低分子量脲醛树脂浸渍速生杨木工艺初步研究

采用木材真空加压浸渍处理专用设备,较系统地研究了浸渍压力和浸渍时间对杨木增重率的影响规律。结果表明:浸渍压力和时间对杨木增重率有很大影响;在本研究范围内,随着浸渍压力的提高和浸渍时间的延长,增重率呈现先快速增长后趋于平缓的趋势,增重率最高可达到36.6%;从节约时间和能源成本方面综合考虑,选定本试验的优化浸渍工艺为浸渍压力1.0 MPa、浸渍时间2 h。     

Improvement of dimensional stability and weatherability of composite board made from water-vapor-exploded wood elements by liquefied wood resin impregnation

High-density and high-resin-content boards were produced by phenolic resin impregnation into board materials prepared by the water-vapor-explosion process (WVE) to develop high-durability wood composite boards for exterior use. Wet-dry cyclic tests and accelerated weathering tests were conducted, and the fundamental properties were determined to examine the effect of resin impregnation on board qualities. Bending and internal bond strength of resin-impregnated boards (I-board) satisfied the criterion for 18-type particleboard described in JIS A 5908. Thickness swelling (TS) after 24-h water immersion was approximately 2%. Resin impregnation improved the dimensional stability of the boards. In wet—dry cyclic testing, TS of I-board was the same as that of plywood. The retention ratio of modulus of rupture of I-board was large; thus, I-board had high bond durability. Color change of I-board was less than that of ordinary particleboard after a 500-h accelerated weathering test. I-Board had lower surface roughness than boards produced by a spray application method (S-board) and higher water repellency, although the difference in resin contents of the face layer was small. Thus, it is suggested that the surface properties and weatherability of I-board were improved by impregnation of phenolic resin. High-density and resin-impregnated boards made from the WVE elements are expected to withstand actual exterior use. Part of this report was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, August 2004     

Acceleration of the cure of phenolic resin adhesives VII: Influence of extractives of merbau wood on bonding

The influence of merbau wood extractives on the gelation rate of a phenolic adhesive and the effects of some cure accelerators on the bond performance of merbau plywood were investigated. The addition of merbau wood extractives slightly increased the gelation rate of the phenolic resin. This increase in the gelation rate was revealed to be due to a fall in the resin pH caused by addition of the extractives. The addition of cure accelerators, sodium carbonate and propylene carbonate, caused a considerable reduction in the hot-pressing time required for the merbau plywood to achieve sufficient bond qualities. Brushing veneer surfaces caused an increase in bond qualities. The combination of the cure acceleration and the surface brushing greatly improved the bondability of merbau wood. The main factor of gluing difficulty is considered to be the poor wettability of the veneer surfaces resulted from the accumulation of migrating extractives.Part of this work was presented at the 47th annual meeting of The Japan Wood Research Society, Kochi, April 3–5, 1997     

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     

Effects of impregnation of simple phenolic and natural polycyclic compounds on physical properties of wood

The impregnation of various simple phenolic and natural polycyclic compounds into wood was investigated from the viewpoints of vibrational property and dimensional stabilizing effect. When simple phenolic compounds were impregnated, the loss tangent (tan ) in the longitudinal direction increased linearly with increasing weight gain. Meanwhile, among the natural polycyclic compounds hematoxylin decreased the tan drastically by impregnation. It was suggested that the five hydroxyl groups and the pyran ring oxygen in the hematoxylin molecule contribute to formation of the crosslinkage-type hydrogen bonds between wood components. The rigidity of hematoxylin molecules may also be important. By impregnation of about 10% catechol, resorcinol, and saligenin, a 40% level of antiswelling efficiency (ASE) was attained, although a significant dimensional stabilizing effect was not observed after impregnation of natural polycyclic compounds.Part of this work has been published as a Rapid Communication inMokuzai Gakkaishi 43(12). It was also presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998     

Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin V: effects of steam pretreatment

This study evaluated the potential of steam pre-treatment for making highly compressed phenol-formaldehyde (PF) resin-impregnated wood at a low pressing pressure. Sawn veneers of Japanese cedar (Cryptomeria japonica) were first subjected to saturated steam at different steaming temperatures (140°-200°C), followed by impregnation with a 20% low molecular weight PF resin aqueous solution resulting in a weight gain of around 50%-55%. Four oven-dried treated veneers were laminated and compressed up to a pressing pressure of 1 MPa at a pressing temperature of 150°C and pressing speed of 5 mm/min, and the pressure was held for 30 min. Steam treatment, causing partial hydrolysis of hemicellulose, accelerated the compressibility of Japanese cedar in the PF resin-swollen condition. As a consequence, a discernible increment in density was achieved at a pressing pressure of 1 MPa due to steam pretreatment between 140° and 200°C for 10 min. It was also found that even a short steaming time such as 2 min at 160°C is sufficient for obtaining appreciable compression of PF resin-impregnated wood. The density, Young’s modulus, and bending strength of steam-treated (200°C for 10 min) PF resin-impregnated wood composite reached 1.09 g/cm³, 20 GPa, and 207MPa, respectively. In contrast, the values of untreated PF resin-impregnated wood composite were 0.87 g/cm³, 13 GPa, and 170MPa, respectively.     

Improvement of wood properties by composite of diatomite and “phenol-melamine-formaldehyde” co-condensed resin

We improved the overall performance of fast-growing poplar by utilizing a low-cost, effective and simple method. The fast-growing poplar was modified by a vacuum-pressure impregnation method with three...     

Changes of chemical composition and crystalline of compressed Chinese fir wood in heating fixation

The changes in relative crystalline, chemical composition and internal structure of compressed Chinese fir wood after different heating fixations were found strictly related to fixation conditions. The compressed wood powders were fixed either by heating at different temperatures all resulting in a 10% recovery, or by incubating at 180℃ for different periods with subsequent recovery levels. Both X-ray diffraction and infrared absorption of those samples have been measured. Relative crystalline increases at early stage of heating fixation, and then decreased gradually. Hemicellulose and lignin decomposition were induced by the fixation process, especially at 180℃, and lignin was degraded actively. Furthermore, absorbed water was lost after heating, but cellulose did not change markedly. Although different fixation pathways can result in the same recovery level, the major chemical reactions underlying them vary, which is consistent with the difference of fixation mechanisms.     

环氧树脂/木质碎料复合材料力学性能

以环氧树脂为胶结材料、不同类型的砂和木质碎料作为集料,利用平板振捣器,采用振实法制备了树脂基木质碎料复合材料.分析环氧树脂用量、木质碎料用量以及砂类型对树脂基木质碎料复合材料的抗折、抗压强度的影响规律.结果表明:试件的最大抗压、抗折强度分别可达5.74和17.16 MPa;在相同胶集比下,试件强度随着木质碎料掺入量的增...     

Mechanism of partial fixation of compressed wood based on a matrix non-softening method

Abstract

Three different mechanisms to explain the partial fixation of the compressive deformation of wood are postulated: non-softening, cross-linking and stress relaxation. This study attempted to fix the compressive deformation of wood by the non-softening mechanism of the cell-wall matrix using acetylation of the cell wall making it more hydrophobic. In this method, partial recovery of compressive deformation by wetting decreased at room temperature as the acetyl content increased. However, almost complete recovery occurred by boiling the compressed wood in water or soaking in acetone. This is due to the ability of boiling water or acetone to soften the cell-wall matrix of acetylated wood enough to enable recovery from compression. It is, therefore, possible to partially fix the compressive deformation of wood, preventing the resoftening of the cell-wall matrix in water.     

Improvement of wood properties by urea-formaldehyde resin and nano-SiO2

In order to improve wood properties of triploid clones of Populus tomentosa, urea-formaldehyde (UF) resin was compounded with nano-SiO₂, coupling agents and flame retardants in different ways to prepare five kinds of modifiers. The poplar wood samples were impregnated with the modifiers and heated to prepare UF-SiO₂-wood composites. The antiswelling efficiency, resistance of water absorption, oxygen index and hardness of the composites were measured. Results show that all of the modifiers reduced water absorption of poplar wood and enhanced flame resistance and hardness. Nano-SiO₂ showed a marked effect in improving the hardness of wood. In addition, all of the modifiers, except UF-C-SiO₂-polymer, improved the dimensional stability of poplar wood. The UF resin and nano-SiO₂ compound improved general properties of poplar wood. __________ Translated from Journal of Beijing Forestry University, 2006, 28(2): 123–128 [译自: 北京林业大学学报]     

Vibrational property changes of spruce wood by impregnation with water-soluble extractives of pernambuco (Guilandina echinata Spreng.)

Sitka spruce (Picea sitchensis Carr.) was treated with water-soluble extractive components of pernambuco (Guilandina echinata Spreng. syn Caesalpinia echinata Lam.) by two methods: impregnation under evacuation using an aspirator and repetitive surface application using a brush. The influence of these treatments on the vibrational properties were examined. The loss tangent (tan ) of the impregnated specimen decreased, up to nearly a half of its original value, with increasing weight gain. It is suggested that the decrease in tan results from impregnation of the extractive components into the amorphous region of cell walls, forming secondary bonds between matrix substances. The surface application of the extractive components, on the other hand, hardly brought about the desirable change in vibrational properties.Part of this work was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997, and the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998     

Impregnation of radiata pine wood by vacuum treatment II: effect of pre-steaming on wood structure and resin content

Radiata pine sapwood and heartwood were dried using high-temperature, conventional-temperature, and air drying schedules with and without pre-steaming. They were then impregnated by vacuum treatment with double-distilled water, toluidine blue, and fluorescein dye. For sapwood, there were only minor differences in uptake between drying methods and when pre-steaming was used. Using microscopy, the primary flow pathways in sapwood were found to be the resin canal network and ray parenchyma cells, which provided conduction without large resistance. In heartwood, uptake was strongly influenced by pre-steaming the green lumber. After pre-steaming heart-wood, there was an increase in uptake from all surfaces but especially from the radial surfaces. Lower extractive contents, disruption of epithelial and ray parenchyma cells, and alteration of the condition of bordered pits were also associated with pre-steaming. It was therefore possible to classify flow paths in radiata pine heartwood five ways, according to uptake values and wood anatomical features.This research was presented in part at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998.     

UF树脂浸注改性橡胶木的物理力学性质

采用尿素-甲醛(UF)共聚树脂浸注处理人工林橡胶树(Hevea brasiliensis)木材,分析树脂增重率(WPG)对各项物理力学性能指标的影响。结果表明:UF树脂浸注对橡胶木的密度、平衡含水率(EMC)、湿胀性和硬度改善明显,并且WPG越大改善效果越好;而对弹性模量(MOE)和冲击韧性影响或高或低,且变化幅度有限;对抗弯强度(MOR)的影响,低WPG时不明显,而在高WPG时提高明显。     

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.     

Deformation fixation,mechanical properties and chemical analysis of compressed <Emphasis Type="Italic">Populus cathayana</Emphasis> wood pretreated by glycerin

In order to find an effective and environmentally friendly method to fix compressive deformation of wood, we determined or measured the recovery ratio, surface hardness, modulus of elasticity (MOE) and the modulus of rupture (MOR) of poplar (Populus cathayana Rehd.) samples pretreated by 40-60% glycerin solutions and then compressed at 160°C for 10-120 min.We analyzed the data statistically by using two-factor analysis of variance.The chemical compositions of thermal treated wood were also analyzed and comp...