Semi-quantitative method to evaluate the α-carbonyl content in lignin

A method to estimate the content of -carbonyl structures in lignin was developed. This method consists of two successive treatments: NaBD₄ treatment of pulp to reduce an -carbonyl structure in lignin, and nitrobenzene oxidation. NaBD₄ was used to convert an -carbonyl structure to a deuterium-labeled hydroxymethine structure. The ratio of D-vanillin [(HO)(H₃CO)C₆H₃CDO] to H-vanillin [(HO)(H₃CO)C₆H₃CHO] or that of their syringyl analogues obtained by nitrobenzene oxidation was used as the measure of the content of -carbonyl structure. Model experiments demonstrated that when sodium hydroxide was used as alkali for the nitrobenzene oxidation, the retention of deuterium at the side chain -position was very low due to the displacement of deuterium with hydrogen by an unknown reaction mechanism. In order to depress this unexpected displacement, the reaction conditions of the nitrobenzene oxidation were modified. The modified nitrobenzene oxidation employs 0.5mol/l of lithium hydroxide as a reaction medium instead of 2.0mol/l sodium hydroxide. By this modification, this method could successfully trace the formation and the degradation of the -carbonyl structure in milled wood lignins.This paper was presented in part at the 11th International Symposium on Wood and Pulping Chemistry, Nice, France, June 2001 and at the 46th Lignin Symposium, Kyoto, Japan, November 2001     

Initial shapes of stress-strain curve of wood specimen subjected to repeated combined compression and vibration stresses and the piezoelectric behavior

This study investigated the relationship between the initial shape of the stress (σ)-strain (ε) curve of a Chamaecyparis obtusa wood specimen subjected to repeated combined compression and vibration stresses at various angles between the fiber direction and load direction and the piezoelectric behavior. The main findings of the study are: (1) the σ-ε curve became convex initially, and then the stress was proportional to the strain. The σ-ε curve had almost the same shape during both loading and unloading. (2) The σ-piezoelectric voltage (P) curve was nonlinear, with a maximal point or cusp on the curve, which had almost the same shape during both loading and unloading, as was also observed for the σ-ε curve. (3) The plot of the first derivative of the stress [dσ/dε (= σ′)] against ε was nonlinear. The σ′-ε and P-ε curves at various angles were fairly similar. (4) The stress at the maximal point (or cusp) of the σ-P curve decreased with an increase in the angle between the fiber direction and load direction. The tendency of the stresses was very similar to that of Young’s modulus and compression strength calculated from Hook’s law and Hankinson’s law, respectively.     

The influences of boiling and drying treatments on the behaviors of tension wood with gelatinous layers in <Emphasis Type="Italic">Zelkova serrata</Emphasis>

This study examined how boiling and drying treatments influenced various physical properties of the tension wood with gelatinous fibers (G-fibers) of a 29-yearold Zelkova branch. By boiling treatment, tension wood with numerous G-fibers contracted considerably in the longitudinal direction and the longitudinal Young’s modulus decreased in spite of the water-saturated condition. The drying treatment caused green tension wood and boiled tension wood with numerous G-fibers to shrink longitudinally and increased their longitudinal Young’s moduli. These specific behaviors in tension wood were highly correlated with the proportion of G-fibers in a specimen and were probably caused by the microscopic behavior of cellulose microfibril (CMF) in the gelatinous layers (G-layers). The longitudinal shrinkage of tension wood due to drying suggests the existence of a hygro-sensible, noncrystalline region in the CMF, which is abundant in the G-layer. Furthermore, the noncrystalline region in the CMF softens during boiling treatment, resulting in the reduction of the longitudinal Young’s modulus in tension wood. The longitudinal contraction of tension wood with G-fibers by boiling might be caused by the tensile growth stress remaining in green G-layers. However, no changes were detected in the 004 d-spacing of cellulose crystal in tension wood from the boiling and drying treatments, regardless of the proportion of G-fibers.     

Dielectric relaxation due to heterogeneous structure in moist wood

Dielectric properties in three main directions for hinoki wood (Chamaecyparis obtusa) specimens conditioned at various levels of relative humidity were measured in the frequency range from 20 Hz to 10 MHz over the temperature range from −150°C to 20°C. Three relaxations were observed in the specimens conditioned at high levels of relative humidity. The relaxation in the highest frequency range was ascribed to the motions of adsorbed water molecules. The relaxation in the middle frequency range remained unchanged by the ethanol–benzene extraction of specimens. The relaxation location was independent of measuring directions. The relaxation in the lowest frequency range was not detected in the specimens impregnated with methyl methacrylate (MMA). This result suggested that the relaxation was due to electrode polarization. The Cole-Cole circular arc law applied well to two relaxations recognized in the specimens impregnated with MMA. The relaxation magnitude in the middle frequency range was extremely large, and the distribution of relaxation times was very narrow. These characteristics suggested relaxation of the Maxwell-Wagner type resulting from the interfacial polarization in the heterogeneous structure, which included adsorbed water with large electrical conductivity within the insulating cell walls.     

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.     

Effects of light and microsite conditions on tree size of 6-year-old Cryptomeria japonica planted in a group selection opening

We examined the extent to which direct and indirect measures of light and microsite conditions could explain variation in tree height and diameter at the base of 6-year-old Cryptomeria japonica trees planted in a group selection opening of about 0.32 ha on a steep slope at Shiiba, Miyazaki Prefecture, southern Japan. We first used the gap light index (GLI) and soil thickness (ST) as directly measured indices. For an indirect measure of light, we used a between-cohort competition index (BCI) estimated from the position and total height of residual trees. For indirect measures of microsite, we examined topographic indices (slope, plan and profile curvature, average slope gradient, and relative elevation) derived from digital elevation models (DEMs) with different resolutions ranging from 2 to 10 m. The multiple linear regression using GLI and ST explained about 45% of variation in tree size, while simple regression using only GLI explained about 35%. The contribution of ST was about half of GLI. The multiple regressions using BCI and the topographic indices did not explain any more variation than using BCI alone (R ² of about 0.26). We conclude that microsite conditions with shallower soil and steeper slope have negative effects on tree growth in group selection openings, although the relative importance is smaller than light conditions. More comprehensive studies considering several openings with more heterogeneous topography including different species are needed to generalize our growth prediction using the indirect measures, which are useful for practical forest management.     

Lignin fragments rich in detached side-chain structures found in water-soluble LCC

The content of the glyceraldehyde-2-aryl ether-type structure in water-soluble lignin–carbohydrate complex (LCC) fractions, which were obtained from Japanese cedar and birch residual wood meal after milled wood lignin isolation, was determined by ozonation. Quite high amounts of the glyceraldehyde-2-aryl ether-type structure were found in water-soluble LCC fractions of both species; about 3–5 times higher than those of other fractions. This result, as well as the high content of the β-1 structure in these fractions shown in our previous reports, suggest that lignin in these fractions has the characteristics of endwise-type lignin, because the glyceraldehyde-2-aryl ether-type structure and β-1 structure are typical characteristics of this type of lignin fraction. These results are in good agreement with the generally accepted hypothesis that the glyceraldehyde-2-aryl ether-type structure and β-1 structure are generated at the same time by a radical coupling reaction. The results also indicated that these two structures are present in close proximity in the lignin.     

Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin II: effects of processing parameters

To obtain high-strength phenol formaldehyde (PF) resin-impregnated compressed wood at low pressing pressure, the effects of resin content, preheating temperature, pressing temperature, and pressing speed on the compressive deformation of oven-dried low molecular weight PF resin-impregnated wood was investigated. With an increase of PF resin content, the Youngs modulus of the cell wall perpendicular to the fiber direction decreases, and collapse-initiating pressure decreases linearly with the Youngs modulus. This indicates that the occurrence of cell wall collapse is strain-dependent. By increasing preheating temperatures, the collapse-initiating pressure increases due to the increment of the Youngs modulus of the cell wall. An increase in pressing temperature results in the thermal softening of the cell wall and causes collapse at a lower pressure. The wood is compressed effectively despite accelerated resin curing. The pressing speed significantly affects the viscoelastic deformation of the cell wall and the wood is well deformed with decreasing pressing speed, although the differences in density and mechanical properties are relatively small after a pressure-holding period of 30min. In all the parameters examined in this study, the Youngs modulus and bending strength increase with increasing density.