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1.
To investigate the affinity of acetylated wood for organic liquids, acetylated yezo spruce wood specimens were soaked in various liquids, and their swellings were compared to those of untreated specimens. The acetylated wood was rapidly and remarkably swollen in liquids having low hydrogen bonding power such as benzene and toluene in which the untreated wood was swollen only slightly or very slowly. On the other hand, the swollen volume of wood in water, ethylene glycol, and alcohols remained unchanged or slightly decreased after the acetylation. The effect of acetylation was greater in liquids having smaller solubility parameters. The easier penetration of aprotic organic liquids into the acetylated wood was considered to be due to the reduction of polarity and the scission of hydrogen bonds in the amorphous wood constituents where the hydrophilic hydroxyl groups were substituted by hydrophobic acetyl groups. 相似文献
2.
To clarify the role of lignin in the affinities of acetylated wood for organic solvents, the effects of delignification on
the solvent adsorption of acetylated wood were investigated. Acetylated wood meals rapidly adsorbed organic solvents that
were hardly adsorbed by unmodified wood. For nonpolar and low-polarity organic solvents, a clear positive correlation was
observed between the amount of adsorption and the lignin content. This indicated that acetylated lignin was responsible for
the excellent affinities of acetylated wood for hydrophobic organic solvents. On the other hand, for lower alcohols and water,
the amount of adsorption reduced with an increase in the lignin content. It was suggested that the adsorption of such polar
solvents was dominated by insufficiently acetylated hydrophilic polysaccharides. 相似文献
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Semi-isostatically densified and native wood samples of Scots pine and European birch were soaked in water. The swelling coefficients
as well as the swelling pressure, that arose when the specimens were restrained in some way prior to the swelling, were measured
using a universal testing machine equipped with a high resolution load-cell and an external extensometer. As densified wood
swells, the native structure is almost restored and the swelling pressure became twice as high as for native wood in the most
compressed directions (radial for pine and birch). That cell-shape recovery increases the swelling pressure can explain the
problems with imbalance in laminated constructions where densified wood is used. The possibility to predict the swelling pressure
from basic material properties was evaluated. The correlations between swelling pressure and material properties were strong
enough to yield good predictive models. 相似文献
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J. Raczkowski 《Wood Science and Technology》1979,13(3):187-196
Summary Swelling pressure of outer bark (rhytidome) of pine, larch, poplar, willow, oak, birch and black locust was investigated. Swelling pressure was determined on oven-dry samples moistened in water, using an accelerated method consisting of initial evacuation of air from the samples. Additionally, free swelling of bark, water-absorption capacity, and stress at proportional limit in compression of wet bark were investigated. Swelling pressure of bark ranges from 0.11 to 0.87 MPa, depending on the species and anatomical direction. These figures are 4 to 71% of respective values for the swelling pressure of wood of the same species. Swelling pressure of bark amounts to 11–71% of stresses at proportional limit when bark is subjected to compression in the wet state. With increasing bark density, a clear tendency was observed for an increase in swelling pressure and stress at proportional limit, as well as a decrease in water-absorption capacity.The author thanks Miss H. Drewek for her valuable technical assistance 相似文献
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S. Chow 《Wood Science and Technology》1994,28(3):189-198
Summary Thermal movement of wood and wood composites was studied and compared with that of random and oriented phenolic foams. Cell orientation was a dominate factor determining the thermal response of these structures. In dried wood, thermal movement in the direction parallel to the cells (longitudinal) decreased in dimension during heating while the radial and tangential directions expanded under similar heating condition. Oriented foams showed more restraint in thermal movement in the parallel to orientation direction. These findings indicate constraining forces act on the direction parallel to the cells while more flexibility exists in perpendicular directions. Wood element size and orientation and the manufacturing process also influence the thermal response in wood composites. The experimental results also revealed the potential fire hazard of waferboard type of composites. 相似文献
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F. C. Beall 《Wood Science and Technology》1971,5(3):159-175
Summary The prolysis of cellulose, hemicelluloses, lignin preparations, and wood was studied by differential calorimetric analysis (DCA) for the range of 25° to 800° C. The test samples included powdered and filter paper celluloses; hardwood xylan; softwood galactoglucomannans, compression wood galactan, and arabinogalactan; a synthetic (DHP), sulfuric acid, Björkman, Brownell, and cellulase lignins; and unextracted and extracted hardwoods and softwoods. Heats of reaction were determined from the DCA thermal transition areas. Distinct differences were found between the thermograms of each hemicellulose and lignin sample. Although wood species could not be separated thermally, hardwood and softwood thermograms differed because of the hemicellulose degradation pattern.Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product by the U.S. Department of Agriculture.Formerly Research Technologist, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture. The Laboratory is maintained at Madison, Wis. 53705, in cooperation with the University of Wisconsin. Present address: The Pennsylvania State University, University Park, Pennsylvania 16802. 相似文献
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通过适当的化学改性反应如酯化、醚化等,可以使木材转化为热塑性高分子材料。这些热塑性材料可单独或与合成高聚物按比例混合热压加工成型为各种板材或其他成型产品,这对扩大木材的加工利用途径、充分利用木材加工剩余物、提高木材利用率等都具有十分重要的意义。本文介绍了酯化、醚化木材的主要方法,产品的特点,以及今后木材及纤维素酯化、醚化的发展方向。 相似文献
10.
Summary Thermodynamic work of adhesion, contact angle, wettability and acid-base contributions of the wetting of four North American wood species were determined using the Wilhelmy technique. The wetting angles with water varied from 60° for Sitka spruce to 74° for Douglas-fir. The wood surfaces had a strong acidic character since the greatest interactions for all the wood species occurred with formamide (basic probe) while lesser interactions were obtained with ethylene glycol (acidic probe). In addition, dispersive and polar surface free energies of wood,
d
s
and
p
s
respectively, were determined using Wu's simultaneous equations. In general, 75 to 80% of the total surface free energy of wood was due to dispersion forces. Specific wettabilities of wood and advancing contact angles in thirty various organic liquids were also evaluated. 相似文献
11.
Summary Wet cross-sections up to several centimetres thick of young trees show marked translucency. Various research applications are suggested by the observation of this phenomenon. 相似文献
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以3株6年生浙江桂幼龄材为试材,研究了其生物量、材积、基本物理力学性能及生长轮的宽度、纤维长度、宽度、微纤丝角和结晶度的径向变异规律。结果表明,浙江桂幼龄材单株平均总生物量27.93 kg,平均材积0.0124 m3,生长轮平均宽度9.15 mm(3.12~10.57 mm),基本密度为0.414 g/ cm3,除髓心外其余各生长轮宽度和密度无明显差异,反映浙江桂生长较为稳定;顺纹抗压强度、抗弯强度和弹性模量等物理力学综合性能中上等;纤维长度为830.6μm(581~1043μm),纤维宽度为23.6μm(21~24μm),结晶度为38.46%~58.43%,微纤丝角为13.6°~24.6°;纤维长度、宽度和结晶度自髓心向外逐渐增加,微纤丝角自髓心向外逐渐减小,结晶度与纤维长度、宽度间相关性极显著。 相似文献
16.
Ulrich Müller Thomas Jost Christian Kurzböck Alexander Stadlmann Wolfgang Wagner Stefan Kirschbichler 《Wood material science & engineering》2020,15(5):312-324
ABSTRACT Multi material mix is a promising approach to reduce weight and the carbon footprint in automotive engineering at competitive costs. As a result, automotive industry is getting more venturous, exploring and applying other materials than metals and plastics – e.g. fibre reinforced plastics (FRPs). In this context, engineered wood products (EWPs) and wood composites should be considered: Wood composites provide high stiffness, strength, excellent damping, high resistance against fatigue and a very low density at low material costs. It is hypothesized that modern wood composites are competitive to metals and artificial fibre-reinforced materials when designed and applied properly. The application of wood and wood composites in automotive engineering calls for precise and reliable material data, required for initial material selection and later in numerical simulation. In this study, a material model normally used for modelling FRPs was adopted. A material database was generated for three hardwood species, to establish the required material parameters and validate material model. Results prove that wooden components can be simulated in crash situations and the selected material model is applicable, even in full vehicle simulation. 相似文献
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Manuel Raul Pelaez-Samaniego Vikram Yadama Eini Lowell Raul Espinoza-Herrera 《Wood Science and Technology》2013,47(6):1285-1319
The objective of this paper is to review the published literature on improving properties of wood composites through thermal pretreatment of wood. Thermal pretreatment has been conducted in moist environments using hot water or steam at temperatures up to 180 and 230 °C, respectively, or in dry environments using inert gases at temperatures up to 240 °C. In these conditions, hemicelluloses are removed, crystallinity index of cellulose is increased, and cellulose degree of polymerization is reduced, while lignin is not considerably affected. Thermally modified wood has been used to manufacture wood–plastic composites, particleboard, oriented strand board, binderless panels, fiberboard, waferboard, and flakeboard. Thermal pretreatment considerably reduced water absorption and thickness swelling of wood composites, which has been attributed mainly to the removal of hemicelluloses. Mechanical properties have been increased or sometimes reduced, depending on the product and the conditions of the pretreatment. Thermal pretreatment has also shown to improve the resistance of composites to decay. 相似文献
19.
Differences in wood properties between juvenile wood and mature wood in 10 species grown in China 总被引:3,自引:0,他引:3
F. C. Bao Z. H. Jiang X. M. Jiang X. X. Lu X. Q. Luo S. Y. Zhang 《Wood Science and Technology》2001,35(4):363-375
This study examined the intrinsic differences in various wood properties between juvenile wood and mature wood in 10 major
reforestation species in China. Comparisons between juvenile wood and mature wood were made in both plantation- and naturally-grown
trees. Considerable differences in most wood properties were found both between plantation-grown juvenile wood and mature
wood, and between naturally-grown juvenile wood and mature wood. This suggests that wood properties of plantation-grown trees,
to a large extent, depends on their juvenile wood contents, and can thus be manipulated effectively through rotation age.
In general, the longer the rotation age, the lower the juvenile wood content, and the stronger the mechanical properties of
the plantation-grown woods. However, the differences between juvenile wood and mature wood vary with wood properties and species.
In general, juvenile wood and mature wood have less difference in chemical composition than in anatomical and physico-mechanical
properties. Compared to the softwoods studied, the hardwoods appear to have less difference between juvenile wood and mature
wood.
Received 25 June 1999 相似文献
20.
Summary The exposure of wood treated with a commercial fire retardant chemical to fire conditions resulted in different patterns of char and fissure development than are seen in untreated whole wood. In addition microstructural observations demonstrated the existence of particulate fire retardant residues in char from treated wood. The source and mode of growth of these particles is considered as well as effects of fire retardants on crack growth, char development and overall appearance of chars from treated wood.The authors wish to acknowledge the general support of the University of California Berkeley Fire Research Group (NSF-RANN-S-22053, NFPCa-S-22584), University of California Berkeley Electron Microscopy Lab. (NSF-GB-38359) and the University of California, Davis Department of Botany (NSF-GB-29653). In addition we would also like to thank Dr. Arno P. Schniewind, University of California Forest Products Laboratory and Dr. R. Falk, University of California, Davis, Department of Botany 相似文献