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1.
Summary Scots pine wood veneers were acetylated to weight gains of 5, 10, 15 or 20% and exposed to natural weathering. Veneers acetylated
to low weight gains of 5 and 10% and exposed to the weather showed greater losses in mass and tensile strength due to increased
delignification and depolymerisation of cellulose than similarly exposed, untreated controls. Acetylation to 20% weight gain
restricted the loss of veneer mass and holocellulose during exposure. Initially it also slightly reduced the depolymerisation
of cellulose, and this was reflected in lower losses in veneer zero-span tensile strength after 35 days exposure. However,
the photoprotective effects of acetylation, with the exception of veneer mass, were lost with prolonged exposure of veneers
to the weather. Acetylation of wood blocks to 20% weight gain caused a bulking of the wood cell wall, particularly the S3 layer of the secondary wall, and reductions in lumen size. Acetylated latewood cells maintained their shape and radial orientation
during exterior exposure, but acetylation did not prevent erosion of the middle lamella. Mechanisms to explain how acetylation
may affect the weathering resistance of wood are suggested.
Received 26 May 1998 相似文献
2.
Roughness models for sanded wood surfaces 总被引:2,自引:1,他引:1
The understanding of the effects of variables is crucial to achieve the desired sanded surface quality at optimum condition. In wood surface evaluation, it is known that anatomies on wood surface could distort the roughness value and cause a misinterpretation of the processing performance. In this study, statistical approaches were taken to characterize the influence of sanding variables as well as to analyze the anatomical noises that were inherited from intra- and inter-species of woods. Four available roughness parameters (R a , R q , R k and R ap) were used to examine the surface of three distinct wood species, viz. kembang semangkok, red oak and spruce in wide-belt sanding. Based on the mean values, analysis of variance showed that species (anatomy) was significant to all conventional parameters except R ap which was filtered by monitoring the second derivative of Abbott-curve. In spite of this, R ap recorded a more widely dispersed deviation of random measurement values than R k and R a . The effects of grit size and feed rate were found to be significant. Empirical roughness models were established using response surface methodology, and the errors were calculated by comparing the model values to all the randomly measured values. Although exhibiting slight species-dependant effect by nature, R k showed reliable consistency by recording the lowest error values (<10%) for both intra- and inter-species measurements. Experimental results also suggested that three random measurements at each run could be sufficient. The method of constructing machinability models can be readily applied in the industry as a quality control tool for wide-belt sander. 相似文献
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Vladimirs Biziks Bruno Andersons Ļubova Beļkova Elīna Kapača Holger Militz 《Wood Science and Technology》2013,47(4):717-735
Birch wood (Betula pendula) samples were treated in a thermal regime (140, 160, 180 °C) for 1 h and investigated by means of scanning electron microscopy (SEM). SEM microimages of the wood cross-section were taken from one and the same place before and after the thermal treatment (magnification 100–2,000×). The results of measurements of areas and linear sizes of the birch wood cells show significant changes, which depend on the thermal treatment conditions and the type of the cell: libriform, tracheid, vessel and ray. After the treatment at 180 °C, the integrity of wood morphological structure begins to break up. Voids and cracks are formed between fibres, thus leading to a decline in the mechanical properties of the wood. 相似文献
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In the present study,described that preparation of oligoesterified wood fibre by theaddition reaction of the wood fibre with maleic anhydride(MA)and allyl glycidyl ether(AGE).Further,made of crosslinkable oligoesterified fiber board at high temperature and underhigh pressues,accompanying plasticization of the wood fibre components.The product exhibitedthe high the modulus of repture in bending(MOR),good water repellency and dimesionalstability. 相似文献
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Summary Wood samples that had been ball-milled and extracted with dioxane under various conditions were observed in the scanning electron microscope. Ball milling causes not only a reduction in size of the cells and cell walls but also an internal disruption of the particles. The intensity of milling has a larger influence on the particle size than a prolongation of the milling time. A direct relation was established between particle size and the previously determined yield of purified milled wood lignin.Submitted by Erwin-Riesch-Stiftung zur Förderung der wissenschaftlichen Forschung. 相似文献
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R. M. Nussbaum 《Wood Science and Technology》1993,27(3):183-193
Summary The effects of an oxidative activation of some different wood surfaces by flame treatment has been studied. Flame treatment markedly increased the wettability and decreased the microbiological activity. No improvement in glue adhesion was discerned for a water-borne PVAc-glue. ESCA measurements showed a considerable increase in oxidation level as a result of the flame treatment. The duration of the activation varied between different wood species.Appreciation is expressed to Prof. E. Back for valuable discussions and to Mr. G. Carlsson, Institute for Surface Chemistry, Stockholm, for ESCA measurements. Financial support from the Swedish Council for Building Research is kindly acknowledged 相似文献
8.
Etching of wood surfaces by glow discharge plasma 总被引:3,自引:0,他引:3
This research tests the hypothesis that plasma will cause differential etching of wood cell walls because of variation in
the susceptibility of aromatic and aliphatic polymers to degradation by plasma. Wood was exposed to glow discharge plasma,
and scanning electron microscopy and chromatic confocal profilometry were used to examine etching of cell walls. Plasma etched
cell walls and made them thinner, but the middle lamella was more resistant to etching than the secondary wall. Plasma created
small voids within the secondary wall, which were separated by thin lamellae connected to the middle lamella and tertiary
wall layers. Larger voids were created in cell walls by the etching of bordered and half-bordered pits. Etching of the uppermost
layer of cells at wood surfaces occurs first and when large voids are created in the walls of these cells then significant
plasma etching of the underlying cells occurs. Etching of wood cell walls can be quantified using confocal profilometry, and
using this technique a strong relationship between applied plasma energy and volume of cell wall etched by plasma was observed.
It is concluded that all of wood’s polymers can be degraded by plasma even though cell wall layers that are rich in lignin
are etched more slowly than other parts of the cell wall. 相似文献
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Fractal dimension of wood surfaces from sorption isotherms 总被引:4,自引:0,他引:4
Summary In this paper the method of fractal dimension is applied to characterize the wood surface by using water-sorption data. Three different methods are implemented to determine the fractal dimension. These methods are based on polymolecular sorption and capillary condensation and are found to estimate the fractal dimension in the range of 2.5–2.8. This implies that the estimation of the surface area of wood by determining the number of molecules of water corresponding to monolayer formation is not true. The surface in fact is far from two dimensional as being closer to a three dimensional one. 相似文献
10.
Studies of the degradation and protection of wood surfaces 总被引:6,自引:2,他引:6
Summary Large weight losses occurred in thin veneers of radiata pine (P. radiata) during natural weathering due mainly to loss of lignin and hemicelluloses. This was demonstrated by direct chemical analysis and by spectrocopic techniques. Treatment of veneers with dilute aqueous solutions of the recognized surface stabilizing compound chromium trioxide was found to dramatically restrict weight loss during weathering, but similar applications of ferric compound were less effective (Evans, Schmalzl 1989). In order to rationalize these protective effects FTIR internal reflectance spectroscopy was used to study chemical changes taking place at the wood surface upon treatment and during weathering. The spectra obtained provide direct evidence for the modification and stabilization of the lignin aromatic system with aqueous chromium trioxide and to a lesser extent with ferric salts. It is postulated that photostable lignin complexes are formed. The implications of these findings for the development of improved surface stabilizing compounds for wood are discussed briefly.The authors wish to thank the following: Tom Syers and Lloyd Vickers (C.S.I.R.O., Division of Forestry and Forest Products); Helen Neave, and Clive Hilliker (Australian National University, Department of Forestry) for technical assistance, and the Stanley Melbourne Bruce fund for financially supporting part of the work 相似文献
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Influence of wood moisture content and wood temperature on fungal decay in the field: observations in different micro-climates 总被引:1,自引:0,他引:1
In this study, Scots pine sapwood (Pinus sylvestris L.) and Douglas fir heartwood (Pseudotsuga menziesii Franco) specimens were exposed in double layer field trials at four different exposure sites and under different exposure
conditions (in total ten test sets). The material climate of wood in terms of wood moisture content (MC) and wood temperature
was automatically monitored over a period of 6 years and compared with the progress of decay. The aim of this study was to
highlight the interrelationship between microclimate, material climate, and decay as a basis for the establishment of dose-response
functions to be used for service life prediction of wood and wood-based products. Differences in resulting decay dynamics
between the test sites as well as between the different types of exposure were quantified and discussed with respect to corresponding
microclimatic and material climatic conditions. The time between the beginning of exposure and the first occurrence of visible
decay varied between the sites and influenced the total decay development. The fundamental importance of direct decay factors,
such as MC and wood temperature, were underlined and basic requirements for establishing dose-response-functions to be used
in service life prediction models were derived. 相似文献
13.
The hydrophilicity of Maritime pine wood surfaces was modified by silicone, an extremely hydrophobic material. A generic
method for the introduction of a variety of silicones at the surface of pre-treated wood was developed. The initial treatment
of wood with maleic anhydride and allyl glycidyl ether resulted in oligoesterified wood bearing terminal alkenes. The hydro-
osilylation of these groups, performed with hydride-terminated silicones, led to very hydrophobic surfaces, even after extensive
soxhlet extraction with good solvents for silicones. Thze presence of silicon, only at the surface of hydrosilylated wood,
was confirmed by ESCA. The silicones appear to be attached to the wood by covalent bonds.
Received 20 December 1998 相似文献
14.
Summary Photodegradation of wood surfaces in the presence of oxygen was studied. ESR studies revealed that free radicals were formed at the wood surface during photoirradiation. These wood free radicals readily interacted with oxygen molecules to form peroxide radicals. Iodometry UV absorption studies showed that hydroperoxide was formed in the photoirradiated wood. The hydroperoxide concentration increased when wood was irradiated in the presence of singlet oxygen generators such as Rose Bengal and Methylene Blue. Hydroperoxide concentration decreased when wood was irradiated in the presence of singlet oxygen quenchers such as 1,4-diazobicyclo (2,2,2) octane, -carotene and triethylamine. These findings imply the participation of singlet oxygen in the photodegradation of wood surfaces. The mechanisms of formation of singlet oxygen and hydroperoxide during photoirradiation are proposed. The consequence of hydroperoxide decomposition reactions on the discoloration and degradation of wood surface is discussed.This study was supported by cooperative research funds provided by the US Forest Products Laboratory, Madison, Wisoonsin. The authors (DNSH and STC) wish to acknowledge this support 相似文献
15.
《Fitoterapia》1999,70(4):333-339
The volatile oil of Cedrus deodara wood, administered orally at doses of 50 and 100 mg/kg, significantly inhibited neutrophil adhesion to nylon fibers, indicating inhibition of process of margination in the blood vessels. It also significantly inhibited Type III hypersensitivity reaction, i.e. Arthus reaction induced by methylated bovine serum albumin, and Type IV, i.e. delayed type hypersensitivity reaction induced by sheep erythrocytes and oxazolone, indicating an inhibitory effect on humoral and cell-mediated immune responses. 相似文献
16.
Altarejos J Salido S Pérez-Bonilla M Linares-Palomino PJ van Beek TA Nogueras M Sánchez A 《Fitoterapia》2005,76(3-4):348-351
The dichloromethane and ethanol extracts of Olea europaea wood (picual olive cultivar) were screened for antioxidant activity, determined by the DPPH free radical scavenging assay. The ethanol extract displayed potent antioxidant activity. 相似文献
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The effect of drying on wood fracture surfaces from specimens loaded in wet condition 总被引:1,自引:0,他引:1
Summary The study describes the effect of drying on fracture surfaces of Scots pinePinus silvestris L. Microtomed specimens of isolated and combined early-and latewood, in green and oven-dried/resoaked state were loaded to failure in uniaxial tension parallel to the grain. The fracture surfaces were studied using scanning electron microscopy (SEM). Both green early- and latewood samples showed rough fracture surfaces, which in latewood was dominated by intrawall failure. In the resoaked state, transwall failure dominated and fracture surfaces were more flat, indicating a more brittle fracture process. Although variation in the data was large, the strength of the resoaked samples were generally lower than those of paired green samples. The observations support irreversible cell wall damage formed during drying which severely affects the failure mechanism. 相似文献