共查询到20条相似文献,搜索用时 15 毫秒
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Yingcheng Hu Tetsuya Nakao Takahisa Nakai Jiyou Gu Fenghu Wang 《Journal of Wood Science》2005,51(1):13-17
Wood plastic plywood (WPPW), composed of veneer and styrofoam, was manufactured without special adhesives such as urea–formaldehyde or phenol–formaldehyde resins, and its vibrational properties were investigated. WPPW can be produced at 1MPa and 160°C for 9min (three-ply) and 12min (five-ply). The dynamic Youngs modulus reached its highest value when the styrofoam thickness was 30mm. The sound velocity and dynamic Youngs modulus had minimum values at a grain angle of 45°. The results for dynamic Youngs moduli measured by a longitudinal vibration method and an in-plane flexural vibration method were almost the same. Dynamic shear moduli were measured by an in-plane surface wave propagation test and an in-plane flexural vibration method. From the experimental results, the dynamic shear moduli at 0° and 90° by the two methods were relatively close, although the surface wave propagation test results were higher than those from the flexural vibration method. Dynamic shear moduli at a grain angle of 45° measured by the in-plane surface wave propagation test and calculated from theory were relatively close. The surface wave propagation test results were smaller than the results calculated from theory. The shear stress distribution factors were about 1.000–1.189 for WPPW. 相似文献
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Vibrational properties of heat-treated green wood 总被引:2,自引:0,他引:2
To investigate the influence of water on heat treatment, green wood was heat-treated. Sitka spruce (Picea sitchensis Carr.) with about 60% moisture content (MC) was used. Young's modulus and loss tangent were measured by the free-free flexural vibration test. The specimens were heated in nitrogen at 160°C for 0.5h. The results were as follows. (1) Recognizing that the effects of heat treatment are mild and that the same specimens cannot be used for both heat treatment and as controls, it was necessary to investigate the effects of the heat treatment based on the variations of properties in the whole of the test lumber. (2) Young's modulus increased and the loss tangent decreased due to heat treatment. When the vibrational properties were measured at various MCs, the MCs at the maximum value of Young's modulus and the minimum value of the loss tangent were lower in heat-treated specimens than in controls. The effects of heat treatment in green wood were similar to those in air-dried wood. (3) The loss tangents of heat-treated specimens were smaller than those of controls at about 0% MC but were larger than those of controls at about 10% MC. We thought that this resulted from the decreased MC at the minimum loss tangent after the heat treatment mentioned above. (4) The properties measured at several MCs were more useful than those at only one moisture content for investigating the effects of heat treatment.This study was presented in part at the 46th annual meeting of the Japan Wood Research Society, Kumamoto, April 3–5, 1996; and at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 3–5, 1997 相似文献
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The effect of compression and incision on wood veneer and plywood physical and mechanical properties
Maija Kymäläinen Akio Yamamoto Kasperi Sokka Lauri Rautkari 《Wood material science & engineering》2020,15(2):97-103
ABSTRACTDrying takes the largest share of energy in plywood production, and varying moisture content of veneers necessitates re-drying that often leads to over-dry veneers with deactivated surfaces, which may promote imperfect bonding. In order to decrease the drying time, reduce the need for re-drying of veneers, and improve the quality of plywood, birch and spruce veneers were subjected to pre-treatment by cold compression, incision, or a combination of the two. The effects of pre-treatment on the veneer and plywood quality were assessed by standard tests. Compression had a beneficial effect on water removal of the wettest veneers (spruce sapwood (SW) and birch), but some thickness reduction was observed in the veneers as well as the finished birch plywood. Compression led to thickness reduction of spruce veneers, but had no effect on SW plywood thickness likely due to higher viscoelasticity. Both compression and the combination of incising and compression levelled the moisture variation within the compressed stacks. Incision improved the modulus of elasticity of birch plywood, shear strength of SW plywood, and both bending and shear strengths of heartwood plywood. Higher surface pressure decreased the drying time of spruce SW in both plain compression and combined incision and compression pre-treatment. 相似文献
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用速生银杏木材和杨木为材料,大豆蛋白胶为胶粘剂制造成的胶合板,它不仅环保,而且银杏胶合板还能起到对人体有益的作用。此种产品主要用在名贵家具、茶叶及其他食品包装等方面,因此对其进行防霉性能的研究是很有必要的。作者对银杏木材胶合板的防霉特性进行了研究,为其在木材加工行业的应用提供了一定的理论基础。 相似文献
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In our study, we replaced traditional adhesives with compounds made with recycled plastic shopping bags in order to make hot-melt plywood using various amounts of plastic film, different hot-pressing temperatures and hot-pressing times.All three variables have an effect on the intensity and water-resistance of plywood.The results show that the bonding strength of plywood does not increase with increasing amounts of plastic film.When the hot-pressing temperature is increased to 150°C, the bonding strength do... 相似文献
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O. V. Startsev B. N. Salin Y. G. Skuridin R. M. Utemesov A. D. Nasonov 《Wood Science and Technology》1999,33(1):73-83
At the Altai State University a new method of synthesizing composite materials from wood without using traditional chemical
components has been developed. The foundation of the method is the physical and chemical treatment of cheap wood waste by
hot water steam under pressure. The paper presents comparative results of an investigation into the structure and properties
of the composite material “thermobalite” synthesized on the basis of birch wood. The investigation has been carried out using
dynamic mechanical analysis, linear dilatometry, wide-angle X-ray diffraction and other physical methods. It has been shown
that “thermobalite” is a partially crystalline composite polymer, whose glass transition temperature is 80 °C lower compared
to the initial wood. It has been established that preliminary moistening affects viscoelastic properties of “thermobalite”.
Certain indicators of “thermobalite” as a structural material have been correlated with similar indicators of standard wood
chip plates on the basis of phenolformaldehyde binders.
Received 6 March 1997 相似文献
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在常压下研究了温度、时间、复配阻燃剂质量分数等不同浸渍工艺参数对薄竹单板载药量的影响,测定了不同载药量薄竹胶合板的燃烧和力学性能。结果表明,在温度为60℃,时间为8h,复配阻燃剂质量分数为30%时,单板载药量趋于稳定;单板厚度增加,单板载药量会相应减少。力学性能表明,经过阻燃处理的薄竹胶合板随着载药量的增加,胶合强度有所下降,与未处理试样的胶合强度相比,经载药量为6%,8%,10%和12%阻燃处理的胶合板胶合强度分别下降了16.1%,22.0%,28.0%和35.6%,含水率范围为12.3%~13.2%,胶合强度和含水率均能满足Ⅱ类胶合板的要求。燃烧性能表明,随着载药量的增加,胶合板的点燃时间和残余质量逐渐增加,而总热释放量和总烟释放量逐渐减小,阻燃效果明显。因此,利用常压浸渍工艺生产阻燃薄竹胶合板是可行的。 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
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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
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Anna Dupleix Domingos De Sousa Meneses Mark Hughes Rémy Marchal 《Wood Science and Technology》2013,47(6):1231-1241
There is a lack of quantitative data on the penetration depth and the amount of energy absorbed by green wood under infrared (IR) radiation. This lack of knowledge is a potential barrier to the development of IR heating as an alternative to soaking as a means of warming logs prior to peeling in the manufacture of plywood. Experimental measurements of normal hemispherical spectral reflectance and transmittance over the range 550–5,500 cm?1 wavenumbers on four wood species, beech, birch, Douglas-fir and spruce have brought new knowledge on mid-infrared absorption properties of green wood and removed some uncertainties. For instance, it is not possible to deliver energy deeper than up to 0.3 mm below the wood surface because 70–90 % of all incident IR radiation on the wood surface is absorbed in this layer. Some wood features, such as surface quality, the presence of knots and of free water in wood (the latter two having a more significant effect) influence the amount of energy absorbed. These results illustrate that IR radiation can heat the surface layers, but then heat penetrates deeper into the inside layers of wood by conduction. 相似文献
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Georgiana Daian Alexander Taube Amikam Birnboim Mihai Daian Yury Shramkov 《Wood Science and Technology》2006,40(3):237-246
A method for calculating the complex dielectric permittivity of an anisotropic wood structure at microwave frequencies is
presented. A numerical model for describing the 3D wood structure containing fibers, rays, vessels and cracks with changeable
dimensions and material composition is built. This model is introduced into an efficient solver that calculates the effective
dielectric constant of any 3D structure of dielectric materials. Using our numerical model we succeeded in theoretically reproducing
the results of recent measurements of the dielectric permittivity of wood, in various directions and various moisture contents.
The qualitative agreement is realistic, reproducing all the trends of the changes in ɛ as the direction of the electric field
and the moisture content are varied. The quantitative agreement is practical and reliable for engineering calculations with
an average deviation of ±10% in ɛ′ and ±5% in ɛ′′. As microwave processing of wood involves internal temperatures as high
as 150°C and pressures of up to 5 atm, the dielectric properties of wood were also calculated with the same numerical model
by simulating high internal temperature and pressure. A comparison between the calculated and measured values shows once again
how accurate the model reproduces the empirical study. 相似文献