. Finally, by improving the six-element Frandsen–Muszynski viscoelastic model, which simultaneously considers the longitudinal and transverse strains, an eight-element model was presented, and the trend of the viscoelastic Poisson’s ratio was well reproduced by this model.     

Time course of δ1¹³C in poplar wood: genotype ranking remains stable over the life cycle in plantations despite some differences between cellulose and bulk wood

Genetic differences in δ13C (isotopic composition of dry matter carbon) have been evidenced among poplar genotypes at juvenile stages. To check whether such differences were maintained with age in trees growing in plantations, we investigated the time course of δ13C as recorded in annual tree rings from different genotypes growing at three sites in southwestern France and felled at ～15-17 years. Wood cores were cut from tree discs to record the time course of annual basal area increment (BAI). The isotopic ratio δ13C was recorded in bulk wood and in extracted cellulose from the annual rings corresponding to the period 1996-2005. Discrimination against 13C between atmosphere and tissues (Δ13C) was computed by taking into account the inter-annual time course of δ13C in the atmosphere. Annual BAI increased steadily and stabilized at about 8 years. An offset in δ13C of ～1‰ was recorded between extracted cellulose and bulk wood. It was relatively stable among genotypes within sites but varied among sites and increased slightly with age. Site effects as well as genotype differences were detected in Δ13C recorded from the cellulose fraction. Absolute values as well as the genotype ranking of Δ13C remained stable with age in the three sites. Genotype means of Δ13C were not correlated to annual BAI. We conclude that genotypic differences of Δ13C occur in older poplar trees in plantations, and that the differences as well as the genotype ranking remain stable while trees age until harvest.     

Laboratory and environmental decay of wood–plastic composite boards: flexural properties

The flexural properties of wood–plastic composite (WPC) deck boards exposed to 9.5 years of environmental decay in Hilo, Hawaii, were compared to samples exposed to moisture and decay fungi for 12 weeks in the laboratory, to establish a correlation between sample flexural properties and calculated void volume. Specimens were tested for flexural strength and modulus, both wet and dry, at 23°C and 52°C. Some specimens degenerated to only 15% of original flexural strength. UV radiation had no impact on flexural properties of field-exposed boards; loss occurred mainly on the side opposite to the sun-exposed surface. The mechanism of the aging process on colonization of WPC by fungi was examined and is consistent with development of slow crack growth in the polyethylene matrix combined with wood decay by fungi. Wood particle decay, moisture, and elevated temperature were the major factors causing composite degradation, indicated by accumulation of voids and a severe decrease in flexural properties. To simulate long-term field impact (including decay) on WPC flexural properties in the laboratory, conditioning of specimens in hot water for an extended period of time is required. Exposure to water (70°C/5 days) was adequate for simulating long-term composite exposure in Hawaii of 4?×?15?×?86 mm³ specimens.     

Mode of action of brown rot decay resistance of acetylated wood: resistance to Fenton’s reagent

Acetylation is known to enhance the resistance of wood to brown rot fungi. As initial decay by some brown rot fungi is assumed to be caused by the Fenton reaction, pine micro-veneers acetylated to various weight percent gains (WPG) were exposed in a solution containing iron ions and hydrogen peroxide, i.e., Fenton’s reagent. Mass loss and tensile strength loss as well as the decomposition of hydrogen peroxide within the incubation time decreased with increasing WPG of the veneers. Incubation of untreated and acetylated veneers in acetate buffer containing ferric ions without H₂O₂ revealed that the modification strongly reduced the uptake of Fe ions by the wood cell wall. FT-IR analysis indicated oxidation of the unmodified control veneers but did not show predominant decay of specific cell wall components. Spectra of acetylated veneers did not reveal any significant changes induced by Fenton’s reagent. It was concluded that one possible reason for the enhanced resistance of acetylated wood to the Fenton reaction could be the reduced or almost completely prevented uptake of Fe ions by the wood cell wall.     

The chemical characteristics of squeezable sap from silver birch (Betula pendula) logs hydrothermally treated at 70 °C: the effect of treatment time on the concentration of water extracts

Wood Science and Technology - In order to study the detailed water extract of wood components in birch under hydrothermal treatment, xylem sap obtained by mechanical...     

Molecular sieving behavior of carbonized wood: selective adsorption of toluene from a gas mixture containing α-pinene

The adsorption properties of wood carbonized at various temperatures were investigated using a mixed gas containing toluene and α-pinene. Hinoki (Chamaecyparis obtusa) samples carbonized at 500°–1100°C were exposed to gas mixtures of toluene and α-pinene at 20°C. The samples carbonized at 500°–700°C only adsorbed toluene, whereas those carbonized at 800°–1100°C adsorbed both toluene and α-pinene. Analysis of the surface structure of the carbonized wood by nitrogen adsorption at liquid nitrogen temperature indicated that the sample carbonized at 700°C had micropores mainly 0.6 nm in diameter and few mesopores, whereas the samples carbonized at 900°C and 1100°C had mesopores and micropores larger than 0.8 nm in diameter. With the sample carbonized at 700°C, the flat-shaped toluene molecules could probably penetrate into the narrower pores, 0.8 nm in diameter, whereas the bulky globular-shaped α-pinene molecules could not. Carbonization at temperatures higher than 900°C probably enlarged the pore size and thereby reduced the selectivity of adsorption. The results revealed that wood carbonized below activation temperature has a unique flat-pore structure that seems to work as a kind of molecular sieving carbon, successfully removing only the harmful volatile organic compound (VOC), toluene, and leaving behind a pleasant aroma of α-pinene in the atmosphere.     

Time dependence of Poisson’s effect in wood III: asymmetry of three-dimensional viscoelastic compliance matrix of Japanese cypress

To understand the viscoelasticity of wood three dimensionally, matched samples of Japanese cypress were loaded in uniaxial tensile creep in the longitudinal (L), radial (R), and tangential (T) directions at approximately 9.7 % equilibrium moisture content. Longitudinal and transverse strains were measured for the determination of viscoelastic Poisson’s ratios and three-dimensional viscoelastic compliance tensors concerning the normal strain. The changes in the transverse strains showed the same tendencies as those in the longitudinal strains, in all directions of loading. That is, during creep, the absolute value of transverse strain continued to increase with the gradual reduction in the increase rate; immediately after the removal of the load, it recovered rapidly, after which it continued to recover slowly. The transverse strain increased most easily in the T direction, followed by R and L, during creep. All the viscoelastic Poisson’s ratios and the absolute values of all elements of the viscoelastic compliance increased logarithmically with creep time. The three-dimensional viscoelastic compliance matrix for Japanese cypress is concluded to be asymmetric.     

Longitudinal shrinkage of wood — Part II: The relation between Longitudinal shrinkage and structure

Summary Models put forward by Preston and Kelsey to represent the longitudinal shrinkage of wood have been extended to take into account shearing stresses between microfibrils and between fibres. Mathematical relationships have been developed and previous models shown to be approximations to that developed here.The suitability of the model from various points of view and the variations in the model parameters with changing moisture content are discussed.The effect of the cross-cutting of the fibres occurring in thin microtomed sections, the effect of delignification and the incidence of an anomalous hysteresis are also discussed.Curves are given for the parameters of the models developed and these are discussed in the light of the results reported in Part I of this paper.It is concluded that the non-linearity observed in the longitudinal shrinkage moisture content relationship is due to the development of restraint against slipping of the chain molecules along one another and that this restraint is caused by increasing inter-chain molecular bonding with decreasing moisture content. It is also suggested that the irreversible interfibrillar shearing strain is a cause of the hysteresis.

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Zusammenfassung Die von Preston und Kelsey entworfenen Modelle zur Darstellung der Längsschwindung von Holz wurden von den Verfassern erweitert und zwar im Hinblick auf Scherspannungen zwischen Mikrofibrillen und zwischen Fasern. Es wurden mathematische Beziehungen aufgestellt und gezeigt, daß früher entwickelte Modelle dem hier entworfenen angenähert entsprechen. sprechen.Die Eignung des Modells wird von verschiedenen Gesichtspunkten aus beleuchtet und die Anderungen der Modellparameter bei wechselndem Feuchtigkeitsgehalt werden erörtert. Der Einfluß des Querschneidens der Fasern beim Mikrotomschnitt, der Einfluß der Delignifizierung und das Auftreten einer anomalen Hysterese werden besprochen.Die Parameter der entwickelten Modelle sind als Kurven dargestellt; diese werden unter Berücksichtigung der in der ersten Mitteilung veröffentlichten Ergebnisse erörtert.Als Schlußfolgerung ergibt sich, daß die Nichtlinearität, die in der Beziehung zwischen Längsschwindung und Feuchtigkeitsgehalt beobachtet wurde auf die Entwicklung eines gewissen Widerstandes gegen das gegenseitige Gleiten der Kettenmoleküle zurückkzuführen ist, und daß dieser Widerstand durch eine Zunahme der zwischen den Ketten bestehenden Molekularverbindungen bei abnehmendem Feuchtigkeitsgehalt verursacht wird.Ebenso wird vorgeschlagen, die irreversible Scherverformung zwischen den Fibrillen als Ursache für die Hysterese anzusehen.

     

Time dependence of Poisson’s effect in wood I: the lateral strain behavior

To understand the viscoelasticity of wood three dimensionally, a longitudinal tensile creep test for 12 species was conducted to examine the changes with time in the lateral strain and the viscoelastic, i.e., apparent Poisson’s ratio. The changes in the lateral strain (ɛ _T and ɛ _R) were similar to those in the longitudinal strain (ɛ _L). That is, during creep, the absolute value of lateral strain continued to increase with the gradual reduction in the increase rate; immediately after the removal of the load, it recovered abruptly; then, it recovered slowly and finally reached a certain value. The rate of increase in the longitudinal strain during creep was smaller than that in the absolute value of lateral strains. The apparent Poisson’s ratio became large during creep because the lateral strain increased more than the longitudinal strain. The analysis of lateral strain by decomposition into three components, that is, instantaneous strain, delayed elastic strain, and permanent strain, has revealed that the lateral permanent strain in the transverse direction contributes most to the increase in the apparent Poisson’s ratio during creep.     

Laboratory and exterior decay of wood–plastic composite boards: voids analysis and computed tomography

After exposure in the field and laboratory soil block culture testing, the void content of wood–plastic composite (WPC) decking boards was compared to unexposed samples. A void volume analysis was conducted based on calculations of sample density and from micro-computed tomography (microCT) data. It was found that reference WPC contains voids of different sizes from the micrometer range up to several cubic millimeters. Large voids were unevenly distributed within the composite sample. Void size and volume increased after conditioning the WPC in water at 70°C. Depending on the effect of exposure conditions, fungal decay during laboratory soil block testing increased the size and volume of voids. For laboratory samples, the calculated void volume was much higher compared to microCT-detected voids because of the limited resolution of the instrument on relatively large samples with many nano- and microvoids present in the material. In both laboratory and field samples, the creation of the voids resulted in a significant decrease in composite density. Decay damage observed as an increase in the size and volume of voids was particularly severe for boards exposed in the field. The calculated void volume in such samples was in reasonable agreement with voids detected by microCT.     

Characterization of mechanically perturbed young stems: can it be used for wood quality screening?

• Introduction   

Genetic testing is the slowest part of a breeding cycle. There is a growing interest in early wood quality screening methodologies. We hypothesized that subjecting 8-month-old radiata pine trees to mechanical perturbance induces reaction wood that permits isolating their likely corewood features.     

Time dependence of Poisson’s effect in wood II: volume change during uniaxial tensile creep

To determine the viscoelasticity of wood three-dimensionally, a longitudinal tensile creep test was conducted on 12 species of wood to examine the change in the rate of volume increase (ΔV/V) with time. Immediately after the beginning of creep, ΔV/V was positive, and during creep, ΔV/V decreased rapidly, then more gradually. The decrease in tangential strain was considered to mainly contribute to the decrease in ΔV/V during creep. Immediately after the removal of the load, ΔV/V decreased to a negative value; thereafter, it decreased slowly and finally reached a certain value. The value of ΔV/V during creep tended to decrease with increasing density of wood. Also, there was a negative correlation between wood density and the rate of increase in ΔV/V.     

Proton spin–lattice relaxation time measurements of solid wood and its constituents as a function of pH: Part I*

Summary  By measuring the proton spin–lattice relaxation times (T_1H) in the solid-state for black spruce softwood, the molecular mobilities of carbohydrates and lignin have been evaluated as a function of pH. These studies have shown that the mobility of the polymeric constituents of wood is affected by the ionization of the different functional groups at different pH's. The analyses of the proton-spin–lattice relaxation time data at constant humidity revealed that the maximum T_1H for both carbohydrates and lignin occurs at about neutrality, while it was found to be depressed at the two extremes of the pH range. By treating a wood sample with propylene oxide, the esterification of the acid groups was affected, thus deactivating the ionization process and their contribution to T_1H. The experimental T_1H values for cellulose and lignin after the esterification were significantly decreased at pH 6 confirming that their ionization plays a very significant role in determining chain mobility. Received 1 December 1998     

Biosorption of methylene blue from aqueous solutions on β-cyclodextrin grafting wood flour copolymer: kinetic and equilibrium studies

The preparation, characterization, and environmental application of β-cyclodextrin/citric acid/wood flour (β-CD/CA/WF) graft copolymer wood-based biosorbent for methylene blue (MB) biosorption were investigated in this paper. The Fourier transform infrared spectroscopy and the technique of phenolphthalein probe were used to characterize the grafting β-CD. Furthermore, the biosorption behavior of MB on β-CD/CA/WF graft copolymer was studied under various conditions of pH, contact time, and initial MB concentration. The results indicated that the biosorption of MB was dependent on both the initial MB concentration and the initial pH. Langmuir isotherm model fitted the isotherm data better than the Freundlich model. The adsorption kinetics followed the pseudo-second-order kinetic model, and intraparticle diffusion was one of the effective rate-controlling steps for the entire biosorption period. Equilibrium and kinetic results have implied that β-CD/CA/WF graft copolymer could be considered as a promising material for the adsorption of dye from aqueous solutions.