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1.
T. E. Timell 《Wood Science and Technology》1973,7(3):163-172
Summary The distribution of lignin in opposite wood has been studied by removing the polysaccharides with hydrofluoric acid and examining the resulting lignin skeletons in the electron microscope. The thick S3 layer was more highly lignified than the S1 and S2 layers in Abies balsamea, Picea rubens, Pinus resinosa, and Tsuga canadensis. In Picea rubens, but not in the other species, there was, adjacent to the S3 layer, a transition zone in S2 with a high concentration of lignin. The S3 layer varied considerably in thickness and was often buckled, especially in the latewood. The structure of the bordered pits was that observed in the original wood. The margo, the torus, and the initial pit border were all highly lignified.This paper is dedicated to Dean Edwin C. Jahn in honor of his 70th birthday. 相似文献
2.
轴向管胞是针叶材中的主要细胞,它的体积约占木材体积的90%以上,其主要功能是输导水分及强固树体(申宗圻,1984). 相似文献
3.
《Wood material science & engineering》2013,8(4):219-227
Abstract Heat treatment of wood is an effective method by which to improve the dimensional stability and biological durability, but the mechanical strength is decreased at the same time. Besides chemical modification of cell-wall constituents, physical weakening of the microstructure owing to heat-induced defects may also contribute to strength loss. Therefore, anatomical properties of heat-treated beech (Fagus sylvatica L.) and spruce (Picea abies Karst.), studied by light microscopic and scanning electron microscopic analysis, and their interrelation with strength properties and structural integrity were investigated. For determination of structural integrity, the high-energy–multiple-impact (HEMI) test was applied. Microscopic analyses showed frequent formation of radial cracks in heat-treated beech close to the rays as well as tangential cracks in the latewood of spruce. In addition, the modulus of rupture was more affected by the heat treatments than the resistance to impact milling (RIM) determined by the HEMI test, because RIM is based on multiple fractures on the microlevel that are not affected by the formation of intercellular cracks or other defects due to the heat treatment. It was concluded that heat-induced defects in the wood microstructure contribute to the substantial strength loss of thermally modified timber. 相似文献
4.
Summary Sapwood, frozen in a conducting state, was freeze-etched for electron microscopy to show undried bordered-pit membranes. These appeared similar in structure to non-aspirated pit membranes observed in wood dried from organic solvents. Freeze-etching showed that, even before drying, the torus is lens-shaped in section and suspended by a margo of large radial strands and numerous smaller fibrils. Globular objects, previously undescribed, whose diameters ranged from 0.3 to 1 m, were found distributed at random on pit membranes and tracheid walls.We thank Mr. D. John for technical assistance, Professor P. E. Weatherley for advice, the Forestry Department, University of Aberdeen for wood samples, and the Canadian Department of the Environment, Canadian Forestry Service, for financial assistance and educational leave to G. S. Puritch. 相似文献
5.
The relation between crack propagation based on fracture mechanics and end-check propagation during drying was evaluated in
this study. Corresponding to the direction of end-check propagation, the mode I fracture toughness of air-dried sugi specimens
in TR, TL, and intermediate systems was examined by single-edge-notched bending tests. The occurrence and propagation of end
checks on sugi (Cryptomeria japonica D. Don) blocks during drying were observed at the scale of the annual rings. It was found that the critical stress intensity
factor (K
IC) decreased as the crack propagation changed from TL to TR. The value of K
IC in the TR system was significantly lower than that in the TL system. As a measure of fracture energy, the area under the
load-crack opening displacement curve in the TR system was more than twice that in the TL and intermediate systems. These
results indicate that cracks perpendicular to the tangential direction initiate radially with ease, and then crack arrest
occurs to prevent growing. This finding provides a consistent interpretation of the end-check propagation observed during
drying as follows: tiny end checks, as an analog of TR cracks, occur easily and selectively in latewood or transition wood
and propagate toward the pith during drying. When there is no corresponding secondary check in the forward latewood, the checks
are arrested and do not propagate further. 相似文献
6.
《Wood material science & engineering》2013,8(3-4):83-93
Abstract Differences in durability between heartwood and sapwood of Norway spruce [Picea abies (L.) Karst.] were investigated to determine wood qualities most favourable for use in outdoor constructions above ground. Trees grown on sites with either good or poor access to water were used. Seventy-eight specimens measuring 20 × 50 × 300?mm3 separated into heartwood and sapwood, half untreated, half painted, were exposed horizontally outdoors above ground for 5.5?years with the pith side up and the bark side down. Crack length and crack number were measured. Fungus growth and surface changes were visually estimated. Fungus type was determined by microscopic analysis. The main finding was that spruce heartwood had fewer and shorter cracks and less surface-discolouring fungus growth than sapwood. This was valid for both painted and untreated wood. After 2?years’ exposure, the cracks in sapwood (upper surface) were more than three times longer and about five times more numerous than in heartwood for both painted and untreated boards. Microscopic study showed that surface discoloration was due mainly to Aureobasidium pullulans, together with a few other discolouring fungi. After 5.5?years, initial decay was established on the surface and in the end grain of four untreated test objects. 相似文献
7.
Sub-alpine fir (Abies lasiocarpa (Hook)) is characterized by its low permeability and that it is then hard-to-dry. Long drying time for the species causes kiln
capacity problems for numbers of spruce-pine-fir (SPF) lumber producers. A high-temperature drying schedule with a rapid rise
in dry-bulb temperature to a temperature above boiling point at the beginning is a potential approach to enhance the drying
productivity. Determinations in permeability of ten sub-alpine fir boards after slow heating and fast heating were carried
out in this study. The results indicated that a rapid rise in temperature increased the permeability of sub-alpine fir. By
statistical analysis, the permeability was increased significantly due to the fast heating in seven boards. The permeability
in other three boards was also increased, but not significantly. Using a scanning electron microscope (SEM), the impact of
heating speed on pit membrane of sub-alpine fir lumber was investigated. A small number of fine fractures were observed on
the pit membrane after slow heating, while in case of fast heating, the torus was partially ruptured and a separation occurred
in pit border and cell wall. By observing the SEM images, it was suggested that the force of vaporization and/or thermal stresses
due to the fast heating were able to open the aspirated pits and/or break the membranes in the wood cells, and therefore increase
the permeability, intensify the moisture transportability and improve the dry-ability of sub-alpine fir lumber. 相似文献
8.
Summary The observations of the inner surface of Japanese red pine (Pinus densiflora Sieb. et Zucc.) earlywood tracheid wall in the various stages of the differentiation allowed the study of the development of the bordered pit. The process of the formation of the bordered pit membrane and the deposition of the cell wall layers in the pit border region were examined in detail by electron microscopy using the replication preparation technique. The microfibrillar structure of the margo and torus, which is characteristic of the bordered pit membrane of this species, was detected in the later stage of primary wall formation. The bordered pit membrane was shown to have the same microfibrillar structure as that of the matured one even at this stage of differentiation, although it was embedded in matrix substances. It appeared that the matrix substances were removed immediately after the warty layer had been formed in the tracheid wall.The initiation of pit border development was observed as the deposition of circularly oriented microfibrils around the vicinity of the pit annulus in the later stage of the primary wall formation. The deposition of the S1-layer was indicated to contribute to the pit border formation until the diameter of the pit aperture reached its final size, simultaneously with the apposition of the layer of so-called B. T. or initial border thickening. So both the S1-layer and initial border thickening were assumed to be formed supplementing each other. In the period of the S1-layer formation, the transversely deposited microfibrils in the tracheid inner surface were detected to generally curve around the pit aperture and some of them extend to the outer surface of the developing pit border beyond the pit aperture. From these observations of replicas of the inner surface of the differentiating tracheid, a concept concerning pit border formation is proposed.The authors are indebted to members in Kyoto University Forest for providing the samples and to Dr. H. Saiki and other members of Wood Structure Laboratory in Department of Wood Science and Technology at Kyoto University for their assistance during this study. They also express their appreciation to Dr. W. A. Cote, Jr. (State University, College of Forestry, N. Y.) and Dr. W. Liese (Universität Hamburg) for their considerate advice. 相似文献
9.
This study evaluated the protection effectiveness of alcohol-borne reagents for the green color of ma bamboo (Dendrocalamus latiflorus Munro) and moso bamboo (Phyllostachys pubescens Mazel). The results show that the types and concentrations of alcohol-borne reagents, the kinds of solvent, and the conditions
of treatment greatly affected the green color of these two bamboo species. Without alkali pretreatment, an excellent green
color protection (a* = −14.5) was obtained when the ma bamboo culms were treated with 0.5% methanol-borne copper chloride (CuCl2) at 60°C for 30 min. Similar results were also obtained when ma bamboo culms were treated with 0.5% methanol-borne copper
nitrate [Cu(NO3)2] at 60°C for 2 h (a* = −13.5). For moso bamboo, an attractive green color in the bamboo culms was achieved by treating the specimens with 1%
methanol-borne copper acetate [Cu(CH3COO)2] at 60°C for 30 min. The a* value of treated specimens was −13.3. In addition, results demonstrated that ultrasonic treatment was more effective on
green color protection than conventional water bath treatment. When moso bamboo was treated with 1% copper acetate at 60°C
in an ultrasonic bath for only 15 min, a remarkable green color with an a* value of −13.6 was obtained on the bamboo epidermis. 相似文献
10.
The technology of steam explosion was applied to pre-treat sub-alpine fir (Abies lasiocarpa (Hook.) Nutt.) lumber and to improve its drying characteristics. Effects of steam explosion on the appearance and structure of the lumber are discussed in this paper. The structure of the wood was examined using light microscope (LM) and scanning electron microscope (SEM). The following results were obtained. With increasing temperature, pressure, and explosion cycles the color of the lumber darkened gradually. No significant structural difference between treated and untreated samples was observed using LM when the treatments were carried out at temperatures below 130°C with ten explosion cycles (group A or B). Some fractures were observed in bordered pit pairs between tracheids after 20 explosion cycles at 130°C (group C). More fractures occurred in bordered pit pairs between earlywood tracheids at a temperature of 160°C (group D). More or less fractures in pits between ray parenchyma cells and earlywood tracheids were observed using SEM in all four cases of treatments. Although no change in bordered pits in the tracheid walls between group A and the control group was discovered, groups B, C, and D showed different extents of ruptures in bordered pits, which may lead to break aspirated pits and improve permeability. In these groups, wrinkles and separations in the inner tracheid walls and detachments in middle lamella also occurred and became more serious as temperature or cycles of the treatment increased. 相似文献
11.
The incidence of longitudinal drought cracks in coniferous trees may increase as a consequence of climate change. While larger diameter trees are more prone to splitting, it is unclear why only some of the larger trees within the same stand typically suffer damage. Matched pairs of trees of the same size with and without cracks were studied in two adjacent pole-stage mixed stands of Sitka spruce/grand fir (Picea sitchensis/Abies grandis) and Sitka spruce/noble fir (Picea sitchensis/Abies procera) located in North-East Scotland. A range of attributes were measured on 15 damaged and undamaged trees of each species. Length and position of cracks on stems were also recorded, and annual ring width and latewood percentage measured on cores. Noble fir had significantly longer cracks and these were located higher in the stem than the other species. Fewer cracks formed on east-facing side of stems in all species suggesting that prevailing westerly winds may place greater tensile forces on the damaged sides of stems. A higher proportion of latewood (associated with higher tangential shrinkage) was found in the firs and may explain the greater incidence of cracking on grand and noble fir stems (13% and 16%, respectively) in comparison with Sitka spruce (3%). 相似文献
12.
The effects of temperature on mechano-sorptive (MS) creep of delignified hinoki wood (Chamaecyparis obtusa Endl.) were investigated using longitudinal (L) and radial (R) specimens during adsorption and desorption over the temperature
range of 20°–80°C. The results were compared with those of stepwise delignified specimens tested at a constant temperature
of 20°C. It was found that the effects of temperature on the MS creep of delignified specimens are more remarkable than for
untreated specimens. The tendencies of increasing MS creep with temperature, delignification, and their combination were observed.
The increase in MS creep for L specimens was relatively small and almost equal in both adsorption and desorption processes,
while for R specimens the MS creep was small in desorption, but significantly different in adsorption. In addition, good correlation
was observed between the MS coefficient (K) and instantaneous compliance (J
0). The increase in MS creep occurs as a result of temperature increase or decrease in lignin content, or their interacting
effects. However, in the case of desorption for R specimens, the increase of MS creep was unexpectedly small due to a remarkably
increased J
0.
Part of this report was presented at the 15th Annual Meeting of the Chubu Branch of the Japan Wood Research Society in Fukui,
October 2005 相似文献
13.
The formation of insoluble metaborates in wood was investigated by impregnating the wood with borax and metallic salts, after which their properties (e.g., leachability in running water and biological resistance) were evaluated. The solubility of three metaborates in acidic solutions was also evaluated. Double-diffusion treatment was carried out to form the precipitates of metaborates in sapwood specimens of Japanese cedar (Cryptomeria japonica) at room temperature. Water-saturated wood specimens were first impregnated by a saturated borax solution and then diffuse-penetrated with Zn2+, Ca2+, or Pb2+ solution. The precipitates of the three metaborates in the wood proved to be insoluble or hardly soluble in water by the leaching test. With the decay test using a brown-rot fungus (Fomitopsis palustris) and a white-rot fungus (Trametes versicolor) and with the termite test using a virulent subterranean termite (Coptotermes formosanus), the metaborate-treated woods showed generally good decay and termite resistance with negligible mass loss of the specimens. Particularly, the lead metaborate formed in the wood provided superb biological resistance against decay and termite attacks. In addition, the precipitates of these metaborates were found to be soluble in acidic solution, suggesting a way to remove these chemicals from wood when disposing of waste materials. 相似文献
14.
《Wood material science & engineering》2013,8(1):12-20
Abstract The development of cracks and changes in appearance have been investigated on radial and tangential sections of pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) after exposure outdoors for 61 months. The degradation of the sections has also been studied at the micro-level. The annual ring orientation was the most important factor affecting crack development on weathering. After 61 months of outdoor exposure, the tangential sections of spruce had 1.7–2.2 times greater mean total crack length per area unit than the corresponding radial sections. In pine, the total crack length per area unit on the tangential sections was 2.2–2.6 times greater than that on the radial sections. Tangential and radial sections show the same colour change as a result of weathering. Tangential sections have more and deeper cracks than radial surfaces. The cracks on the tangential sections occur frequently in both earlywood and latewood. On radial sections, cracks occur primarily at the annual ring borders, but to a certain extent also in the earlywood. Decomposition of the cell wall takes place in both radial and tangential cell walls, and cracks tend to follow the fibril orientation in the S2-layer of the cell wall. The radial cell wall of the earlywood has a large number of pits which are degraded at an early stage. 相似文献
15.
Micromorphology of the bacterial attack of wood 总被引：1，自引：0，他引：1
H. Greaves 《Wood Science and Technology》1969,3(2):150-166
Summary This paper describes fully the various patterns of bacterial attack to be observed in wood. It is based on many observations made with bacterially infected wood, both in pure laboratory cultures and in naturally attacked wood from diverse environments. Patterns of attack are described for tracheids, fibres, vessles and rays and three types of pit border decay are figured, together with attack of the pit margo and torus. A brief section also deals with the macroscopic appearances of wood subject to bacterial attack.
Zusammenfassung Auf Grund zahlreicher Versuche und Beobachtungen werden die verschiedenen Formen bakteriellen Befalles von Holz, sowohl bei inokulierten Laborkulturen als auch bei natürlich infizierten Hölzern von verschiedenen Waldstandorten, eingehend beschrieben.Im einzelnen umfassen die geschilderten Befallsformen diejenigen, von denen Tracheiden, Fasern, Gefäße und markstrahlen betroffen werden; außerdem werden drei Typen von Tüpfelwulstfäule, sowie je ein Fall von Bakterienbefall eines Tüpfelhofes und einer Tüpfelschließhaut dargestellt.Dem makroskopischen Aussehen bakterienbefallener Hölzer wird ein kurzer Abschnitt gewidmet.相似文献
16.
The main purpose of this study was to investigate the changes in heat flux and temperature after the subject's palm was in contact with interior decorating materials. The relations among heat flux, temperature, and sensation of cold/warm during contact were studied. Ten men and ten women were selected and introduced to 21 materials for the contact test. They were in contact with the specimens for 30min without seeing them in a climate-controlled room at 25°±1°C and 65% RH. Changes in the heat flux and temperature of the specimens were determined by a heat flux meter. A sensory evaluation test was applied to evaluate the cold-warm contact. Results indicated that the heat flux and temperature increased with increasing time after the subject's palm was in contact with the specimens. The heat flux (Q
30) and temperature (T
30) 30min after the subject's palm contacted the specimens were greater for male subjects than for female subjects. A positive linear regression equation existed between the values for Q30 andT
30, whereas a negative linear regression formula existed the sensation of cold-warm by contact (5) and the values of ln(Q
1·). Therefore, the sensation of cold/warm by contact could be estimated simply by using the thermal physical properties of the interior decorating materials.Part of this report was presented at the International Conference on Effective Utilization of Plantation Timber, Chi-Tou, Taiwan, ROC, May 1999 相似文献
17.
Jonas Blomberg 《Journal of Wood Science》2005,51(4):401-404
Quarter-sawn and plain-sawn specimens of Scots pine were semi-isostatically compressed at 5, 15, 50, and 140 MPa in a Quintus press. Elastic strain was measured using a telescope device that was pushed together when wood was compressed and remained in this position at release of pressure. Delayed elastic and plastic strains were assessed through repeated callipering during 5 years after densification. At 140 MPa, wood reached an almost compact structure (ρ ≈ 1450 kg/m3) but as a result of elastic springback the density decreased to just below 1000 kg/m3. At 140 MPa, the elastic and delayed elastic strains were 14.6% and 1.8%, respectively, in quarter-sawn specimens, and were 13.1% and 0.8%, respectively, in plain-sawn specimens. The higher elastic strains in quarter-sawn specimens can be attributed to elastic springback in the tangentially deformed latewood bands. 相似文献
18.
Maximilian Wentzel Tim Koddenberg Holger Militz 《Wood material science & engineering》2020,15(4):223-228
ABSTRACT Eucalyptus nitens specimens were thermally modified under open and closed systems. The anatomical characteristics from selected modifications that presented similar mass losses were investigated by analyzing images taken from scanning electron microscopy, transmission light microscopy, and X-ray micro-computed tomography. Wood cell wall thickness, fiber, and lumen area were measured and compared to unmodified specimens, and the crack formation after modification was also analyzed. There was only a slight decrease in the measured characteristics when compared to unmodified specimens. The wood cell wall thickness was less affected than the fiber and lumen areas, and both modifications presented similar crack formations. Overall, there were no significant differences between open and closed system modifications in the anatomical structure. 相似文献
19.
Outdoor exposure tests of structural laminated veneer lumber I: evaluation of the physical properties after six years 总被引：2，自引：2，他引：2
To investigate the durability of structural laminated veneer lumber (LVL), outdoor exposure tests have been conducted since 1990 at a field-testing site at the Forestry and Forest Products Research Institute. This paper is an interim report on the results after 6 years' exposure. Seven kinds of structural LVL with no preservative treatment were subjected to the tests. These specimens were sampled at the testing site each year and then stored for more than 1 year in a testing room conditioned at 20°C and 65% relative humidity. We then measured the modulus of elasticity (MOE) by longitudinal vibration frequency, the penetration depth by the Pilodyn method, weight loss, color difference (E
*) by the CIEL
*
a
*
b
* system, swelling, compression strength, and bending-shear strength. Deterioration caused by outdoor exposure was obvious in the color, weight, MOE, and compressive strength of LVLs, but not in the penetration depth by the Pilodyn method or the bending-shear strength. The retention values of MOE and compressive strength after 6 years of exposure were 78% and 77%, respectively. The difference in durability among material species was not significant in general, except that heavy decay by brown rot fungi took place on some of the grand fir specimens. It should be noted that no significant delamination occurred in any of the adhesive layers, although slight checks developed on the surface of the specimens. 相似文献
20.
Yingcheng Hu Fenghu Wang Jiyou Gu Yixing Liu Tetsuya Nakao 《Wood Science and Technology》2005,39(6):439-447
The effects of grain angle, thickness of face veneer, and shelling ratio on dynamic modulus of elasticity (E) of veneer-overlaid particleboard composite (VOP) were examined by using nondestructive test. In this study, the possibility
that E of VOP can be predicted by means of some empirical formula was also discussed. This study has shown that grain angle, thickness
of face veneer, and shelling ratio have substantial effects on E of VOP. The E at 0° of grain angle of face veneer was the largest, decreasing rapidly with increase in the grain angle. The lowest value
of E occurred at 90° of grain angle of face veneer. The relationship between grain angle of face veneer and E of VOP can be expressed in the form of Jenkin’s and Hankinson’s equations. The orthotropic properties of wood and VOP defined
as the ratio E
0/ E
90 were 25.7 for wood and 4.7 for VOP. When the grain direction of face veneer was parallel to the length of the specimens,
the E of VOP increased with increasing shelling ratio. VOP increased E from 125 to 179% over that of the particleboard and veneer thickness from 2.1 upto 3.6 mm. However, when the grain direction
of face veneer was perpendicular to the length of the specimens, the E of VOP decreased with increasing shelling ratio. VOP decreased E from 23 to 41% over that of the particleboard and veneer thickness from 2.1 upto 3.6 mm. The relationship between E of VOP and face veneer thickness can be expressed in the form of a second-order parabolic equation. Rule of Mixture (ROM)
can be used to predict E of VOP from the E of wood element and particleboard element. 相似文献