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1.
Viscoelastic properties of wood in swelling systems 总被引：2，自引：0，他引：2
T. Sadoh 《Wood Science and Technology》1981,15(1):57-66
Summary The torsion modulus and the mechanical damping were investigated on wood swollen with formamide and a series of glycols, at frequencies of 0.5 and 0.02 Hz as a function of temperature. In wood swollen with formamide to the same extent as it would swell when saturated with water, the temperature of maximum damping was about 48° and above 100°C for wood swollen with polyethylene glycols, while that of water saturated wood was 80°C. For more highly formamide swollen wood (1.2 times the swelling in water) the temperature at which maximum damping develops decreased to 30°C. With regard to the influence of swelling and temperature on the torsion modulus of wood, three regions of viscoelastic behavior were recognized in these swelling systems. They are the glassy region in non-swollen wood, where the torsion modulus decreases gradually with increasing temperature, the transition region where the torsion modulus decreases abruptly with increasing temperature and swelling, and a plateau region appearing at high temperatures for highly swollen wood where the torsion modulus remains fairly constant with temperature with a value of about one tenth the modulus for non-swollen wood. 相似文献
2.
B. A.. -L. Östman 《Wood Science and Technology》1985,19(2):103-116
Summary The immediate tensile strength parameters for spruce parallel to the grain and for hardboard have been determined at equilibrium conditions at temperatures up to 250°C. Below 100°C the moisture content has been varied between 0 and 30%. Above 100°C dry samples have been studied. An increase in moisture content up to about 12% leads to a slight increase in the tensile strength of spruce whereas the modulus of elasticity remains constant. With a further increase in moisture content, both properties decrease significantly. At any given moisture content, both properties decrease with increasing temperature. The corresponding strain at rupture is constant. An increase in temperature leads to a more or less linear decrease in the tensile strength and in the modulus of elasticity up to about 200°C. Above 200°C there is a more rapid decrease due to thermal softening. It is most relevant to consider the relative strength decrease since the absolute levels may be quite high due to the fact that wood samples without any irregularities were used. Such relative strength data are compared with the small amount of similar data found in the literature. The effects on the modulus of elasticity are discussed in terms of thermal softening and of water as a softener for the cellulose/hemicellulose polymers. The glass transition temperature is determined as a function of the moisture content.A special thank to Ms. K. Bojadzijev for skillful experimental assistance, to Prof. E. L. Back for stimulating discussions and to the fund for research in woodworking industries for financial support 相似文献
3.
The radial compression behaviors of acetylated cedar wood were measured in various liquids. The compressive Young’s modulus
(E) of acetylated wood was reduced by soaking in water, toluene, and acetone, but it was always greater than that of water-swollen
unmodified wood at the same swelling level. The behaviors of acetone-swollen unmodified wood were similar to those of acetylated
wood rather than those of water-swollen unmodified wood. These results indicated that the swelling of hydrophobic wood components
had a lesser influence on the E of wood than the water-swelling of unmodified hydrophilic components. After large compression (ε > 45%), a part of the strain
remained unrecovered because of irreversible mechanical deformation. Since the remaining strain was smaller in the wood specimens
indicating greater stress relaxation, it was assumed that the viscoelastic deformation of amorphous matrix components is important
for lesser irreversible deformation and effective shape recovery of wood. In contrast with water-swollen unmodified wood,
the acetylated wood and acetone-swollen unmodified wood exhibited greater shape recovery despite their relatively higher E. This suggested that the swelling of hydrophobic wood components reduced the viscosity of the matrix rather than its elasticity,
resulting in more effective shape recovery with lesser softening. 相似文献
4.
Miscanthus sinensis was pretreated and used to produce fiberboard with no synthetic binders. The lignocellulosic material was steam exploded with a thermomechanical aqueous vapor process in a batch reactor. The effect of the pretreatment and the pressing conditions on the physicomechanical responses of the fiberboard was evaluated and the conditions that maximize the responses were found. Response surface methodology with a central composite design was used. The variables studied and their respective variation ranges were: pretreatment temperature, 196–236°C; pretreatment time 1–6 min; pressing temperature, 130–230°C; pressing time, 1.6–18.4 min. The boards obtained were of very good quality (modulus of elasticity up to 6070 MPa, modulus of rupture up to 48 MPa, internal bond up to 2.9 MPa, thickness swelling up to 4% and water absorption up to 8%) and more than satisfy the requirements of the relevant standard specifications. The effect of the pretreatment influence on the lignin, cellulose and hemicelluloses content was also determined by a fractionation of the previous experimental design. The decrease in hemicelluloses is clearly related to the increase in the dimensional stability of the boards.Abbreviations MOE
Modulus of elasticity
- MOR
Modulus of rupture
- IB
Internal bond
- TS
Thickness swelling
- WA
Water absorption
- Tr
Pretreatment temperature
- tr
Pretreatment time
- Tp
Pressing temperature
- tp
Pressing time 相似文献
5.
Sudijono Dwianto Wahyu Yusuf Sulaeman Iida Ikuho Furuta Yuzo Minato Kazuya 《Journal of Wood Science》2004,50(4):371-374
Mechanical property changes due to the moisture content (MC) and/or temperature changes were examined for 15 Indonesian wood species. A static bending test was carried out at 20°C, 65% relative humidity (air-dry), and water-saturated at 20°C (wet-20) and 80°C (wet-80). For individual test conditions, modulus of elasticity (MOE) and modulus of rupture (MOR) increased linearly with specific gravity regardless of wood species; however, maximum deflection did not correlate with specific gravity for any MC or temperature conditions. The relative values of MOE and MOR measured in wet-20 to air-dry conditions were variously affected from slightly to strongly depending on the wood species. However, the relative values always decreased markedly when saturated in water at 80°C, regardless of wood species. The relative MOE, MOR, and maximum deflection values due to the change in MC or MC and temperature combined were independent of specific gravity but may be dependent on wood type: softwood or hardwood. 相似文献
6.
Sitka spruce (Picea sitchensis Carr.) wood was heated for 0.5–16.Oh at temperatures of 120°–200°C in nitrogen gas or air. The values for Young's modulus, shear modulus, and loss tangent were measured by free-free flexural vibration tests. X-ray diffractometry was carried out to estimate the crystallinity index and crystallite width. The results obtained are as follows: (1) Density decreased at higher temperatures and longer heating times. The specific Young's modulus, specific shear modulus, crystallinity index, and crystallite width increased during the initial stage and were constant after this stage at 120°C and 160°C, whereas they increased during the initial stage and decreased later when the temperature was high. Loss tangent in the longitudinal direction increased under all conditions, whereas that in the radial direction increased at 120°C and decreased at 160°C and 200°C. (2) From the relation between Young's modulus and moisture content, it can be safely said that Young's modulus is increased by the crystallization and the decrement in equilibrium moisture content, and that crystallization (rather than degradation) is predominant at the initial stage of the heat treatment, whereas the latter is predominant as the heating time increases. (3) It is implied that the specific Young's modulus, specific shear modulus, crystallinity index, and crystallite width decreased more in air than in nitrogen gas because of oxidation in air.This study was presented in part at the 43th Annual Meeting of Japan Wood Research Society at Morioka, August 1993, the 44th Annual Meeting of Japan Wood Research Society at Nara, April 1994, and the 45th Annual Meeting of Japan Wood Research Society at Tokyo, April 1995 相似文献
7.
Changes in the modulus of elasticity (MOE), modulus of rupture (MOR), and stress relaxation in the radial direction of wood (hinoki:Chamaecyparis obtusa) moisture-conditioned by the adsorption process from a dry state and by the desorption process from a moisture content slightly below the fiber saturation point were investigated. The MOE and MOR of wood conditioned by the adsorption process showed significant increases during the later stages of conditioning when the moisture content scarcely changed. However, with the desorption process they did not increase as much during later stages of conditioning, though they increased during early stages of conditioning when the moisture content greatly decreased. The stress relaxation of wood decreased with an increase in the conditioning period with both the adsorption and desorption processes. These results suggest that wood in an unstable state, caused by the existing state of moisture differed from that in a true equilibrium state shows lower elasticity and strength and higher fluidity than wood in a true equilibrium state. Furthermore, the present study demonstrates that the unstable states of wood induced during the course of drying, desorption, and possibly adsorption of moisture are slowly modified as wood approaches a true equilibrium state. 相似文献
8.
Wood-to-bark adhesion strengths were tested at 25 to –78°C under moisture contents of 0–200%. The freezing temperature of the cambium appeared to be between –20 and –40°C. The low freezing temperature was assumed to be due to the high pectin and protein contents in the cambium cells. At temperatures above the freezing point of the cambium (–20 to 25°C), the adhesion strength was curvilinearly and negatively related to moisture content. At temperatures below the freezing point of the cambium (–40 to –78°C), adhesion strength was not correlated with moisture content. For practical application, maintaining logs at high moisture content and temperatures above –20°C would assure a good debarking and yield high quality wood chips for pulping, with less wood loss to hog fuel. 相似文献
9.
Yuka Miyoshi Ai Sakae Nao Arimura Keisuke Kojiro Yuzo Furuta 《Journal of Wood Science》2018,64(2):157-163
In this study, to summarize the changes of thermal-softening behaviors of wood and acetylated wood due to differences in the kinds of swelling liquids, the following measurements were conducted. Untreated and acetylated wood samples were swollen by various liquids and the temperature dependences of the dynamic viscoelastic properties were measured after the heating and cooling histories were unified among the samples. The results obtained are as follows. Untreated samples swollen by high-polarity liquid had lower peak temperature of tanδ, however acetylated samples had higher peak temperature of tanδ than those of untreated wood. On the other hand, untreated wood samples swollen by low-polarity liquid had higher peak temperature of tanδ, however acetylated samples had lower peak temperature of tanδ than those of untreated wood. The amount of swelling is determined by interaction between wood and liquid due to proton-accepting power and molar volumes of liquid and so on, therefore the peak temperature of tanδ and degree of reduction in dynamic elastic modulus (E´) with increasing temperature were corresponded to the amount of swelling. 相似文献
10.
Summary Familiarity with the mechanical and thermal processes in the mechanical defibering of wood is a prerequisite for an understanding of mechanical pulping methods. The thermal softening behaviour of wood components, which can be described by glass transitions, is of particular significance. Investigations on the thermoplastic behaviour of solid wood confirm that the thermal softening of wood occurs at 115–145°C. The thermal softening behaviour is largely dependent on wood moisture but also on the nature of the wood. The results obtained permit conclusions regarding the layout of technological processes in groundwood. 相似文献
11.
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. 相似文献
12.
Influence of moisture sorption history on the swelling of sugar maple wood and some tropical hardwoods 总被引：2，自引：0，他引：2
Roger E. Hernández 《Wood Science and Technology》1993,27(5):337-345
Summary Samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to perform moisture sorption tests associated with swelling tests at 25 °C. The results demonstrate that, for a given equilibrium moisture content, tangential and radial dimensions, and hence the volume of wood, are greater after desorption than after adsorption. The importance of these differences, so-called second-order effects of moisture sorption, varied with the species and with the direction of swelling. These effects are proportionally greater in the tangential direction of wood than in its radial axis. Finally, two types of samples showed similar swellings for three equilibrium moisture contents.The author wishes to thank Professor M. Goulet for his support and help. This research was supported by the Canadian International Development Agency and the Natural Sciences and Engineering Research Council of Canada 相似文献
13.
A Miscanthus Sinensis plantation in Galicia, Spain, provided the raw material for experimental fiberboards. After harvesting, the Miscanthus stems were cleaned and chipped. The chips were steam exploded with a thermo-mechanical aqueous vapor process in a batch reactor. The resulting material was dried, slightly milled, and used to produce fiberboard with no synthetic binders. The pretreatment and the pressing conditions that optimize the physico-mechanical responses were determined. Response surface methodology with a central composite design was used. The variables studied and their respective variation ranges were: pretreatment time, 4–14 min; pressing temperature, 195–245°C; pressing pressure, 1.9–14.6 MPa. The boards obtained were very good quality (modulus of elasticity as high as 7630 MPa, modulus of rupture as high as 61 MPa, internal bond as high as 4.1 MPa, thickness swelling as low as 2.5%, and water absorption as low as 8.9%) and more than satisfied the requirements of the relevant standard specifications. 相似文献
14.
Preparation of sulfuric acid-catalyzed phenolated wood resin 总被引：22，自引：0，他引：22
Summary Birch wood meal was phenolated in the presence of sulfuric acid used as a catalyst by changing several reaction conditions, such as, phenol-to-wood ratio, temperature, time, and catalyst concentration to make novolak-type resin. A phenol-to-wood ratio of 2–5, reaction temperature of 60–150 °C, time of 60–120 min, and acid concentration of 1–3% were found to be usable values for obtaining good enough amounts of combined phenol and less amounts of unreacted wood residue. The flow properties (flow temperature and apparent melt-viscosity) of the phenolated wood obtained increased with the increase in the amount of combined phenol, however, decreased with the increase in the moisture content and free phenol in the phenolated wood. Furthermore, it was found that the solubility of the phenolated wood in the organic solvents depended, greatly, on the hydrogen bonding strength of the solvents. 相似文献
15.
Three-layered composite oriented strand boards were manufactured using very thin hinoki (Japanese cypress, Chamaecyparis obtusa Endl.) strands oriented in the faces and mixtures of sugi (Japanese cedar, Cryptomeria japonica D. Don.) and hinoki particles in the core. The boards were composed of two density levels, with 1:8:1, 0.5: 9 : 0.5, and 0: 10 : 0 face: core: face ratios. Polymeric and emulsion type isocyanate resins were used. The resin contents for the strands in the face and particles in the core were 10% and 5%, respectively. The steam-injection press was applied at 0.62MPa (160°C), and the steam-injection time was 2min. The mechanical and physical properties of the boards were evaluated based on the Japanese Industrial Standard. The parallel moduli of rupture and elasticity along the strand orientation direction and the wood screw retaining force increased with increasing face/core ratios. Incorporation of 10%–20% of thin strands in the face of the boards improved the parallel moduli of rupture and elasticity by 47%–124% and 30%–65%, respectively. In addition, the thickness swelling after water-soaking at 20°C for 24h, and the parallel linear expansion after boiling for 2h and water-soaking at 20°C for 1 h, of the three-layered composite boards were below 8% and 0.15%, respectively, despite a short steam-injection press time. The thickness swelling of the boards decreased with increasing face/core ratios. In contrast, the presence of face strands seems to have a minimal effect on the moduli of rupture and elasticity along the perpendicular direction of the three-layered composite boards. A similar trend was observed for the internal bond strength, hardness, and linear expansion along the perpendicular direction.This paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997 相似文献
16.
Dynamic viscoelastic properties of wood acetylated with acetic anhydride solution of glucose pentaacetate 总被引：1，自引：0，他引：1
Spruce wood specimens were acetylated with acetic anhydride (AA) solutions of glucose pentaacetate (GPA), and their viscoelastic
properties along the radial direction were compared to those of the untreated and the normally acetylated specimens at various
relative humidities and temperatures. Higher concentrations of the GPA/AA solution resulted in more swelling of wood when
GPA was introducted into the wood cell wall. At room temperature the dynamic Young's modulus (E′) of the acetylated wood was enhanced by 10% with the introduction of GPA, whereas its mechanical loss tangent (tan δ) remained almost unchanged. These changes were interpreted to be an antiplasticizing effect of the bulky GPA molecules in
the wood cell wall. On heating in the absence of moisture, the GPA-acetylated wood exhibited a marked drop in E′ and a clear tan δ peak above 150°C, whereas the E′ and tan δ of the untreated wood were relatively stable up to 200°C. The tan δ peak of the GPA-acetylated wood shifted to lower temperatures with increasing GPA content, and there was no tan δ peak due to the melting of GPA itself. Thus the marked thermal softening of the GPA-acetylated wood was attributed to the
softening of wood components plasticized with GPA.
Received: March 29, 2002 / Accepted: May 21, 2002
Correspondence to:E. Obataya 相似文献
17.
Influence of wood planing on the second-order effects of moisture sorption in sugar maple 总被引：1，自引：1，他引：0
Summary Two types of machines, a conventional planer, and a fixed-knife pressure-bar planer were used to prepare matched specimens
of sugar maple wood. After adsorption and desorption, both experiments at 21 °C, the EMC, swelling in all principal directions
as well as compliance coefficient in radial compression were measured. Two specimen sizes were used for these expe‐riments.
For a given equilibrium moisture content, tangential and radial dimensions were greater after desorption than after adsorption,
as previously described. When equilibrium was reached by gaining moisture, the wood was stiffer in radial compression compared
to when the equilibrium was reached after losing moisture. The magnitude of this phenomenon, second-order effects of moisture
sorption, was slightly affected by the type of planing. These effects on swelling were greater for large specimens prepared
by conventional planing compared to fixed-knife pressure-bar planing. Small specimens showed similar magnitudes of this phenomenon
with both planing methods. No differences between planing methods were found for the radial compliance coefficient measured
on either specimen size. Therefore, the second-order effects of moisture sorption appeared to be a bulk phenomenon and not
restricted to the superficial layers of wood.
Received 9 December 1997 相似文献
18.
Summary For this study, urea-bonded particleboards with three resin levels and three specific gravity values were made in the laboratory. Specimens for modulus of rupture, modulus of elasticity, and internal bond strength tests were conditioned at 14 relative humidity values over the range 13–97 per cent. Results for the three mechanical properties were fitted to cubic equations in moisture content with a high degree of accuracy (correlation coefficients of over 0.99 in most cases). 相似文献
19.
Compression of wood under saturated steam, superheated steam, and transient conditions at 150°C, 160°C, and 170°C 总被引：1，自引：1，他引：0
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. 相似文献
20.
Rosilei A. Garcia Alexandre Monteiro de Carvalho Jo?o Vicente de Figueiredo Latorraca Jorge Luis Monteiro de Matos Wanessa A. Santos Rafael Fonseca de Medeiros Silva 《Wood Science and Technology》2012,46(1-3):41-52
The objectives of this study were to evaluate the effect of heat treatment of eucalypt wood (Eucalyptus grandis Hill ex Maiden) on the dynamic modulus of elasticity by using the stress wave nondestructive method and also to determine the air-dry density variation, weight loss and equilibrium moisture content following treatment. Heat treatments were performed at four different temperatures (180, 200, 215 and 230°C) and for three different durations (15?min, 2 and 4?h). The results revealed a significant reduction in air-dry density following heat treatment independent of temperature and time. A significant weight loss was observed between and within treatments. The treatment at 230°C for 2 and 4?h produced a weight loss of 20.5 and 26.5%, respectively, which was statistically different from other treatment conditions. The dynamic modulus of elasticity decreased by about 13% in the most severe treatment (230°C for 4?h). Depending on the temperature and time, the equilibrium moisture content was significantly reduced within the range of 40–74%. 相似文献