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1.
Changes in physical and mechanical properties of wood were analyzed using sorption tests combined with dimensional measurements and perpendicular-to-the-grain tangential compression tests. In order to determine the influence of wood structure on these changes, three hardwood species (Fagus grandifolia, Brosimum alicastrum and Cariniana domestica) presenting different anatomical structures were studied. Two experimental techniques were used to perform moisture sorption tests at 25°C. The first technique used saturated salt solutions (from 33 to 90% relative humidity) and the second used the pressure membrane method (above 96% relative humidity). Special attention was given to the “fiber saturation region”, where changes in wood properties started to take place. Results showed that at equilibrium moisture content (EMC), radial, tangential and volumetric shrinkage, as well as changes in transverse strength occurred above the fiber saturation point (FSP). This behavior can be explained by the effect of hysteresis at saturation on wood properties. This hysteresis indicates that loss of bound water takes place in the presence of liquid or capillary water, which contradicts the concept of FSP. The initial EMC at which bound water starts to be removed varied largely among the wood species.  相似文献   

2.
Wood Science and Technology - The distribution of liquid and bound water in wood samples under equilibrium moisture contents (EMC) below fiber saturation point (FSP) was assessed by magnetic...  相似文献   

3.
Summary Two new proton magnetic resonance techniques, relaxation spectra and relaxation selective imaging, have been used to investigate the distribution of water in samples of normal white spruce sapwood, heartwood, and juvenile wood as well as two rehydrated heartwood samples containing incipient decay and compression wood respectively. It is demonstrated that the spin-spin (T2) relaxation behavior in wood is best presented as a continuous spectrum of relaxation times. Spectra of T2 for white spruce show separate peaks corresponding to the different water environments. Bound water gives a peak with an T2 time of about 1 ms and lumen water gives a distribution of T2 times in the range of 10 to 100 ms. The lumen water T2 time is a function of the wood cell radius. Consequently, the different cell lumen radii distributions for spruce sapwood, juvenile wood, and compression wood are readily distinguishable by the shape of their T2 spectra. Water environments which are separable on a T2 spectrum may be imaged separately. Imaging has been carried out in one dimension for bound water and lumen water of a spruce sapwood sample at four different moisture contents ranging from 100% to 17%. For the first time, we demonstrate that above the fibre saturation point the moisture density profile of the bound water is largely independent of moisture content. The feasibility and utility of using these techniques for internal scanning of logs and lumber is discussed. These techniques should provide new insights into the wood drying process.We would like to thank Michael Weiss of the Biological Science Electron Microscopy Facility at the University of British Columbia for his assistance with the microscopy and image analysis. This research was supported by grants from the Natural Sciences and Engineering Research Council of Canada and the Canadian Forestry Service  相似文献   

4.
Abstract

In this study, water content in black spruce (Picea mariana Mill.) and aspen (Populus tremuloides Michx.) sapwood samples was investigated with time-domain magnetic resonance (MR). Time-domain MR measurements easily distinguish water in different environments in wood according to the spin-spin relaxation time and provide quantitative information on water content. The MR techniques employed can distinguish and quantify the individual signal components. Both black spruce and aspen have two signal components at moisture contents above the fiber saturation point. These two signal components correspond to motionally restricted water, often referred to as bound water, and unrestricted, or free water. Bound water content is constant above 40% moisture content. No signal from free water was detected at or below 20% moisture content in either species. We also demonstrate the use of a recently developed portable unilateral magnet that can be employed as a powerful tool in the study and measurement of water content in wood.  相似文献   

5.
Beech wood (Fagus sylvatica L.) was modified with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU). The equilibrium moisture content (EMC) of wood modified with DMDHEU calculated on a dry modified basis is reduced. Previous results have shown that the modification with DMDHEU does not alter the capillary condensation; therefore, the reduction in EMC seems exaggerated. The equilibrium constants of the Hailwood–Horrobin model (K d and K h) and the molecular weight of a hypothetical polymer of modified wood capable of adsorbing one molecule of water (W i) were calculated from the EMC on a dry modified wood basis (M) and on a dry wood basis (M R). The hypothetical polymer was also calculated by stoichiometry (W c) and compared to W i to estimate the number of operative OH groups. The number of operative OH groups decreased when M was used, in contradiction with the previously obtained results of differential heat of adsorption (∆H s). Therefore, the use of M R is recommended for the analysis of moisture sorption in wood modified with DMDHEU.  相似文献   

6.
The structural features of bast fiber and core lignins in kenaf (Hibiscus cannabinus), bark and wood lignin of paper mulberry (Broussonetia papyrifera (L.) Vent × Broussonetia kazinoki Sieb.) and mulberry (Morus bombycis) were characterized by alkaline nitrobenzene oxidation, ozonation and methoxyl group determination. Bj?rkman lignins were isolated from bast fiber and core, and bark and wood fractions of the plant samples, and structural characteristics were investigated by 1H NMR and 13C NMR spectroscopies. Kenaf bast fiber gave very high molar ratio of syringaldehyde to vanillin (S/V) of alkaline nitrobenzene oxidation products, while methoxyl content was about the same as that of the core fraction. Results of 1H NMR and 13C NMR of Bj?rkman lignin suggested the presence of aliphatic fragments in lignins isolated from paper mulberry and mulberry bark, but not in kenaf bast fiber. The lower yield of alkaline nitrobenzene oxidation products from bast fiber and bark might be due to the higher content of condensed structure of lignin compared to core fraction. Total yield of erythronic (E) and threonic (T) acids of ozonation products and the molar ratio of erythronic acid to threonic acid (E/T) of the bast fibers and bark were lower than the corresponding core and wood fractions, suggesting that the contents of arylglycerol-β-aryl ether intermonomer linkages in the bast fiber and bark lignin were lower than those of the core and wood fractions. Methoxyl content of bark lignin was lower than the corresponding wood lignin. The methoxyl content of the extract-free kenaf bast fiber was similar to that of the core fraction, while the values of paper mulberry and mulberry bark were about one-half of the corresponding wood fractions, respectively. In bark lignins, the methoxyl contents of Klason lignin and Bj?rkman lignin from bark were lower than those of the extract-free barks. This result suggests that the purity of Klason lignin and Bj?rkman lignins of bark may be rather low.  相似文献   

7.
Summary Various chemicals are used for protecting wood samples against fungi, and some of them are released in water, leading to pollution of the water. The kinetics of pentachlorophenol release in water has here been studied by considering the diffusion through the wood along the three principal axes of diffusion. The experiments and the modelling of the process is successfully coupled. The numerical model takes into account the three principal diffusivities, the partition factor, the volumes of wood and water. The effect of wood sample length along the longitudinal axis of diffusion is studied especially, as longitudinal diffusivity is much higher than the other two principal diffusivities. The effects of the relative volumes of wood and water are also of considerable interest not only for the concentration of the chemical in water but also for the rate of release.Symbols C concentration of liquid (g/cm3)_ - C c ,C eq concentration of liquid on the surface, at equilibrium with the surrounding, respectively - C i,j,k concentration of liquid in the wood at positioni, j, k - D diffusivity (cm2/s) - h coefficient of mass transfer on the surface (cm/s) - K partition factor - i, j, k integers characterizing the position in the wood - M L ,M R ,M T dimensionless numbers - M t ,M amount of chemical released after time t, after infinite time, respectively - t increment of time - L, R, T thickness of the slices taken in the wood for calculation - N L ,N R ,N T number of slices taken in the wood - x, y, z coordinates - V water volume of the surrounding water  相似文献   

8.
Two experimental techniques were used to test the water permeability of two Korean hardwood species: diffuse porous Populus tomentiglandulosa T. Lee (eunsasi poplar) and ring porous white oak, Quercus serrata Thunb (konara oak). The first technique measured the void volume filled at different moisture content (MC) levels. Samples were treated with water via a schedule of full-cell impregnation. A significant relation between MC and permeability (the fractional void volume) was found. A reduction in liquid permeability was observed at MC above the fiber saturation point (FSP), whereas the opposite result was observed at MC below FSP due to the effect of the voids available in the wood. However, the differences of increased permeability from MC level 20% to 0% were found satistically the same in either wood species. The second technique measured the speed of liquid penetration in vessels, fibers, and rays with no application of external pressure. In this method, liquid flow was captured via video and the penetration speed was measured. Vessels, fibers, and rays in poplar were found to be more permeable than those in oak. Different anatomical factors such as cell diameter, cell length, pit number, pit aperture area, and thickness of the pit membrane seemed to be responsible for the variation of liquid flow rate in different cells of the two hardwood species.  相似文献   

9.
In order to investigate the effects of chemical components and matrix structure on the destabilization of quenched wood, we examined the physical and mechanical properties of steam-treated wood, hemicellulose-extracted wood, and delignified wood, which were treated at different levels. For steam-treated and hemicellulose-extracted wood,the relative relaxation modulus of the quenched sample was lower than that of the respective control sample. For delignified wood, the relative relaxation modulus fell with weight loss and reached a minimum value at a certain weight loss, and subsequently increased significantly. The hygroscopicity of all treated samples changed slightly by steaming, whereas increased with removing the component. More-over, the average volumetric swelling per 1% MC at 100% relative humidity (RH) was less than at 75% RH and 93% RH for component-removed wood. It was clear that a void structure existed. As a result, the destabilization evaluated by the fluidity (1 - E t/E 0) of steam-treated wood was influenced by the amount of adsorbed water. For component-removed wood, destabilization increased temporarily at lower weight loss because of nonuniform cohesive structure. At high weight loss, destabilization will decreased because capillary-condensed water gathered in the voids and obstructed the motion of adsorbed water. However, the destabilization of all treated wood changed less than that of chemically modified wood.  相似文献   

10.
Summary 13C CP MAS NMR spectroscopy was used to characterize the structural changes of cell wall polymers in beech wood Fagus sylvatica during drying processes. The analysis of five wood samples, namely, untreated, untreated dried, pre-treated by steam and/or NaOH subjected to drying showed partial depolymerization of lignin component as well as the change of the ratio of the crystalline and of the amorphous parts of cellulose as the consequence of wood pre-treatment. In addition, T1ρ(1H) relaxation times were determined in beech wood sample pre-treated with steam at 135 °C and the lignin isolated from this sample. The magnitudes of the relaxation times were found comparable in both samples as well as in the lignin-cellulose model compound. These unique T1ρ (1H) values indicate that spin diffusion is complete and homogeneous due to spatial proximity of spins and confirmed the formation of lignin-cellulose complex during thermal treatment of wood. Received 30 June 1997  相似文献   

11.
We investigated clonal and site variations in wood fiber length, microfibril angle, and specific gravity of seven natural hybrid clones of Acacia (Acacia mangium × Acacia auriculiformis) grown in northern and southern Vietnam. Fiber length did not differ between clones or between sites. The microfibril angle of the S2 layer did not significantly differ between clones but significantly differed between sites. Clone and site significantly affected specific gravity. The significant effects of genetic × environmental interactions on wood properties indicated the difference in the response of clones to different growing conditions. The trends of changes in fiber length, microfibril angle, and specific gravity from the vicinity of the pith to near the bark were similar for all clones at each site; however, variations in fiber length, microfibril angle, and specific gravity were more visible in northern Vietnam than in southern Vietnam, with a significant effect of genetic factors. This difference may be attributable to winter, which is experienced in northern Vietnam but not in southern Vietnam. For clone selection for plantation in the northern region, combining growth rate with wood properties was recommended. On the other hand, for plantation in the southern region, clone selection depends mainly on the growth rate, taking into consideration the specific gravity.  相似文献   

12.
The effects of physical properties of wood, including specific gravity, porosity, and water retention, on the water activity (a w) of wood meal media for the cultivation of edible mushrooms were examined. Five species of wood, selected from an initial set of 11 species, and six species of fungi popularly cultivated in Japan were used. The water activity of each fungal species was measured using liquid media in which a w had been reduced by adding NaCl, KCl, sucrose, or ethylene glycol. From the water activities of the media and fungi, we estimated the most suitable wood species for the cultivation of each edible mushroom in wood meal media. Suitable wood species for the wood meal cultivation of shiitake, nameko, and maitake, which had relatively high a w, was limited to hardwoods like arakashi, konara, and irohakaede because of their higher water activities. Edible mushrooms with lower levels of a w, like hiratake, enokitake, and bunashimeji, could be cultivated in all kinds of wood species used in this experiment, but especially in sugi.Parts of this report were presented at the 49th, 50th, 51st, and 52nd Annual Meetings of the Japan Wood Research Society, in Kyoto (April 2000), Tokyo (April 2001), Gifu (April 2002), and Fukuoka (March 2003), Japan  相似文献   

13.
In vitro laboratory decay tests on Ailanthus excelsa Roxb. wood revealed that I. hispidus exhibits a combination of both white-rot and soft-rot patterns of wood decay. Early stages of wood decay showed dissolution of the middle lamella as well as defibration and localized delignification of fiber walls; vessels, axial, and ray parenchyma remained unaltered. Delignification commenced from the middle lamellae at the cell corners without any marked effect on the primary and secondary wall layers. In later stages of growth, the species produces typical soft-rot decay pattern by forming erosion channels through the S2 layers of fiber walls, transverse bore holes in the cell walls, and erosion channels alongside/following the orientation of cellulose microfibrils. The rays showed signs of cell wall alterations only after the extensive damage to the fiber walls. After 120 days of incubation, the vessels also showed localized delignification, the erosion of pits, and separation from associated xylem elements. The extensive weight losses under natural and in vitro decayed wood as well as the very soft nature of severely degraded wood indicate that I. hispidus alters wood strength and stiffness.  相似文献   

14.
This study was designed to reveal the role of the cement/wood ratio in a hydration test of wood-cement mixtures. The compatibility of oil palm (Elaeis guineensis Jacq) fronds-cement mixtures was tested in the hydration test, with the addition of magnesium chloride as an accelerator at different water/cement ratios. To prove the findings on the hydration behavior of components, the cement-bonded boards were manufactured using a conventional cold-pressing method at different cement/wood ratios. Results indicated that the optimum weight ration of cement/wood increased with decreasing wood powder size based on the equal specific surface area ratio of cement/wood in the hydration test and board manufacturing. The addition of magnesium chloride improved the compatibility of oil palm fronds with cement; the compatibility factor (C A) increased by more than 90% with the addition of 5% magnesium chloride. TheC A factor increased proportionally with a higher magnesium chloride content and a higher water/ cement ratio. The addition of magnesium chloride also enhanced the cement hydration and ultimate board strength properties. However, the addition of 5% magnesium chloride did not improve the properties of boards sufficiently at a cement/wood ratio of 2.21.0.  相似文献   

15.
Wood samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to perform moisture sorption tests associated with parallel-to-grain and tangential compression tests using a multiple step procedure at 25°C. Cold-water and hot-water extractives, sequential cyclohexane (CYC), acetone (ACE) and methanol (MET) extracts, ash content (ASH), wood density and interlocked grain (IG) were evaluated on matched samples too. Wood density corrected for the accessory substances was by far the major factor positively affecting the compressive properties of tropical hardwoods. The total amount of accessory substances is required in order to establish better relationships between physico–mechanical properties and density of tropical hardwoods. For a given wood density, the ultimate stress in parallel-to-grain compression was higher in tropical hardwoods than in temperate hardwoods. However, the compliance coefficients for both types of woods were quite similar. Sequential extraction with organic solvents was the most suitable method for evaluating the effect of extractives on compressive properties of tropical hardwoods. The CYC and ACE fractions did not contribute to variation in these mechanical properties. The substances dissolved in MET affected positively the compliance coefficient s 11 in parallel-to-grain compression and negatively the compliance coefficient s 33 in tangential compression. The IG decreased the compliance coefficient s 11 but also decreased the ultimate stress in parallel-to-grain compression. Finally, variations in compressive properties that were due to changes in equilibrium moisture content (EMC) were clearly influenced by wood density; denser woods were more sensitive to changes in EMC than lighter woods.  相似文献   

16.
Cunninghamia lanceolata wood meal samples with different lignin contents after delignification with an acidic NaClO2 system were carboxymethylated, and the degree of substitution (DS) and the distribution of the carboxymethyl (CM) groups were investigated by proton nuclear magnetic resonance (1H NMR) spectroscopy. Cellulose samples prepared from bleached kraft softwood pulp, food-grade konjac mannan, and commercial oat xylan (containing 10% arabinosyl and 15% glucosyl residues) were also investigated. The chemical shift of methylene protons in 1H NMR spectra of CM groups of carboxymethyl konjac mannan and commercial oat xylan appeared in the same region as those of carboxymethylcellulose. The DS of carboxymethyl lignocellulose (CMLC) increased slightly from 1.36 to 1.48 with decreasing lignin content, but the water solubility of CMLC clearly increased with decreasing lignin content. It was suggested that the covalent linkages between lignin and cell-wall polysaccharides play the role of cross-linker in CMLC. Water absorbents were synthesized by graft-copolymerization of acrylic acid onto CMLC samples with different lignin contents. The highest level of water absorbency was obtained from CMLC containing 14% of lignin, suggesting the importance of lignin as the cross-linker.  相似文献   

17.
To provide information on the feasibility of using exploded wood fiber strand (WFS) obtained by the water-vapor explosion process in wood-cement mixtures, the compatibility between cement and exploded WFS and its improvement with various additive chemicals were investigated by observation and analysis on hydration behaviors in terms of hydration characteristics: maximum hydration temperature (T max) and required time (t max). The three types of cement, six additive chemicals, and exploded WFS (sugi, air-dried and water-soaked) were employed as raw materials in this study. The hydration behaviors of mixtures demonstrated that exploded WFS had strong retarding effects on cement hydration and completely prevented mixtures from setting. The analysis of sugar revealed that the sugar contents of exploded WFS were much higher than those in unexploded wood and increased to about 20-fold (air-dried) and 10-fold (water-soaked), respectively. The degraded polysaccharides became a major factor and played an important role in inhibiting the setting of cement. Moreover, high-performance liquid chromatography analysis proved that the main peaks representing the molecular weight of polysaccharides in extractives of exploded WFS shifted markedly to a lower range of polymerization. MgCl2 was determined to be an effective additive chemical for restraining the inhibitory influences. Addition contents of 2%–3% and 4%–5% were available and acceptable for quick-curing cement and ordinary Portland cement, respectively. As for the furnace-slag cement, the composite additive chemicals of MgCl2 (4%) and CaO (2%) were found to have an obvious accelerating effect.Part of this report was presented at the 51th Annual Meeting of the Japan Wood Research Society, Tokyo, April 2001  相似文献   

18.
To clarify the lowering mechanism of loss tangen (tan) of sitka spruce (Picea sitchensis Carr.) wood impregnated with extractives of pernambuco (Guilandina echinata Spreng. synCaesalpinia echinata Lam.), we examined the vibrational properties of the impregnated wood in relation to the adsorbed water. The results obtained were as follows: (1) The equilibrium moisture content (EMC) of impregnated sitka spruce decreased to some extent compared with untreated wood. (2) Frequency dependencies of tan a about 400–8000Hz showed that impregnated wood has much lower tan than untreated wood at around 9% mois ture content (MC), except for the high-frequency region. At high relative humidity, impregnated wood has a minimum tan (at around 4000Hz); and at other frequency ranges the tan of impregnated wood did not differ considerably from that of untreated wood. (3) The apparent activation energy of the mechanical relaxation process (E) concerned with adsorbed water molecules was higher for impregnated specimens than for untreated ones at moderately high relative humidity, whereas at high relative humidity the difference was not observed. Based on these results, it is thought that the tan of impregnated wood decreased at low rela tive humidity because of the formation of direct hydrogen bonds between impregnated extractives and wood components. However, when the specimen is at higher relativePart of this work was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998 humidity, the formation of direct hydrogen bonds are disturbed by the existence of a large number of water molecules, and some extractives act as a plasticizer.  相似文献   

19.
Summary Various chemicals are used for protecting wood samples against fungi, and some of them are released in water, leading to pollution of the water. The kinetics of release of pentachlorophenol in water has here been studied, by considering the diffusion through the wood along the three principal axes of diffusion. The experiments and the modelling of the process is successfully coupled. The numerical model takes the three principal diffusivities, the partition factor, the volumes of wood and water into account. The effect of the length of the wood sample taken along the longitudinal axis of diffusion is especially studied, as the longitudinal diffusivity is much higher than the other two principal diffusivities. The effect of the relative volumes of wood and water is also of considerable interest not only for the concentration of the chemical in water but also for the rate of release.Symbols C concentration of liquid (g/cm3) - Cs, Ceq,t concentration of liquid on the surface, at equilibrium with the surrounding, respectively - Ci,j,k concentration of liquid in the wood at position (i, j, k) - D diffusivity (cm2/s) - h coefficient of mass transfer on the surface (cm/s) - i, j, k integers characterizing the position in the wood - K partition factor - L, R, T dimensions of the parallelepipedic wood sample - Mini amount of chemical contained in the wood at the beginning of the desorption - ML, MR, MT dimensionless numbers - Mt, M amount of chemical released up to time t, up to infinite time, respectively - N half-number of slices taken in the wood parallelepiped along each dimension - Vwater volume of the surrounding water - x, y, z coordinates - L, R, T thickness of the slices taken in the wood for calculation - t increment of time  相似文献   

20.
This study examined the origin of the moisture dependency of the longitudinal Youngs modulus of wood (E L ) in relation to the microfibril angle (MFA) of the S2 layer of the secondary wall. Microtomed early wood specimen of sugi (Cryptomeria japonica D.Don) were used for the experiment. The following was revealed:
1.  E L tends to decrease as the moisture content increases in the region below the fiber saturation point (FSP).
2.  The percentage reduction of E L from the oven-dried state to the FSP is almost constant regardless of the MFA.
Subsequently, the relationship between E L and the moisture content was simulated theoretically using the simplified wood fiber model proposed in our previous paper (Part 1, 2002). The simulation considered the two hypotheses proposed in Part 1 for the origin of the moisture content dependency of E L . The first is a traditional theory that the reduction of E L is caused mainly by the moisture dependency of the lignin-hemicellulose matrix. The second assumes that an intermediate domain exists between the rigid crystal and the compliant disordered amorphous regions in wood cellulose microfibril (CMF). It is assumed that such a domain fluctuates between the rigid crystal-like and the compliant amorphous-like states at which the elastic modulus is of the same order as the lignin-hemicellulose matrix in accordance with the moisture sorption.When the first hypothesis is adopted for the simulation, the percentage reduction of E L from the oven-dried state to the FSP should increase as MFA increases; this was contradicted by the experimental results (2). On the other hand, when the second hypothesis is applied to the simulation, the experimentally obtained results (1) and (2) are simulated reasonably. This suggests that the moisture dependency of E L is controlled by the second hypothesis.  相似文献   

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