热处理后超高分子量聚乙烯纤维结构及力学性能

超高分子量聚乙烯纤维是一种高强、高模量、高结晶及高取向的纤维,但由于其耐热性较低,在使用过程中难免会遇到热的作用,因此研究其受热后力学性能的变化具有一定的实际意义.通过DSC、广角X衍射及力学性能分析,探讨热处理对成型纤维力学性能的作用.通过DSC发现随着热处理温度的升高纤维的熔融温度范围变窄.从X衍射图谱上观察,纤维的结晶形式并没有发生变化,只是微晶尺寸有减小的趋势.通过研究不同温度处理超高分子量聚乙烯纤维力学性能的变化,表明不同温度处理后纤维的力学性能差异并不大,即熔融温度以下的短时间的热处理不会给纤维的力学性能带来损伤.     

日本落叶松热处理材表面显微硬度变化研究

以过热蒸汽为传热介质和保护性气体,在热处理温度为165℃、180℃、195℃、210℃,热处理时间为10h的条件下对日本落叶松木材进行高温热处理,研究日本落叶松木材在不同热处理温度下的表面显微硬度变化。结果表明,随着热处理温度升高,热处理材表面显微硬度逐渐升高,当热处理温度低于195℃时,木材表面显微硬度变化趋势不明显,当热处理温度达到210℃时,热处理材的表面显微硬度显著提高,变化率高达44.12%。     

Changes in the properties of light-irradiated wood with heat treatment

This study investigated the changes in the color of wood with heat treatment after exposure to light at various conditions. The change with exposure is attributed to the decomposition of lignin, and the process follows a first-order reaction law. The degree of color change in softwood was greater than in hardwood, while there was no significant difference between the reaction rates for softwood and hardwood. This is attributed to differences in the lignin content. The change in the color of light-irradiated wood with heat treatment increased with light-irradiation time, heating temperature, while the changes in the color of wood irradiated for more than 30 to 40 h were similar. With the investigation of the effect of wavelength, the change in the lightness, L*, of all the woods tested decreased with wavelength. L* became positive for light-irradiated Japanese cypress and hackberry; however, this effect disappeared with heat treatment. The chroma coordinates a* and b* of all species were minimal when irradiated with wavelengths longer than 500 and 440 nm, respectively. However, this effect disappeared with heat treatment. In softwood, b* was negative when exposed to light longer than 440 nm, while in hardwood, it turned negative when exposed to 390, 440, and 500 nm. However, the minimum value observed with light-irradiation disappeared with heat treatment after light-irradiation. Therefore, it is thought that chemical changes involved in the color changes due to light-irradiation differ form those involved in the color changes due to heat treatment.

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Veränderung der Eigenschaften von Licht-bestrahltem Holz nach HitzebehandlungTeil 2: Einfluss von Bestrahlungszeit und Wellenlänge

Zusammenfassung Die Farbänderungen von Holz durch Hitzebehandlung nach Lichtbestrahlung unter verschiedenen Bedingungen wird untersucht. Die Farbänderung wird auf Ligninabbau zurückgeführt. Der Prozess folgt einer Reaktion 1. Ordnung. Das Ausmass der Farbänderung war bei Nadelholz größer als bei Laubholz, während die Reaktionsraten keine signifikanten Unterschiede aufwiesen. Dies wird auf Unterschiede im Ligningehalt zurückgeführt. Die Farbänderung der Licht-bestrahlten Proben nach Hitzebehandlung verstärkt sich mit der Bestrahlungszeit und der Temperatur der Hitzebehandlung; nach Behandlungszeiten von mehr als 30 bis 40 Stunden gleichen sich die Farbänderungen jedoch an. Auch der Einfluss der Wellenlänge wurde untersucht. Dabei erhöhte sich die Helligkeit, L*, bei allen Proben mit der Wellenlänge. L* wurde positiv für japanische Zypresse und Zürgelbaum; allerdings verschwand dieser Effekt nach Hitzebehandlung. Die Koordinaten a* and b* waren bei allen Proebn minimal, wenn mit Wellenlängen >500 bzw. >440 nm bestrahlt wurde. Auch dieser Effekt verschwand nach Hitzebehandlung. Bei Nabelholz war b* negativ nach Bestrahlungen mit Wellenlängen von 390, 440 und 500 nm. Die beobachteten Minima verschwanden allerdings nach der anschließenden Hitzebehandlung. Daraus ergibt sich, daß die chemischen Veränderungen aufgrund der Bestrahlung anderer Art sind als die durch Hitzebehandlung verursachten.

     

Effect of thermal treatment on some properties of lime wood

Thermal treatment of lime wood was performed in a drying oven at two temperature levels (180 and 200 °C) and for four durations (1, 2, 3 and 4 h). Mass loss, color change, swelling and hygroscopicity were investigated. The dimensional stabilization reached up to 66.4 % and the hygroscopicity reduction up to 33 %, both maximum values being attained at 200 °C/4 h, associated with a mass loss of 9.3 %. The results will be realized in the manufacturing of solid wood panels made of heat-treated lime wood lamellas for outdoor uses.     

Effect of water activity on the mechanical properties of selected legumes and nuts

Two legumes (kidney beans and chickpeas) and two nut kernels (almonds and hazelnuts) were compressed intact with a Universal testing machine at various a_w levels in the range of 0·11–0·85 at an ambient temperature of 22°C. Mechanical characterisation of the four was done through four parameters; the slope of the initial part of force–displacement curve, considered a measure of stiffness, the failure force, considered a measure of strength, the deformation at failure, considered a measure of brittleness or deformability and the area under the force–displacement curve corresponding to 20% compression, considered a measure of toughness. Among these parameters only the latter could be determined and used effectively in all four seeds and along the whole water activity range. The jaggedness of the force–displacement curve was also determined in terms of its apparent fractal dimension calculated with two different algorithms for verification. There was a noticeable difference between the mechanical behaviour of the two groups. The nut kernels, apparently because of their high oil content, had a much smoother force–displacement curve, and the effect of absorbed moisture on their texture was generally more moderate than on that of the legumes. But in all the four types of seeds tested, each mechanical property had its own specific moisture dependency, an observation consistent with previous reports on cereal-based products. ©1997 SCI     

木桁架齿板连接性能模拟的研究现状

从齿板连接构件材料及连接性质确定和连接性能模拟两方面介绍国内外木桁架齿板连接性能理论及模拟研究现状,并对三种常用的齿板连接性能研究的分析软件SAT、PPSAⅡ和ANSYS作了简单介绍。通过对文献资料的系统分析,认为齿板连接性能研究具有重要的科研和应用价值。     

Comparison of selected physical and mechanical properties of densified beech wood plasticized by ammonia and saturated steam

Gaseous ammonia treatment in combination with densification of wood has been known for several decades, but these days there is no industrial production of materials modified in this way; also, little has been published in this area of wood science. In this study, selected physical and mechanical properties, i.e. density profile, bending strength, hardness and moisture absorption were investigated for Lignamon (1), which was obtained from the Czech industrial production. Selected properties were also investigated using steam-densified beech (2) and native beech (3) and compared with each other. Densitometry of Lignamon showed a large variability in the density profile compared to that of only densified beech. It is affected by the degree of densification, temperature and moisture gradients, and their relationship to the glass transition of the wood cell wall. Modulus of elasticity, hardness, moisture exclusion and anti-swelling efficiency of Lignamon are enhanced compared to densified beech. The enhanced dimensional stability and lower hygroscopicity of Lignamon are probably caused by heat treatment during the process. Further investigation will be carried out with self-produced Lignamon samples.     

Influence of steaming on selected wood properties of four hardwood species

Influence of steaming on various mechanical and physical properties of two European (Robinia pseudoacacia L., Quercus robur L.) and two tropical (Intsia bijuga, Hymenolobium petraeum) hardwood species were investigated. Each of these wood species requires adequate adhesive systems for the use as dimension stock because of their highly reactive surface chemistry. In order to optimize the gluing behaviour of the timbers involved, steaming processes with five different sets of parameters (steaming time and temperature) were carried out. In addition to the adhesive test, bending strength, hardness, and colour of the modified timbers were examined. The result of steaming highly depends on the wood species. For black locust, steaming is a suitable method of colour homogenization and colourization. Short term, low temperature treatment improves the adhesion performance also, whereas the colour change value reaches its maximum in the case of long term, high temperature steaming. Hue shift of oak and sapupira was inconsiderable for any applied set of parameters, only a small L* decrease was observed at higher temperatures. The colour of merbau samples shifted slightly during the treatment. Bending strength and hardness of wood samples in all of the four wood species decreased during the treatment. However, steaming time is more important than temperature while aspect of colour change both time and temperature has the same significance. Adhesive properties of sapupira can be greatly improved by hydrothermal treatment.     

Effect of accelerated aging on selected physical and mechanical properties of Bambusa rigida bamboo

Bambusa rigida bamboos were subjected to accelerated aging test, and the main physical and mechanical properties before and after aging were comparatively investigated. The results revealed that the aged bamboos lost parts of their original physical and strength properties. Furthermore, mechanical strength properties and basic density of both control and aged specimens increased significantly with the height of the culms, while that for the volumetric shrinkage was reverse. The effect of accelerated aging on the properties of base portion specimens was much more significant than that of the middle and top portions.     

Effects of chemical modification on the mechanical properties of wood

Chemical modification has been recognized as an efficient strategy for dimensionally stabilizing wood and protecting it from environmental damage, such as deterioration due to weathering and fungal decay during the service period. Studies reported in the literature mainly concern the establishment of workable modification techniques, testing methodologies, and assessment of the durability of modified wood. The development of wood modification techniques has recently been reviewed; limited information is however given on the effects of chemical modification on the mechanical properties of wood that are of importance to it as an engineering material. This paper reviews the effects of wood modification, typically by heat treatments and impregnation with low molecular weight resins, reactive monomers, or hot melting paraffins on the mechanical properties of wood. The modifying variables associated with mechanical properties of wood such as wood species, treating temperature and time, catalyst, type of solvent, weight percent gain, and molecular structures of the modifying agent were analysed and the results interpreted. The reasons for changes in the mechanical properties of wood are discussed.     

Influence of heat pressure steaming (HPS) on the mechanical and physical properties of common oak wood

Common oak (Quercus robur) was thermally treated applying a heat pressure steaming procedure. Physical and mechanical properties of treated and untreated samples were investigated extensively. Swelling, water absorption, water vapour resistance, porosity and thermal conductivity were tested and the mechanical properties of tensile, bending and compression strength and of Young’s modulus (static and dynamic) as well as Poisson’s ratio and shear modulus were determined. The tests were carried out in the standard climate 20 °C and 65 % relative humidity and also in all three anatomical main directions: longitudinal, radial and tangential. The equilibrium moisture content at 20 °C and 65 % relative humidity for HPS (heat pressure steamed) oak (determined in adsorption test) was 6.7 % and for untreated oak 9.1 %. Swelling in longitudinal direction was not affected: a reduction of 17 and 10 % could be observed in radial and tangential direction, respectively. The porosity of the treated samples was 53.9 % in comparison to the untreated samples with 51.0 %. The thermal conductivity depending on the modification procedure changed only slightly which was related to the different densities of the samples. The water vapour resistance of the modified samples increases compared to the untreated samples. The values are double (dry-cup) respectively three times (wet-cup) higher than those of the reference samples. The elastic properties were not influenced by heat pressure steaming. The MOE does not show a significant change depending on the treatment. Bending and tensile strength of HPS oak decrease. In longitudinal direction, the tensile strength drops by 26 % and the bending strength by 25 %.     

Effect of radiata pine juvenile wood on the physical and mechanical properties of oriented strandboard

This work analyzes the impact of radiata pine (Pinus radiata D. Don) juvenile wood on the physical and mechanical properties of oriented strandboards (OSB). Radiata pine logs were obtained from 10 trees of a 26-year old managed stand located in the 8th Region of Chile. The experimental design considered the proportion of juvenile wood and strand orientation as independent variables. OSB panels of 0.4 m×0.4 m×12 mm were produced and tested. The results show that the juvenile wood proportion has a significant impact on the physical and mechanical properties of OSB. Strands orientation had a significant impact on all the properties studied with the exception of the modulus of elasticity in bending. However, this impact was small in all cases and would not change panel grade with the exception of linear expansion. In this case, panels made from tangential strands showed a higher linear expansion. According to these results, radiata pine juvenile wood can be used for the manufacturing of OSB up to a proportion of 70% of the oven-dry wood weight without significant losses of the physical and mechanical properties if the juvenile wood strands are located in the surface layers.     

Effect of heat treatment duration on the thermal conductivity of spruce and poplar wood

Changes in the thermal conductivity and density of Pannónia poplar (Populus x euramericana cv. Pannónia) and spruce (Picea abies) caused by heat treatment were examined. The specimens were treated at 180?°C for 15, 25 and 35 h. Treatment duration had different impact on both the density and the thermal conductivity of poplar and spruce. The density of poplar decreased by 9.1, 12.1 and 13.4%, and the thermal conductivity decreased by 16.9, 24.0, 29.1% after 15, 25 and 35 h of treatment, respectively. In the case of spruce, the density decreased by 5.2, 7.6 and 8.7%, and the heat conductivity by 7.4, 14.1 and 22.0%, respectively.     

热处理对荞麦淀粉糊化特性的影响研究

研究了热处理及食品添加剂对荞麦淀粉糊化特性的影响,结果表明,荞麦淀粉经过热处理后,易糊化,易凝沉,透明度降低,冻融稳定性差。添加蔗糖、食盐、磷酸盐、乳化剂后荞麦淀粉较难糊化,透明度降低,但蔗糖、乳化剂阻止荞麦淀粉凝沉,而食盐、磷酸盐则相反;添加维生素C、溴酸钾对荞麦淀粉的糊化特性影响不大。     

木材热处理研究的进展

介绍了木材热处理技术在国内外的研究进展情况,并对该项技术的发展进行了展望。     

Influence of ageing on mechanical properties of wood to wood bonding with wheat flour glue

Earlier research into native wheat flour for wood to wood bonding showed excellent bonding properties comparable to synthetic adhesives, but no data about ageing behaviour is available. Short and long term effects on mechanical properties were analysed by lap joint testing and modified DCB-specimens. Results showed no significant reduction in bonding properties, but a trend to lower adhesive strength after 12 months of storage was noticeable. Changes in wheat polymers were observed by means of DSC and FTIR-ATR. Soluble degradation products of starch were analysed by GC-FID after methanolysis and derivatisation. FTIR measurements indicated changes in the structure of starch, but no appreciable alteration of proteins. Investigations by DSC showed increasing crystallinity during 3 months of storage. After 6 months more degradation products were detected. Results indicated that hydrolysis of starch is responsible for a moderate decrease of bonding performance; wheat proteins seem to be less affected.     

Effect of heat treatment intensity on wood chemical composition and decay durability of Pinus patula

Heat treatment is an effective method to improve biological resistance of low natural durability wood species. The aim of this study was to enhance the decay resistance of Pinus patula, an African low natural durability softwood species, via wood thermal modification technique. Heat treatment was performed on wood specimens under inert conditions at different heat treatment intensities to reach mass losses of 5, 10 and 15%. Heat treated specimens were exposed to fungal decay using the brown rot fungus Poria placenta. The wood chemical and elemental composition was determined as well as extractives toxicity before and after wood thermal modification to understand the reasons of durability improvement. The treated specimens exhibited a significant increase in their durability against wood decay in line with the severity of the treatment. Wood holocellulose was found to be distinctly more sensitive to the heating process than the lignin constituent. In addition, obvious correlations were observed between weight losses recorded after fungal exposure and both holocellulose decrease and lignin ratio increase. The same correlations were observed with the elemental composition changes allowing using the observed differences for predicting of wood durability conferred by heat treatment. Furthermore, no significant differences were observed between the toxicity of Pinus patula wood extractives before and after its thermal modification.     

日本落叶松木材单根纤维的力学性能研究

试验以人工林日本落叶松成熟材早材为试验材料,采用植物短纤维力学性能测试仪对日本落叶松单根纤维的纵向力学性能进行了测量.试验采用球槽型夹紧方式,夹持木材短纤维,以及在测试过程中避免木材纤维扭转和剪切,试验测出平均纵向抗拉强度为230MPa,平均纵向弹性模量为1.12GPa,平均断裂载荷为128.37MPa,平均断裂应变为20.52％.