Mechanical properties of wood in an unstable state due to temperature changes,and analysis of the relevant mechanism VI: dielectric relaxation of quenched wood

To analyze the effects of lignin on the destabilization of wood due to quenching, we examined the dielectric properties of untreated and delignified wood before and after quenching at 20°C from 50 Hz to 100 MHz. For untreated wood, the inflection points of log ε′ and log σ vs log f and the peak of log(tan δ) vs log f were attributed to interfacial polarization before quenching, and the location of the inflection point shifted to a higher frequency with increasing moisture content because of changes in the water cluster. After quenching, the inflection points of log ε′ and log σ and the peak of log(tan δ ) shifted to higher frequency; however, the values of log ε′, log σ recovered to those before quenching with the passage of time. For delignified wood, dielectric relaxation was observed at a higher frequency than for untreated wood irrespective of quenching. It was inferred that the mobility of water molecules was influenced by the cluster surroundings because of increased number of adsorption sites in hemicellulose. Moreover, after quenching, the recovery process did not change greatly over time; it was shown that the matrix structure was affected more by quenching with the loss of lignin.     

Dielectric relaxation due to the heterogeneous structure of wood charcoal

Delignified hinoki wood and cellulose as well as hinoki and lauan woods were carbonized at 590°C for 1 h. The dielectric properties of these specimens were measured at 20°C in a frequency range of 20 Hz to 1 MHz. Inflection points in the dielectric constant (ε′) versus the logarithm of frequency (log f) curves as well as in the logarithm of the electric conductivity (log σ) versus log f curves for all specimens prepared were recognized. Peaks in the dielectric loss and the imaginary part of the complex conductivity versus the log f curves were detected in the frequency location corresponding to the inflection point in the ε′ and log σ versus log f curves. It was considered that this relaxation was responsible for the interfacial polarization observed in heterogeneous materials because no permanent dipoles existed in the specimens carbonized above 500°C. The Cole–Cole circular arc law was applied to account for this relaxation. Similar average relaxation times were obtained for all specimens. These results suggested that the observed relaxation was ascribed to interfacial polarization at microscopic levels in the cell walls.     

A mathematical verification of the reinforced-matrix hypothesis using the Mori-Tanaka theory

This article presents a theoretical verification of the reinforced-matrix hypothesis derived from tensor equations, σ ^W = σ ^f + σ ^m and ε ^W = ε ^f = ε ^m (Wood Sci Technol 32:171–182, 1998; Wood Sci Technol 33:311–325, 1999; J Biomech Eng 124:432–440, 2002), using classical Mori-Tanaka theory on the micromechanics of fiber-reinforced materials (Acta Metall 21:571–574, 1973; Micromechanics — dislcation and inclusions (in Japanese), pp 141–147, 1976). The Mori-Tanaka theory was applied to a small fragment of the cell wall undergoing changes in its physical state, such as those arising from sorption of moisture, maturation of wall components, or action of an external force, to obtain 〈σ ^A〉_D = ϕ·〈σ ^F〉_I + (1−ϕ)·〈σ ^M〉_D−I. When the constitutive equation of each constituent material was applied to the equation 〈σ ^A〉_D = ϕ·〈σ ^F〉_I + (1−ϕ)·〈σ ^M〉_D−I, the equations σ ^W = σ ^f + σ ^m and ε ^W = ε ^f = ε ^m were derived to lend support to the concept that two main phases, the reinforcing cellulose microfibril and the lignin-hemicellulose matrix, coexist in the same domain. The constitutive equations for the cell wall fragment were obtained without recourse to additional parameters such as Eshelby’s tensor S and Hill’s averaged concentration tensors A^F and A^M. In our previous articles, the coexistence of two main phases and σ ^W = σ ^f + σ ^m and ε ^W = ε ^f =ε ^m had been taken as our starting point to formulate the behavior of wood fiber with multilayered cell walls. The present article provides a rational explanation for both concepts.     

Mechanical behavior of the crystal lattice of natural cellulose in wood under repeated uniaxial tension stress in the fiber direction

This study investigated the relationship between the cellulose crystal lattice strain (crystalline region) and the macroscopic surface strain in specimens of Chamaecyparis obtusa wood under repeated uniaxial tension stress in the fiber direction. Changes in the strain of the crystal lattice were measured from the peak of (004) reflection using the transit X-ray method. The macroscopic surface strain of each specimen was measured with a strain gauge. In both loading and unloading, the surface strain changed linearly with changes in stress. However, crystal lattice strain was not linear but exhibited changes along a curve with changing stress. Under stressed conditions, the crystal lattice strain was always less than the surface strain, regardless of the frequency of repetition in the loading and unloading cycle. The ratio of the crystal lattice strain to the surface strain showed a negative correlation for stress in both loading and unloading. That is, the ratio decreased with increasing stress, and finally tend to converge to a specific value. The ratio (I/I ₀) between the diffracted intensity (I ₀) in the (004) plane in the unloaded condition and the diffracted intensity (I) in the (004) plane in the loaded condition tend to converge on a specific value with increasing frequency of repetition. When the substantial tension Young’s modulus of the wood in the longitudinal direction decreased, the ratio of the strain of the crystal lattice to the surface strain also decreased. Moreover, the ratio decreased with increasing microfibril angle of the specimen.     

Chemical constituents from Gmelina arborea bark and their antioxidant activity

Gmelina arborea Roxb. is a fast-growing species and is known to have been used in traditional Indian medicine. Chemical constituents from the bark have not been reported, although some chemical constituents from part of this plant (heartwood, leaf, and root) are known. In this study, the bark meal was successively extracted with acetone and methanol. Fractionation of the acetone extract with n-hexane, diethyl ether, and ethyl acetate and subsequent chromatographic separation of the fractions led to the isolation of four compounds. The diethyl ether-soluble fraction yielded tyrosol [2-(4-hydroxyphenyl)ethanol] (1); (+)-balanophonin (2), an 8-5′ neolignan, with opposite optical rotation to known (−)-balanophonin; and gmelinol (3), a known lignan. The ethyl acetate-soluble fraction afforded a new phenylethanoid glycoside to the best of our knowledge, which was identified as (−)-p-hydroxyphenylethyl[5′″-O-(3,4-dimethoxycinnamoyl)-β-d-apiofuranosyl(1′" → 6′)]-β-d-glucopyranoside (4). From the methanol extract, two known compounds, 2,6-dimethoxy-p-benzoquinone (5) and 3,4,5-trimethoxyphenol (6), were isolated and identified. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay of the identifi ed compounds indicated that 3,4,5-trimethoxyphenol (6) exhibited moderate activity. Part of this report was presented at the 57th and 58th Annual Meetings of the Japan Wood Research Society, Hiroshima and Tsukuba, August 2007 and March 2008, respectively     

Heartwood extractives from the Amazonian trees <Emphasis Type="Italic">Dipteryx odorata,Hymenaea courbaril</Emphasis>, and <Emphasis Type="Italic">Astronium lecointei</Emphasis> and their antioxidant activities

Heartwood extracts from Amazonian trees cumaru-ferro (Dipteryx odorata), jatoba (Hymenaea courbaril), and guarita (Astronium lecointei) exhibit antioxidant activities comparable with that of α-tocopherol, a well-known antioxidant. This article reports the characterization of the antioxidant compounds in the extracts of the three heartwoods. Silica gel column chromatography of the cumaru-ferro EtOAc extract yielded (−)-(3R)-7,2′,3′-trihydroxy-4′-methoxyisoflavan and (+)-(3R)-8,2′,3′-trihydroxy-7,4′-dimethoxyisoflavan. Silica gel column chromatography followed by preparative high-performance liquid chromatography of the jatoba EtOAc extract yielded (−)-fisetinidol and (+)-trans-taxifolin. Chemical structures were assigned using electron-ionization mass spectrometry, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy including nuclear Overhauser effect spectroscopy (NOESY), as well as optical rotation and circular dichroism. Gas chromatography-mass spectrometry demonstrated that the isolated compounds were predominant in the EtOAc extracts. In the guarita EtOAc extract, catechin and gallic acid were identified by comparing their retention times and mass fragmentation patterns with those of authentic samples. Antioxidant activity determined by the 1,1-diphenyl-2-picrylhydrazyl assay demonstrated that all these compounds had activities comparable with that of α-tocopherol. Part of this report was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007     

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.     

Stereochemistry and biosynthesis of (+)-lyoniresinol, a syringyl tetrahydronaphthalene lignan in Lyonia ovalifolia var. elliptica I: isolation and stereochemistry of syringyl lignans and predicted precursors to (+)-lyoniresinol from wood

Steps leading to the biosynthesis of syringyl lignans and tetrahydronaphthalene and naphthalene lignans, especially the formation of the C2–C7′ linkage, have not been elucidated. Lyoniresinol is a typical syringyl lignan, as well as a tetrahydronaphthalene lignan found in Lyonia ovalifolia var. elliptica. To demonstrate the biosynthetic pathway for (+)-lyoniresinol, three putative biosynthetic intermediates of lyoniresinol, syringaresinol, 5,5′-dimethoxylariciresinol, and 5,5′-dimethoxysecoisolariciresinol, were isolated from wood. The identity of the putative intermediates was confirmed by spectroscopic analyses, as well as by comparison of spectral and chromatographic data with those of authentic samples previously synthesized. The stereochemistry (enantiomeric composition and absolute configuration) of the isolated lignans were determined as (±)-syringaresinol, (8S,8′S)-(−)-5,5′-dimethoxylariciresinol [46% enantiomeric excess (e.e.)], (8S,8′S)-(+)-5,5′-dimethoxysecoisolariciresinol (91% e.e.), and (8R,8′R)-(+)-lyoniresinol (42% e.e.). The absolute configurations of (+)-and (-)-5,5′-dimethoxylariciresinols, and (+)-and (-)-5,5′-dimethoxysecoisolariciresinols were determined by their synthesis (catalytic reduction) from (8R,8′R)-(+)-and (8S,8′S)-(-)-syringaresinols and by subsequent chiral high-performance liquid chromatography analysis. This report was presented at the 55th Annual Meeting of the Japan Wood Research Society, Kyoto, March 2005     

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.     

Compression behaviors of acetylated wood in organic liquids. Part I. Compression in equilibrium conditions

The radial compression behaviors of acetylated cedar wood were measured in various liquids. The compressive Young’s modulus (E) of acetylated wood was reduced by soaking in water, toluene, and acetone, but it was always greater than that of water-swollen unmodified wood at the same swelling level. The behaviors of acetone-swollen unmodified wood were similar to those of acetylated wood rather than those of water-swollen unmodified wood. These results indicated that the swelling of hydrophobic wood components had a lesser influence on the E of wood than the water-swelling of unmodified hydrophilic components. After large compression (ε > 45%), a part of the strain remained unrecovered because of irreversible mechanical deformation. Since the remaining strain was smaller in the wood specimens indicating greater stress relaxation, it was assumed that the viscoelastic deformation of amorphous matrix components is important for lesser irreversible deformation and effective shape recovery of wood. In contrast with water-swollen unmodified wood, the acetylated wood and acetone-swollen unmodified wood exhibited greater shape recovery despite their relatively higher E. This suggested that the swelling of hydrophobic wood components reduced the viscosity of the matrix rather than its elasticity, resulting in more effective shape recovery with lesser softening.     

Effects of high temperature kiln drying on the practical performances of Japanese cedar wood (Cryptomeria japonica) II: Changes in mechanical properties due to heating

Japanese cedar wood specimens were steamed at 80°, 100°, and 120°C over 14 days, and their equilibrium moisture content (M) at 20°C and 60% relative humidity, longitudinal dynamic Young’s modulus (E), bending strength (σ _max), and breaking strain (ε _max) were compared with those of unheated specimens. Steaming for a longer duration at a higher temperature resulted in a greater reduction in M, σ _max, and ε _max. The E of wood was slightly enhanced by steaming at 100°C for 1–4 days and 120°C for 1–2 days, and thereafter it decreased. The slight increase in the E of sapwood was attributable to the reduction in hygroscopicity, while sufficient explanation was not given for a greater increase in the heartwood stiffness. Irrespective of the steaming temperature, the correlations between M and the mechanical properties of steamed wood were expressed in terms of simple curves. M values above 8% indicated a slight reduction in E and s max, whereas M values below 8% indicated a marked decrease in the mechanical performances. In addition, the e max decreased almost linearly with a decrease in the value of M. These results suggest that hygroscopicity measurement enables the evaluation of degradation in the mechanical performances of wood caused by steaming at high temperatures.     

Stereochemistry and biosynthesis of (+)-lyoniresinol,a syringyl tetrahydronaphthalene lignan in <Emphasis Type="Italic">Lyonia ovalifolia</Emphasis> var. <Emphasis Type="Italic">elliptica</Emphasis> II: feeding experiments with <Superscript>14</Superscript>C labeled precursors

To clarify the biosynthetic pathway for syringyl lignans, especially syringyl tetrahydronaphthalene lignans and formation of the C2–C7′ linkage, production of (+)-lyoniresinol (LYR) and its predicted intermediates [syringaresinol (SYR), 5,5′-dimethoxylariciresinol (DMLR), and 5,5′-dimethoxysecoisolariciresinol (DMSLR)] in Lyonia ovalifolia var. elliptica was investigated by means of feeding experiments with radiolabeled precursors. Following individual administration of l-[U-¹⁴C]phenylalanine (Phe), [8-¹⁴C]sinapyl alcohol (SA), and [8,8′-¹⁴C]SYR to excised young shoots of L. ovalifolia and their subsequent metabolism, free [¹⁴C]lignans and [¹⁴C]lignan glycosides were extracted with methanol from stems and leaves and were divided into ethyl acetate-soluble fractions (lignans) and aqueous fractions (lignan glycosides), respectively. Using a combination of xylanase, cellulase, and β-glucosidase, the glycosides were hydrolyzed to liberate [¹⁴C]lignans as aglycones. l-[U-¹⁴C]Phe was incorporated into (+)-[¹⁴C]SYR [stem 0.38%, 8% enantiomeric excess (e.e.)], (−)-[¹⁴C]SYR (leaves 2.75%, 72% e.e.), (+)-[¹⁴C]DMLR (stem 0.07%, 18% e.e. and leaves 0.009%, 58% e.e.), (−)-[¹⁴C]DMSLR (stem 0.03%, 46% e.e. and leaves 0.05%, 20% e.e.), (+)-[¹⁴C]LYR (leaves 0.013%, 22% e.e.) and glycosides of (+)-[¹⁴C]LYR (stem 0.036%, 50% e.e.) in 24h. Based on the percent incorporation and enantiomeric composition of the lignans, the biosynthetic pathway of (8R,8′R)-(+)-LYR was proposed as follows: a nonselective dehydrogenative dimerization of sinapyl alcohol yields (±)-SYR, which is reduced with low specificity to give (8R,8′R)-(+)-DMLR. This is cyclized to directly give (+)-LYR as well as reduced again to (8R,8′R)-(−)-DMSLR. Although further transformation of (−)-DMSLR also leads to the formation of (+)-LYR, cyclization could be a main pathway for (+)-LYR biosynthesis. This report was presented at the IAWPS 2005 International Symposium on Wood Science and Technology, Yokohama, November 2005     

Vegetative propagation of two endemic species of <Emphasis Type="Italic">Cloezia</Emphasis> Brongn. &; Gris for conservation and mining revegetation activities in New Caledonia

A study to determine the best vegetative propagation protocol was carried out for two species of the endemic genus Cloezia for conservation and mining revegetation activities in New Caledonia. Effects of clonal capacities and auxin treatments on rooting of C. buxifolia and C. aquarum semi-hardwood cuttings taken from wild populations were evaluated in four experiments. Different phenotypes varied in their capacity to root (from 0 to more than 80%) and this underlines the importance of collecting cuttings from different plants when revegetation programs are based on vegetative propagation. The experiments evaluated the effectiveness of IBA at 5, 10 and 20 g kg⁻¹, IAA at 5 and 10 g kg⁻¹ and NAA at 1 and 2 g kg⁻¹ treatments to enhance rooting of C. buxifolia tip cuttings and C. aquarum tip and stem cuttings compared to control cuttings with no applied auxin. With the exception of IAA, auxin treatments enhanced the percentage of cuttings with roots and significantly improved the number of roots per cutting and root length. In this study, the best treatment is 10 g kg⁻¹ IBA for C. buxifolia. For C. aquarum, 20 g kg⁻¹ IBA significantly enhances quantitatively and qualitatively rooting of both tip and stem cuttings.

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Résumé  Cette étude porte sur la définition d’un protocole de multiplication végétative optimale de deux espèces du genre endémique Cloezia dans un but de conservation et de revégétalisation en Nouvelle-Calédonie. Quatre essais visent à déterminer les potentialités clonales de différents individus et l’effet de divers traitements hormonaux sur l’enracinement de boutures de C. buxifolia et C. aquarum. L’enracinement des boutures dépend du pied-mère sur lesquelles elles sont récoltées et peut varier de 0 à plus de 80%, ce qui indique l’intérêt de la méthode d’échantillonnage lors de la collecte des boutures. L’effet de traitements hormonaux à base d’AIB, AIA et ANA à différentes concentrations, respectivement de 5, 10 et 20 g kg⁻¹, 5 et 10 g kg⁻¹ et 1 et 2 g kg⁻¹ est également étudié sur des boutures de tête de C. buxifolia et des boutures de tête et de tige de C. aquarum. Ces traitements améliorent le pourcentage d’enracinement et augmentent significativement le nombre de racines produites et la longueur des racines des boutures de Cloezia, à l’exception des traitements à base d’AIA. Dans cette étude, le meilleur traitement est 10 g kg⁻¹ d’AIB pour C. buxifolia et 20 g kg⁻¹ d’AIB pour C. aquarum.

     

Dielectric properties of silicon dioxide/wood composite

For a better understanding of the binding between silicon dioxide and wood as well as the dielectric properties of silicon dioxide/wood composite, dielectric relaxation was measured for untreated wood [Cunninghamia lanceolata (Lamb.) Hook] and for silicon dioxide/wood composite with different weight percentage gain (WPG). Cole–Cole’s circular arc law, distribution spectrum of relaxation time and relation model were applied to the results of relaxation due to motions of the methylol groups. The results were as follows. The generalized relaxation time and ε _s − ε _∞ decreased with increasing WPG. The distribution spectrum of relaxation time decreased more and more and broadened with increasing WPG. The methylol group in the amorphous region of the wood cell wall participated in hydrolysis reaction and condensation reaction caused by tetraethylorthosilicate (TEOS), and there is a cross-link between silicon dioxide and wood. The value of apparent activation energy (ΔE) increased for silicon dioxide/wood composite, and increased with increasing WPG. Activation enthalpy (ΔH) and activation entropy (ΔS) increased, while activation free energy (ΔG) decreased with increasing WPG. The number of hydroxyl groups cut in dielectric relaxation increased with increasing WPG.     

Effect of extractions on dynamic mechanical properties of white mulberry (Morus alba)

Vibrational properties of wood are affected by several parameters, of which extractives can be one of the most important ones. Wood for European musical instruments has been often studied, but traditional Middle Eastern ones had been left unnoticed. In this study white mulberry (Morus alba L.), the main material for long-necked lutes in Iran, was extracted by five solvents of various polarities (water included). Free-free bar forced vibrations were used to measure longitudinal (L) loss tangent (tanδ), storage (elastic) modulus (E′) and specific modulus (E′/γ) in the acoustic range. Their anisotropy between the 3 axes of orthotropy was determined by dynamic mechanical analysis. Native wood had a quite low E _L′/γ but its tanδ was smaller than expected, and the anisotropy of tanδ and E′/γ was very low. Removal of extractives caused tanδ to increase and moduli to decrease. Acetone, the most effective solvent on damping despite a moderate extraction yield, increased tanδ _L by at least 20% but did not modify E′/γ as much. When used successively, its effects masked those of solvents used afterwards. Anisotropy of E′/γ was nearly unchanged after extraction in methanol or hot water, while tanδ was much more increased in R than in T direction. Results suggest that in white mulberry, damping is governed more by nature and localization of extractives rather than by their crud abundance.     

封山育林对小兴安岭东部地区蒙古栎林主要乔木种群径级结构的影响

在黑龙江省小兴安岭东部地区(东经444-4726 N?北纬2633-13141? 海拔400-1000 m), 对不同封育时间、不同坡向的蒙古栎林中的主要乔木树种径级结构进行分析。在阳坡,针对封育5年 16年和24年蒙古栎种群, 分别选择6个重复样地。在阴坡,也同样分别选择6块样地。每块样地的面积为20 m×20 m。在每块样地中, 测量各树的胸高直径,树高和冠幅直径。结果表明:在封育5年样地内,蒙古栎、糠椴和黄榆种群的数量均随着径级的增加而单调下降,表明均为增长型种群;在封育16年以后,由于林内乔木层的盖度较大,糠椴和黄榆种群均呈不同程度的衰退,已经成为蒙古栎种群的伴生种群;封育24年样地中,蒙古栎种群明显成为优势树种。在阳坡随封育时间延长乔木层盖度增长较快,而阴坡乔木层盖度增长较慢;糠椴和黄榆种群随封育时间延长逐步衰退的现象在阳坡比阴坡表现明显。图2表1参8。     

Spatial pattern of paulownia witches’ broom and its effects on the growth of Paulownia elongata in Shaanxi Province, China

The spatial pattern of paulownia witches’ broom was investigated using an Iwao’s (m*&#8722;m) model in Shaanxi Province, China. Iwao’s (m*&#8722;m) model revealed that spatial pattern of paulownia witches’ broom exhibited a uniform distribution in sample plots. In this model, characteristics of contagiousness coefficient (α) justified the probability of infection by virus-transmission vectors. For tree age less than six, susceptible individuals were aggregated as clusters in the plots and then mutually repelled over age. A preliminary survey of stand volume show that from age five to six, stand volumes of disease grade II showed excessive vegetative growth and returned to normal level between ages ten and 11. Loss rate of volume increment with disease grade II decreased, and then returned to raising trend both at grades III and IV. This phenomenon is possibly caused by an over-compensation effect and by environmental factors. The redundancy of growth hormones in branches, shoots, leaves, buds and roots increased the stem volume of entire trees.     

Growth and photosynthetic responses of Gallesia integrifolia (Spreng.) Harms and Schinus terebinthifolius Raddi seedlings in dense shade

We analyzed the growth and photosynthetic behavior of Gallesia integrifolia (‘pau-d’alho’) and Schinus terebinthifolius (‘aroeirinha’) under shade, seeking to obtain ecophysiological information for introducing seedlings of those species in previously established cacao agroforestry systems. Considering that light intensity under the shade of cacao trees varied between 5 and 10% daylight, 5 months old seedlings were exposed to four irradiance levels (25, 17, 10 and 5% daylight) for 92 days. With shade increase both species displayed trends of decrease leaf mass per unit leaf area, leaf area per plant (LA), relative growth rate (RGR) and net assimilation rate (NAR), and increase leaf area ratio (LAR). The mean values of light-saturated net photosynthetic rate (P _nmax) in 25 and 5% daylight were 12.8 and 8.0 μmol CO₂ m⁻² s⁻¹ for G. integrifolia and 17.9 and 7.4 μmol CO₂ m⁻² s⁻¹, respectively, for S. terebinthifolius. Based on the measurements of photosynthetic photon flux density and estimated values of photosynthetic saturated irradiance (Is) we concluded that, in all shaded conditions, the leaves of both species were under sub optimal light conditions to reach P _nmax. In spite of the lowest P _nmax values, RGR and NAR were significantly higher for G. integrifolia in all irradiance levels. Differences in growth rates can be explained by the higher values of LA, LAR and leaf mass ratio (LMR), as well as by the lower values of Is, photosynthetic compensation irradiance and dark respiration rates observed for G. integrifolia. Even though seedlings of G. integrifolia presented higher capacity to adapt under conditions of dense shade, we concluded that both species were under stress conditions induced by shade in light environments below 25% daylight. On a practical point of view it is possible to conclude that seedlings of both species should be introduced in light gaps, formed after the fall of big trees, or in places in which cacao trees are cultivated using large plant spacing.     

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     

Radial variations of vibrational properties of three tropical woods

The radial trends of vibrational properties, represented by the specific dynamic modulus (E′/ρ) and damping coefficient (tan δ), were investigated for three tropical rainforest hardwood species (Simarouba amara, Carapa procera, and Symphonia globulifera) using free-free flexural vibration tests. The microfibril angle (MFA) was estimated using X-ray diffraction. Consistent patterns of radial variations were observed for all studied properties. E′/ρ was found to decrease from pith to bark, which was strongly related to the increasing pith-bark trend of MFA. The variation of tan δ along the radius could be partly explained by MFA and partly by the gradient of extractives due to heartwood formation. The coupling effect of MFA and extractives could be separated through analysis of the log(tan δ) versus log(E′/ρ) diagram. For the species studied, the extractive content putatively associated with heartwood formation generally tends to decrease the wood damping coefficient. However, this weakening effect of extractives was not observed for the inner part of the heartwood, suggesting that the mechanical action of extractives was reduced during their chemical ageing.