Influence of moisture content on the vibrational properties of hematoxylin-impregnated wood

The vibrational property of hematoxylinimpregnated wood was investigated from the aspect of moisture content dependence. The specific dynamic Young's modulus (E/) and loss tangent (tan) of hematoxylin-impregnated wood were determined in the relative humidity (RH) range of 0%–97%, and were compared with those of the untreated and some conventional chemically treated woods. The changes in theE/ and tan of wood with increasing RH were suppressed by acetylation and formaldehyde treatment because of a marked reduction in the hygroscopicity of the wood. Although the hematoxylin impregnation did not significantly affect the hygroscopicity of the wood, its influence onE/ and tan were similar to that of formaldehyde treatment at low RH and of acetylation at medium RH. It was supposed that at low to medium RH hematoxylin restrains the molecular motion of amorphous substances in the cell wall because of its bulkiness and rigidity. On the other hand, at high RH it seems to work as a plasticizer with adsorbed water molecules.     

Effect of shear deflection on vibrational properties of compressed wood

In this paper, we have investigated vibrational properties of compressed Japanese cedar (Cryptomeria japonica D. Don). The test specimens were compressed in the radial direction at 180°C for 5 h. Compression ratios (the ratio of deformation to the initial thickness) were 33% and 67%, and the vibrational properties were measured by free-free flexural vibration test. The contribution of shear deflection was large when the length-to-depth ratio was small and the Youngs modulus to shear modulus ratio was large. The Youngs to shear modulus ratio increased as the compression ratio increased and was larger under vibration in the radial than in the tangential direction. The loss tangent increased when the contribution of shear deflection to total measured flexural deflection increased.     

Variation of the viscoelastic properties of wood as a surface finishes substrate

The variation of the viscoelastic properties of wood during exposure to sunlight-type radiation of thin specimens of Abies grandis as a model of the thin surface film of solid timber was followed by thermomechanical analysis (TMA) tests in compression and in tension. For all the types of tests carried out, the TMA traces obtained present only a single inflexion point, which has been assigned to lignin softening. Sunlight radiation was found to have a degrading effect on lignin while the cellulose to hemicelluloses interactions do not appear to be worsened during exposure to the same. The softening temperature variation as a function of sunlight radiation exposure appears to be a parameter which can be used both to observe wood degradation as well as to control the effectiveness and durability of wood stabilization treatments. Received 17 June 1997     

Real-time measurement of vibrational properties and fine structural properties of wood at high temperature

Vibrational properties and fine structural properties of wood were measured at high temperatures. Sitka spruce (Picea sitchensis Carr.) and Shioji (Japanese ash, Fraxinus spaethiana Lingelsh.) were used as specimens. The specimens, the system to support them, a magnetic driver, and a deflection sensor were in an electric drying oven, where vibration tests were conducted. The heating temperatures ranged from room temperature to 200 °C in 25 °C increments in both heating and cooling processes. X-ray diffractometry was carried out using positive sensitive proportional counter (PSPC) at room temperature to 200 °C in 20 °C increments in both heating and cooling processes. Received 13 December 1999     

Temperature dependences of the dynamic viscoelastic properties of wood and acetylated wood swollen by water or organic liquids

In this study, to summarize the changes of thermal-softening behaviors of wood and acetylated wood due to differences in the kinds of swelling liquids, the following measurements were conducted. Untreated and acetylated wood samples were swollen by various liquids and the temperature dependences of the dynamic viscoelastic properties were measured after the heating and cooling histories were unified among the samples. The results obtained are as follows. Untreated samples swollen by high-polarity liquid had lower peak temperature of tanδ, however acetylated samples had higher peak temperature of tanδ than those of untreated wood. On the other hand, untreated wood samples swollen by low-polarity liquid had higher peak temperature of tanδ, however acetylated samples had lower peak temperature of tanδ than those of untreated wood. The amount of swelling is determined by interaction between wood and liquid due to proton-accepting power and molar volumes of liquid and so on, therefore the peak temperature of tanδ and degree of reduction in dynamic elastic modulus (E´) with increasing temperature were corresponded to the amount of swelling.     

Influence of histories on dynamic viscoelastic properties and dimensions of water-swollen wood

The influences of heating history, cooling method, and cooling set on microstructures and the mechanical properties of water-swollen wood were studied by measuring viscoelastic properties and dimensional changes while elevating temperatures between 20°C and 90°C. Both the viscoelastic properties and dimensional changes of waterswollen wood in the first heating process were quite different from those in the other heating processes. The results revealed that the molecular state of green wood around room temperature was stabilized and could not return to this state if drying or heating was carried out. Cooling methods greatly affected the viscoelastic properties, while they hardly affected dimensional changes when the temperature was elevated. Localized stress in the microstructures of water-swollen wood produced by quenching affected the mechanical properties in the heating process, while external stress less than the proportional limit caused by a cooling set had no effect. This revealed that much greater localized stress linked to the instability of waterswollen wood than the external stress in relation to the cooling set occurred. Part of this report was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003     

Moisture-dependent orthotropic viscoelastic properties of Chinese fir wood in low temperature environment

The influence of moisture content (MC) on the orthotropic viscoelasticity of Chinese fir wood (Cunninghamia lanceolata [Lamb.] Hook.) has been examined in low temperature environment. Storage modulus E′ and loss modulus E″ of wood with six different levels of MC ranging from 0.6 to 22.0% were determined from ??120 to 40 °C and at multi-frequency range of 0.5, 1, 2, 5, and 10 Hz using a TA instruments^® Dynamic Mechanical Analyzer (DMA 2980). The results showed that a distinct moisture dependency is exhibited by the orthotropic viscoelastic behaviour of Chinese fir wood. With the exception of some apparent activation energy (ΔE) for β-relaxation process, the E′ decreased and the E″ peak temperatures moved towards lower temperature and the ΔE for α-relaxation process became lower with MC increasing in all orthotropic directions, whereby individual decline of E′ and the E″ peak temperatures were affected by MC to different degrees. Besides, a little E″ peak at around 0 °C was only seen in L direction, which could be attributed to the melting of frozen water. Furthermore, the dynamic viscoelastic behavior of wood is also dependent on the measurement frequency. The findings suggest that the orthotropic structure and moisture content have an important influence on the viscoelastic performance in low temperature environment.     

Identification of anisotropic vibrational properties of Padauk wood with interlocked grain

Grain deviations and high extractives content are common features of many tropical woods. This study aimed at clarifying their respective impact on vibrational properties, referring to African Padauk (Pterocarpus soyauxii Taub.), a species selected for its interlocked grain, high extractives content and uses in xylophones. Specimens were cut parallel to the trunk axis (L), and local variations in grain angle (GA), microfibril angle (MFA), specific Young’s modulus (E′ _L /ρ, where ρ stands for the density) and damping coefficient (tanδ_L) were measured. GA dependence was analysed by a mechanical model which allowed to identify the specific Young’s modulus (E′₃/ρ) and shear modulus (G′/ρ) along the grain (3) as well as their corresponding damping coefficients (tanδ₃, tanδ_G). This analysis was done for native and then for extracted wood. Interlocked grain resulted in 0–25° GA and in variations of a factor 2 in E′_L/ρ and tanδ_L. Along the grain, Padauk wood was characterized, when compared to typical hardwoods, by a somewhat lower E′₃/ρ and elastic anisotropy (E′/G′), due to a wide microfibril angle plus a small weight effect of extracts, and a very low tanδ₃ and moderate damping anisotropy (tanδ_G/tanδ₃). Extraction affected mechanical parameters in the order: tanδ₃ ≈ tanδ_G > G′/ρ > > E′₃/ρ. That is, extractives’ effects were nearly isotropic on damping but clearly anisotropic on storage moduli.     

Characterisation of juvenile wood in teak

Juvenile wood properties are studied in a ring-porous tropical hardwood – teak (Tectona grandis L. F), to assess the utilisation potential of short rotation timber. Compared to mature wood, it is characterised by wide rings, short fibres, small diameter, low vessel percentage, high cell wall, wide microfibrillar angle and relatively low or almost similar mechanical properties. While the average modulus of elasticity and modulus of rupture in juvenile wood are 85% and 82% respectively of the mature wood value, the longitudinal compression strength is similar. With relatively small fibrillar angle of 15° and the scope for genetic selection of individual trees, teak juvenile wood has potential for desired dimensional stability. The segmented regression models and visual interpretation of radial patterns of variation in anatomical properties reveal that juvenility in plantation grown teak extends up to 15, 20–25 years depending on the property, growth rate and individual tree and plantation site. The fitted regression models, to explain the age-related variations in juvenile wood properties range from simple, linear to exponential, reciprocal and quadratic equations. Fibre length, microfibrillar angle, vessel diameter/percentage and ring width appear to be the best anatomical indicators of age demarcation between juvenile and mature wood, although maturation age often varies among the properties. The projected figures for proportion of juvenile wood in plantation grown teak at breast height are 80–100% and 25% at ages 20 and 60 years respectively. Received 3 November 1998     

Influence of heating history on dynamic viscoelastic properties and dimensions of dry wood

To obtain new information about the mechanical and physical properties of dry wood in unstable states, the influence of heating history on viscoelastic properties and dimensional changes of dry wood in the radial, tangential, and longitudinal directions was studied between 100° and 200°C. Unstable states of dry wood still existed after heating at 105°C for 30 min and were modified by activated molecular motion in the first heating process to temperatures above 105°C. This phenomenon is thought to be caused by the unstable states reappearing after wetting and drying again. Dry wood components did not completely approach the stable state in the temperature range tested, because they did not entirely surpass the glass transition temperatures in most of the temperature range. In constant temperature processes at 135° and 165°C, E′ increased and E″ decreased with time regardless of the direction. This indicated that the unstable states of dry wood components were gradually modified with time at constant temperatures. On the other hand, anisotropy of dimensional change existed and dimension increased in the longitudinal direction, was unchanged in the radial direction, and decreased in the tangential direction with time at constant temperatures. Part of this report was presented at the 13th Annual Meeting of the Chubu Branch of the Japan Wood Research Society, Shizuoka, August 2003     

Preliminary study of viscoelastic properties of MAPP-modified wood flour/polypropylene composites

Viscoelastic properties of maleated polypropylene (MAPP)-modified wood flour/polypropylene composites (WPC) were investigated by both a compression stress relaxation method and dynamic mechanical analyses (DMA). Three wood to polymer ratios (40:60, 60:40, and 80:20) and five MAPP loading levels (0, 1, 2, 4 and 8%) were used to study their effects on the viscoelastic properties of MAPP-WPC. The results show that: 1) higher wood to polymer ratio corresponds to higher stress relaxation levels for unmodified WPC. The modification with MAPP has an obvious effect on the stress relaxation of MAPP-WPC at higher wood to polymer ratios (60:40 and 80:20), but almost no effect at the 40:60 wood to polymer ratio. The optimal MAPP loading level for the wood to polymer ratio of 60:40 appears at 1%; 2) the storage modulus reaches its maximum at a MAPP loading level of 1% for wood to polymer ratios of 40:60 and 60:40, while for the 80:20 wood to polymer ratio, a higher storage modulus is observed at higher MAPP loading levels, which is quite consistent with the stress relaxation results. The results suggested that a suitable loading level of MAPP has a positive effect on the viscoelastic properties of WPC at higher wood to polymer ratios. Excessive MAPP loading would have resulted in adverse effects.     

Differences in wood properties between juvenile wood and mature wood in 10 species grown in China

 This study examined the intrinsic differences in various wood properties between juvenile wood and mature wood in 10 major reforestation species in China. Comparisons between juvenile wood and mature wood were made in both plantation- and naturally-grown trees. Considerable differences in most wood properties were found both between plantation-grown juvenile wood and mature wood, and between naturally-grown juvenile wood and mature wood. This suggests that wood properties of plantation-grown trees, to a large extent, depends on their juvenile wood contents, and can thus be manipulated effectively through rotation age. In general, the longer the rotation age, the lower the juvenile wood content, and the stronger the mechanical properties of the plantation-grown woods. However, the differences between juvenile wood and mature wood vary with wood properties and species. In general, juvenile wood and mature wood have less difference in chemical composition than in anatomical and physico-mechanical properties. Compared to the softwoods studied, the hardwoods appear to have less difference between juvenile wood and mature wood. Received 25 June 1999     

Dynamic viscoelastic properties of wood acetylated with acetic anhydride solution of glucose pentaacetate

 Spruce wood specimens were acetylated with acetic anhydride (AA) solutions of glucose pentaacetate (GPA), and their viscoelastic properties along the radial direction were compared to those of the untreated and the normally acetylated specimens at various relative humidities and temperatures. Higher concentrations of the GPA/AA solution resulted in more swelling of wood when GPA was introducted into the wood cell wall. At room temperature the dynamic Young's modulus (E′) of the acetylated wood was enhanced by 10% with the introduction of GPA, whereas its mechanical loss tangent (tan δ) remained almost unchanged. These changes were interpreted to be an antiplasticizing effect of the bulky GPA molecules in the wood cell wall. On heating in the absence of moisture, the GPA-acetylated wood exhibited a marked drop in E′ and a clear tan δ peak above 150°C, whereas the E′ and tan δ of the untreated wood were relatively stable up to 200°C. The tan δ peak of the GPA-acetylated wood shifted to lower temperatures with increasing GPA content, and there was no tan δ peak due to the melting of GPA itself. Thus the marked thermal softening of the GPA-acetylated wood was attributed to the softening of wood components plasticized with GPA. Received: March 29, 2002 / Accepted: May 21, 2002 Correspondence to:E. Obataya     

Anisotropy of wood vibrational properties: dependence on grain angle and review of literature data

The anisotropy of vibrational properties influences the acoustic behaviour of wooden pieces and their dependence on grain angle (GA). As most pieces of wood include some GA, either for technological reasons or due to grain deviations inside trunks, predicting its repercussions would be useful. This paper aims at evaluating the variability in the anisotropy of wood vibrational properties and analysing resulting trends as a function of orientation. GA dependence is described by a model based on transformation formulas applied to complex compliances, and literature data on anisotropic vibrational properties are reviewed. Ranges of variability, as well as representative sets of viscoelastic anisotropic parameters, are defined for mean hardwoods and softwoods and for contrasted wood types. GA-dependence calculations are in close agreement with published experimental results and allow comparing the sensitivity of different woods to GA. Calculated trends in damping coefficient (tanδ) and in specific modulus of elasticity (E′/ρ) allow reconstructing the general tanδ-E′/ρ statistical relationships previously reported. Trends for woods with different mechanical parameters merge into a single curve if anisotropic ratios (both elastic and of damping) are correlated between them, and with axial properties, as is indicated by the collected data. On the other hand, varying damping coefficient independently results in parallel curves, which coincide with observations on chemically modified woods, either “artificially”, or by natural extractives.     

Method for measuring viscoelastic properties of wood under high temperature and high pressure steam conditions

A method for measuring the viscoelastic properties of wood under high temperature and high pressure steam was developed using a testing machine with a built-in autoclave. A newly developed load cell capable of resisting a steam pressure of 16kgf/cm² and a temperature of 200°C was installed in the autoclave. This load cell could be used to determine precisely the loads while steaming at temperatures from 100°C to 200°C. In addition to load-detection problems, it was necessary to avoid the nonuniform thermal degradation of wood during the measurement process under steaming at high temperatures. This nonuniform degradation could be minimized by shortening the time required for the wood to attain thermal equilibrium using specimens conditioned to the fiber saturation point. According to this method, a stress relaxation curve for sugi (Cryptomeria japonica D. Don) wood being compressed while steaming at 180°C was obtained. The stress was seen to decrease rapidly with time, reaching almost zero at 3000s.     

Density profile and morphology of viscoelastic thermal compressed wood

The viscoelastic thermal compression (VTC) of low-density hybrid poplar (Populus deltoides × Populus trichocarpa) from fast growing trees was performed in order to produce specimens with three different degrees of densification (63, 98, and 132%). The morphology and density profile of the VTC specimens were studied. Three different methods for the preparation of specimens for microscopy were used in order to find a technique that makes it possible to examine the VTC wood microscopically in the completely deformed state. It was found that the abrasive surface preparation of oil-embedded blocks was the most promising technique. Microscopic observation revealed that the deformations in the VTC wood were mostly the result of the viscous buckling of cell walls without fracture. The volume of the void areas in the specimens decreased with the degree of densification. The results showed that the density profile of the VTC wood varied with the degree of densification as a consequence of different temperature and moisture gradients formed before and during wood compression. The density profile is also visible on the cross-section of the VTC specimens.     

COMPARATIVE STUDY OF WOOD PROPERTIES BETWEENWHITE WOOD OF DAHURIAN LARCH AND MONGOLIANSCOTCH PINE

DahurianlarchandMongolianscotchpinearetwomajorconunerciaIconilbroustTeesinDaxing'anlingForesnyArea.Itisob-viousthattbcwoodproPertiesandworkability'ofthetWoplantsarecompletelydifferent.Butlnrecert'years,ltlsfoundthattherearetwodiffer':nttypesinparameterofwood'scolour.phy'sicalandmechanicalproPertiesandwork-ability'inDahurianlarch,namelyredwoodandx"hite..od.l']Andthepropertiesofwhite`voodaresligl1tlyyellow-white,medianweightandhardness,goodinworkability'andLard-ness,goodinwodability'anduneas…     

Characterisation of the curing of liquefied wood by rheometry, DEA and DSC

Liquefied wood is a naturally based product which has the potential to be used as an adhesive. The bonding of wood with liquefied wood requires a high enough temperature to cure the liquid polymers and achieve bond strength. Dielectric analysis, rheometry and differential scanning calorimetry were used to analyse the curing process of low solvent liquefied wood. For the liquefaction, ethylene glycol was used as a solvent and sulphuric acid was used as a catalyst. The dielectric analysis was used for in situ measurements of the curing of liquefied wood during the bonding of wood. It was found that curing started after a temperature of 100 °C had been reached in the bond. This is correlated with the water evaporation and the diffusion of water and ethylene glycol from the liquefied wood into the wood substrate. Rheological measurements proved the influence of the substrate on the curing of the liquefied wood during bonding. Differential scanning calorimetry showed that the curing of liquefied wood occurs in two parts: first, the initial elimination of water and ethylene glycol from the liquefied wood, and then the chemical reaction of the liquefied wood at higher temperatures.