Effect of thermomechanical densification on surface roughness of wood veneers

The effect of short-term thermomechanical densification of veneer on the surface roughness and surface anatomical changes in four wood species – alder (Alnus glutinosa Gaertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) – was studied. Veneer sheets were densified at a temperature of 100, 150, or 200°C and at a pressure of 4, 8, or 12 MPa for 4 minutes. Seven roughness parameters such as R_a, R_z, R_q, R_p, R_v, R_sk, and R_ku were determined. Profile surface was recorded using a modified Carl Zeiss ME-10 profile gauging profilometer. Surface anatomical changes of veneer were examined using scanning electron microscopy. The results showed that densification temperature and pressure affect surface roughness of veneer. The surface became smoother, and roughness values decreased significantly (except for R_ku which increased slightly) with increasing temperature and pressure of densification. The effect of temperature on surface roughness changes is more pronounced compared with that of densification pressure. The lowest values of surface roughness were recorded for pine veneer samples followed by alder, birch, and beech samples. These results can be used to provide initial data for adhesive application processes in woodworking industry.     

木质材料激光表面处理研究进展

激光以其能量密度高、运行轨迹自如、方向性好等优点,被广泛用于木质材料切削加工以及表面处理等领域.其中,木质材料激光表面处理,即利用激光热/光电子效应促进材料发生物理、化学变化,以实现改性的目的.笔者对木质材料激光表面处理原理、激光类型与用途以及激光表面处理技术特点与应用领域等内容的研究现状进行了综述与分析.现有研究表明...     

The effect of compression and incision on wood veneer and plywood physical and mechanical properties

ABSTRACT

Drying 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.     

Abrasive wear properties of compressed sugi wood

We examined the abrasive wear properties and the effect of abrasive grain size on the rate of wear when sugi wood (Cryptomeria japonica D.Don), compressed to various densities, was rubbed with abrasive paper. The results showed that the wear resistance of compressed wood increased linearly with the increased compression ratio; and under the condition of a low compression ratio it tended to be higher in comparison with the strength of compressed wood. The critical grain size effect, which can be witnessed during the abrasive wear of metals and plastics, was seen when low pressure was applied to the abrasive material. At higher pressures, the wear rate of the compressed wood increased with grain size, but the critical grain size effect was not observed. The pressure required to create the critical grain size effect was found to be higher than that needed for other types of uncompressed wood with the same yield properties.Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000     

混合组坯对杨木单板层积材弹性常数及力学性能的影响

单板层积材具有结构均匀、强度高等优点,材料、结构、制造工艺等差异对其性能影响显著。以13层22 mm厚全顺纹、2层及3层横纹其余顺纹混合组坯的杨木单板层积材为对象,通过电测法、三点弯曲及拉伸实验,对其主要弹性常数及力学性能参数进行测试,得出以下结论:1)随着横纹层数的增加,顺纹方向的弹性模量下降,横纹方向的弹性模量增加,层积方向的弹性模量先减小后增加,单板层积材的各向异性降低;2)随着横纹层数的增加,静曲强度减小,变异性逐渐增大,进行结构设计时需更多考虑材料的性能稳定性;3)组坯方式对LVL抗拉强度的影响不大,适当增加横纹层板可提高抗拉强度;4)组坯方式对泊松比的影响较大,随着横纹层数的增加,泊松比总体降低,采用纵横混合式组坯可能有利于抵抗由拉、压载荷所造成的材料变形。     

Wettability and adherence of acrylic paints on long and short rotation teaks

ABSTRACT

The quality of finished wood products depends on the quality of its coating layer. An important indicator for evaluating the quality is Adherence of the paint on the wood surface. The purpose of this research was to analyze the effect of wood surface roughness and the viscosity of acrylic paints (pure acrylic and acrylic copolymer) to the wettability and Adherence for long and short rotation teaks. Wood surface with various degrees of roughness was prepared by sanding with abrasive papers of P120, P240, and P360 grits. Different viscosity of the acrylic paints was prepared composition between paint and water (w/w) of 100:0, 90:10, 80:20, and 70:30. The wettability of the acrylic paints on teak wood surfaces was measured using a sessile drop contact angle method with the S/G model. Adherence of the coating layer was measured using a crosscut test. The results showed that the increase in the roughness (Ra) and the decrease in the viscosity of the paints resulted in the increase in the wettability which leads to better Adherence of acrylic paints on the surface of teak woods. The pure acrylic paint generated better wettability and Adherence compared to the acrylic copolymer.     

Radial mechanical properties of high-temperature dried Norway spruce (Picea abies) wood

Abstract

Wood drying experiments were conducted in which the temperature and the drying rate were controlled independently. The mechanical properties of dried wood in radial loading were analysed in relation to drying parameters. Mass loss, due to thermal degradation of the wood structural components, occurred predominantly in slow high-temperature drying processes. Despite the higher mass loss, slowly dried wood showed similar radial strength and stiffness to rapidly dried wood. The formation of irreversible hydrogen bonds (hornification) within the wood structure may compete with the effects of mass loss on the radial mechanical behaviour of wood. However, both the mass loss and the hornification resulted in wood specimens with lower hygroscopicity. Application of slow high-temperature drying to reduce microscopic cell-wall damage, caused by anisotropic shrinkage of cell-wall layers, did not seem to affect the radial mechanical properties of wood. The effects of stress relaxation within the wood cell wall on the mechanical behaviour of wood may be offset by the degradation of structural components along with drying. Radial mechanical properties may be improved by rapid high-temperature drying up to high final dryness.     

Effects of inorganic acid catalysts on liquefaction of wood in phenol

In order to obtain the effects of acid catalysts on wood liquefaction in phenol, we investigated the liquefaction of wood powder from Chinese fir (Cunninghamia lanceolata) and poplar (Triploid Populus tomentosa Carr) in the presence of phenol with the following weak inorganic acids as catalysts: phosphoric acid (85%), sulfuric acid (36%), hydrochloric acid (37%) and oxalic acid (99.5%). Results show that phosphoric acid (85%) and sulfuric acid (36%) are better than the other catalysts. It was found that lower residue ratios can be obtained under defined reaction conditions: phenol/wood ratio is 4, a 10% catalyst based on the weight of phenol, a temperature of 150°C for 2 h and phosphoric or sulfuric acid. The residue ratios are 3.2% and 4.0%, respectively. __________ Translated from Journal of Beijing Forestry University, 2004, 26(5) [译自: 北京林业大学学报, 2004, 26(5)]     

加压因素对杨木单板压缩率和回弹率的影响

以速生杨木的边/心材单板为研究对象,对其进行水热密实化处理,通过单因素试验方法,分别研究了加压温度和加压压力对杨木边/心材单板的压缩率、气干24和48 h的厚度回弹率的影响,初步探讨了各个因素的作用机理.研究发现:各因素水平下,杨木边/心材单板的压缩率和厚度回弹率均呈现出一定的规律性,心材单板的压缩率高于边材单板,但厚度回弹率低于边材单板,且各因素的作用机理有所差异.边/心材单板水热密实化处理的较佳条件均为:加压温度150℃,加压压力5 MPa.     

Fundamental studies on wood/cellulose-plastic composites: effects of composition and cellulose dimension on the properties of cellulose/PP composite

Although wood/cellulose-plastic composites (WPC) of low wood/cellulose content have been more accepted worldwide and are promoted as low-maintenance, high-durability building products, composites containing high wood/cellulose content are not yet developed on an industrial scale. In this study, flow properties, mechanical properties, and water absorption properties of the compounds of cellulose microfiber/polypropylene (PP) and maleic anhydride-grafted polypropylene (MAPP) were investigated to understand effects of the high cellulose content and the dimensions of the cellulose microfiber. The molding processes studied included compression, injection, and extrusion. It was found that fluidity is not only dependent on resin content but also on the dimension of the filler; fluidity of the compound declined with increased fiber length with the same resin content. Dispersion of the composite was monitored by charge-coupled device (CCD) microscope. Increasing the plastic content in the cellulose-plastic formulation improved the strength of mold in addition to the bond development between resin and filler, and the tangle of fibers. The processing mode affected the physicomechanical properties of the cellulosic plastic. Compression-molded samples exhibited the lowest modulus of rupture (MOR) and modulus of elasticity (MOE) and the highest water absorption, while samples that were injection-molded exhibited the highest MOR (70 MPa) and MOE (7 GPa) and low water absorption (2%).     

疏水改性对杉木微观力学性能的影响

为提高木材尺寸稳定性,利用烷基烯酮二聚体对杉木进行疏水改性处理,同时运用纳米压痕技术分析评价疏水处理对木材纳米力学性能的影响.结果表明,当处理剂的质量分数为5％、处理时间为30 min时,疏水效果最好,同时最节约成本;疏水处理会降低杉木S2层细胞壁的弹性模量,当处理剂质量分数为5％时影响较小;杉木S2层细胞壁蠕变值会随处理剂质量分数和处理时间的增加呈现上升的趋势.     

Effects of semi-isostatic densification of wood on the variation in strength properties with density

The variation in strength properties with density was compared between semi-isostatically densified and non-densified wood. Strength properties were compared with published data from earlier studies using other methods for densification. Small clear specimens of eight species were analysed for compression strength in axial, radial and tangential direction, three-point bending and Brinell hardness. After densification, all tested strength properties increased with density, but especially strength perpendicular to grain became lower than expected from the density of non-densified wood. Strength of densified wood relative to what could be expected for non-densified wood of similar density was denoted as ‘strength potential index’. For axial compression strength and bending strength, strength potential index of individual wood species varied between 0.7 and 1.0, i.e. densified wood is slightly weaker than what could be expected from its density. Strength potential index was lower for properties much determined by strength perpendicular to grain. In radial direction, densified wood was rubbery with low modulus of elasticity and nearly no proportional limit or modulus of rupture. Generally, wood was apparently weakened in proportion to the degree of compression in respective direction. Strength potential index also increased with increasing original density of the species.     

竹木复合中密度纤维板工艺条件的研究

研究了竹木纤维混合比、空比和纤维筛分值工艺条件对木复合中密度性能的影响。结果表明，在合适的工艺条件下，可以生产出具有优良性能的竹木复合中密度纤维板。竹木复合中密度纤维板的静曲强度、弹性模量和吸水厚度膨胀率随竹木纤维混合比的增大而增大；而平面抗拉强度在０／１～１／１范围内随竹木纤维混合比加大模量和吸水厚度膨胀率随竹木纤维混合比为１／１时，ＩＢ最小。板的静曲强度、弹性模量、平面抗拉强度和吸水厚度膨胀率     

Variations in compression strength and surface roughness of heat-treated Turkish river red gum (Eucalyptus camaldulensis) wood

This article reports the effects of heat treatment on compression strength parallel to the grain, the surface roughness [average roughness (R_a)], and the air-dry den-sity of wood from the river red gum tree (Eucalyptus camaldulensis Dehn.) planted in Turkey. Eucalyptus wood was heat-treated at temperatures varying from 120° to 180°C for durations of 2–10 h. Samples cut from the heat-treated wood were tested for air-dry density, compression strength parallel to grain, and surface roughness properties. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Based on the findings in this study, the results showed that density, compression strength, and surface roughness values decreased with increasing treatment temperature and treatment times. Eucalyptus wood could be utilized by using proper heat treatment techniques without any losses in strength values in areas where working, stability, and surface smoothness, such as in window frames, are important factors.     

The influence of silane coupling agent and poplar particles on the wet-tability,surface roughness,and hardness of UF-bonded wheat straw （Triticum aestivum L.）/poplar wood particleboard

We used silane coupling agents to improve the bonding ability between wheat straw particles and UF resin, and investigated surface properties （wettability and surface roughness） and hardness of parti-cleboard made from UF-bonded wheat straw （Triticum aestivum L.） combined with poplar wood as affected by silane coupling agent content and straw/poplar wood particle ratios. We manufactured one-layered particleboard panels at four different ratios of straw to poplar wood par-ticles （0%, 15%, 30% and 45% wheat straw） and silane coupling agent content at three levels of 0, 5% and 10%. Roughness measurements, average roughness （Ra）, mean peak-to-valley height （Rz）, and root mean square roughness （Rq） were measured on unsanded samples by using a fine stylus tracing technique. We obtained contact angle measurements by using a goniometer connected to a digital camera and computer sys-tem. Boards containing greater amounts of poplar particles had superior hardness compared to control samples and had lower wettability. Panels made with higher amounts of silane had lower Rq values.     

Effect of thinning on the development of compression wood in stems of Corsican pine

This study considered the effects of thinning on the development of compression wood in stems of 35-year-old stand of Corsican pine (Pinus nigra L.). Part of the stand had been thinned at 5-yearly intervals and part left unthinned. Twenty trees each from the thinned and unthinned stands were randomly selected and felled. Measurements were made on tree height, stem diameter, stem slenderness and canopy depth. Wood samples were removed from the central part of the main log and cross-sectional measurements made on ring width, basic density and compression wood content. Cross-sectional area of compression wood was found to be three time higher in stems from the unthinned trees in comparison with those from the thinned trees. No significant differences in mean radial ring width or basic density were found between treatments. Correlations indicated that, with increasing in stem diameter, compression wood content increased in the unthinned trees, while a decline in compression was observed in the thinned trees. Tree height was also positively correlated with compression wood content in unthinned trees, while no equivalent relationship was observed in thinned trees. Observations from this study, while not conclusive, suggest that phototropic stimulus may be producing stem inclinations in the unthinned stand as trees compete for space in the canopy, whereas crown competition has been largely eliminated in the thinned stand; and that this is responsible for compression wood levels recorded in this study.     

Role of the gelatinous layer on the origin of the physical properties of the tension wood

To discuss the role of the gelatinous layer (G-layer) on the origins of the physical properties peculiar to the tension wood fiber (TW fiber), the deformation process of an isolated TW fiber caused by a certain biomechanical state change was formulated mathematically. The mechanical model used in the present formulation is a four-layered hollow cylinder having the compound middle lamella (CML), the outer layer of the secondary wall (S1) and its middle layer (S2), and the G-layer (G) as an innermost layer. In the formulation, the reinforced matrix mechanism was applied to represent the mechanical interaction between the cellulose microfibril (CMF) as a framework bundle and the amorphous substance as a matrix skeleton in each layer. The model formulated in the present study is thought to be useful to investigate the origins of extensive longitudinal drying shrinkage, large tensile growth stress, and a high axial elastic modulus, which are rheological properties peculiar to the TW. In this article, the detailed process of the mathematical formulation is described. In a subsequent article, some TW properties from a 70-year-old Kohauchiwakaede (Acer sieboldianum Miq.) will be analyzed using the newly developed model.     

STUDIES ON PHYSICAL AND MECHANICAL PROPERTIES OF DAHURIAN LARCH-WOOD OF TWO WOOD COLOURS

Dahurian1arch[Larixgmelini(Rupr.)Rupr.jisamaintimbertreespe-ciesinDaxing'anLingForestRegion,and'itisalsoafast-growingandregenerationtreeinNorthChina-Becauseitsecologicalamplitudeisverywild,therearemanyva-riabletypesinvarioushabitats.Themostsignificativetypes,whichhavebeenfoundrecentlyininvestigation,aretheredwoodandwhitewood.Theformerisfromyellow-browntored-brown,andthelat-tCrisfrompaleyellowtowhite.Theyaresimilarto'Redscotchpine#and'Whitescotchpine#.Theparametersofwoodcol-ourandphysico-…     

糠醇化对橡胶木性质的影响

以平衡含水率(EMC)和线性湿涨系数(LSC)为评价指标,研究了不同质量增加率(WPG)的糠醇改性对橡胶木吸湿尺寸稳定性的影响,并从尺寸稳定性角度探讨糠醇改性的临界WPG;还分析了糠醇改性对抗弯强度(MOR)和抗弯弹性模量(MOE)的影响,并探讨了减量平衡含水率(EMCR)衡量浸渍改性材吸湿性的可行性.结果表明:糠醇化可以显著降低橡胶木的EMC和LSC,EMC受WPG的影响明显,LSC随着WPG的增加而显著下降,基于LSC和胞壁充涨系数推导的临界WPG两者之间存在较大误差;改性材的MOE随WPG提高而增加,增幅约在30％ ～40％,但MOR却略有下降;与基于浸渍材绝干质量的EMC相比,基于浸渍前绝干质量的EMCR能更客观地评价浸渍改性后木材的吸湿能力,可用于吸湿性的研究中,但鉴于用户和第三方检测不方便,不推荐其作为改性产品的评价指标.     

珍稀速生树种翅荚木栽培技术研究

对湖南翅荚木人工林进行了生长测定。结果表明：翅荚木在湖南丘陵红壤土年均胸径生长量可达2．0cm以上，年均树高生长量可达1．5m以上，蓄积年生长量为16．1m^3／hm^2以上。对翅荚木材性进行了分析与比较，木材密度为0．314g／cm^3，5a生翅荚木纤维长度1010μm，纤维宽度19．6μm，纤维长宽比为52。其木材材性与杨树、桉树相比十分接近。因此，翅荚木是一优质纸浆原料。由于其生长快，又可作为胶合板、家具用材定向培育。提出了相应的苗木培育与造林技术，并建议今后加强翅荚木优树选择、子代测定、良种基地建设等遗传改良的力度，加强其栽培技术研究，为我省营造翅荚木人工林提供技术支撑。