Misato Norimoto

Study on Young's Modulus and Internal Friction of Wood in Relation to the Evaluation of Wood for Musical Instruments

Youngs modulus E and internal friction Q-1 in longitudinal (L) direction and specific gravity γ were measured for numerous specimens of 25 softwood species. There was a high correlation between Q-1/(E/γ) and E/γ, and the suitability of wood for musical instruments can be evaluated by using the value of E/γ. Furthermore, effects of grain angle in the longitudinal-radial plane on Youngs modulus and internal friction of wood were investigated. From these results, it is concluded that the value of internal friction as well as Youngs modulus of wood is determined in large part by microfibril angle in the S2 layer of tracheid against the L direction.

The effects of adsorbed water on dynamic mechanical properties of wood

Abstract The storage modulus and the loss tangent of Sitka spruce wood ( Picea Sitchensis ) in the longitudinal direction at various moisture contents were measured at 20°C, and the effect of adsorbed water was investigated by using a uniaxial rheological model to eliminate the contribution of matrix swelling. The largest value for Youngs modulus of matrix was obtained at around 8% moisture content. The rearrangement of matrix molecules accompanied by the adsorption of hydrated water increased the value of Youngs modulus up to about 8% moisture content, whereas the plasticization of matrix molecules by the adsorption of dissolved water decreased it at above 8% moisture content. The loss tangent of matrix had two peaks at ∼1% and 20% moisture contents. It was considered that the former was due to the motion of the adsorbed water itself and the latter to the relaxation related to the micro-Brownian motion of matrix substances, especially hemicelluloses.

Physical and Mechanical Properties Required for Violin Bow Materials

Pernambuco (Guilandina echinata Spreng. syn Caesalpinia echinata Lam.), which has been used for the production of violin bows, was compared with alternative wood species from some physical and mechanical aspects and the reasons for why it is suitable for bows were discussed. A low value of loss tangent (tanδ) may be helpful for bow material, as the tanδ of pernambuco was much lower than that of the other wood species. On the other hand, the most suitable Youngs modulus could not be clarified, but the lower limit of Youngs modulus needed for the bow must exist. Low tan δ of pernambuco seems to be due to a high content of extractives. However, not only the quantity but also the chemical component and/or the location of extractives in the wood structure may have a different effect on the tanδ. From the result that the wood with a higher extractive content showed a lower softening temperature, it can be concluded that the extractive in pernambuco is probably influential in the thermal bending of the bow. Redness (a*) of pernambuco has a correlation with tan δ. Indentation hardness of pernambuco was somewhat higher at the same level of specific gravity than that of the other wood species, but hardness would not be an inevitable property for the bow.

Moisture Adsorption Thermodynamics of Chemically Modified Wood

The isotherms for untreated and chemically modified wood specimens were analyzed using the Hailwood-Horrobin equation. The enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) changes during moisture adsorption were estimated. The ΔH, ΔS and ΔG 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 ΔH 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 ΔH for formalization and acetylation indicates the remarkable loss of the hydrated water as a result of those reactions. A peak of the absolute ΔS 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 ΔH and ΔS observed in glyoxal treated specimens will be due to the ester groups introduced. The ΔG 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.

Stress Relaxation of Sugi (Cryptomeria japonica D.Don) Wood in Radial Compression under High Temperature Steam

Summary To clarify the mechanism of the permanent fixation of compressive deformation of wood by high temperature steaming, stress relaxation and stress-strain relationships in the radial compression for Sugi (Cryptomeria japonica D.Don) wood were measured under steam at temperatures up to 200°C. The stress relaxation curves above 100°C were quite different in shape from those below 100°C, showing a rapid decrease in stress with increasing temperature. In the stress-strain relationships measured above 140°C, the stress reduced as pre-steaming time increased when compared at the same strain. The recovery of compressive deformation (strain recovery) was decreased with steaming time and reached almost 0 in 10 min at 200°C. The relationship between the residual stress and the strain recovery at the end of relaxation measurements could be expressed by a single curve regardless of time and temperature. The permanent fixation of deformation by steaming below 200°C was considered to be due to chain scission of hemicelluloses accompanying a slight cleavage of lignin. In some cases, the increase in regularity of the crystalline lattice space of microfibrils or the formation of crosslinks between the cell wall polymers seemed to play an important role in the permanent fixation of compressive deformation.

Contractive force and transformation of microfibril with aqueous sodium hydroxide solution for wood.

Summary The mechanism of longitudinal contraction of Yezo spruce (Picea jezoensis Carr.) during treatment with aqueous NaOH solution is discussed. The contraction of wood samples increased with an increase in the concentration of NaOH solution and in heating temperature. Measurements of the stress relaxation and the twist angle during the alkali treatment showed that the alkali treatment caused the contractive and twist forces of a tracheid cell wall in longitudinal and tangential directions, depending on the components of contractive force. The temperature dependence of the contraction and the thermodynamics led to the conclusion that the longitudinal contraction of samples is due to that of microfibrils via an entropy-elastic force.

The Effects of Water Soluble Extractives on the Acoustic Properties of Reed ( Arundo donax L.)

Summary The storage modulus (E′) and the loss tangent (tanδ) of reed (Arundo donax L.) used for woodwinds were measured at 20°C and 60% relative humidity and the effects of water soluble extractives on these properties were discussed. The extractives increased both the E′ and tanδof reed. There was a linear relationship between the tanδ change and the weight loss due to extraction. By using an uniaxial rheological model considering the anatomical structure of reed, the E′ and tanδ of reed were described using the storage moduli, loss tangents, and volume fractions of bundle sheaths and parenchyma cells. It was suggested that the extractives in parenchyma cells increased the modulus of elasticity for parenchyma cells by 25% and reduced the relaxation time of parenchyma cells by a factor of three. The main constituents of extractives were glucose, fructose and sucrose.

The analysis of dimensional changes due to chemical treatments and water soaking for hinoki (Chamaecyparis obtusa) wood

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).

Anisotropy of Dielectric Constant in Coniferous Wood

The dielectric constants in the thrce principal directions for coniferous wood at various moisture contents were calculated and their anisotropy was discussed. The anisotropy in the longitudinal and transverse directions was mainly due to the difference in the arrangement of cell wall and lumen in addition to the anisotropy of dielectric constant in cell wall substance, while that in the radial and tangential directions depcnds mainly on percentagc of late wood, ratio of cell wall area to cell area and irregulär array of cells. The calculated values were in satisfactory agreement with the experimcntal oncs.

Tangential Young's modulus of coniferous early wood investigated using cell models

Summary The relationship between the tangential Youngs modulus and the transverse cell shape in coniferous early wood was investigated by using cell models constructed by power spectrum analysis. The calculated Youngs moduli of the cell models explained qualitatively the change of the experimental Youngs moduli with density as well as the difference in the experimental values among species. The calculated Youngs moduli differed significantly among species depending on the cell model shapes when compared at the same density. With increasing element angle in the model, the Youngs modulus greatly increased without a significant change in the density, especially at the larger ratios of the axial length of the tangential cell wall to that of the radial cell wall.