International audienceContext Increased knowledge on diversity in wood properties would have implications both for fundamental research and for promoting a diversification of uses as material. *Aims The objective is to contribute to overcoming the critical lack of data on the diversity of wood dynamic mechanical/viscoelastic vibrational properties, by testing lesser-known species and categorizing sources of variability. *Methods Air-dry axial specific dynamic modulus of elasticity (E'/γ) and damping coefficient (tanδ) were measured on a wide sampling (1792 specimens) of 98 wood types from 79 species. An experimental device and protocol was designed for conducting systematic (i.e. rapid and reproducible) characterizations. *Results Diversity at the specimens' level corroborates the "standard" relationship between tanδ and E'/γ, which is discussed in terms of orientation of wood elements and of chemical composition. Diversity at the species level is expressed on the basis of results for normal heartwood, with specific gravity (γ) ranging from 0.2 to 1.3. Axial E'/γ ranges from 9 to 32 GPa and tanδ from 4×10-3 to 19×10-3. Properties distribution follows a continuum, but with group characteristics. The lowest values of tanδ are only found in certain tropical hardwoods. Results can also suggest alternative species for musical instruments making

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Extractives can affect vibrational properties tan1 (damping coefficient) and E'/2 (specific Young's modulus) but this is highly dependent on species, compounds, and cellular locations. This paper investigates such effects for African Padauk (Pterocarpus soyauxii Taub.), a tropical hardwood with high extractives content and a preferred material for xylophones. 5 groups of 26 heartwood specimens with large, yet comparable, ranges in vibrational properties were extracted in different solvents. Changes in vibrational properties were set against yields of extracts and evaluation of their cellular location. Methanol (ME) reached most of compounds (13%), located about half in lumen and half in cell-wall. Water solubility was extremely low. tan1 and E'/2 were very strongly related (R 2 30.93), but native wood had abnormally low values of tan1, while extraction shifted this relation towards higher tan1 values. ME extracted heartwood became in agreement with the average of many species, and close to sapwood. Extractions increased tan1 as much as 60%, irrespective of minute moisture changes or of initial properties. Apparent E'/2 was barely changed (+2% to -4%) but, after correcting the mass contribution of extracts, was in fact slightly reduced (down to -10% for high E'/2), and increasingly so for specimens with low initial values of E'/2.

Summary To clarify tangential and radial dimensional changes in hinoki (Chamaecyparis obtusa) wood by ten kinds of treatments and successive water soaking, a vector expression on the tangential-radial coordinates was proposed and a new measure (ASE′) to evaluate the dimensional stability of wood was defined. The ASE′ is expressed by 100(1 − Vs′ /Vu ) where Vu is the volumetric swelling coefficient of untreated wood and Vs′ is that of treated wood calculated on the basis of its oven-dried volume before treatment. The results from formaldehyde treated, heat treated and steam treated wood showed large positive ASE′ values and the ratio of radial swelling to tangential swelling (swelling anisotropy) of these treated woods decreased with increasing weight percent gain or weight loss. The results from acetylated wood, wood impregnated with polyethylene glycol and wood treated with a low molecular weight phenol-formaldehyde resin showed either small positive or negative ASE′ values, and those of wood treated with propylene oxide showed large negative values. The swelling anisotropy of treated woods accompanied by cell wall bulking was larger than that of untreated wood. The swelling anisotropy decreased when the cell lumen was filled with a hydrophobic resin (WPC-MMA), and increased when the cell lumen was filled with a hydrophilic resin (WPC-HEMA).

The isotherms for untreated and chemically modified wood specimens were analyzed using the Hailwood-Horrobin equation. The enthalpy (ΔΗ), entropy (AS) and free energy (AG) changes during moisture adsorption were estimated. The AH, AS and AG values of untreated wood were compared with those found in literature as well as those of specimens treated with formaldehyde (formalization), acetic anhydride, glyoxal, glutaraldehyde and dimethylol dihydroxy ethyleneurea (DMDHEU). The AH of the untreated specimen was almost constant up to ca. 3 % of moisture content differing from the results reported by others. However, the bonding energy of hydrated water molecules, which represented a large portion of the adsorbed water in the low moisture content range, should not depend on the moisture content, so that the result was undoubtedly reasonable. The decrease of the absolute A// for formalization and acetylation indicates the remarkable loss of the hydrated water as a result of those reactions. A peak of the absolute AS found at ca. 3 % of moisture content except for acetylation may reflect the rearrangement of adsorption sites associated with taking up a little amount of water. In the acetylation, such rearrangement could not occur because of the introduction of bulky hydrophobic groups. Remarkable increases of both absolute AH and AS observed in glyoxal treated specimens will be due to the ester groups introduced. The AG values of all treated specimens became less negative than that of untreated. This indicates the formation of some bond which restricts the swelling of wood structure. IntroductionIn a previous paper , the Hailwood-Horrobin adsorption equation (Hailwood and Horrobin 1946) was applied to the moisture adsorption data of chemically modified wood. In that case, the adsorbed water was separated into hydrated water (monolayer adsorption water) and dissolved water (multilayer adsorption water), and the change in the amount of each water was investigated by chemical treatment. As a result of treatment with formaldehyde (formalization) and acetic anhydride (acetylation), the amounts of both hydrated and dissolved water decreased, whereas only the dissolved water decreased fairly by a treatment with glyoxal because of cross-linking and bulking effects.