基于纳米压痕技术的木材胶合界面力学行为

【目的】研究木材胶合界面的静态和动态力学行为,探讨树脂渗透对木材管胞壁层力学性能的影响,为木质复合材料制造工艺优化和增强改性提供理论依据。【方法】采用纳米压痕静态和动态力学测试技术(Nano-DMA),对针叶材火炬松与酚醛树脂(PF)、脲醛树脂(UF)胶黏剂所形成胶合界面区域各相材料的静态弹性模量、硬度、蠕变性能以及储能模量和损耗模量等力学行为进行分析。【结果】静态力学行为方面,在界面区域,PF和UF渗透进入管胞壁层后,木材管胞壁的弹性模量( E r)和硬度( H )提高;经PF渗透后,木材管胞壁的 E r和 H 分别增加7%和26%;Burgers蠕变力学模型可有效描述胶合界面区域管胞壁的纳米压痕蠕变特性,经树脂渗透后,木材管胞壁的瞬时弹性模量增加,黏弹性模量和黏性系数减小;在保载初期,PF界面区域木材管胞壁的蠕变柔量约下降60%,UF界面区域木材管胞壁的蠕变柔量约下降58%。动态力学行为方面,随着加载频率增加,界面材料的储能模量( E ′ r)逐渐增大,而损耗模量( E ″ r)和损耗因子(tan δ)呈减小趋势;当加载频率为10 Hz时,PF和UF树脂渗透使得管胞壁层的储能模量分别增加16%和29%。【结论】胶合界面区域胶黏剂进入管胞壁层,对木材管胞的静态力学性能具有增强作用,同时胶黏剂可提高管胞壁的短期抗蠕变能力;木材管胞壁具有较高的储能模量和损耗模量,而树脂的储能模量和损耗模量较低,经树脂渗透后,木材管胞壁的储能模量增加,但损耗模量和损耗因子呈下降趋势,可能对界面传递和分散应力产生不利影响。     

A comparison of nanoindentation cell wall hardness and Brinell wood hardness in jack pine (Pinus banksiana Lamb.)

Nanoindentation is a powerful tool for hardness testing on a very small scale. Since the technique was first introduced for studying wood cell wall mechanics, it has been integrated as an important tool for measuring the modulus of elasticity and hardness of wood cell walls. In this study, hardness measured with nanoindentation (nanohardness) was compared with hardness measured by the standard Brinell test method (Brinell hardness) on jack pine (Pinus banksiana Lamb.) wood. Nanoindentation was performed on both the S2 layer of the secondary cell wall and the middle lamella (ML) of early- and latewood fibers. Four annual growth rings were studied. The influence of growth ring and initial spacing on both measurements was analyzed. The relationship between Brinell hardness, nanoindentation measurements, and average ring density was also studied. Results suggest that Brinell- and nanohardness are controlled by different mechanisms and factors. The location of nanohardness measurements (i.e., S2 layer or ML) also influenced hardness differently. It was concluded that nanomeasurements are not an exact representation of wood mechanical properties conducted at the macro level because of the hierarchical structure of wood. The effect of other factors such as moisture or wood extractive content may also need consideration.     

Nanoindentation of juvenile and mature loblolly pine (<Emphasis Type="Italic">Pinus taeda</Emphasis> L.) wood fibers as affected by thermomechanical refining pressure

The effects of thermomechanical refining pressures, varying from 2 to 18 bars, on the cell-wall properties of refined wood fibers of a 54-year-old loblolly pine (Pinus taeda L.) with reference to both juvenile (JW) and mature wood (MW) were investigated using nanoindentation and atomic force microscopy. The results of this study indicate that refining pressure plays a significant role in the physical damage sustained by refined wood fibers. No obvious damage was observed in the cell walls of MW fibers refined at 2 and 4 bar. Nanocracks (<500 nm in width) were found in fibers refined at pressures in the range of 2–12 bar for JW and 6–12 bar for MW, and micro cracks (>3,000 nm in width) were found in both MW and JW fibers subjected to a refining pressure of 14 and 18 bar. The micro damage to the fibers refined at higher pressures was more severe inside the lumen than on the surface of the fibers, and the lumen or S₃ layer was significantly damaged. The elastic modulus, hardness, and creep resistance of MW fibers were higher than those of the JW fibers subjected to the same refining-pressure conditions. The elastic modulus and hardness decreased, whereas nanoindentation creep increased, with increasing refining pressure. This study also suggests that lower refining pressures (<4 bar) and higher pressures (>14 bar for MW and >12 bar for JW) should be avoided in the manufacture of fiberboards and wood fiber–polymer composites, because of the lower aspect ratio of the fiber bundles, shorter length of the fibers and fines, and severe damages to the fiber cell walls.     

纳米压痕技术测量管胞次生壁S2层的纵向弹性模量和硬度

重点研究和详细介绍了利用纳米压痕技术测试管胞次生壁S2 层纵向弹性模量以及硬度的实验技术 ,并测试了人工林杉木早晚材管胞S2 层的纵向弹性模量和硬度。结果表明 :杉木晚材管胞S2 层的平均纵向硬度为0 390GPa ,弹性模量的平均值为 1 4 84 4GPa ;早材管胞S2 层的硬度和模量则小于晚材 ,平均值分别为 0 30 6GPa和9 82 3GPa。     

Evaluation of quality indexes of bending performance and hardness for hardwoods

The mechanical properties of 613 small clear specimens of 35 species (11 ring-porous hardwoods, 19 diffuse-porous hardwoods, and 5 softwoods) were evaluated. The aim of the study was to examine indexes of wood quality that are easy to measure and that exhibit a high correlation with bending performance and hardness that are essential properties of hardwood products. The modulus of rigidity, dynamic modulus of elasticity, bending properties (modulus of elasticity, modulus of rupture, stress at the proportional limit, absorbed energy, Tetmajer’s modulus), dynamic energy absorption by an impact bending test, compressive strength parallel to the grain, shear strength, partial bearing strength, and Brinell’s hardness were measured. A high correlation was found between dynamic modulus of elasticity and static modulus of elasticity. Bending stress at the proportional limit was found to be approximately equivalent to the compressive strength parallel to the grain. Static energy absorption correlated with dynamic energy absorption. Tetmajer’s modulus was found to be closely related to the ratio of the initial stiffness within the elastic range to the secant modulus at the maximum load. A high correlation was observed between Brinell’s hardness and partial bearing strength. The difference in the regression coefficients obtained for these correlations between the species groups was small. Part of this study was presented at the All Division 5 Conference of IUFRO, Taipei, October 2007     

In situ measurement of tensile elastic moduli of individual component polymers with a 3D assembly mode in wood cell walls

We attempted to measure in situ the tensile elastic moduli of individual component polymers with a three-dimensional (3D) assembly mode in the cell walls of Sugi (Cryptomeria japonica D. Don) without isolating the polymers. To prepare wood tangential slices [50 × 6 × 0.2 mm (L × T × R)] consisting of lignin with a 3D assembly mode in the cell walls, cellulose and hemicellulose were removed using the method of Terashima and Yoshida (2006) to obtain methylated periodate lignin slices. To prepare wood slices consisting of polysaccharide with a 3D assembly mode in the cell walls, lignin was removed using the method of Maekawa and Koshijima (1983) to obtain holocellulose slices. Static tensile test was applied to determine the elastic moduli of 3D lignin and 3D polysaccharide slices. The followings were revealed. The elastic modulus of the 3D lignin slices was 2.8 GPa, regardless of the microfibril angle (MFA) in the slices. The elastic moduli of the 3D polysaccharide slices with MFAs of 14°, 23°, 34°, and 42° were 18, 12, 9, and 4 GPa, respectively. The former shows that the lignin with a 3D assembly mode behaves as an isotropic substance in the cell walls, while the latter suggests that the 3D polysaccharide slice shows marked anisotropic structure in the cell wall. Despite the fact that cellulose content increased after lignin removal, values of substantial elastic modulus of the cell wall slightly decreased regardless of MFA. Following two possible reasons were pointed out for explaining this phenomenon. First, lignin removal caused an artifactual deterioration in the polysaccharide slices at the level of macromolecular aggregate. Second, rigid and fusiform-shaped cellulose crystallites are dispersed in the soft matrix of amorphous polysaccharide, and those are loosely connected to each other by the intermediary of matrix polysaccharide. Those suggest that the rigid cellulose crystallite can optimize its strong mechanical performance in the polysaccharide framework of the wood cell wall in combination with the ligninification.     

落叶松木材的高强度微波辐照法改性

The larch wood was treated by microwave irradiation under different radiant intensity and treating duration. The microwave-treated wood specimens together with the un-treated for comparison were impregnated by water in pressure vessel and then tested for permeability, mechanical properties and microstructure change by SEM to study the modification performance of microwave treatment on larch wood. The results showed that under suitable conditions of microwave treatment the permeability of larch wood was improved without noticeable decreasing of the modulus of rupture （MOR） and the modulus of elasticity （MOE）. The radial parenchyma and some pit membrane were ruptured, and tiny cracks were formed in the cell walls. The formation of tiny cracks in the cell walls serves as man-made channels of gas and liquid and this contribute to improve the permeability of the wood.     

Effects of density and anatomical feature on mechanical properties of various wood species in lateral tension

This study is focused on what factor mainly affects the mechanical properties of each wood species in the lateral direction. At first, the influence of the density which is closely related to mechanical properties in the longitudinal direction was also researched in the lateral direction. Thus, the elastic modulus, strength, and failure strain in the lateral tension were measured using thin cross-sectional samples of softwoods and hardwoods, having wide varieties in the density and anatomical features. The results obtained are as follows. The linear relationship between the density and the elastic modulus which has been verified in the longitudinal direction was not observed in the lateral tension for the samples with the annual ring inclination of 90°, which samples were influenced by ray arranged parallel to the tensile direction. However, samples with the annual ring inclination of 45° showed the high correlation between the density and the elastic modulus due to the shearing deformation of the cell shape. On the other hand, the proportional relationship between the elastic modulus and strength which has been verified in the longitudinal direction was not observed in the lateral tension except for the samples with the annual ring inclination of 90°. From the results obtained, it was revealed that the mechanical properties of wood in the lateral direction were significantly affected not only by the density but also by the structural features such as deformation of cell shapes, arrangement of ray or vessels, and the degree of the transition from the earlywood to the latewood.     

人工林落羽杉力学性能研究

对江汉平原人工林落羽杉物理力学性能进行了研究,结果表明:落羽杉的气干密度为0.413 g/cm3,气干密度等级为轻;综合强度为74 MPa,强度等级为Ⅰ级;径向横纹抗压强度略大于弦向横纹抗压强度;端面硬度最高,弦面硬度与径面硬度差别不大。落羽杉南北面近树皮处木材的密度、抗弯强度、弹性模量、顺纹抗压强度均大于近髓心处,南北方向对落羽杉的密度、顺纹抗压强度在5%水平上差异均不显著,而对其抗弯强度、弹性模量在1%水平上差异显著。     

三倍体毛白杨新无性系木材气干密度和力学性质性状的遗传控制及对单板材育种的意义

该文利用 9个 9年生三倍体毛白杨无性系木材试样 ,研究了木材气干密度组成及力学性质的遗传变异规律 .结果表明 ,木材气干密度组成及力学性质在无性系间存在显著或极显著差异 ,并受到中等强度的遗传控制 ;气干密度的径向和纵向变异与多数研究结果一致 ;力学性质除抗弯弹性模量和端面硬度外其株内变异趋势也基本符合木材学理论 .在力学性质指标中 ,抗弯弹性模量和弦面硬度是遗传性很强的性状 ,其无性系重复力分别为 0 90和 0 80 ,抗弯强度、顺纹抗压强度和硬度的无性系重复力稍低 .遗传相关表明对单板材可通过木材密度与干形等形质指标进行优良无性系选择     

Effect of the amount of lignin on tensile properties of single wood fibers

Chemical components are the main factors affecting the mechanical properties of wood fibers. Lignin is one of the main components of wood cell walls and has a critical effect on the mechanical properties of paper pulp and wood fiber based composites. In this study, we carried out tensile tests on single mature latewood tracheids of Chinese fir (Cunninghamia lanciolata (Lamb.) Hook.), using three different delignified treatment methods to obtain different amounts of lignin. We applied single fiber tests to study the effect of the amount of lignin on mechanical tensile properties of single wood fibers at the cellular level. The results show that in their dry state, the modulus of elasticity of single fibers decreased with the reduction in the amount of lignin; even their absolute values were not high. The amount of lignin affects the tensile strength and elongation of single fibers considerably. Tensile strength and elongation of single fibers increase with a reduction in the amount of lignin.     

Mechanical characterization of Pinus massoniana cell walls infected by blue-stain fungi using in situ nanoindentation

Characterizing the mechanical properties of wood cell walls will lead to better understanding and optimization of modifications made to wood infected by the blue-stain fungi.In this study,in situ nanoindentation was used to characterize the mechanical properties of the cell walls of Pinus massoniana infected by blue-stain fungi at the cellular level.The results show that in situ nanoindentation is an effective method for this purpose and that blue-stain fungi penetrate wood structures and degrade wood cell walls,significantly reducing the mechanical properties of the cell walls.The method can also be used to evaluate and improve the properties of other wood species infected by blue-stain fungi.     

Performance of three-layer composites with densified surface layers of Nothofagus pumilio and N. antarctica from Southern Patagonian forests

Nothofagus pumilio and N. antarctica forests of Southern Patagonia, Argentina are currently being managed for production of saw logs with fast growing conditions. The result of these management strategies is faster growing forests, but also an increase in the percentage of low-density wood. The motivation for this study was to find a way to valorise this low-density wood. Surface and bulk densification treatments were applied these wood species and were then applied as face layers in three-layer composites. The mechanical properties of three-layer composites were studied. The modulus of elasticity, modulus of rupture, and modulus of hardness were improved compared to many types of structural composite lumber. This increase in mechanical properties of N. pumilio and N. antarctica wood opens the possibility for its use in structural composites and added value to these otherwise underutilised and undervalued species.     

15年生巨尾桉人工林木材物理力学性质的研究

为了更好开发利用15年生巨尾桉人工林木材,本研究以广西南宁市树木园15年生巨尾桉(Eucalyptus×E.urophylla)人工林木材为研究对象,对其物理以及力学性质进行了测试、分析。结果表明,15年生巨尾桉属中密度等级材,体积干缩系数小;抗弯强度,抗弯弹性模量、顺纹抗压强度和冲击韧性分别为83.9、12790、44.2、65KJ/m2,对应的强度等级分别为2级、3级、1级、2级;端面、弦面和径面的硬度分别为68.9、51.3、55.1MPa,其中端面硬度已经达到了4级标准,弦面和径面的硬度也达到了三级标准。木材综合强度为128.1MPa,属高强度树种;木材的综合品质系数达到了191.2GPa,属于低等级材。     

Determination of formic-acid and acetic acid concentrations formed during hydrothermal treatment of birch wood and its relation to colour, strength and hardness

Formation of benzyl esters from acetic and formic acids during heat treatment of birch at 160–200°C has been studied by gas chromatography. High concentrations of formic and acetic acids formed by the wood itself during hydrothermal treatment were found. The concentrations of acids increased with both treatment time and temperature. The maximum formic- and acetic acid concentrations found at 180°C and after 4 h of treatment performed in this work were 1.1 and 7.2%, based on dry-weight wood, respectively. The treated wood material was characterised by mechanical testing [bending tests perpendicular to the grain, modulus of rupture, modulus of elasticity, Brinell hardness, impact bending and colour measurements (CIE colour space)]. The experiments, where high concentration of acids was formed, showed severe losses in mass and mechanical strength. Indications of possible enhanced mechanical properties for the treated, compared with untreated birch wood were found around 180–200°C at short treatment times. This paper discusses possible degradation reactions coupled with the colour and mechanical properties in relation to acid formation, and suggestions for process optimisations.     

针叶树木材细胞力学及纵向弹性模量的计算--试件纵向弹性模量的预测

依据针叶树木材管胞和射线细胞的结构模型。使用计算机抽样模拟解剖结构参数。以及使用针叶树木材纵向弹性模量计算公式和方法,计算人工林杉木,马尾松幼龄材和成熟材试件纵向弹性模量,计算结果与常温条件下气干试件测定结果十分符合。在试件晚材率和管胞解剖结构参数改变的条件下。计算预测了人工林杉木,马尾松幼龄材和成熟材纵向弹性模量的变化。结果表明：试件纵向弹性模量随晚材率,管胞长度,管胞壁厚度的增加而增加,而试件纵向弹性模量随管胞直径增加而减小。本文提出的纵向弹性模量计算的预测方法,对于运用现代生物技术控制和改变针叶树木材的材质,材性有实际意义。     

人工林杉木木材力学性质对高温热处理条件变化的响应

以人工林杉木为试材,分别用空气和菜子油为介质,在温度为180,200和220 ℃对其分别热处理1,3和5 h,研究试材的抗弯强度(MOR)、抗弯弹性模量(MOE)、顺纹抗压强度、表面硬度对高温热处理条件变化的响应,同时对处理材的主要化学成分进行分析,用扫描电镜对处理材横切面微观结构进行观察.结果表明:人工林杉木试材的4种主要力学性质对不同条件热处理的响应程度不同.无论是空气热处理还是油热处理,试材的MOR,MOE,顺纹抗压强度与对照比有不同程度的降低,且随处理温度升高、时间延长,下降幅度增大,相比于时间,温度的影响更显著;180 ℃热处理1,3和5 h时,试材的MOR,MOE与对照比未发生明显变化(降幅在3%以内),而顺纹抗压强度则明显低于对照,两介质中降低幅度分别在3.29%～9.58%和3.89%～7.18%;200 ℃以上处理时,不同时间处理的3种主要力学性质不仅显著或极显著低于对照,且各性质问的差异也达显著或极显著水平;对硬度的测试结果表明:180 ℃热处理时,试件的径面硬度和弦面硬度均随时间的延长而增大;200 ℃热处理3 h时,试件的硬度达最大,与对照差异达显著水平;随后热处理试件的硬度开始降低,220 ℃热处理5 h后试件的硬度又明显低于对照.在隔氧的油介质中进行热处理,4种主要力学性质的变化程度低于空气介质处理材,当温度高于200 ℃时,两介质处理间的差异达显著水平.而热处理过程中木材主要化学组成与横切面微观结构变化的差异,反映了4种主要力学性质对不同条件热处理时表现出的响应差异.     

培育措施对人工林樟子松木材力学性质的影响

研究了不同培育措施(初植密度、间伐强度、坡向、坡位)对人工林樟子松(Pinus sylvestris var.mongolica)木材的密度和力学性质(横纹抗弯强度、抗弯弹性模量、顺纹抗压强度、冲击韧性、端面硬度)的影响。初植密度(1.5m×1.0m,1.5m×2.0m和1.5m×2.5m)对木材密度和抗弯弹性模量有显著的影响。初植密度为1.5m×1.0m时,木材主要力学指标值最大。适当间伐可提高木材的抗弯弹性模量和顺纹抗压强度,但重度间伐则会降低木材的力学强度。坡向(阳坡和阴坡)对木材的抗弯弹性模量影响显著,阳坡高于阴坡。坡位(上坡位和下坡位)对除端面硬度外的木材力学性质指标影响都显著,各项力学指标值均是坡下高于坡上。表5参9。     

不同立地条件香椿人工林木材材质的比较

通过对不同立地条件下香椿人工林木材物理力学性质的测定和比较分析表明:香椿人工林木材密度和干缩性随着立地级的提高而减小;木材顺纹抗压强度、抗弯强度和硬度:Ⅰ级地<Ⅱ级地<Ⅲ级地,抗弯弹性模量、抗劈力、冲击韧性:Ⅱ级地>Ⅰ级地>Ⅲ级地,顺纹抗剪强度:Ⅱ级地>Ⅲ级地>Ⅰ级地。差异显著性t检验表明:香椿人工林木材密度Ⅰ级地、Ⅱ级地、Ⅲ级地间差异不显著。香椿人工林木材干缩性和力学性质指标Ⅰ级、Ⅱ级、Ⅲ级地3者间有的指标差异极显著,有的指标差异显著,大部分指标差异不显著。     

异叶南洋杉木材的物理力学性质研究

采取常规方法对异叶南洋杉木材物理力学性质进行了测定研究,试验结果表明,异叶南洋杉的气干密度、基本密度、绝干密度分别为0.480、0.466、0.4576 g·cm^-3;径向、弦向和体积干缩率平均值分别为2.73%、2.5%和11.25%;干缩系数分别为0.116%、0.095%和0.46%;端面、径面、弦面等三个面的硬度分别为35、18.6和17.7 MPa;顺纹抗压强度平均为36.9 MPa;抗弯弹性模量为9334.36 MPa;冲击韧性为32.63 kg·m^-2;物理力学性质除了体积干缩系数、冲击韧性之外的所有指标都处于第2级,体积干缩系数和冲击韧性分别处于第3级和第1级。