Treatment of timber products with gaseous borate esters

Summary Several factors which influence the treatment of timber products with vapour phase preservatives such as borate esters are considered. Gas flow rate through the substrate was found to be a significant factor limiting both preservative penetration and its rate of deposition. A theoretical model of the treatment process was developed and tested experimentally to determine the influence of several factors on the retention and distribution of boric acid. Gas flow into the timber product was influenced by permeability, pressure gradient and substrate moisture content. The implications of the findings are considered with regard to the treatment of wood and wood products with gaseous reagents.The authors wish to thank the following for their financial support and interest in this research programme — Rentokil Ltd, Rhone-Poulenc/Manchem Ltd, Forestry Commission, UK and Ireland Particleboard Association (now Panel Products Association), Norbord Highland plc (formerly Highland Forest Products plc), IMPEL     

Effects of borate impregnation on the response of wood strength to heat treatment

Based on the strong correlation between acidity and thermal degradation in wood reported in previous studies, the effect of borate impregnation as an alkali-buffering medium was investigated on the strength properties of thermally modified wood. Wood samples were impregnated with 0.1 M Sodium borate solution (pH=9) before they were subjected to heat treatment at temperatures of 180°C and 200°C for durations of 2 and 4 h. The borate impregnation results in some reductions in the severity of strength loss during heat treatment and this is invariably due to buffering effect of the alkali on the acidity of wood, which could have mitigated the degree of degradation. The positive effects of borate impregnation as a pretreatment on the strength properties of heat-treated wood depend on the degree of heat treatment. Hence, the use of borate impregnation as a pretreatment method for heat treatment is recommended only where a relatively mild heat treatment is involved.     

Determination of optimum borate concentration for alleviating strength loss during heat treatment of wood

Based on the already established mitigating potentials of borate salt on the negative effects of heat treatment on the strength properties of wood (Awoyemi and Westermark 2005), the optimum concentration of the alkali buffer solution required to minimize strength loss was determined. Wood samples were impregnated with 0.1, 0.3 and 0.5 M sodium borate solution and exposed to heat treatment for 4 h at 200°C. The mitigating effect of borate salt on the degree of strength loss during heat treatment increases significantly with increasing concentration from 0.1 to 0.3 M. Increasing the concentration of sodium borate from 0.3 to 0.5 M did not produce significant differences in the degree of strength loss during heat treatment. The increase in the buffering effect observed with increasing concentration of the sodium borate preservative is more pronounced on the modulus of rupture than on the modulus of elasticity. It is evidenced therefore that the buffering effect of borate salt on the modulus of elasticity of wood exposed to heat treatment did not start significantly until the 0.3 M concentration is reached and further increase in concentration beyond this point did not produce any appreciable improvement in strength properties.     

Moisture content gradient in a softwood board during drying: simulation from a 2-D model and measurement

Summary A 2-D mathematical model was developed to simulate moisture movement and heat transfer in width and thickness directions within a softwood board during drying. The model is based on wood physiological features and behaviour observed during drying. In sapwood, liquid water movement is assumed to be a consequence of capillary action between liquid and gas phases inside the cell lumens. However, liquid flow does not occur in wood close to the exposed surfaces because at timber surfaces the wood cells are damaged during the sawing process and consequently the liquid column is broken. In heartwood, liquid flow is negligible since the pits are normally aspirated during the formation of heartwood in the growing tree. Water vapour moves under a partial vapour pressure gradient while bound water diffuses within the wood material due to differences in chemical potential. The model was solved numerically to predict moisture-content profiles. Experiments were undertaken to measure the moisturecontent gradient. Samples were removed from a tunnel dryer at intervals throughout drying, frozen overnight and then cut into slices for moisture-content determination. The experimental results were used to verify the model.This work is supported by the New Zealand Foundation of Research, Science and Technology under contract CO4415     

Effects of Stump-treatment Substances for Root-rot Control on Ground Vegetation and Soil Properties in a Picea abies forest in Sweden

There is increasing commercial interest in treating stumps to restrict the spread of root rot [Heterobasidion annosum (Fr.) Bref.] when thinning Swedish coniferous forests during the summer. Both chemical and biological substances are used for this purpose. During the treatment, however, a large proportion of the substance applied is spilled beside the stumps. A field study was conducted on the effects of stump-treatment substances on various ground-vegetation species in a Picea abies (L.) Karst. forest in Sweden. Three different substances commonly used in forestry were studied: urea solution (0.23 kg N m^-2), borate solution (10 g B m^-2) and a fungal preparation of Phlebiopsis gigantea (Fr.) Jül. spores (1 g spores m^-2). The principal objectives were to assess whether any of the substances were harmful to plants and whether plant species differed in their sensitivity. Both borate and urea solution caused severe damage to most ground-vegetation species tested. Bryophytes were affected more strongly than vascular plants and urea was slightly more toxic than borate. Treatments with P. gigantea caused no obvious damage. The size and persistence of chemical changes in the soil induced by the treatments were also analysed. Transient changes were apparent in topsoil where borate or urea had been added. Very high concentrations of B were initially observed where borate had been applied, and even after 1 yr they were slightly higher than the threshold concentration at which plant injuries are expected. Urea treatment initially resulted in a pH increase of 2 units and a substantial increase in soil ammonium content. After 1 yr these effects had largely disappeared, although some increase in ammonium was still detectable.     

几种提取杜仲RNA方法的比较

杜仲富含酚类、多糖、蛋白、杜仲胶等代谢物质,用普通方法提取杜仲RNA时很难将其去除,比较研究了Trizol、CTAB和热硼酸盐3种方法,发现改进的CTAB法和热硼酸盐法均能从杜仲中提取纯度较高的RNA,热硼盐法分离效果最好,凝胶电泳显示条带清晰完整,分光光度计检测OD260/OD280=1.92.用该方法提取的杜仲RNA可以进行RT-PCR、Northern-blot、RACE等分子生物研究.     

磷酸三聚氰胺复配硼酸锌阻燃中密度纤维板的燃烧性能

选用磷酸三聚氰胺与硼酸锌复配,制备阻燃中密度纤维板(MDF),并采用锥形量热仪测试其燃烧性能,分析复配阻燃剂对板材燃烧性能的影响.结果表明:复配阻燃剂可有效提高MDF试材的阻燃抑烟性能,降低其热释放速率、总热释放量、产烟速率、总产烟量、CO及CO2生成速率,以磷酸三聚氰胺和硼酸锌等质量复配时,MDF试材的阻燃效果最优.     

基于ANSYS的木质基复合材料的静力学分析

采用有限元软件ANSYS对木质基复合板进行静力分析,分析其在加载过程中的位移和应力等情况,得出材料的变形及受力规律,以便人们在板的制作过程中对其大应力及大位移区做特殊处理,保证在使用过程中不因结构的部分失效而影响整个结构的工作。本文中分别就不同铺层方向四层结构复合板以及相同铺层方向单、四层等厚度板分别建立模型,并在相同受力与约束情况下进行静力学分析,得出一些对生产实际具有指导意义的结论。     

芦苇－麻屑刨花板的研制Ⅰ．制板工艺初探

为适应农村种植结构的变化，选择芦苇和麻屑为原料，就原料特性对混合比例、各种改性剂及用量，热压条件等关键技术因子进行了研究，并确定了较佳制板工艺与实施方案。试验结果表明，当芦苇的混合量为３０％时，刨花板的静曲强度与厚度膨胀率能达到国标对一级品的要求，但内结合强度低于国标要求。为消除芦苇表层胶合性能不良，增加芦苇的混合比例，提高芦苇－麻屑刨花板的性能，将从胶粘剂改性，芦苇表面处理两个方面作进一步研究。     

Effects of silane coupling agent level and extraction treatment on the properties of UF-bonded reed and wheat straw particleboards

Urea formaldehyde resin bonded reed and wheat particleboards with a density of 0.7g/cm³ were manufactured from two types of particle: fine and coarse particles. The effects of the silane coupling agent (SCA) level and ethanol-benzene (EB) treatment on the board properties were examined. For SCA, epoxide silane (SiEP) and amino silane (SiNH) were used for reed and wheat particles, respectively. The results are summarized as follows. (1) For both reed and wheat boards, the internal bond (IB) strength and thickness swelling (TS) were significantly improved at up to 5% SCA content, but the effectiveness of treatment kept constant at above 5%. (2) The level of SCA had little effect on the bending strength, especially for the boards composed of coarse particles. (3) EB treatment upgraded both the IB and TS of wheat board significantly. (4) SiEP incorporation improved the IB and TS of reed board significantly, whereas EB treatment was more effective for wheat board. (5) The dimensional stability of both reed and wheat boards under varying humidity could be improved by increasing the level of SCA and by EB treatment. EB treatment was more effective than SCA addition.     

The mechanical and physical properties of strand boards treated with preservatives at different stages of manufacture

The physical and mechanical properties of boards treated with a preservative at different points during the manufacture process were evaluated to determine the best stage for the application of preservative. A copper boron tebuconazole amine water-based preservative was used in 3% PF-bonded strand boards to achieve five different retentions. Preservative addition was examined at different stages of the manufacture cycle, namely, green strand diffusion, dry strand vacuum treatment, glue-line spray addition, heat and cold quench of manufactured board, and by post-manufacture vacuum treatment. The treatment methods had marked effects on the mechanical properties of some of the boards when the boards with the highest preservative retention were compared with their respective untreated controls. The best results were achieved where the preservative was applied by vacuum treatment of dry strands or by diffusion of green strands before board manufacture. Increasing preservative retention had minimal effects on board properties with these two methods but significant deterioration was noted when the preservative was applied by spraying dry strands or by post-board-manufacture heat and cold quench. An increase of pressing temperature resulted in significant improvements to the mechanical properties of the spray-treated boards. Post-manufacture vacuum treatment of boards caused excessively high losses in internal bond strength.     

Changes of chemical properties and the water vapour sorption of <Emphasis Type="Italic">Eucalyptus pellita</Emphasis> wood thermally modified in vacuum

The aim of this study was to evaluate the chemical composition and the dynamic water vapour sorption properties of Eucalyptus pellita wood thermally modified in vacuum. For this purpose, wood samples were thermally modified in a vacuum oven at 160–240 °C for 4 h. Chemical composition were investigated by wet chemical analysis, elemental analysis, as well as Fourier transform infrared (FTIR) analysis, and dynamic water vapour sorption properties were evaluated by dynamic vapour sorption apparatus. The results showed that holocellulose and alpha-cellulose contents decreased and lignin and extractives contents relatively increased during the heat process. Elemental analysis showed a reduction in hydrogen content and an increase in carbon content. FTIR analysis indicated that the degradation of hemicellulose and condensation reactions of lignin occurred. In addition, the thermo-vacuum resulted in a reduction in the equilibrium moisture content of wood during the adsorption or desorption process. And the sorption hysteresis had a decreasing trend with increasing treatment temperature. The development of the hygroscopicity was related to the increase in the relative content of lignin, the degradation of the carbonyl groups in xylan and the loss of carbonyl group linked to the aromatic skeleton in lignin after heat treatment.     

Treatment of timber products with gaseous borate esters

This paper forms a continuation of the work on treatment of timber products with gaseous borate esters. Turner and Murphy (1995) in an earlier paper indicated that gas flow rate into the wood substrate was the principle factor limiting the rate of boric acid retention and the depth of penetration into wood products. The current paper considers the impact of this factor on treatment efficacy and considers experimental work designed to evaluate qualitatively, the impact of proposed modifications to the process. Significant improvements in treatment performance were observed.     

细木工板甲醛捕捉设备的设计及其捕捉工艺技术

针对目前细木工板甲醛捕捉剂人工喷涂和简单机械喷涂效率低、不均匀的现状,设计、研制出甲醛捕捉剂喷施的机械化设备,并对其捕捉工艺参数进行研究和细木工板理化性能测定,结果表明:甲醛释放量为E_2级细木工板(2.8 mg·L~(-1)),使用甲醛捕捉设备,用喷施量33.6 g·m~(-2)的W-BC甲醛捕捉剂处理之后,甲醛释放量可以降低到了E_1级水平,对物理力学性能无不利影响。因此,该甲醛捕捉设备适合于机械化处理细木工板,大幅提高了捕捉剂喷施均匀性、加工效率及其产品质量,降低了生产成本。     

GRC隔墙板的应用技术--省委高职住宅楼工程

本文结合工程实践,总结了单层GRC轻质隔墙板的安装方法和防止板接缝开裂的处理技术.     

人工林杉木压缩整形过程中的定形工艺

以蒸汽压力、时间及定形结束时蒸汽卸压速度为参数,对杉木压缩整形工艺的定形进行了试验.结果表明:1)整形过程中定形的蒸汽压力、定形时间对杉木定形后的体积压缩恢复率影响显著,而定形完成后的蒸汽卸压速度无显著影响;2)定形的蒸汽压力、定形时间的各个水平之间的定形效果差异极显著,理想的定形效果是在0.8 MPa的饱和蒸汽压下持续40 min.     

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     

定向结构板内水蒸气稳态扩散系数的研究

采用扩散杯法研究了定向结构板内水蒸气稳态扩散系数。结果表明，定向结构板内平行于板面的水蒸气稳态扩散系数约是垂直于板面的水蒸气稳态扩散系数的１０倍左右。定向结构板内水蒸气稳态扩散系数随着板密度的增加而减小，并且与密度成二次函数关系。     

Heat Post-Treatment to Reduce Thickness Swelling of Particleboard from Fast-Growing Poplars

IntroductionInrecentyears,particleboardhasbeenusedmoreandmorewidely,Itisnotonlyusedforfurnituremanufac-turingandinteriordecoratingbutalsoaseXteriorbuild-ingmaterial.Becauseofthechangesofthesurroundingatmosphere,thevariationinmoisturecontentofparti-'cleboa…     

Biological performance of particleboard incorporated with boron minerals

We compared resistance to decay, mold fungi,termites and insect larvae of particleboards incorporated with the raw boron minerals ulexite and colemanite to that of particleboards impregnated with the commercial boron preservative zinc borate, or boric acid plus a borax mixture.We also quantified water absorption, thickness swell and boron release of particleboards. Ulexite had the best decay resistance, and colemanite had the best termite resistance.However, ulexite and colemanite were not as effective as zinc borate or the boric acid/borax mixture in preventing mold growth. In general, the boric acid/borax mixture combination was more effective against Anobium larvae than the other treatments. Less boron was released by specimens containing zinc borate and colemanite than bythose containing ulexite or the boric acid/borax mixture. In general, water absorption and thickness swell were similar among the different treatments, but both were slightly higher in the ulexite-incorporated specimens. Further mechanical tests will be needed to evaluate the particleboard properties and thereby the compatibility of these boron minerals with various manufacturing processes.