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1.
The viscoelastic thermal compression (VTC) of low-density hybrid poplar (Populus deltoides × Populus trichocarpa) from fast growing trees was performed in order to produce specimens with three different degrees of densification (63, 98, and 132%). The morphology and density profile of the VTC specimens were studied. Three different methods for the preparation of specimens for microscopy were used in order to find a technique that makes it possible to examine the VTC wood microscopically in the completely deformed state. It was found that the abrasive surface preparation of oil-embedded blocks was the most promising technique. Microscopic observation revealed that the deformations in the VTC wood were mostly the result of the viscous buckling of cell walls without fracture. The volume of the void areas in the specimens decreased with the degree of densification. The results showed that the density profile of the VTC wood varied with the degree of densification as a consequence of different temperature and moisture gradients formed before and during wood compression. The density profile is also visible on the cross-section of the VTC specimens. 相似文献
2.
Characterisation of pore size distributions in variously dried Pinus radiata: analysis by thermoporosimetry 总被引：1，自引：0，他引：1
Warren J. Grigsby Hank Kroese Elizabeth A. Dunningham 《Wood Science and Technology》2013,47(4):737-747
The pore size distribution and networks within the wood cell wall tend to decrease on drying wood from its green state having implications for water ingress and further processing such as in preservative treatment. Thermoporosity measurements using differential scanning calorimetry have been applied to determine the pore size distribution of green Pinus radiata wood and how well this pore network is retained on supercritical fluid (SCF) dewatering compared with kiln drying. Generally, in green sapwood, the majority of bound water was distributed in pore sizes less than 50 nm diameter with only a small proportion present in pore sizes between 50 and 200 nm. On SCF dewatering, most bound water was found to reside in pore sizes <20 nm, consistent with dewatered wood being at fibre saturation point (FSP). Generally, on rewetting dewatered, kiln- or oven-dried wood, proportionately less bound water was present compared with green wood, consistent with reduced pore sizes and network accessibility for water ingress. Furthermore, on rewetting, there were distinctions between earlywood and latewood (LW) sections with the LW sections having a statistically greater proportion of water occupying smaller-sized pores (<20 nm). There was also greater variability of pore size distributions on sample rewetting, inferring drying does not uniformly reduce pore size volumes. Analysis suggests the extent of variability was generally less in the rewetted dewatered wood sample compared to kiln- or oven-dried samples, which may be a consequence of SCF drying only to FSP. 相似文献
3.
人工兴安落叶松次生木质部的解剖学研究 总被引：1，自引：0，他引：1
运用木材解剖图像分析系统和显微照相的方法对人工兴安落叶松次生木质部的解剖结构进行研究,结果表明:落叶松具正常树脂道和受伤树脂道两种类型,前者常见于晚材。落叶松生长轮内的早晚材在干和枝内急变,在根内缓变。早材管胞呈六边形至多边形,胞壁常见单列具缘纹孔,偶见对列具缘纹孔;晚材管胞多呈矩形,胞壁鲜见具缘纹孔,通常为单列具缘纹孔。落叶松木射线同时具有单列木射线和纺锤形木射线两种类型,纺锤形木射线中仅含一枚纵行树脂道。纵行管胞与木射线交叉形成的纹孔场为云杉型。从根到干再到枝,管胞逐渐细化,管胞长度逐渐减小,木射线分布由密到疏。 相似文献
4.
Shrinkage at the tissue level has been evaluated satisfactorily using relatively simple equipment, comprising an optical microscope equipped with reflected light, a standard objective, a water immersion objective of same magnification and a digital camera connected to a computer. Shrinkage is calculated from pairs of images taken at the same magnification, one collected during immersion in water and the other in air-dry state. A novel software program has been developed to determine shrinkage based on a closed chain of reference points chosen from the anatomical markers at the external part of the zone of interest. Measurements were performed on earlywood, latewood and compression wood zones from two softwood species (Douglas fir and spruce), isolated from the rest of the annual ring with the aid of a diamond wire saw. As main results, reference should be made to the low degree of shrinkage and high anisotropy factor of earlywood, the marked and practically isotropic shrinkage in latewood and the low shrinkage (with respect to cell wall thickness) and inverse anisotropy ratio in compression wood. 相似文献
5.
The anatomical features of earlywood vessels often reflect information about past climatic conditions. We examined the relationships between mean monthly temperature and mean vessel lumen area (MVA) in various categories of earlywood vessels. Subsets of earlywood vessels of chestnut (Castanea sativa Mill.) were selected from a previously reported dataset based on several progressive size-related procedures. To include all earlywood vessels, the minimum size considered was 10,000 microm2. Changes in the correlations between MVA and the mean air temperature in March are described and discussed. The results show that not all vessels embody the same information. The MVA of a proportion of the largest earlywood vessels in each annual ring was most closely related to March temperature, whereas MVA of the smallest earlywood vessels was better correlated with June temperature. This difference is probably a result of the vessels being formed at different times: early spring for the largest earlywood vessels and later in spring for the smallest earlywood vessels. Analyses combining large and small vessels yielded lower correlations between MVA and monthly temperature. The number, size and distribution of vessels can vary greatly from ring to ring. In making year-to-year comparisons, the best information is provided by observations on vessels of contemporaneous ontogenesis. Criteria for the selection and analysis of vessels in the assessment of temperature during the season of wood formation are proposed and discussed. 相似文献
6.
Summary The effects of air-drying and solvent-drying on the sapwood of Abies grandis have been investigated by a new method for the determination of the size and number of conducting tracheid lumina and pit membrane pores which involves the measurement of gaseous permeability at various mean pressures. Both earlywood and latewood tracheids (83% of the total) were found to be conducting in solvent-dried wood, but in air-dried wood only latewood tracheids (32% of the total) were conducting. In solvent-dried wood there were on average 27,000 pit membrane pores per conducting tracheid compared with only 600 in air-dried wood. In both, the average pit membrane pore radius was about 0.1 m.Liquid permeabilities have been predicted from the calculated radii and numbers. The liquid permeability of solvent-dried wood was 31 times greater than that of air-dried wood in which the lumina were responsible for 13% of the total resistance to flow. The lumina were responsible for 39% of the resistance in solvent-dried wood and it is suggested that in first-formed earlywood the lumina may cause more than half the total resistance.A new method is described for the cleaning of direct carbon replicas of wood. In this the cellulose is removed by cellulase instead of sulphuric acid, and no wax backing is required. This provides much cleaner replicas. Electron micrographs have been obtained of both earlywood and latewood dried by the two methods.The authors wish to thank Mr. A. R. Sayers for preparing the computer programme used in this work, Dr. R. Ph. C. Johnson for his help and advice regarding the electron microscopy and Professors Matthews and Weatherley for their advice and encouragement. 相似文献
7.
Purportedly, large Douglas-fir trees in the American Pacific Northwest use water stored in bole tissues to ameliorate the effects of seasonal summer drought, the water content of bole tissues being drawn down over the summer months and replenished during the winter. Continuous monitoring of bole relative water content (RWC) in two 110-120-year-old Douglas-fir trees with ThetaProbe impedance devices provided an integrated measure of phloem-sapwood water content over 4 years. Seasonal changes in RWC closely tracked cambial activity and wood formation, but lagged changes in soil water content by 2-3 months. The RWC in the combined phloem and sapwood markedly increased during earlywood production in the late spring and early summer to maximum values of 64-77% as plant available soil water (ASW) decreased by approximately 60%. With transition and latewood formation, RWC decreased to minimum values of 59-72%, even as ASW increased in the fall. The difference between minimum RWC in the fall and maximum RWC in midsummer was only approximately 5%. Seasonal changes in bole RWC corresponded to cambial phenology, although decreasing AWS appeared to trigger the shift from earlywood to latewood formation. 相似文献
8.
Boštjan Lesar Miha Humar Frederick A. Kamke Andreja Kutnar 《Wood Science and Technology》2013,47(5):977-992
Hybrid poplar (Populus deltoides × Populus trichocarpa) and Douglas-fir (Pseudotsuga menziesii) wood specimens were densified with three variations of thermo-hydro-mechanical (THM) treatment. The THM treatments differed in the steam environment, including transient steam (TS), saturated steam (SS), and saturated steam with 1-min post–heat treatment at 200 °C (SS+PHT). The bending properties, FTIR spectra, and colour of the THM wood specimens were studied before and after exposure to two different wood decay fungi, brown rot Gloeophyllum trabeum, and white rot Trametes versicolor. The results showed that the performance of densified hybrid poplar wood was considerably poorer than the performance of Douglas-fir heartwood. The FTIR spectra measurements did not show changes in the densified hybrid poplar wood, while some changes were evident in densified Douglas-fir specimens. After fungal degradation, the most prominent changes were observed on the SS+PHT specimens. Colour is one of the most important parameter predominantly influenced by the wood species and the intensity of the densification process for both wood species, while after fungal exposure, the colour of all densified Douglas-fir specimens obtained more or less the same appearance, and densified hybrid poplar specimens resulted in lighter colour tones, indicating that the pattern of degradation of the densified and non-densified specimens are similar. The 3-point bending test results determined that the THM treatment significantly increased the modulus of rupture (MOR) and modulus of elasticity (MOE) of the densified wood specimens, while fungal exposure decreased the MOE and MOR in hybrid poplar and Douglas-fir specimens. 相似文献
9.
The interactions of alkaline copper quat (ACQ) components with the earlywood and latewood tissues of southern pine were investigated. There was a highly significant redistribution of the copper amine component from the earlywood to the latewood during post-treatment fixation at 50°C, which was mainly attributed to diffusion of copper amine from the earlywood into the latewood. A small amount of copper amine redistributed between the tissues and toward the wood surfaces during drying following fixation. The redistribution within the wood was similar whether the preservative penetrated longitudinally, tangentially, or radially into the wood during pressure treatment. This redistribution resulted in lower solubility of copper, and this effect contributes to the overall copper fixation in ACQ-treated wood. The quat component did not significantly diffuse after treatment, and its concentration remained much higher in the earlywood compared to the latewood. 相似文献
10.
对10个10年生日本落叶松无性系的木材基本密度、管胞参数进行了测定.结果表明:木材基本密度,早、晚材管胞宽度和早材长宽比无性系间差异显著;木材基本密度,早、晚材管胞长度,早晚材管胞宽度和早晚材长宽比径向变异模式相似,即从髓心向外以曲线形式不断增加,有时亦有起伏;早材从髓心向外以近似直线的形式缓慢增加,晚材从髓心向外以曲线形式增加,初期增加幅度较大,到一定年龄后趋于水平变化并略有波动;材质性状与树木年轮间的关系以对数方程、幂函数方程、指数方程拟合效果较好;除了晚材壁腔比和早材壁厚外,其它木材性质的重复力均在0.5以上,受中度或中度以上的遗传制约,按照20%的选择率,长宽比和晚材管胞长能获得较高的遗传增益. 相似文献
11.
Summary In a previous article of the authors a model was developed for estimating elastic and shrinkage properties of a softwood cell-wall. In the present article this model is enlarged to simulate the elastic properties of defect-free softwoods. The wood model consists of earlywood, latewood and ray cells, each of which have a different cell-wall structure. In the model the ratio of earlywood to latewood is defined by a given wood density. The calculated elastic properties are in good agreement with test results. 相似文献
12.
Summary Intra-increment variation in specific gravity of wood is studied in relation to the types of annual increments in Pinus wallichiana. In the normal annual increments specific gravity increases almost linearly across the ring, displaying minimum value in the first-formed earlywood and maximum value in the last-formed latewood. The occurrence of false rings and that of compression wood in an annual ring causes a localized increase in specific gravity. The change in specific gravity at the false growth ring boundary is slight and gradual, whereas at the true annual rings boundary the change is steep and abrupt. The specific gravity in the first-formed earlywood portion gives the most consistent value as compared to whole earlywood, whole latewood and whole ring when studied around the circumference.The financial support from University Grants Commission (India) is gratefully acknowledged 相似文献
13.
《Scandinavian Journal of Forest Research》2012,27(5):462-469
Abstract Wood properties, including tracheid cross-sectional dimensions, show a large degree of variation. To improve the properties of products made from wood, different methods to control variation have been developed. This study aims to determine the theoretical efficiency of three control strategies: the fractionation of pulped tracheids into earlywood and latewood, the separation of juvenile and mature wood, and sorting of logs according to tree size. The efficiency of each method was studied by first constructing virtual trees from measured tracheid cross-sectional dimensions, then simulating the efficiency of above-mentioned methods. The tracheid dimension data include Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.). The simulations show that separation into earlywood and latewood classes has the highest theoretical efficiency and yields the lowest variances in raw material. Classification into juvenile and mature wood groups is the second most efficient method, and the sorting of logs according to the size class of the tree is the least efficient method. It was also concluded that the variation in cell-wall thickness and radial diameter mainly originates from differences between earlywood and latewood, whereas the variation in tangential diameter mainly originates from differences between mature and juvenile wood. 相似文献
14.
Cornelia Krause Sergio Rossi Maxime Thibeault-Martel Pierre -Y. Plourde 《Annals of Forest Science》2010,67(4):402-402
15.
Far-Ching Lin Chih-Hsin Chung Jia-Lin Zeng Te-Hsin Yang Song-Yung Wang Cheng-Jung Lin 《Journal of Wood Science》2012,58(2):104-112
The purpose of this study was to explore the ring characteristics of Japanese cedar (Cryptomeria japonica) tree growth with thinning and unthinning regimes. The trees grown with thinning regimes increased in average ring width
(RW), earlywood width, latewood width, ring density (RD), earlywood density, latewood density, maximum ring density, and latewood
percentage (LWP) for the entire period of 16 years after thinning, as compared to those grown with unthinning regimes. The
RW and RD components showed different reactions lasting several years after thinning. Overall, thinning caused immediate production
(first year) of higher RD, lasting for several years; however, wider RW was delayed up to several years after treatment. There
was a weak relationship between RW (growth rate) and wood density; and there were significant positive relationships between
the RD and LWP. The results suggest that the compression wood produced after thinning. 相似文献
16.
Genetic parameters for various wood density traits were estimated in 29-year-old trees of 18 full-sib families of hybrid larch
(Larix gmelinii var. japonica × Larix kaempferi) F1. Intra-ring density variation (IDV) was also evaluated using a model that expresses the pattern curve from earlywood to latewood
as a power function. A high IDV indicates an abrupt change in wood density from earlywood to latewood. The ring width and
wood density traits of individual rings were determined by X-ray densitometry. Overall wood density (RD) was shown to increase
with increasing ring number, ranging from 0.42–0.59 g/cm3, whereas IDV of individual rings decreased gradually from pith outwards. Estimates of individual tree narrow-sense heritability
of RD and IDV were 0.66 and 0.67, respectively. IDV showed negative genetic and phenotypic correlations with RD (r
g = −0.99, r
p = −0.72). The predicted genetic gains in latewood proportion and IDV were higher than that of RD. These results suggest that
the intra-ring density variation is under moderate genetic control equivalent to wood density. The trend of increasing wood
density from earlywood to latewood was associated with changes in both tracheid diameter and cell wall thickness. 相似文献
17.
The morphological changes in wood tissues of Japanese beech (Fagus crenata) upon treatment with the ionic liquid, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which can dissolve cellulose, were investigated. Treatment with [C2mim][Cl] induced significant swelling of all wood tissues. However, the swelling behavior of wood fibers was different from that of vessels. Intervascular pits were occluded, and pit membranes in ray-vessel pits were broken after treatment with [C2mim][Cl]. No significant differences in swelling behavior were found between latewood and earlywood, although different morphological changes for latewood and earlywood during [C2mim][Cl] treatment were seen in our previous studies on sugi (Cryptomeria japonica). We have found that the effects of [C2mim][Cl] on Japanese beech tissues are inhomogeneous and different from those found for other wood species. 相似文献
18.
Trairat Neimsuwan Siqun Wang Adam M. Taylor Timothy G. Rials 《Wood Science and Technology》2008,42(6):493-506
A better understanding of the sorption behavior of different wood structures could be useful in protecting wood against wood
deterioration and fungal attack. The purpose of this study was to investigate the effect of differences among earlywood, latewood,
and tree ring location within the stem cross-section of loblolly pine (Pinus taeda) on the sorption kinetics and statics of water vapor under ambient conditions. The water vapor sorption of earlywood and
latewood in different tree rings was recorded using a dynamic contact angle analyzer under relative humidity changes from
11 to 89%, as provided by saturated salt solutions. Earlywood had higher sorption rates and diffusion coefficients than latewood,
while outer tree rings had higher sorption rates and diffusion coefficients than inner tree rings. The sorption isotherms
of earlywood, latewood, and different tree ring locations within the stem cross-section were fitted very well by a Hailwood–Horrobin
model. 相似文献
19.
《Wood material science & engineering》2013,8(2):189-196
AbstractElectrical impedance spectra of wood taken at macroscopic scales below the fibre saturation point have led to inferences that the mechanism of charge conduction involves a percolation phenomenon. The pathways responsible for charge conduction would necessarily be influenced by wood structure at a variety of sub-macroscopic scales – at a mesoscale – but these questions have not yet been addressed. The goal of this work is to explore if mesoscale anatomical features in wood affect impedance spectra. Small (0.5 mm diameter) needles were used as electrodes and were configured such that the line segment between the electrodes could be oriented radially, tangentially, longitudinally and in combinations of those directions in both earlywood and latewood, including comparisons of earlywood–latewood transitions. The spectra were fit to an equivalent circuit model with a constant phase element in parallel with a resistor and Warburg element that describes ionic conduction. Finite element simulations were run to examine the effect of the fringing electric field near the electrodes. The simulations revealed that the current density was concentrated at the electrodes, resulting in a lack of dependence on electrode spacing thus explaining why measurements taken with pin-type electric moisture metres are nearly independent of electrode geometry. 相似文献
20.
Acoustic emission from softwoods in tension 总被引：3，自引：0，他引：3
M. P. Ansell 《Wood Science and Technology》1982,16(1):35-57
Summary Acoustic emission (AE) monitoring is a non-destructive testing technique widely used to detect flaw development and crack propagation in metals, ceramics, polymers and composite materials.This paper relates the AE-strain characteristics from three softwoods tested in tension to mechanisms of deformation observed by scanning electron microscopy. All wood specimens are identical in size and radial-longitudinal in orientation, enabling the path of failure through planes of earlywood and latewood to be examined.It is found that the proportion of earlywood to latewood in each species has a marked effect on the shape of the AE-strain curves. Parana pine, containing very few latewood tracheids, exhibits a close to linear relationship between log cumulative emissions and strain until close to failure when the count rate increases rapidly. Douglas-fir, which has well-defined earlywood-latewood boundaries generates many AEs at low strain and there is greater variation in the shape of the AE characteristic between samples.Parana pine and Douglas-fir are tested at 20 °C (12.5 % EMC). Scots pine is also stressed at 20°C (12.5%EMC), 20°C (0.7%EMC) and 80°C (0.7%EMC), to assess the effect of moisture content on AE.Values of Young's modulus, stress at failure and work of fracture for the three softwoods are compared with the AE-strain data. Although the work of fracture is related to the total AEs to failure, no direct proportionality exists between the two parameters.Finally, the AE-strain data for plywood and glass-reinforced plastic (GRP), both man-made composite materials, are compared with those of wood, the natural composite material.S.R.C. support for this work under grant No. GR/A/13257 is gratefully acknowledged. The support of Professor Bryan Harris of the School of Materials Science, University of Bath and Dr. J. M. Dinwoodie of the Building Research Establishment, Princes Risborough is greatly appreciated. Mr. B. Dobraszczyk performed the impact tests. 相似文献