Makoto Ohkoshi

FTIR-PAS study of light-induced changes in the surface of acetylated or polyethylene glycol-impregnated wood

The objective of this study was to characterize the surface changes in acetylated and polyethylene glycol (PEG)-impregnated wood caused during light irradiation by Fourier transformed infrared photoacoustic spectroscopy analysis to determine their effects on the reduction of light deterioration. Light irradiation made the color of the chemically modified wood lighter or more vivid, whereas it deepened the color of the untreated wood. The color difference during light irradiation was less in the chemically modified wood than the untreated wood. The color difference of PEG-impregnated wood increased with increasing irradiation time. The light irradiation generated much carbonyl and significantly degraded lignin in the untreated wood. The generation of carbonyl and lignin degradation diminished in the acetylated wood in comparison with the untreated wood, indicating that acetylation restrained the photochemical degradation of wood. Deacetylation did not occur during light irradiation of the acetylated wood. The PEG impregnation decreased the generation of carbonyl and degradation of lignin during light irradiation. However, the irradiation occurred a little photochemical degradation of PEG, generating the carbonyl. Therefore, longer light irradiation should increase the degradation of PEG, thus reducing the effect of treatment. The correlation between the color difference and lignin degradation was high, indicating that the color changes during light irradiation significantly depended on lignin degradation. The chemical modification reduced the degradation of lignin and consequently decreased the color difference. Some of the compounds containing the carbonyl generated during light irradiation were water-soluble.

Characterization of acetylated wood decayed by brown-rot and white-rot fungi

The objective of this study was to characterize the decay of acetylated wood due to brown-rot and white-rot fungi by analysis of chemical composition, X-ray measurements, and13C-NMR spectroscopy. The decay by brown-rot fungus became inhibited at a weight percent gain (WPG) due to acetylation of more than 10%, and the mass loss (LOSS) due to decay became zero at a WPG of about 20%. The LOSS due to white-rot fungus decreased slowly with the increase in WPG, reaching zero at a WPG of about 12%. The losses of lignin by brown-rot decay increased initially with the decrease in LOSS owing to the progressing acetylation and then decreased at a LOSS of less than 60%. Polysaccharides were more easily decomposed than lignin during the decay of acetylated wood due to brown-rot fungus. The losses of both components due to white-rot decay decreased as the LOSS decreased with progressing acetylation. The white-rot fungus tended to preferentially decompose the lignin during the decay of acetylated wood. The brown-rot fungus decomposed the cellulose in the crystalline region to a large degree when the LOSS was more than 40%, whereas the white-rot fungus decomposed the crystalline region and the noncrystalline region in acetylated wood to the same degree. The brown-rot fungus preferentially decomposed unsubstituted xylose units in acetylated wood and partly decomposed the mono-substituted xylose units. It was suggested that the mono- and disubstituted cellulose were partly decomposed by brown-rot fungus.

Changes in micropores in dry wood with elapsed time in the environment

To investigate the changes in microstructures of wood with elapsed time in the environment, CO2 adsorption onto dry wood was measured at ice-water temperature (273 K) for samples aged from 0.1 years to over 1000 years. The micropore size distribution was obtained using the Horvath-Kawazoe method. Micropores smaller than 0.6 nm in wood decreased in number with elapsed time in the environment, and a negative correlation was found between cumulative pore volume for pores smaller than 0.6 nm and elapsed time in the environment. Cumulative pore volume in the 1000-year sample was almost half of that in the 0.1- year sample. Micropores smaller than 0.6 nm in wood with a few decades or more of elapsed time increased in number after rewetting and drying. Consequently, microstructures of wood with longer time elapsed in the environment were considered to be more stable, because of longer-term thermal motion and possibly more repeated moisture adsorption and desorption and/or temperature variation in the environment.

Characteristics of antibacterial molecular activities in poplar wood extractives

As one of the dominant plantations in north and central China, poplar was considered as the uppermost wood raw materials, however, the chemical constituents of poplar wood weren’t effectively used by high added value. Therefore, the molecules of wood extractives in Populus lasiocarpa and Populus tomentosa were extracted and studied to further utilize the bio-resources. The results showed that the LD-010, LD-021, LD-150, LD-174 wood extractives were identified as having 3, 24, 3 27 components, respectively. P. lasiocarpa wood was fit to extract 2,4-hexadiyne, 1,3,3-trimethyl-2-hydroxymethyl-3,3-dimethyl-4-(3-methylbut-2-enyl)-cyclohexene, and P. tomentosa wood was fit to extract 1,5-hexadien-3-yne, (all-E)-2,6,10,15,19,23-hexamethyl-2,6,10,14,18,22-tetracosahexaene. So the extractives of poplar wood contained rich and rare drug and biomedical activities.

Cooling set and its recovery in water-saturated bamboo under large bending deformation.

To clarify the bending properties and cooling set for bamboo under large deformation, the relationship between applied deflection and residual deflection was investigated, and comparison was made with the results of thermal recovery and anatomical changes due to deformation. No clear effect of initial deflection on set measured after a long time was found for wood and bamboo loaded on the epidermis side (Bepi). On the other hand, set for bamboo loaded on the endodermis side (Bendo) increased with deformation level. Recovery from the deformation with time for Bendo was almost complete at around 1000 min after unloading in the three-point bending method. This recovery behavior was not seen for Bepi or wood. It was considered that no failure was caused in the bent specimen, because most of the deformation was completely recovered by reheating to the temperature at which the specimens were deformed before cooling. The recovery from deformation for Bendo loaded by the four-point bending method continued even after 1000 min. From microscopic observations, shearing deformations were seen for Bendo loaded by the three-point bending method. From these results, it can be considered that shearing deformations between the two loaded points effectively contribute to decreased recovery force from deformations for Bendo.

The effect of lignin on the bending properties and fixation by cooling of wood

To clarify the effects of lignin on the fixation of bending deformation by cooling, cooling set for delignified woods with various lignin residues were investigated to compare with mechanical and dynamic viscoelastic properties. Bending tests showed that steep reductions occurred in the modulus of elasticity and modulus of rupture with delignification during the initial stage of delignification. The dynamic viscoelastic measurements revealed that the peak temperature of tan δ due to micro-Brownian motion of lignin was reduced with delignification, and the peak disappeared in the temperature range of 5°–100°C for the specimens that had lost more than 21% of their weight. On the other hand, no clear change in residual set was found in the range of 0%–15% of weight loss in spite of a marked reduction in lignin content. Subsequently, set decreased steeply for the specimens delignified beyond 15% of weight loss. It was suggested that cooling set is not determined solely by lignin content but is influenced by changes in the quality of lignin due to delignification. Lignin quality affects the balance of the elastic potential to recover from deformation and its viscosity, which is an indication of resistance against flow.

Characteristics of bamboo tissue in relation to cooling set

To clarify the effects of tissue and structure of bamboo on its bending properties and set by cooling (bent at 90°C and cooled to 20°C with bending), the effects of set in bast-fiber-rich (Bfib) and parenchyma-cell-rich (Bpar) specimens were investigated with regard to their dynamic viscoelastic properties, chemical composition, and recovery from deformation with time. The results are summarized as follows: (1) while no clear effect of the proportion of parenchyma cells and bast fibers on residual set immediately after cooling was found, the relative recovery from the deformation with time for Bfib was larger than that for Bpar. (2) Slightly higher lignin content and a-cellulose were seen in Bfib than in Bpar. (3) The peak temperature of loss modulus (E″) found for Bpar, which was attributable to micro-Brownian motion of lignin, was obviously lower than that for Bfib. This was considered to be due to differences in the degree of condensation of lignin or higher-order structure. From these results, it was deduced that the bastfiber-rich specimen, which showed a higher peak temperature regarding thermal softening of lignin allowing the induction of insufficient thermal-softening in the range of 20° to 90°C, caused a larger recovery from deformation with time.