Influence of the thermo-hydro-mechanical treatments of wood on the performance against wood-degrading fungi

Hybrid poplar (Populus deltoides × Populus trichocarpa) and Douglas-fir (Pseudotsuga menziesii) wood specimens were densified with three variations of thermo-hydro-mechanical (THM) treatment. The THM treatments differed in the steam environment, including transient steam (TS), saturated steam (SS), and saturated steam with 1-min post–heat treatment at 200 °C (SS+PHT). The bending properties, FTIR spectra, and colour of the THM wood specimens were studied before and after exposure to two different wood decay fungi, brown rot Gloeophyllum trabeum, and white rot Trametes versicolor. The results showed that the performance of densified hybrid poplar wood was considerably poorer than the performance of Douglas-fir heartwood. The FTIR spectra measurements did not show changes in the densified hybrid poplar wood, while some changes were evident in densified Douglas-fir specimens. After fungal degradation, the most prominent changes were observed on the SS+PHT specimens. Colour is one of the most important parameter predominantly influenced by the wood species and the intensity of the densification process for both wood species, while after fungal exposure, the colour of all densified Douglas-fir specimens obtained more or less the same appearance, and densified hybrid poplar specimens resulted in lighter colour tones, indicating that the pattern of degradation of the densified and non-densified specimens are similar. The 3-point bending test results determined that the THM treatment significantly increased the modulus of rupture (MOR) and modulus of elasticity (MOE) of the densified wood specimens, while fungal exposure decreased the MOE and MOR in hybrid poplar and Douglas-fir specimens.     

酚醛树脂密实化杨木的机械加工性能研究

以水溶性低分子量酚醛树脂处理人工林杨木板材,参考ASTM标准,并结合国内实木地板的生产工艺,对处理前后板材的横截、刨切、榫槽加工和砂光性能进行评价.结果表明:经过处理后,杨木板材的各项加工性能均得到明显改善,加工缺陷明显减少,表面光洁度和平整度明显好于未处理材,适合用于制造实木地板.     

浸渍塑化杨木单板顺纹弯曲性能研究

本研究以酚醛树脂为浸渍液,杨木单板为木材试样,对经浸渍塑化处理的杨木单板进行三点弯曲试验,探索了木/竹复合层合板的组分材料--塑化杨木单板受不同压力时的顺纹弯曲弹性性能,并分析了其与塑化压力间的关系.结果表明,塑化杨木单板的静曲模量和静曲强度与塑化压力呈非线性关系.通过对杨木单板试验研究,为木材/竹材复合材料制造过程中的结构设计和生产工艺提供一定的理论依据和基本思路,并对产品的设计、组织现场生产和产品质量评估提供一定的参考.     

A feasibility study of using two-component polyurethane adhesive in constructing wooden structures

This investigation was conducted to determine the feasibility of using a two-component polyurethane （PUR） adhesive, with special waterproof properties, in constructing wooden structures. We designed and conducted tests to compare the shear strength and adhesion performance of PUR with polyvinyl acetate （PVAc） adhesive on block-shear specimens constructed of oriental beech （Fagus orientalis L.）, fir （Abies alba Mill.）, poplar （Populus deltoides Bartr.）, white oak （Quercus alba L.）, sycamore （Platanus orientalis L.） and white walnut （Juglans cinerea L.）. The values of the percentage of wood failure were also determined in specimens constructed with each adhesive. The highest shear strength values of both adhesives were obtained in specimens constructed of beech, while the lowest shear strength values were obtained in fir and poplar specimens. Average shear strength of the PUR adhesive was 16.5% higher than that of the PVAc adhesive. Specimens constructed of fir, poplar and sycamore were characterised by the highest percentages of wood failure, whereas the lowest average percentages of wood failure were obtained in beech and oak specimens. With the exception of oak specimens, there was no statistically significant difference between percentage of wood failure among the PUR and PVAc adhesives. Generally, the PUR adhesive showed an acceptable adhesion performance on wood materials used in our study.     

重组竹制造工艺的研究

本文是作者在施胶量、热压温度和热压时间三个主要因子对重组竹性能影响的初步研究基础上又进一步探讨了施胶方式、竹纤维束水洗、胶种以及胶的浓度等因素对产品性能的作用。研究结果表明:竹纤维束水洗有较显著的作用;水溶性酚醛胶比醇溶性酚醛胶更适用于重组竹的制造,胶液浓度过稀不仅自身性能差,而且还会使重组竹性能降低;采用浸胶方法虽有利于胶液的均勻分布,但对IB未产生明显的作用。     

Effects of densification on untreated and nano-aluminum-oxide impregnated poplar wood

Effects of densification of poplar wood (Populus nigra) impregnated with nano-aluminum oxide (NA) and pre-treated with water vapor for 4 and 6 h were investigated in the present study. Physical and mechanical properties of treated poplar wood were measured according to the ASTM D-143 standard specifications, and then compared with the untreated specimens. Results showed significant improvement in all properties as a result of densification. A 4-h vapor pre-treatment improved effects on both physical and mechanical properties. When the duration of vapor-treatment increased to 6 h, wood polymers degraded to the extent that the improvements due to the vapor pre-treatment decreased substantially, though the final results were still significant improvements compared with the control specimens. High thermal conductivity coefficient of NA slightly but not significantly improved properties. Due to the high spring-back after 15 days, densified poplar is not recommended for applications in which densified wood will be exposed for long periods to high humidity or to direct water.     

Compression of wood under saturated steam, superheated steam, and transient conditions at 150°C, 160°C, and 170°C

In this paper, the compressive deformation of hybrid poplar wood (Populus deltoides?×?Populus trichocarpa) at high temperature (150, 160, and 170°C) and under various conditions of steam pressure was studied. Temperature and conditions of steam environment affected the relative density change and creep deformation during compression, as well as properties of the resulting densified material. While the temperature significantly affected the compression deformation of specimens compressed under transient and superheated steam conditions, temperature within the range studied had little effect on the compressive deformation in saturated steam. In all tested conditions, compression deformation was achieved without cell wall fractures. Higher temperature of compression, regardless of steam condition, resulted in lower equilibrium moisture content. In specimens compressed under saturated steam, the modulus of rupture (MOR) and modulus of elasticity (MOE) were increased proportionally to the increase in density, while the compression under superheated steam produced lower increase in the MOE and MOR than expected based on the increase in density. Compression in transient steam conditions at 170°C produced densified wood with higher MOE and MOR than expected based on the increase in density.     

杨木材性对酚醛树脂浸渍改性材的影响

采用低分子量酚醛树脂对速生杨木进行浸渍处理、干燥定型,使树脂固化制得改性材。试验表明：低分子量酚醛树脂对杨木具有较好的浸注性,改性材的密度和力学强度均有明显的提高,两组试件改性后浸注性和密度相差不大,但前期经过热水处理的试件改性后密度相对均匀,力学强度略好于直接浸渍的试件。杨木自身材性对改性后物理力学性能的影响各不相同,在实际生产中要根据指标的重要性程度选取最佳方案。     

PF树脂浸渍ACQ防腐杨木的基本特性

采用低分子量酚醛树脂对ACQ防腐后的速生杨木进行浸渍处理、干燥定型后制得改性材.试验表明,ACQ防腐处理对酚醛树脂的浸渍没有影响,PF树脂对杨木具有较好的浸注性,但不同杨木试件的浸注性差异较大.通过分析杨木自身材性及试件不同尺寸与增重率的关系,发现不同的杨木树株和木材纹理对杨木浸注性有显著的影响.     

Adhesive penetration in beech wood: experiments

A study with synchrotron radiation X-ray tomographic microscopy (SRXTM) of PUR, PVAc, and UF adhesive bond lines in beech wood, bonded under various growth ring angles, is presented. The bond line morphologies and the adhesive penetration into the wood structure were evaluated after determining the hardening characteristics of the adhesives. Distinct bond line imperfections were found for the different adhesive systems. To describe the adhesive distribution inside the bond line, the saturation of the pore space instead of the commonly used maximum penetration depth seems to be adequate.     

Microstructure of viscoelastic thermal compressed (VTC) wood using computed microtomography

The paper describes for the first time the analysis of the structure of compressed wood using computed tomography. The anatomical structures of Douglas-fir and hybrid poplar before and after densification with the viscoelastic thermal compression (VTC) process were described by pore size distributions and mean pore sizes and compared. The compression of Douglas-fir mainly affected earlywood, while the compression of hybrid poplar mainly occurred in the vessels. In both wood species, the densification resulted in a significant decrease in the pore volumes. The porosity decreased to less than half of the original value for Douglas-fir earlywood and to approximately one-quarter for the vessels in hybrid poplar. The relevant mean pore sizes also decreased dramatically to about one-quarter compared to the original values. In contrast, latewood in Douglas-fir and libriform fibers in hybrid poplar are quite stable under compression. Douglas-fir latewood retained its original structure after compression and did not show any reduction in pore size. The results confirmed that the anatomical structure of VTC densified wood can be described by pore size distributions and mean pore sizes. However, in the case of broad or bimodal distributions, the mean pore sizes are of less significance.     

LARCH BARK TANNIN ADHESIVE FOR EXTERIOR PARTICLEBOARD

INTR0DUCTI0NChinaisacountrywhichhasnotade-quateforestresources.Itsforestcoverson-lyaboutl3%ofthewh01ecountry.Inor-dertomeetthedevelopmentofnationaleconomy,wemustmakegreateffortstodevelopman-madepanelindustryandmoreefficientlyusetheforestresources.Inthepresent,becauseoftheshortsupplyofchemicalmaterials,thepriceofphenolinthemarketcontinuestogoupwhichledtheincreaseofadhesivemanufacturecost.Findingnewphenolicmateria1sinplaceofphenolisaneffectivemethodtoreducetheadhesivecost.Vegetab1etanninsar…     

Reducing set-recovery of compressively densified poplar wood by impregnation–modification with melamine–formaldehyde resin

ABSTRACT

Densification of resin impregnated wood under hot-pressing is a method that along with the potential for the reduction of set-recovery could additionally increase the density of wood and further improve other technical properties. In this study, the effect of the methylated melamine-formaldehyde modification on the shape memory effect of densified Populous nigra wood at various compression ratio levels was investigated. Furthermore, the effects on moisture content and compression ratio were also assessed. The most important conclusion drawn was that MF can act as a means for reducing set-recovery of compressed poplar wood since it is obvious that the use of MF significantly improved the stability of densified wood due to the formation of new bonds between cell wall components and MF. In the case of densification under stress of 10?kg/cm², the stabilization was improved by the use of MF to about 50% compared to water-treated specimens. The effect of MF on the stabilization of densified wood was not very clear for stresses higher than 10?kg/cm² since due to the outflow of MF solution during the first minutes of compression.     

低分子量酚醛树脂与阻燃剂复配改性大青杨木材的研究

用低分子量酚醛树脂分别与阻燃剂ＦＲＤＬ－１１２或硼酸复配改性大青杨木材的研究表明,ＰＦ树脂与ＦＲＤＬ－１１２复配使用时的渗透性优于与硼酸复配;对处理材的顺纹抗压强度和硬度有降低作用,但与未处理素材相比仍有提高,与硼酸复配对处理材的阻湿性和抗胀缩性能有较大负面影响。阻燃效果是ＦＲＤＬ－１１２明显优于硼酸;与ＦＲＤＬ０－１１２复配可处理材的防腐能力下降,与硼酸复配处理材的防腐效果优于单纯的酚醛树脂处理     

Shear fracture characterization of green-glued polyurethane wood adhesive bonds at various moisture and gluing conditions

Abstract

The shear fracture properties of green-glued one-component polyurethane (PUR) wood adhesive bonds subjected to kiln drying were investigated. The local shear strength and fracture energy of the wood adhesive bonds were determined from experimentally recorded complete shear stress versus deformation curves of the bond line. A stable test set-up and small specimens that were anti-symmetrically loaded were used in order to get a uniform and pure state of shear stress. Different moisture contents (MCs) and pressing times were investigated. The fracture properties of conventionally dry-glued wood adhesive bonds and of solid wood were used as reference. The results show that the fracture energy of green-glued bonds with PUR adhesive is dependent on the MC of wood and on the pressing time. The same fracture energy and strength can be obtained by green gluing as by dry gluing, but there seems to exist a maximum MC of sapwood, in the range between 78% and 160%, and a minimum pressing time, in the range between 3 h and 48 h, for which it can be achieved. Both dry- and green-glued polyurethane adhesive bonds were more ductile than solid wood.     

Comparative analysis of a wood: adhesive bondline

The wood–adhesive interface was analyzed using five methods with the objective of quantitatively assessing penetration of adhesive into the porous wood network. Methods included fluorescence microscopy, scanning electron microscopy, backscatter electron imaging, wavelength dispersive spectroscopy, and X-ray microtomography (XMT). Each method provided a visual inspection, and all of the analysis methods were applied to the same field of view. XMT was the primary technique of interest. Rubidium hydroxide was used in place of sodium hydroxide in the formulation of phenol–formaldehyde adhesive. Rubidium was found to increase the X-ray attenuation of the adhesive. However, rubidium migrated beyond the adhesive interphase during specimen preparation, thus reducing its effectiveness for image contrast enhancement. The wood species studied included red oak (Quercus rubra), Douglas-fir (Pseudotsuga menziesii), and hybrid poplar (Populus deltoides × Populus trichocarpa). All techniques used for this study were useful, but each presented some limitations for bondline analysis. Despite the problem with rubidium migration, XMT for this application was promising.     

喷蒸真空热压对水溶性PF胶在杨木大片刨花中的渗透及对板性能的影响

反射荧光显微镜可观察水溶性酚醛树脂胶（ＰＦ）在杨木大片刨花中的渗透情况。通过显微观察及板内结合强度测试,结果表明,蒸汽冷凝水对水溶性ＰＦ树脂胶有稀释作用,改变胶的流动和渗透性能。采用喷蒸真空热压工艺时,须对水溶性ＰＦ胶进行改性,ＰＦ的分子量要大于传统工艺所要求的分子量,而且有必要采用适当的喷蒸保持时间     

药剂种类和浓度对杨木强化改性效果的影响

以杨木板材为研究对象,选择不同浓度的酚醛树脂胶粘剂、异氰酸酯胶粘剂、硅溶胶／苯丙乳液试剂为浸渍药剂,利用真空压力装置,对杨木板材进行加压浸渍强化改性,并利用扫描电镜分析木材的微观结构。研究表明,浓度35％的酚醛树脂（PF）、浓度25％的异氰酸酯（PAPI）及浓度25％的苯丙乳液配比方案较优;3种药剂处理后的杨木强化效果优异程度为：异氰酸酯（PAPI）〉酚醛树脂（PF）〉硅溶胶／苯丙乳液。     

Adhesive performance of woods treated with alternative preservatives

The extended use of woods treated with traditional or alternative preservatives for exterior applications requires an assessment of wood adhesive performance. This study attempts to evaluate the performance of wood adhesives for woods treated with various waterborne preservatives. Two softwood species, i.e. Korean pine (Pinus koraiensis Sieb. et Zucc.) and Japanese Larch (Larix leptolepis [Sieb. et Zucc.] Gordon) were treated with copper–chrome–arsenic (CCA), CB-HDO, or copper azole (CY), and then bonded with four different wood adhesives such as urea–melamine–formaldehyde (UMF) resin, melamine–formaldehyde (MF) resin, phenol–formaldehyde (PF) resin, and resorcinol–formaldehyde (RF) resin. The performance of these adhesives was evaluated by measuring the dry shear strength of adhesive-bonded wood block on compression. Both UMF and MF resins produced a relatively strong adhesive strength for CY-treated pine and larch woods. The PF resin also produced good bond strength when bonded with either larch wood treated with CY or pinewood treated with CB-HDO. The best result was obtained when the CB-HDO-treated woods were bonded with RF resin. For a better bond strength development, a proper combination of adhesive, preservative, and wood species should be selected by taking into consideration of the characteristics of these three parameters as well as their interactions.