Kazuya Minato

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.

Vibrational property changes of spruce wood by impregnation with water-soluble extractives of pernambuco (Guilandina echinata Spreng.)

Sitka spruce (Picea sitchensis Carr.) was treated with water-soluble extractive components of pernambuco (Guilandina echinata Spreng. syn Caesalpinia echinata Lam.) by two methods: impregnation under evacuation using an aspirator and repetitive surface application using a brush. The influence of these treatments on the vibrational properties were examined. The loss tangent (tan δ) of the impregnated specimen decreased, up to nearly a half of its original value, with increasing weight gain. It is suggested that the decrease in tan δ results from impregnation of the extractive components into the amorphous region of cell walls, forming secondary bonds between matrix substances. The surface application of the extractive components, on the other hand, hardly brought about the desirable change in vibrational properties.

Chemical treatment of wood for musical instruments

After a review of the structure of wood concerning its acoustic properties and a discussion of the merits and demerits of wood as a material for making soundboards of stringed instruments, the effects of three chemical treatments (a low molecular weight phenolic resin treatment, a resorcin/formaldehyde treatment, and a saligenin/formaldehyde treatment) on the acoustic properties of Sitka spruce wood are reported and compared with those of formaldehyde treatment. All three chemical treatments increased the specific dynamic Young’s modulus and greatly decreased damping (tan δ) without greatly increasing specific gravity. The range was almost equivalent to that with formaldehyde treatment whose superb effects have already been confirmed in the violin. With saligenin/formaldehyde treatment, the frequency dependence of tan δ could be controlled over a wide range by changing the saligenin concentration. In all treatments, hygroscopicity was reduced and dimensional stability was improved significantly.

Chemical characteristics of surfaces of hardwood and softwood deteriorated by weathering

The factors that cause weather-induced deterioration of wood surfaces were determined by chemical and spectroscopic analyses. Albizzia (Paraserianthes falcata Becker.) and sugi (Cryptomeria japonica D. Don) were exposed to two temperate conditions of natural weathering with and without rainfall and to accelerated conditions of artificial weathering coupled with ultraviolet (UV) light irradiation and water flashing. Infrared spectroscopic analysis showed that the oxidative reaction of lignin was observed under all conditions of weathering for both wood species. However, a marked decrease in lignin and hemicellulose content were recognized when albizzia woods were exposed to weathering with water. Lignin content in the softwood sugi did not decrease as much as in albizzia even in the presence of water, but the modification of lignin macromolecules was assumed to be accelerated by water, as seen by electron spin resonance spectroscopy. These results showed that the presence of water promotes the weathering deterioration of wood under UV irradiation.

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).

Effects of impregnation of simple phenolic and natural polycyclic compounds on physical properties of wood

The impregnation of various simple phenolic and natural polycyclic compounds into wood was investigated from the viewpoints of vibrational property and dimensional stabilizing effect. When simple phenolic compounds were impregnated, the loss tangent (tan δ) in the longitudinal direction increased linearly with increasing weight gain. Meanwhile, among the natural polycyclic compounds hematoxylin decreased the tan δ drastically by impregnation. It was suggested that the five hydroxyl groups and the pyran ring oxygen in the hematoxylin molecule contribute to formation of the crosslinkage-type hydrogen bonds between wood components. The rigidity of hematoxylin molecules may also be important. By impregnation of about 10% catechol, resorcinol, and saligenin, a 40% level of antiswelling efficiency (ASE) was attained, although a significant dimensional stabilizing effect was not observed after impregnation of natural polycyclic compounds.

Physical and mechanical properties required for violin bow materials II: Comparison of the processing properties and durability between pernambuco and substitutable wood species

Pernambuco (Guilandina echinata Spreng. syn Caesalpinia echinata Lam.), which has been used for a material of violin bows, was compared with substitutable wood species from the viewpoint of processing properties and durability. The properties required for bow material are discussed. The shearing strength of pernambuco was higher than that of the other wood species at the same specific gravity. High shearing strength seems to be effective for preventing damage to the head (top part) of the bow. The presence of extractives affects the thermal softening of wood material, but ease of handling and permanent retention of form are not particularly superior for pernambuco, although it does have a high extractives content. A peculiarly low loss tangent (tan S) of pernambuco can probably be attributed to the large amount of extractives, rather than the mean microfibril angle.

Chemical modification of wood by non-formaldehyde cross-linking reagents

SummaryUsing sulfur dioxide (SO2) as catalyst, wood specimens were treated with nonformaldehyde cross-linking reagents such as glyoxal, glutaraldehyde and dimethylol dihydroxy ethyleneurea (DMDHEU). The results of dimensional stability, acoustic properties, and mechanical strength tests were compared with those obtained from formaldehyde treatment. With glyoxal and glutaraldehyde treatments, antiswelling efficiency (ASE) reached around 70%, which is comparable to the values attained by formaldehyde treatment, although the accompanying weight gain was much larger than for the latter, whereas DMDHEU did not give sufficiently high ASE. None of the treatments, significantly increased specific dynamic Youngs modulus (E/ρ) with the exception of the DMDHEU treatment, loss tangent (tan δ) decreased substantially, about 50 and 60% in longitudinal and radial directions respectively, which were somewhat exceeding the formaldehyde treatment. The results suggested that the improvement of the dimensional stability and acoustic properties is partly attributed to the formation of cross-links.

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