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1.
Fibre morphological effects on mechano-sorptive creep 总被引：2，自引：2，他引：0
The increased creep rate of paper under load during moisture cycling conditions as compared to that at high constant humidity
is a problem in the use of packaging materials. In order to investigate the influence of morphological factors of the fibres
on the occurrence and magnitude of this phenomenon, i.e. the occurrence of mechano-sorptive creep, studies on wood fibres
isolated from different parts of spruce wood were performed. Thus, creep properties were studied on earlywood and latewood
fibres from both juvenile wood and mature wood. In general, latewood fibres showed a higher degree of mechano-sorptive creep
than earlywood fibres, and mature wood showed a higher degree of mechano-sorptive creep than juvenile fibres. The difference
in mechano-sorptive creep rate between different fibres was shown to be correlated to the differences in fibril angle. The
smaller the fibril angle the higher was the mechano-sorptive creep ratio. It was suggested that at fibril angles approaching
45° wood fibres do not exhibit mechano-sorptive creep. 相似文献
2.
Fibril angle variability in earlywood of Norway spruce using soft rot cavities and polarization confocal microscopy 总被引：4，自引：0，他引：4
Anna Bergander Jonas Br?ndstr?m Geoffrey Daniel Lennart Sahnen 《Journal of Wood Science》2002,48(4):255-263
The main purpose of this study was to investigate the variability of the fibril angle of tracheids in earlywood of Norway spruce (Picea abies L. Karst.). Polarization confocal microscopy was chosen and compared with the method utilizing the orientation of soft rot cavities. There was a significant correlation between the soft rot and polarization confocal microscopy methods, which showed the same trend of high fibril angles in the first part of the earlywood followed by a decrease toward the end of earlywood. This declining trend was less pronounced in annual rings containing compression wood. Moreover, large variations in fibril angle occurred between neighboring tracheids. The investigation also emphasized the differences between X-ray diffraction and microscopic methods, as the large variation seen by the latter methods is not seen by the X-ray diffraction approach because of its large area of measurement. No correlation was found between fiber morphology (i.e., average length, width, density) and the average fibril angle in the investigated annual rings. 相似文献
3.
Juvenile wood properties are studied in a ring-porous tropical hardwood – teak (Tectona grandis L. F), to assess the utilisation potential of short rotation timber. Compared to mature wood, it is characterised by wide
rings, short fibres, small diameter, low vessel percentage, high cell wall, wide microfibrillar angle and relatively low or
almost similar mechanical properties. While the average modulus of elasticity and modulus of rupture in juvenile wood are
85% and 82% respectively of the mature wood value, the longitudinal compression strength is similar. With relatively small
fibrillar angle of 15° and the scope for genetic selection of individual trees, teak juvenile wood has potential for desired
dimensional stability. The segmented regression models and visual interpretation of radial patterns of variation in anatomical
properties reveal that juvenility in plantation grown teak extends up to 15, 20–25 years depending on the property, growth
rate and individual tree and plantation site. The fitted regression models, to explain the age-related variations in juvenile
wood properties range from simple, linear to exponential, reciprocal and quadratic equations. Fibre length, microfibrillar
angle, vessel diameter/percentage and ring width appear to be the best anatomical indicators of age demarcation between juvenile
and mature wood, although maturation age often varies among the properties. The projected figures for proportion of juvenile
wood in plantation grown teak at breast height are 80–100% and 25% at ages 20 and 60 years respectively.
Received 3 November 1998 相似文献
4.
An improved fibril angle measurement method for wood fibres 总被引：3，自引：0，他引：3
H. H. Wang J. G. Drummond S. M. Reath K. Hunt P. A. Watson 《Wood Science and Technology》2001,34(6):493-503
A rapid, reliable technique for the observation and measurement of the fibril angle in wood cell walls has been developed.
Sonication in the presence of solutions of certain cobalt and copper salts (5%, wt/vol) was found to be most effective in
facilitating fibril angle visualisation. Latewood fibre fibril angle, which previously had been difficult to measure, was
also visible, though less frequently. This method has been successfully applied to a number of softwood species including
coastal Douglas-fir whose prominent spiral thickenings make it difficult to determine the fibril angle by other methods. The
method was also used to determine the fibril angle of some hardwood species as well as a non-woody material, flax straw. It
can also be used to determine the microfibril angle of pulp fibres although this procedure is less convenient than with wood
sections.
Received: 24 June 1999 相似文献
5.
本文就中条山油松株内幼龄材与成熟材材性差异的比较研究,讨论对幼龄期划分的依据。根据木材解剖特征、物理力学性质的径向变异规律,确定其幼龄期为14年。随着树干高度的增加,油松木材幼龄期逐渐缩短、株内幼龄材范围及所占断面上的比例变小。株内幼龄材与成熟材材性差异显著。幼龄材管胞长度短、直径小,胞壁薄,微纤丝角度大,生长轮较宽,晚材率低,浸提物含量高,基本密度较大。幼龄材的力学强度远远小于成熟材。 相似文献
6.
Julien Ruelle Jacques Beauchêne Hiroyuki Yamamoto Bernard Thibaut 《Wood Science and Technology》2011,45(2):339-357
Growth strains were measured in situ in nine trees of three species from a French Guiana tropical rainforest in a clearly
active verticality restoration process. The aim was to detect tension wood within the samples. Wood specimens were cut in
the vicinity of the growth strain measurements in order to determine the microfibril angle and some mechanical and physical
properties. As suspected, tensile growth strain was much higher in tension wood zones, as shown by the slightly higher longitudinal
modulus of elasticity. Conversely, tension wood showed reduced compression strength. Longitudinal shrinkage was much higher
in tension wood than in opposite wood. Clear relationships between the microfibril angle and longitudinal properties were
noted in comparison (i) with those observed in gymnosperm compression wood and (ii) with expected relationships from the organization
of wood fibres cell wall structure. 相似文献
7.
I. D. Cave 《Wood Science and Technology》1997,31(3):143-152
Summary The property of fibre symmetry as exhibited by wood cellulose can be used to derive an explicit relationship between the orientation of a cellulose microfibril and the orientation of the X-ray beam diffracted by any of its crystallographic planes. The solution applies to a microfibril of any orientation and so is well suited to evaluating the microfibril angle distribution in wood containing cells of any cross-sectional shape. The (002) and (040) reflections of cellulose have complementary properties that could be exploited to enable current problems associated with the use of each individually for evaluating the mean microfibril angle of the S2 layer to be overcome. It is expected that it will be possible to measure the microfibril angle distribution throughout the whole cell wall and also measure the average cell cross-section of a wood sample, by analysing (002) and (040) diffraction profiles in conjunction with each other.This work is supported by the NZ Foundation for Research, Science and Technology under contract # UOC 401 相似文献
8.
A. Reiterer H. F. Jakob S. E. Stanzl-Tschegg P. Fratzl 《Wood Science and Technology》1998,32(5):335-345
Summary The spiral angle of the elementary cellulose fibril in the wood cell wall, often called microfibril angle, is of primary importance for the mechanical properties of wood. While there are a number of methods to estimate this angle, x-ray diffraction (XRD) techniques have recently obtained a lot of attention because of their ability to provide information averaged over a significantly large specimen volume. Here, we present results from a related method, small-angle x-ray scattering (SAXS). The advantage of SAXS is that, unlike XRD, it does not require any assumption on the orientation of the cellulose crystal axis with respect to the fibril axis. Full three-dimensional scattering patterns were collected using an area detector by rotating the sample around one axis. The distribution of fibrillar orientations was seen to reflect the typical cross-sectional shape of the tracheids (square or circular). In the stem, the spiral angle was found <5° in earlywood and 20° in latewood. In branches the angle was 30° in the upper part and 40° in the lower part, which strongly supports the idea that the spiral angle has primarily mechanical function.We thank W. Laube, F. Einramhof, H. Königshofer and H. Löppert for their technical assistance. Financial support from the Fonds zu Förderung der Wissenschaftlichen Forschung (Proj. P10729-BIO) is gratefully acknowledged 相似文献
9.
10.
在对马尾松和日本柳杉的管胞次生壁中层径壁纤丝角与弦壁纤丝角进行测定的基础上,(?)统计分析方法,对其进行了比较分析,并进行了分布类型检验及方差和期望的检验,结果表明,针叶材管胞次生壁中层的径壁纤丝角和弦壁纤丝角不存在显著性差异。为人们在木材纤丝角的研究中只讨论弦壁纤丝角的作法,提供了必要的理论依据。 相似文献
11.
《Wood material science & engineering》2006,1(3):146-170
The purpose of this review is to re-examine some of the existing knowledge on the ultrastructure of softwood fibres and modelling of the hygroelastic properties of these fibres. The motivation is that the ultrastructure of wood fibres has a strong influence on fibre properties such as stiffness and hygroexpansion. This structure-property relationship can be modelled with, for instance, composite mechanics to assess the influence of ultrastructure on the fibre properties that in turn control the engineering properties of wood fibre composites and other wood-based materials. Comprehensive information about the ultrastructure is presented that can be useful in modelling the hygroelastic behaviour of wood fibres. Many attempts to model ultrastructure-property relationships that have been carried out over the years are reviewed. Even though models suffer from limiting approximations at some level, they have been useful in revealing valuable insights that can help to clarify experimentally determined behaviour of wood fibres. Still, many modelling approaches in the literature are of limited applicability, not the least when it comes to geometry of the fibre structure. Therefore, an example of finite element modelling of geometrically well-characterized fibres is given. This approach is shown to be useful to asses the influence of the commonly neglected irregular shape on elastic behaviour and stress state in wood fibres. Comparison is also made with an analytical model which assumes cylindrical fibre shape. Predictions of the elastic properties made with analytical modelling of cylindrical fibres and with finite element modelling of geometrically characterized fibres are in concert, but the stress state and failure predictions only show qualitative similarity. It can be concluded that calculations on fibres with the irregular and more realistic geometry combined with experiments on single fibres are necessary for a better and more quantitative understanding of the hygroelastic behaviour and particularly failure of wood fibres. It is hoped that this paper can provide a foundation and an inspiration for modelling, in combination with experiments and microscopy, for better predictions of the mechanical behaviour of wood fibres and wood fibre composites. 相似文献
12.
《Wood material science & engineering》2013,8(3-4):146-170
Abstract The purpose of this review is to re-examine some of the existing knowledge on the ultrastructure of softwood fibres and modelling of the hygroelastic properties of these fibres. The motivation is that the ultrastructure of wood fibres has a strong influence on fibre properties such as stiffness and hygroexpansion. This structure–property relationship can be modelled with, for instance, composite mechanics to assess the influence of ultrastructure on the fibre properties that in turn control the engineering properties of wood fibre composites and other wood-based materials. Comprehensive information about the ultrastructure is presented that can be useful in modelling the hygroelastic behaviour of wood fibres. Many attempts to model ultrastructure–property relationships that have been carried out over the years are reviewed. Even though models suffer from limiting approximations at some level, they have been useful in revealing valuable insights that can help to clarify experimentally determined behaviour of wood fibres. Still, many modelling approaches in the literature are of limited applicability, not the least when it comes to geometry of the fibre structure. Therefore, an example of finite element modelling of geometrically well-characterized fibres is given. This approach is shown to be useful to asses the influence of the commonly neglected irregular shape on elastic behaviour and stress state in wood fibres. Comparison is also made with an analytical model which assumes cylindrical fibre shape. Predictions of the elastic properties made with analytical modelling of cylindrical fibres and with finite element modelling of geometrically characterized fibres are in concert, but the stress state and failure predictions only show qualitative similarity. It can be concluded that calculations on fibres with the irregular and more realistic geometry combined with experiments on single fibres are necessary for a better and more quantitative understanding of the hygroelastic behaviour and particularly failure of wood fibres. It is hoped that this paper can provide a foundation and an inspiration for modelling, in combination with experiments and microscopy, for better predictions of the mechanical behaviour of wood fibres and wood fibre composites. 相似文献
13.
幼龄材范围的确定及树木生长速率对幼龄材生长量的影响 总被引：8，自引：1，他引：8
本文以杉木、日本落叶松的人上林和天然林木材为对象，选择ｙ＝ａ＋ｂｌｎｘ回归模式。利用其管胞特征因子随年轮数的变化，研究划分幼龄材年轮界限的最适因子，并就生长速率对幼龄材生长量的影响进入了探讨。结果表明：杉木和日本落叶松的人工林及天然林木的管胞特征值在径向水平上的变化均遵循ｙ＝ａ＋ｂｌｎｘ模式，尤其管胞长度与年轮数回归的相关系数Ｒ均达０．９８以上；管胞长度与管胞宽度及纤丝用相比，遗传率最大，随年轮数变化的模式最稳定，是划分幼龄材界限的最佳因子，由此得出杉木人工林幼龄材界限年轮为２０－２２（距髓心距离为１２．９－１３．２ｃｍ）、天然林为１６－１８（４．１－４．５ｃｍ），日本落叶松人工林为１９－２３（８．７－１０．５ｃｍ）、天然林为２３－２４（２．９－３．１ｃｍ）；幼龄材生长量与树木生长速率成正比。 相似文献
14.
Fibril angle of loblolly pine wood as related to specific gravity,growth rate,and distance from pith 总被引：1，自引：0，他引：1
Charles W. McMillin 《Wood Science and Technology》1973,7(4):251-255
Summary Fibril angles were greater for earlywood (avg. 33.4°) than for latewood tracheids (avg. 26.9°). For earlywood, fibril angle did not differ between growth rates when the specific gravity was low (avg. 33.3°). When the specific gravity was high, wood of fast growth had a higher fibril angle (avg. 35.1°) than wood of slow growth (avg. 32.0°). No differences were detected between core, middle, and outer wood. In latewood tracheids, fibril angles were greater in corewood (avg. 28.0°) than in middle or outer wood (avg. 26.3°). For whole wood (a weighted average of earlywood and latewood), fibril angle averaged 30.7° and was greater in corewood (avg. 32.2°) than in middle or outer wood (avg. 29.9°). 相似文献
15.
M. J. Fuhr C. Stührk B. Münch F. W. M. R. Schwarze M. Schubert 《Wood Science and Technology》2012,46(4):769-779
The visualization and the quantification of microscopic decay patterns are important for the study of the impact of wood-decay fungi in general, as well as for wood-decay fungi and microorganisms with possible applications in biotechnology. In the present work, a method was developed for the automated localization and quantification of microscopic cell wall elements (CWE) of Norway spruce wood such as bordered pits, intrinsic defects, hyphae or alterations induced by white-rot fungus Physisporinus vitreus using high-resolution X-ray computed tomographic microscopy. In addition to classical destructive wood anatomical methods such as light or laser scanning microscopy, this method allows for the first time to compute the properties (e.g., area, orientation and size distribution) of CWE of the tracheids in a sample. This is essential for modeling the influence of microscopic CWE on macroscopic properties such as wood strength and permeability. 相似文献
16.
Summary Fibrillar angles were determined in the secondary wall layers of three rings across the stem of a mature red pine. The Senarmont compensation method was adopted for this study since it gives results for all three wall layers. It involves the determination of birefringence in a series of sections cut at various angles to the long axis of the tracheids. Maxima and minima in the resultant plots of birefringence versus section angle correspond to fibrillar orientations. In the early latewood of each ring, the S2 layr was found to contain a single Z helix of small fibrillar angle and the S1 dual S and Z helices of much flatter orientation. Results for S3 were found to be so close to those for the corresponding S2 layers that there was some doubt as to their validity. In each layer a slight decrease in fibrillar angle was observed between rings 4 (juvenile wood) and 12 (transition zone); a sharper decrease was seen between ring 12 and the mature ring 20. This trend corresponds inversely to tracheid length differences for the three rings. Correlations of tracheid wall thickness and overall cross-sectional dimensions with the fibrillar angle variations were less readily apparent.Contribution No. 59 from Empire State Paper Research Institute, State University College of Forestry, Syracuse, New York 13210. The authors gratefully acknowledge the discussions and advice of Drs. W. A. Côté, Jr. and R. E. Mark. 相似文献
17.
18.
The hygroscopicity and thermodynamic properties of Pinus canariensis wood buried in volcanic ash, dating from 1100 BC, were studied and compared with recently felled juvenile and mature wood of the same species. The sorption isotherms were obtained by the saturated salt method at 35 and 50 °C. The isotherms were fitted using the Guggenheim–Anderson–de Boer model. The thermodynamic parameters were determined following the Clausius–Clapeyron integration method. To understand the behaviour of each type of wood, the chemical composition, infrared spectra and X-ray diffractograms were determined for each sample. The mature wood has a higher sugar content and lower extractive content than the juvenile and the buried wood. For both temperatures, the isotherm of the mature wood is above the isotherm of the juvenile wood and this, in turn, is above the isotherm of the buried wood, primarily influenced by the higher cellulose and hemicellulose contents and lower extractives content in the mature wood, resulting in a higher number of accessible –OH groups. Degradation of the buried wood due to high temperatures explains why its isotherms are below the isotherms of the recent wood. The energy involved in the desorption process is greater than in adsorption. Similarly, more energy is involved in the mature wood than in the juvenile wood, and the energy involved in the juvenile wood is greater than in the buried wood. 相似文献
19.
Christoph Buksnowitz Ulrich Müller Robert Evans Alfred Teischinger Michael Grabner 《Wood Science and Technology》2008,42(2):95-102
The orientation of the tracheid cells with respect to the stem axis (grain angle, spiral grain) exerts a strong influence
on numerous material properties. Therefore, several methods have been developed to assess this wood anatomical feature. The
current study compares SilviScan spiral grain measurements, which uses X-ray diffractometry, with direct goniometer readings.
The correlation between these two methods yielded an r2 of 0.874 and a root mean square error of prediction (RMSEP) of 1.21 clearly demonstrating that X-ray diffractometry can provide
accurate and rapid information on the grain orientation in Norway spruce (Picea abies (L.) Karst.) or similar structured softwoods. 相似文献
20.
Tension wood (TW) fibres from maple, beech and oak were analysed with special emphasis on the cell wall fine structure and deposition of aromatic compounds within the gelatinous layer (GL). For this purpose, transmission electron microscopy (TEM) was applied after section staining with potassium permanganate. There was evidence for the occurrence of aromatic compounds in the GLs of fibres of all three species. Some GLs showed a concentric sub-layering. Hence, conclusions about the biosynthetic activities during cell wall formation in TW could be derived. Additional information about structural characteristics of TW fibres were obtained by means of field emission electron microscopy. High-resolution micrographs of cell walls were used for measurements of diameter and microfibril angle (MFA) of cellulose aggregates (CAG). CAG of 7 nm were observed although their diameter varied greatly in the GLs. MFA in the secondary wall of TW was slightly smaller than in opposite wood. The microscopic methods provided complementary ultrastructural and topochemical information on tension wood fibres. The subcellular localisation of aromatic compounds and the observations of the ultrastructural morphology will contribute to the understanding of origin and functionality of TW and its characteristic GL. 相似文献