共查询到20条相似文献,搜索用时 31 毫秒
1.
Clemens M. Altaner Elena N. Tokareva Janet C. T. Wong Adrian I. Hapca J. Paul McLean Michael C. Jarvis 《Wood Science and Technology》2009,43(3-4):279-290
As the severity of compression wood influences the mechanical and chemical properties of wood it is desirable to be able to measure compression wood severity. However, so far no satisfactory method has been reported in the literature. Here we describe how scanning FTIR micro-spectroscopy can be employed to achieve CW severity measurements on increment cores of Norway spruce (Picea abies (L. Karst.) and Sitka spruce (Picea sitchensis (Bong.) Carrière). Radial wood strips were converted into sawdust by a process that maintained their spatial orientation. Samples prepared in this way were scanned with an FTIR-microscope in reflective mode and from the spectra obtained a CW-indicator was calculated representing aromatic and carboxyl signals. This FTIR CW-indicator correlated well with alternative CW identification techniques (namely microfibril angle, transmitted light and immunolabelling of beta 1–4 galactan), which have been used to validate the method. Repeatability of the measurements was good and no systematic difference between spruce species was found. The achievable resolution of the measurements was of sub-mm order. The CW indicator described offers the opportunity to correlate CW severity with mechanical wood properties in spruce. 相似文献
2.
Norway spruce [Picea abies (L.) Karst.] heartwood and sapwood have differing wood properties, but are similar in appearance. An investigation was made
to see whether near-infrared spectroscopy (NIRS) could be used with multivariate statistics for separation between heartwood
and sapwood in dry state on tangential longitudinal surfaces. For classification of wood into sapwood and heartwood, partial
least square (PLS) regression was used. Orthogonal signal correction (OSC) filtering was used on the spectra. This study shows
that a separation of sapwood and heartwood of spruce is possible with NIR spectra measured in a laboratory environment. The
visible-wavelength spectra have significant influence on the predictive power of separation models between sapwood and heartwood
of spruce. All 44 specimens in the calibration set were correctly classified into heartwood and sapwood. Validation of the
model was done with a prediction set of 16 specimens, of which one was classified incorrectly. 相似文献
3.
Characterisation, quality assessment and property prediction are several of the major industrial challenges for widespread
acceptance of thermally modified wood (TMW). This study shows the potential of the multivariate analysis of mid-infrared (MIR)
spectral data for the prediction of impact strength, five mechanical parameters in bending, moisture content, weight loss,
density and chemical composition of small specimens of thermally modified beech, Norway spruce and Scots pine woods. Anti-swelling
efficiency was also studied using DRIFT spectroscopy for spruce wood only. Calibrations were successfully accomplished by
partial least-squares regression, with R
Y
2 and Q
CUM2 values >0.96 for 64 out of 67 models. Predictions were also successful, with relative prediction values >0 and RMSEP:SD ratios
<1 in most cases. Changes in the MIR spectra of TMW show that bands arising from the lignin environment and new bands appearing
due to the degradation of carbohydrates, giving negative loadings, were related to strength loss, while those bands arising
from the polysaccharides were associated with property retention. It is concluded that this approach is a powerful tool to
characterise a number of properties of TMW with a single after-treatment measurement. 相似文献
4.
Proton magnetic resonance techniques for characterization of water in wood: application to white spruce 总被引:3,自引:0,他引:3
C. D. Araujo A. L. MacKay J. R. T. Hailey K. P. Whittall H. Le 《Wood Science and Technology》1992,26(2):101-113
Summary Two new proton magnetic resonance techniques, relaxation spectra and relaxation selective imaging, have been used to investigate the distribution of water in samples of normal white spruce sapwood, heartwood, and juvenile wood as well as two rehydrated heartwood samples containing incipient decay and compression wood respectively. It is demonstrated that the spin-spin (T2) relaxation behavior in wood is best presented as a continuous spectrum of relaxation times. Spectra of T2 for white spruce show separate peaks corresponding to the different water environments. Bound water gives a peak with an T2 time of about 1 ms and lumen water gives a distribution of T2 times in the range of 10 to 100 ms. The lumen water T2 time is a function of the wood cell radius. Consequently, the different cell lumen radii distributions for spruce sapwood, juvenile wood, and compression wood are readily distinguishable by the shape of their T2 spectra. Water environments which are separable on a T2 spectrum may be imaged separately. Imaging has been carried out in one dimension for bound water and lumen water of a spruce sapwood sample at four different moisture contents ranging from 100% to 17%. For the first time, we demonstrate that above the fibre saturation point the moisture density profile of the bound water is largely independent of moisture content. The feasibility and utility of using these techniques for internal scanning of logs and lumber is discussed. These techniques should provide new insights into the wood drying process.We would like to thank Michael Weiss of the Biological Science Electron Microscopy Facility at the University of British Columbia for his assistance with the microscopy and image analysis. This research was supported by grants from the Natural Sciences and Engineering Research Council of Canada and the Canadian Forestry Service 相似文献
5.
Summary Specimens of spruce (Picea abies) were taken to compression failure in the SEM while the backscattered electron imaging was used. Control specimens were taken to failure with no beam exposure. Failure morphology was studied using the secondary electron imaging. Wood exposed to the electron beam during testing showed a glassy fracture, while wood exposed to high vacuum but not to the electron beam showed a ductile fracture. There was found no evidence of any significant brittleness for unexposed wood at different moisture content levels. Although electron beam damage may be reduced, it can never be avoided. Caution is therefore to be exercised in the interpretation of results of compression tests in the SEM. 相似文献
6.
Evaluation of thermally modified beech and spruce wood and their properties by FT-NIR spectroscopy 总被引:2,自引:2,他引:0
Helmut Bächle Bernhard Zimmer Elisabeth Windeisen Gerd Wegener 《Wood Science and Technology》2010,44(3):421-433
Quality assessment of thermally modified spruce (Picea abies (L.) Karst) and beech (Fagus sylvatica L.) wood and of the corresponding reference samples was carried out by means of non-destructive FT-NIR spectroscopic measurements
and PLS regression. Oven-dry and basic density as well as MOE and MOR determined by 3-point bending tests were evaluated.
The focus was put on specimens produced from material that had been thermally modified in an industrial scale kiln. Modelling
results range from poor to very good. The results of the spectra taken from the spruce samples resulted in better prediction
results than the spectra of the beech samples. This could be due to different proveniences or variation in the industrial
modification process. The results indicate that FT-NIR surface measurements of sound thermally modified wood samples could
be applied to evaluate several characteristics before and after the modification process. The method could be used for screening
during pre-sorting of thermally modified wood. 相似文献
7.
The feasibility of identifying internal wood characteristics in computed tomography (CT) images of black spruce was investigated
using two promising classifiers: the maximum likelihood classifier (MLC) and the back propagation (BP) artificial neural network
(ANN) classifier. Nine image features including one spectral feature (gray level values), a distance feature, and seven textural
features were employed to develop the classifiers. The selected internal wood characteristics to be identified included heartwood,
sapwood, bark, and knots. Twenty cross-sectional CT images of a black spruce log were randomly selected to develop the two
classifiers. The results suggest that both classifiers produced high classification accuracy. Compared with the MLC classifier
(80.9% overall accuracy), the BP ANN classifier had better classification performance (97.6% overall accuracy). Moreover,
statistical analysis reveals that the heartwood of the black spruce log used in this study is the easiest to identify by either
classifier compared with the other three log features. The results also suggest that the separability of one wood characteristic
from the other wood characteristics in black spruce CT images is mainly related to moisture content. 相似文献
8.
Stem deformation has often been observed in young black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) plantations. Whenever important stem deformations are observed at the time of harvesting, timber value is negatively affected especially during the wood transformation process. The present work was undertaken to quantify and qualify the importance of stem deformation of black spruce and jack pine in the boreal forest of central Quebec at the stand and tree levels. In 30 black spruce and jack pine plantations, approximately 22% of spruce trees and 27% of pine trees exhibited stem deformation. The proportion of deformed trees was higher in the youngest plantations and decreased with the age of the plantations. Stem deformation caused the formation of compression wood which is another factor that can reduce the value of wood products. Thirty-nine black spruces and 34 jack pines were analysed at the tree level. On average, compression wood represented 14% and 20% of stem volume in 7- and 10-year old black spruce plantations, respectively. These proportions ranged from 18% in the youngest jack pine plantation to 26% in the oldest one. Stems of both species classified as normal contained a lower volume of compression wood than stems classified as deformed or very deformed. Annual percentages of compression wood and annual shoot length increased significantly with tree age (p < 0.0001 for both variables). Statistically significant correlations were also found between the range of displacement of the stem and the percentage of compression wood. The fewer number of trees with deformed stems in older plantations combined with high compression wood formation suggests that, over time, a deformed tree can become normal and straight in appearance. 相似文献
9.
Batch measurements of wood density on intact or prepared drill cores using x-ray microdensitometry 总被引:1,自引:0,他引:1
The performance of a batch scanning x-ray densitometer for measuring wood density without sample preparation, i.e., on intact
drill cores, or on rectangular samples prepared from drill cores, was analysed. Effects of x-ray intensity, sample thickness
and fiber direction, as well as extractives content, were evaluated for young (mainly sapwood) and old (mainly heartwood)
wood from Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.). The x-ray power level used as standard (1.4 kW; 40 kV and 35 mA) seemed appropriate for the tested species
and specimen thickness. The density of intact drill cores could be determined with a mean standard deviation of 1.6% for each
sample, with a single machine run, if the cores were mounted with a fixed fiber direction and calibrations were made for each
wood type. The corresponding precision for rectangular samples was 1.0%. Further improvements are attainable by using standard
reference samples in each machine run and batch-wise analysis. For the chosen wood types and measurement technique, a sample
thickness of 5 mm should give the best precision. However, for species with very narrow rings, thinner samples would improve
the spatial resolution when ring boundaries are angled or curved. Extractives should be removed, especially for pine, but
possibly also for spruce, if high precision in density determination is required.
Received 19 January 2000 相似文献
10.
Elena N. Tokareva Andrey V. Pranovich Bjarne R. Holmbom 《Wood Science and Technology》2011,45(4):767-785
Different model compounds for lignin, hemicelluloses and pectins were studied by time-of-flight secondary-ion mass spectrometry
(ToF–SIMS). Mass spectra of Klason lignin from normal and compression spruce wood, aspen wood and wheat straw were compared.
Spectra of brominated spruce and aspen wood sections showed fragment ions attributed to brominated guaiacyl and syringyl units
in lignin at m/z 215, 217, 229 and 231, and m/z 245, 247, 249 and 261, respectively. Spectra of mono-, oligo- and polysaccharides
showed fragment ions at m/z 127 and 145 characteristic for hexose units, and ions at m/z 115 and 133 characteristic for pentose
units. The same ions were detected in spectra of delignified spruce and aspen wood sections. Labelling of anionic groups by
Sr2+ ions followed by ToF–SIMS analysis showed that pectins were present at specific locations on the surfaces of spruce and aspen
wood sections still after delignification with hydrogen peroxide in acetic acid. 相似文献
11.
Abel Rodrigues Miguel Casquilho Hélène Oliveira João Bordado 《European Journal of Forest Research》2010,129(2):145-153
An appraisal was made about the impact of pinewood nematode (Bursaphelenchus xylophilus, Nickle) attack symptomatology on the mechanical behaviour of wood from Pinus Pinaster Ait. Two sets of 200 wood specimens were obtained for the study of both mechanical and other physical properties. The specimens,
about half of which presented symptoms of nematode, were obtained from a set of 66 wood planks, cut from an equal number of
trees, originating from the Setúbal Peninsula (Portugal). Logistic analysis using symptomatology as a binary dependent variable
showed adequacy of models containing compression tension to rupture and number of wood rings per unit radial length for the
prediction of nematode attack. Analysis of variance revealed that the presence of the disease symptoms was correlated to static
bending rupture, modulus of elasticity, work to maximum bending load, and axial compression rupture, causing their decrease
at a significance level of 5%. 相似文献
12.
Study of the transverse liquid flow paths in pine and spruce using scanning electron microscopy 总被引:4,自引:0,他引:4
Samples of pine (Pinus sylvestris) and spruce (Picea abies) were impregnated with a low-viscous epoxy resin using a vacuum process. The epoxy was cured in situ and the specimens sectioned. Deposits of the cured epoxy was then observed in the wood cavities using a scanning electron microscope. The investigation concentrated on tracing the transverse movements of a viscous liquid in the wood, and special attention was therefore given to the cross-field area between ray cells and longitudinal tracheids. A damage hypothesis is proposed based on the results obtained in the present investigation in combination with those from earlier studies on linseed oil-impregnated pine: In addition to the morphology of the bordered pits, viscous liquid flow in wood is dependent on damage that occurs during the impregnation procedure. For pine sapwood, liquid flow is enabled through disrupted window pit membranes, which divide the longitudinal tracheids and the ray parenchyma cells. A mechanism accounting for the reduced permeability of pine heartwood is believed to be deposits of higher-molecular-weight substances (extractives) in the ray parenchyma cells and on the cell walls. In spruce the thicker ray cells in combination with the smaller pits, which are connected to the longitudinal tracheids, reduce permeability considerably. 相似文献
13.
Studying the impregnation and distribution of oil-based preservative in dried wood is complicated as wood is a nonhomogeneous, hygroscopic and porous material, and especially of anisotropic nature. However, this study is important since it has influence on the durability of wood. To enhance the durability of thermally modified wood, a new method for preservative impregnation is introduced, avoiding the need for external pressure or vacuum. This article presents a study on preservative distribution in thermally treated Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) sapwood using computed tomography scanning, light microscopy, and scanning electron microscopy. Secondary treatment of thermally modified wood was performed on a laboratory scale by impregnation with two types of preservatives, viz. Elit Träskydd (Beckers) and pine tar (tar), to evaluate their distribution in the wood cells. Preservative solutions were impregnated in the wood using a simple and effective method. Samples were preheated to 170 °C in a drying oven and immediately submerged in preservative solutions for simultaneous impregnation and cooling. Tar penetration was found higher than Beckers, and their distribution decreased with increasing sample length. Owing to some anatomical properties, uptake of preservatives was low in spruce. Besides, dry-induced interstitial spaces, which are proven important flow paths for seasoned wood, were not observed in this species. 相似文献
14.
Liquid penetration of precompressed wood VII: combined treatment of precompression and extraction in hot water on the liquid penetration of wood 总被引:1,自引:0,他引:1
The object of this study was to determine the cause of differences in the improvement in liquid penetration of precompressed wood species. The maximum amount of water uptake by the capillary rise method and changes in the aspirated pits seen with scanning electron microscopy before and after of preextraction and precompression were investigated using heartwood samples of four softwoods. The height of penetration and the weight by the capillary rise method for preextractive wood powders are discussed. Three wood species andLarix leptolepis showed marked increases in the amount of solution uptake after precompressed treatment only.Larix leptolepis wood required compression after extraction by boiling in water. These differences among wood species were caused by the accumulation of extractive material. It was also recognized that the accumulative material inLarix wood has plasticity and that inPseudotsuga is brittle. Based on these results it was found that it is difficult to destroy aspirated pits in the former and easy in the latter. On the other hand, the difference in penetration of each wood species was caused by the quantity and quality of the extraction material in addition to the extent of the wettability of the surface of the cell cavity as well as aspirated pit.Part of this report was presented at the 46th annual meeting of the Japan Wood Research Society, Kumamoto, April 1996 相似文献
15.
Summary The effects of temperature and sulfonation on the deformation of spruce wood at conditions comparable to those during screw press impregnation prior to mechanical pulping were studied using a dynamic testing method. In addition to the physical properties of wood, shear fracture surfaces obtained at different deformation temperatures and at different sulfonation levels were studied using scanning electron microscopy (SEM).The results showed that the failure energy of wood decreased gradually with increased deformation temperature in the tested range of 20–95 °C, due to thermal softening of the material. In addition to thermal treatment, the failure energy could also be reduced by sulfite treatment of the wood before deformation, and decreased with increasing sulfonation degree.The SEM analysis showed that increasing the deformation temperature causes the fracture plane to travel around the fiber walls instead of through them, thus exposing a smoother wood surface with less fiber damage. At a given deformation temperature, particularly at the lower temperatures, sulfonation improves fiber separation.Financial support from the Swedish National Board for Industrial and Technical Development (NUTEK) is gratefully acknowledged 相似文献
16.
Variations in compression strength and surface roughness of heat-treated Turkish river red gum (Eucalyptus camaldulensis) wood 总被引:1,自引:0,他引:1
This article reports the effects of heat treatment on compression strength parallel to the grain, the surface roughness [average roughness (Ra)], and the air-dry den-sity of wood from the river red gum tree (Eucalyptus camaldulensis Dehn.) planted in Turkey. Eucalyptus wood was heat-treated at temperatures varying from 120° to 180°C for durations of 2–10 h. Samples cut from the heat-treated wood were tested for air-dry density, compression strength parallel to grain, and surface roughness properties. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Based on the findings in this study, the results showed that density, compression strength, and surface roughness values decreased with increasing treatment temperature and treatment times. Eucalyptus wood could be utilized by using proper heat treatment techniques without any losses in strength values in areas where working, stability, and surface smoothness, such as in window frames, are important factors. 相似文献
17.
For estimating the amount of carbon (C) in dead wood, conversion factors from raw volume per decay class to dry weight were developed using three different classification systems for the species Norway spruce (Picea abies L. Karst), Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth and B. pubescens Ehrh) in Sweden. Also the C concentration in dead wood (dry weight) was studied. About 2500 discs were collected from logs in managed forests located on 289 temporary National Forest Inventory (NFI) sample plots and in 11 strips located in preserved forests. The conversion factors were based on an extensive data compilation with a wide representation of different site-, stand-, species- and dead wood properties and were assumed to represent the population of fallen dead wood in Sweden. The density decreased significantly by decay class and the range in density for decay classes was widest for the NFI decay classification system, suggesting this to be the most suitable. The C concentration in dead wood biomass increased with increasing decay class and in average Norway spruce (P. abies) showed a lower C concentration than Scots pine (P. sylvestris). The average dead wood C store of Swedish forests was estimated to 0.85 Mg C/ha. 相似文献
18.
Strength graded boards of Norway spruce (Picea abies (L.) Karst.) are important products for many Scandinavian sawmills. If the bending strength of the produced boards can be predicted before sawing the logs, the raw material can be used more efficiently. In previous studies it is shown that the bending strength can be predicted to some extent using discrete X-ray scanning of logs. In this study, we have evaluated if it is possible to predict bending strength of Norway spruce boards with higher accuracy using computed tomography (CT) scanning of logs compared to a combination of discrete X-ray and 3D scanning. The method was to construct multivariate models of bending strength for three different board dimensions. Our results showed that CT scanning of logs produces better models of bending strength compared to a combination of discrete X-ray and 3D scanning. The main reason for this difference was the benefit of knowing the position of where the boards were cut from the logs and therefore detailed knot information could be used in the prediction models. Due to the small number of observations in this study, care should be taken when comparing the resulting prediction models to results from other studies. 相似文献
19.
Colour responses from wood,thermally modified in superheated steam and pressurized steam atmospheres
《Wood material science & engineering》2013,8(3-4):211-219
Abstract In this study, two different methods were used to produce thermally modified wood. One was carried out in a typical kiln drying chamber using superheated steam (SS) and the other used pressurized steam in an autoclave cylinder (PS). Overall, both processes followed the same principles and the wood was not treated with any chemicals. Two wood species were studied, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Treatments in the autoclave were carried out under pressure using temperatures of 160°C, 170°C and 180°C. Temperatures of 190°C and 212°C were used in treatments in the chamber at normal air pressure. The colour was measured using L*C*H colour space. Results for both species showed that similar L* (lightness) can be reached at lower (20–30°C) temperatures using PS compared with SS treatment. The hue angle of PS-treated wood was smaller than that of SS-treated wood. No significant difference in C* (chroma) was detected. The difference in E value between PS- and SS-treated wood was smaller for Norway spruce than for Scots pine. The residual moisture content was about 10% higher in wood treated by the PS process compared with the SS process. 相似文献
20.
The three-dimensional structure of a transverse sawn wood surface was investigated using several methods, to compare techniques,
and to study the types of deformation in tracheids at the saw cut. A sample of spruce sapwood was cut with a fret saw across
the grain. The transverse sawn surface was imaged by confocal microscopy, field emission scanning electron microscopy (FESEM),
and by light microscopy combined with serial sectioning and three-dimensional (3D) reconstruction. Both confocal microscopy
and FESEM were restricted to visualising the cut surface of the wood. However, serial sectioning was able to reveal the internal
structure below the cut surface providing more information on the types of cell deformation present. The wood structure was
deformed to depths of more than 600 μm below the surface with twisting, crushing and tearing deformations. Near the outer
surface, gaps were formed between groups of tracheids where the cell walls had been torn away to form saw dust. The deformation
tended to form groups of tracheids that were twisted relative to each other. Latewood was less distorted, forming a dense
solid surface compared to the highly fibrous earlywood. 相似文献