Preparation and properties of waste tea leaves particleboard

Urea-formaldehyde (UF) adhesive is the main source of formaldehyde emission from UF-bonded boards. The components in waste tea leaves can react with formaldehyde to serve as a raw material in the production of low formaldehyde emission boards. In our study, waste tea leaves and UF adhesive were employed in the preparation of waste tea leaves particleboard (WTLB). An orthogonal experimental method was applied to investigate the effects of process parameters on formaldehyde emission and mechanical properties of WTLB. The results indicated that: 1) waste tea leaves had the ability to abate formaldehyde emission from boards; and 2) density of the WTLB was a significant factor affecting its modulus of rupture (MOR), modulus of elasticity (MOE) and internal bonding (IB).     

The effect of urea pretreatment on the formaldehyde emission and properties of straw particleboard

For manufacturing low-formaldehyde emission particleboard from wheat straw and urea-formaldehyde (UF) resins using urea treatment for indoor environments, we investigated the influence of urea treatment on the formaldehyde emission, physical and mechanical properties of the manufactured particleboard. Wheat straws were treated at three levels of urea concentration (5%, 10%, 15%) and 95℃as holding temperature. Wheat straw particleboards were manufactured using hotpress at 180℃and 3 MPa with two types of UF adhesive (UF-45,UF-91). Then the formaldehyde emission values, physical properties and mechanical properties were considered. The results show that the formaldehyde emission value was decreased by increasing urea concentration. Furthermore, the results indicate that the specimens under urea treatment have better mechanical and physical properties compared with control specimens. Also specimens under urea treatment at 10% concentration and UF-91 type adhesive have the most optimum physical and mechanical strength.     

Effect of log position in European Larch (Larix decidua Mill.) tree on the technological properties of particleboard

The impact of log position in European Larch (Larix decidua Mill.) tree on the physical, mechanical, and surface properties of the particleboard was investigated. The logs were divided into five segments from the butt to the top of tree, which were 0–3 m, 3–6 m, 6–9 m, 9–12 m, and 12–15 m, respectively. The fiber length and wall thickness of the wood decreased with the increase in the tree height while the lumen diameter decreased. Similarly, the amount of cellulose and lignin decreased with the increase in tree height while the amount of hemicelluloses increased. The highest solubility values (hot and cold water, NaOH, and alcohol-benzene) and pH of the wood were found in the butt log, followed by the middle log, and top log, respectively. The physical (thickness swelling, water absorption) and mechanical properties (modulus of rupture, modulus of elasticity, and internal bond), and surface quality (surface roughness and contact angle) of the particleboards were negatively affected by increasing tree height. The best properties were obtained for the particleboards produced from the particles of the butt log (0–3 m).     

Physical and mechanical properties of particleboard from roselle (Hibiscus sabdariffa) stalks and eucalyptus (Eucalyptus camaldulensis) wood particles

Abstract

The objective of this work was to evaluate the performance of particleboard manufactured from roselle (Hibiscus sabdariffa) stalks and eucalyptus (Eucalyptus camaldulensis) wood. The manufacturing parameters were various roselle (Hibiscus sabdariffa) ratios in the mixture (0, 25, 50, 75 and 100%) and press time (3, 5 and 7 min). Modulus of elasticity (MOE), modulus of rupture (MOR), internal bonding (IB) strength values and thickness swelling (TS) after 24-hour water soaking of the panels were determined according to the procedure of European Union (EN) Standard. The results of the study demonstrate that roselle stalks can be an alternative raw material source for particleboard industry. With an increase of roselle particles from 0% to 100%, the TS was reduced, and the IB, MOR and MOE were increased. The highest MOE, MOR, IB strength and TS values of the samples were found as 2754.18, 16.81, 0.89 N/mm² and 15.26% for the panels made using 100% roselle with a 7-min press time, respectively.     

Effects of press closing time on mat consolidation behavior during hot pressing and on linear expansion of particleboard

Mat consolidation behavior was investigated at various press closing times (PCTs) using hinoki (Japanese cypress) particle mats. The temperature in the core layer of the mat, press pressure, and platen distance were measured. At the plateau stage during hot pressing, the core temperature decreased with increasing PCT. The core temperature did not increase before the platen distance equaled the target board thickness in the PCT range of 4–50 s and rose slightly when the PCT exceeded 100s. There was a linear relation between the logarithm of PCT and the maximum press pressure. The density profile across board thickness was strongly affected by the PCT. As the PCT increased, the position of the peak density (PD) moved toward the core layer as the PD itself decreased. The effect of PCT on the linear expansion (LE) of the board is discussed in relation to the density profile. There was no difference in LE after high relative humidity treatment in the PCT range 4–50s. LE appeared to be related to the low density and the precured region of the board surface. The LE after drying treatment was around –0.1%, and the thickness swelling after high relative humidity and drying treatments increased with increasing PCT.Part of this report was presented at the 51st Annual Meeting of the Japan Wood Research Society, Tokyo, April 1988     

Micromorphology,moisture sorption and mechanical properties of a biocomposite based on acetylated wood particles and cellulose ester

Abstract

One of the major issues in a long-term perspective for the use of wood–plastic composites (WPCs) in outdoor applications is the moisture sensitivity of the wood component and the consequent dimensional instability and susceptibility to biological degradation of the composite. In this work, the effects of using an acetylated wood component and a cellulose ester as matrix on the micromorphology, mechanical performance and moisture uptake of injection-moulded WPCs have been studied. Composites based on unmodified and acetylated wood particles, specially designed with a length-to-width ratio of about 5–7, combined with both cellulose acetate propionate (CAP) and polypropylene (PP) matrices were studied. The size and shape of the wood particles were studied before and after the processing using light microscopy, and the micromorphology of the composites was studied using a newly developed surface preparation technique based on ultraviolet laser irradiation combined with low-vacuum scanning electron microscopy (LV-SEM). The water vapour sorption in the composites and the effect of accelerated weathering were measured using thin samples which were allowed to reach equilibrium moisture content (EMC). The length-to-diameter ratio was only slightly decreased for the acetylated particles after compounding and injection moulding, although both the unmodified and the acetylated particles were smaller in size after the processing steps. The tensile strength was about 40% higher for the composite based on acetylated wood than for the composite with unmodified wood using either CAP or PP as matrix, whereas the notched impact strength of the composite based on acetylated wood was about 20% lower than those of the corresponding unmodified composites. The sorption experiments showed that the EMC was 50% lower in the composites with an acetylated wood component than in the composites with an unmodified wood component. The choice of matrix material strongly affected the moisture absorptivity of the WPC. The composites with CAP as matrix gained moisture more rapidly than the composites with PP as matrix. It was also found that accelerated ageing in a Weather-Ometer® significantly increased the moisture sensitivity of the PP-based composites.     

Response of beech and oaks to wounds made at different times of the year

Tree care, especially pruning, is still mostly done in the dormant time. Such treatments expose live inner bark, the vascular cambium, and functioning outer sapwood to harsh external influences followed often by infection of pathogens. Investigations about response reactions of beech and oak to wounding made in different times of the year showed that wound closure was significantly slower for December and February wounds than in April and October. The length of discoloured sapwood was in October and December wounds greater than in February and April. Sapwood reaction expressed by the soluble phenol concentration index indicated however no significant differences among wounding dates. Overall, woundings in the vegetation period will be more effectively compartmentalized than in the dormant season. Consequently, tree care like pruning with many woundings should not be done in the winter period.Presented at the 6th ISA European Conference, 9.-12. June 2004, Maastricht, The Netherlands     

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.     

油浴热处理对竹材干缩性和力学性能的影响

为了探明竹材独特结构和油浴热处理对竹材干缩性和力学性能的协同影响,本研究以机油为导热介质对毛竹进行油浴热处理,分析了不同热处理温度（150、180、210℃）和不同处理时间（1、3、5 h）条件下竹材干缩性及力学性能的变化情况。结果表明：经过热处理后,竹材含水率和横向干缩率均有下降,表明高温热处理克服了竹材亲水性强和干缩性差的缺点。但是经过热处理后,竹材的力学性能总体呈下降趋势。在同样的热处理条件下,带青带黄竹材的物理力学性能均高于去青去黄竹材,说明保留竹材的竹青竹黄对热处理十分有利,且同时能提高竹材的利用率。     

真空热处理改性马尾松木材物理性能研究

文章采用间歇抽真空法及利用木材自身含有的水分对马尾松木材进行热处理,并研究了热处理温度和时间对马尾松木材的尺寸稳定性（ASE值）和力学性能的影响。结果表明：处理温度和时间均显著影响着木材的力学强度和ASE。综合考虑处理温度和处理时间对ASE、顺纹抗压强度和抗弯强度的影响,较佳的真空热处理工艺为：压力-0.09 Mpa、处理温度200℃,处理时间1 h。     

Utilisation of wood biomass residues from fruit tree branches,evergreen hardwood shrubs and Greek fir wood as raw materials for particleboard production. Part A. Mechanical properties

This paper investigates the potential of utilising wood biomass from fruit tree branches and evergreen hardwood shrubs as raw materials in the production of particleboards when mixed with Greek fir wood particles. The main mechanical properties of the boards made therefrom were determined and compared with those made of typical industrial wood (IW) particles. The highest modulus of rupture and elasticity (30.0 N/mm² and 4330 N/mm², respectively) in bending and screw withdrawal (SW) resistance (127.8 N/mm) were reported for boards made of Greek fir and were downgraded when the fruit tree branches or evergreen hardwood shrub particles also participated. The participation of fruit tree branch particles in proportions higher than 50% improved the internal bond (IB) of fir produced boards, while the highest IB strength (0.95 N/mm²) was reported for boards made of fruit tree branches. Particleboards made of evergreen hardwood shrubs showed inferior mechanical properties compared with those made of IW particles. The latter also showed superior bending strength but inferior SW resistance compared with boards made of fruit tree branches. Hygroscopic and other properties are under determination and will be presented and discussed in the second part of the work.     

Corrosion of metal fasteners embedded in acetylated and untreated wood at different moisture contents

ABSTRACT

Acetylated wood is now commercially available and designed to be used in certain outdoor applications as an alternative to preservative-treated wood. Fastener corrosion can be a concern in preservative treated wood when the wood remains wet for long periods. However, little data on the corrosiveness of acetylated wood exists beyond the product literature. Here we examine the corrosiveness of commercially obtained acetylated wood and compare it against unmodified (untreated) southern pine (Pinus spp.). Corrosion rates of plain carbon steel, hot dip galvanized steel, and stainless steel were calculated gravimetrically after a one year exposed in the wood. Four different moisture conditions were examined: 90% relative humidity (RH), 95% RH, 100% RH, and a fully water saturated condition. When compared to literature data on the corrosion of fasteners in preservative treated wood at 100% RH, the acetylated wood had much lower steel corrosion rates than all preservatives examined; the measured corrosion rates for galvanized steel were lower than all preservatives except chromated copper arsenate. These measured corrosion rates across a range of moisture conditions can be used to inform the selection of appropriate corrosion resistant fasteners when building with acetylated wood.     

Relationship between stomatal behavior and characteristics of photosynthesis and transpiration of Adenophora lobophylla and A. potaninii at different altitudes

IntroductionAdenOPhoraIObOPhytheandAdOnoPhorapot8niniiareperennialherbunderthejurisdictionofAd8no-phoraofCampanuIaceae.A.IObOPhyIfapopulationdistributesinthenorthwestareaofJinchuanCounty,innorthwestSichuanProvince,ataItitudesfrom2ooomto34oom,andthedistributionareaises-timatedIess5ookm2.A.pot8niniipopuIationisanextensivespecieswhichdistributesnotonIyinthenorthwestareaofSichuanProvincebutalsoinQinghai,Gansu,Shanxi,NingxiaandShanxi.Inre-centyears,thestudiesonendangeredmechanismforA.…     

Relationship between stomatal behavior and characteristics of photosynthesis and transpiration of Adenophora Iobophylla and A. potaninii at different altitudes

The photosynthesis and transpiration characteristics ofAdenophora Iobophylla and A. potaninii, as well as stomatal behavior such as stomatal size, stomatal density, stomatal open and stomatal conductivity were measured at different altitudes. The relationship between the photosynthesis and transpiration characteristics and the stomatal behavior was analysed by correlation coefficient and path coefficient analysis with altitude changes.The results showed that the influences of stomatal behavior were not evident on the photosynthesis and transpiration characteristics of A. Lobophylla, but evident on that of A. potaninii.     

DMA技术在木材科学中的应用及展望

介绍了动态力学实验研究及动态热机械分析(DMA)在木材科学中的应用及其发展方向.     

Bondability of tropical fast-growing tree species III: curing behavior of resorcinol formaldehyde resin adhesive at room temperature and effects of extractives of <Emphasis Type="Italic">Acacia mangium</Emphasis> wood on bonding

The effects of curing time at room temperature and methanol extracts from Acacia mangium on the curing behavior of resorcinol formaldehyde (RF) adhesive were examined by using the thermomechanical analysis spring method. For a specimen that was cured for 3 months at room temperature, the relative elasticity (E _r) curve did not change to a hard glass state from room temperature to 200°C and the adhesive had cured completely. The initial temperature of the reactive zone for chemical and mechanical changes was 15° and 25°C higher than that for the control when 10 and 15 parts by weight methanol extract was added to the liquid adhesive, respectively. It appears that the extractives of A. mangium in RF adhesive interferes with the chemical cure of the adhesive. It is suggested that a combination of curing time and sweeping by methanol on the laminae surface can improve the bonding performance of A. mangium laminates bonded with RF at room temperature.     

常规木材干燥室不同供热状况的 损失分析

着重分析常规木材干燥室蒸汽管道不同供热状态的损失:当蒸汽管道供热温度一定时,干燥室温度越低,传热温差越大,损失越大;当干燥室温度及蒸汽管道外壁温度一定时,蒸汽管道供热温度越高,传热温差越大,损失越大。传热温差对损失的影响很大,当蒸汽管道供热温度110℃时,传热温差由40℃降到30、20、10℃,其损失分别减少46.08%、77.01%和94.48%,所以要根据干燥室需要的温度尽量减少供热温差,以减少损失。压差流动损失随压差增大而增加,而且压力较高时比压力较低时压降的损失大。蒸汽在管道内压差流动的损失数值比温差传热损失大许多,至少要大1～2个数量级。因此,由锅炉向干燥室供热,应该尽量减少降压节流的情况。     

32个杉木无性系木材密度和力学性质的变异*

３２个杉木无性系间，木材密度和抗弯弹性模量、抗弯强度、顺纹抗压强度均有较大差异，无性系内株间亦存在一定差异。木材密度与抗弯弹性模量、抗弯强度、顺纹抗压强度间的相关极显著，相关系数分别为０．３９５７、０．８３６８和０．９０２０；木材密度与生长速度呈负的遗传相关。     

高温条件下木材升温时间的理论计算和实测

提出了木材热处理过程中高温干燥阶段升温时间的理论计算公式,并以20、40、60 mm厚的杨木为试材,进行了验证试验.试验设置100、130、180 ℃三个升温阶段,测定了试材表面和芯层达到温度平衡的时间.结果表明,理论计算时间与试验实测时间能较好地吻合,应用理论计算公式,可为合理制定木材高温热处理工艺参数提供依据.     

Relationship between stomatal behavior and characteristics of photosynthesis and transpiration ofAdenophora lobophylla andA. potaninii at different altitudes

The photosynthesis and transpiration characteristics ofAdenophora lobophylla andA. potaninii, as well as stomatal behavior such as stomatal size, stomatal density, stomatal open and stomatal conductivity were measured at different altitudes. The relationship between the photosynthesis and transpiration characteristics and the stomatal behavior was analysed by correlation coefficient and path coefficient analysis with altitude changes. The results showed that the influences of stomatal behavior were not evident on the photosynthesis and transpiration characteristics ofA. Lobophylla, but evident on that ofA. potaninii. This study is supported by the National Natural Science Foundation of China (No. 39391500). Responsible editor: Zhu Hong