Eiichi Obataya

Bending characteristics of bamboo (Phyllostachys pubescens) with respect to its fiber–foam composite structure

The bending properties of split bamboo culm were compared with those of spruce and beech wood specimens. The bamboo allowed large flexural deformation since its outer layer retains the tensile stress while the softer inner layer undergoes large compressive deformation. The results suggested that the combination of the fiber-rich outer part and the compressible inner part was responsible for the flexural ductility of split bamboo. To clarify the compressible nature of the inner part of bamboo, the longitudinal surfaces of the bamboo and wood specimens were microscopically observed before and after a large longitudinal compression. Although the wood specimens showed serious and localized buckling, the inner part of the bamboo specimens showed no such visible buckling. In the latter case, the foam-like parenchyma cells absorbed the large compressive deformation by their microscopic buckling and simultaneously, the alignment of sclerenchyma fibers was maintained by the surrounding parenchyma matrix. The flexural elasticity of the bamboo was compared to that of the wood in respect of remaining strain during cyclic bending tests. No clear difference was recognized between their remaining strains. This fact indicated that the bamboo was not so flexible elastically, although its fiber–foam combination and intelligent fiber distribution improve flexural ductility.

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.

Working mechanism of adsorbed water on the vibrational properties of wood impregnated with extractives of pernambuco (Guilandina echinata Spreng.)

To clarify the lowering mechanism of loss tangen (tanδ) of sitka spruce (Picea sitchensis Carr.) wood impregnated with extractives of pernambuco (Guilandina echinata Spreng. synCaesalpinia echinata Lam.), we examined the vibrational properties of the impregnated wood in relation to the adsorbed water. The results obtained were as follows: (1) The equilibrium moisture content (EMC) of impregnated sitka spruce decreased to some extent compared with untreated wood. (2) Frequency dependencies of tanδ a about 400–8000Hz showed that impregnated wood has much lower tan δ than untreated wood at around 9% mois ture content (MC), except for the high-frequency region. At high relative humidity, impregnated wood has a minimum tanδ (at around 4000Hz); and at other frequency ranges the tanδ of impregnated wood did not differ considerably from that of untreated wood. (3) The apparent activation energy of the mechanical relaxation process (ΔE) concerned with adsorbed water molecules was higher for impregnated specimens than for untreated ones at moderately high relative humidity, whereas at high relative humidity the difference was not observed. Based on these results, it is thought that the tanδ of impregnated wood decreased at low rela tive humidity because of the formation of direct hydrogen bonds between impregnated extractives and wood components. However, when the specimen is at higher relative

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 Youngs modulus (E/γ) and loss tangent (tanδ) 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/γ and tanδ 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/γ and tanδ 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.

Extractives of muirapiranga (Brosimun sp.) and its effects on the vibrational properties of wood

The potential of muirapiranga (Brosimun sp.) as a substitute material for violin bows was estimated in terms of vibrational properties, and the influence of extractives on the vibrational properties was examined. The loss tangent of muirapiranga was somewhat higher and the specific dynamic Young’s modulus was rather lower than the respective values for pernambuco, which is regarded as the best material for violin bows. Therefore, muirapiranga is a poorer bow material in terms of vibrational properties. Impregnation of crude extractives from muirapiranga decreased the loss tangent of other wood specimens. The main compounds of the extractives were identified as xanthyletin and luvangetin. Impregnations of isolated xanthyletin and commercially available methoxsalen, which was tested as an analogue of luvangetin, markedly decreased the loss tangent of other wood specimens. Methoxsalen and xanthyletin differ from conventional loss tangent-decreasing substances, namely protosappanin B and hematoxylin, in terms of water insolubility and the absence of hydroxyl groups. From the similarity in molecular characteristics of loss tangent-decreasing substances found so far, restriction of molecular motion due to an impregnated substance in the wood matrix is suggested as one loss tangent-decreasing mechanism.

Effects of high temperature kiln drying on the practical performances of Japanese cedar wood (Cryptomeria japonica) I: changes in hygroscopicity due to heating

The effect of heating on the hygroscopicity of Japanese cedar wood was investigated as a simple evaluation of thermal degradation in large-dimension timber being kiln-dried at high temperatures (>100°C). Small wood pieces were heated at 120°C in the absence of moisture (dry heating) and steamed at 60°, 90°, and 120°C with saturated water vapor over 2 weeks, and their equilibrium moisture contents (M) at 20°C and 60% relative humidity (RH) were compared with those of unheated samples. No significant change was induced by steaming at 60°C, while heating above 90°C caused loss in weight (WL) and reduction in M of wood. The effects of steaming were greater than those of dry heating at the same heating temperature. After extraction in water, the steamed wood showed additional WL and slight increase in M because of the loss of water-soluble decomposition residue. The M of heated wood decreased with increasing WL, and such a correlation became clearer after the extraction in water. On the basis of experimental correlation, the WL of local parts in large-dimension kiln-dried timber was evaluated from their M values. The results indicated that the thermal degradation of inner parts was greater than that of outer parts.

Dimensional stability of wood acetylated with acetic anhydride solution of glucose pentaacetate

Five wood species were acetylated with acetic anhydride (AA) solution of glucose pentaacetate (GPA) at 120°C for 8h, and the effect of GPA on the dimensional stability of the acetylated wood was investigated. Some GPA was introduced into the wood cell wall during acetylation. The GPA remaining in the cell lumen penetrated the cell wall effectively after heating to more than 140°C for 10min. The bulking effects of GPA resulted in a 10%–30% increase in the anti-swelling efficiency of the acetylated wood with 20% GPA/AA solution in place of AA. Hydrophobic GPA did not deliquesce under highly humid conditions and it remained in the cell wall after boiling in water.

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 (σmax), and breaking strain (εmax) were compared with those of unheated specimens. Steaming for a longer duration at a higher temperature resulted in a greater reduction in M, σmax, and εmax. 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.

Potassium acetate-catalyzed acetylation of wood at low temperatures II: vapor phase acetylation at room temperature

Ezomatsu wood blocks were impregnated with potassium acetate (KAc) and then exposed to acetic anhydride vapor at 25°C and 120°C. The KAc-impregnated wood was rapidly acetylated at 120°C, and only 6 min was needed to achieve 20% weight percent gain (WPG). The WPG increased with increasing catalyst loading (CL), but it turned to decrease above 20% CL probably because the diffusion of acetic anhydride vapor was hindered by excess KAc depositing in the cell lumina. Thus, careful control of CL is necessary in the vapor-phase acetylation. KAc was also effective in catalyzing the vapor-phase acetylation at 25°C: the KAc-impregnated wood attained 20% WPG within 7 days, whereas the WPG did not exceed 10% even after 1 month in the uncatalyzed system. Irrespective of treatment methods, the hygroscopicity of wood was reduced and its dimensional stability was improved with an increase of WPG. These results confirm that the use of KAc simplifies the acetylation process at room temperature with minimal loss of acetic anhydride.

Viscoelastic properties of Japanese lacquer film

The storage modulus (E′) and loss modulus (E″) of Japanese lacquer films were measured over a temperature range of −150 to 400°C. Three relaxation processes labeled α, β, and γ were detected at 80, −60, and −140°C, and their apparent activation energies (ΔE) were 63–91, 13, and 9 kcal/mol, respectively. These were attributed to the micro-Brownian motions of polymerized urushiol, the molecular motion related to the absorbed water, and the motions of methylene groups in the side chains, respectively. With aging at room temperature, the location of the α peak shifted to higher temperature and its ΔE value decreased. This result was ascribed to the autoxidative polymerization of urushiol. The E′ of lacquer films increased with heat treatments at 100°C or above. When treated at temperatures below 200°C, the location of the α peak shifted to higher temperature, with a reduction in the ΔE value. Heat treatments at 200°C or above resulted in remarkable shrinkage and weight loss of films owing to the pyrolysis of lacquer constituents.