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.     

Potassium acetate-catalyzed acetylation of wood: extraordinarily rapid acetylation at 120°C

The catalytic effect of potassium acetate (KAc) on wood acetylation was investigated. Spruce wood specimens were impregnated with KAc and then heated in acetic anhydride at 120°C. The degree of acetylation was evaluated by the weight percent gain (WPG). In the presence of KAc, the reaction time to achieve a 20% WPG decreased by a factor of 200: 2 min was required in the KAc-catalyzed acetylation, while the uncatalyzed acetylation required at least 5 h. The hygroscopicity and dimensional stability of acetylated wood depended on the WPG irrespective of the treatment methods. This fact proved that KAc had no adverse influence on the dimensional stability of acetylated wood. As KAc is a cheap, water-soluble and non-toxic salt it can be a useful catalyst for the extraordinarily rapid acetylation of wood.     

Potassium acetate-catalyzed acetylation of wood at low temperatures I: simplified method using a mixed reagent

Ezomatsu wood blocks were acetylated in a mixture of acetic anhydride and acetic acid containing excess potassium acetate (KAc). The mixture method enabled rapid acetylation at 120°C: a 20% weight gain (weight percent gain; WPG) was achieved within 30 min while the WPG did not exceed 18% after 120 min of conventional uncatalyzed acetylation. At 40°C, however, a satisfactory WPG was not achieved with the mixture method because both the wood swelling and KAc concentration in the reagent solution were limited at that temperature. In addition, the antiswelling efficiency attained by the mixture method was irregularly low, probably because of nonuniform reaction involving shrinkage of the cell lumina. These results suggest that the mixture method is not advantageous for low-temperature acetylation, whereas it enables simple and rapid acetylation at high temperature.     

Preparation of acetylated wood meal and polypropylene composites I: acetylation of wood meal by mechanochemical processing and its characteristics

Wood meals of Sugi (Cryptomeria japonica D.Don) passing 2.0 mm and retained on 1.0 mm mesh screens were milled along with acetic anhydride (AA) and pyridine as a catalyst in a high-speed vibration rod mill at ambient temperature. The weight percent gain (WPG) of the chemically modified wood was calculated based on the yield after washing with deionized water. The effects of amounts of AA and catalyst added, pulverization time, and saponification of the acetylated wood on WPG were examined. In addition, FT-IR analysis, and water vapor adsorption and desorption tests were performed as functions of the WPG. Increases in WPG, the acetyl contents of the acetylated wood after saponification, changes in the FT-IR spectra after pulverization, and the water vapor sorption isotherms showed that the one-step acetylation systematically modified the hydroxyl groups of the wood into acetyl groups. Up to 38 % WPG was obtained at 100 phr AA and 15 phr catalyst, and 120 min pulverization. Pulverization time and the amounts of AA and catalyst added to the wood meals could be adjusted to obtain acetylated wood meal with the desired WPG. These demonstrated that the mechanochemical acetylation is a method to prepare acetylated wood meals with high WPG at less reaction time and required AA addition.     

Non-uniform reaction of solid wood in vapor-phase acetylation

To clarify the non-uniform reaction of wood during vapor-phase acetylation, spruce wood blocks were exposed to acetic anhydride vapor at 120°C. Weight percent gain (WPG) due to the acetylation was estimated from the equilibrium moisture content at 25°C and 60% relative humidity. The diffusion of reagent vapor was much faster along the longitudinal direction than along the tangential direction. When the end surface was exposed to the reagent vapor for 48?h, 20% WPG, which was known to have sufficient stability and durability, was achieved to a depth of 42.5?mm. However, this depth was only 6.5?mm when the straight-grain surface was exposed. The reaction profiles were successfully approximated using reaction time (t), reaction rate (k′), delay time (t _d′), and a parameter n reflecting the diffusion-controlled reaction. The t _d′ value increased almost linearly as the depth increased from the surface. The k′ value ranged from 0.02 to 0.03?h^?1, regardless of the depth and direction of diffusion. The n value decreased with an increase in the depth and approached 1–2. These values enabled the prediction of the degree of acetylation at any reaction time and positions of wood during vapor-phase acetylation.     

Effects of previous solvent exchange on acetylation of wood

Wood specimens were prepared in a swollen state using solvent exchange (PS) treatment. The swollen wood specimens were acetylated using acetic anhydride by heating at 80–120°C. At the beginning of heating, the weight percent gain (WPG) of PS-treated wood was greater than that of conventionally acetylated wood. This acceleration effect of the PS treatment was explained by the introduction of treating reagent into the wood polymers where the intermolecular hydrogen bonds were previously broken. On the other hand, the PS treatment had no influence on the final WPG and moisture sorption characteristics of acetylated wood. This indicated that the intrinsic reactivity of wood constituents was unaffected by the PS treatment. The acetylation of PS-treated wood produced greater bulking and slightly higher dimensional stability than that in the case of conventional acetylation at the same WPG. It was speculated that the expansion of cell lumina due to the PS treatment resulted in greater bulking on acetylation and lesser swelling of acetylated wood with moisture sorption.     

Preparation of acetylated wood meal and polypropylene composites II: mechanical properties and dimensional stability of the composites

Acetylated wood meals of Sugi (Cryptomeria japonica D.Don) wood were prepared by mechanochemical processing using a high-speed vibration rod mill. Weight percent gain (WPG) of the acetylated wood meals ranged from 7.0 to 35.5 %. Wood–plastic composites (WPCs) containing 50 % acetylated woods were produced by an injection molding technique. The polymer matrix used was polypropylene homopolymer. Maleic anhydride-grafted polypropylene (MAPP) was also used as a compatibilizing agent. The mechanical properties of WPCs in bending and tensile tests were independent of WPG of acetylated wood meals, and the test values for WPCs containing acetylated wood meals were lower than that of unmodified wood meal. The use of MAPP increased bending and tensile strength, but no effect on bending modulus was found. An increase in WPG significantly decreased water absorbability and thickness swelling of WPCs as measured by dimensional stability tests. These results demonstrated that mechanochemical processing is a promising technique for preparing WPC material with improved dimensional stability. The future challenge is to inhibit the decreases in mechanical properties of WPCs containing acetylated wood meals.     

A novel method of acetylation of wood using supercritical carbon dioxide

Sugi heartwood was acetylated with acetic anhydride in supercritical carbon dioxide (CO₂) (120°C or 130°C, 10–12 MPa). As a result, the weight percent gain increased with increasing acetylation time up to 16%–20% at 1 h and 24%–28% at 24 h. The antiswelling efficiency of the acetylated specimens reached 75%–80% at 3–4 h of acetylation. It is supposed that the acetylation in supercritical CO₂ has a high bulking effect compared with liquid-phase and vapor-phase acetylation with uncatalyzed acetic anhydride. The results showed that the acetylation progressed rapidly because supercritical CO₂ and acetic anhydride formed a single phase at more than 90°C, and the acetic anhydride reached the reaction sites in the wood quickly.     

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.This paper was presented at the 46th and 47th annual meetings of the Japan Wood Research Society at Kumamoto and Kochi in April 1996 and April 1997, respectively     

Temperature dependence of the dynamic viscoelasticity of bases of Japanese cypress branches and the trunk close to the branches saturated with water

With the aim of obtaining findings on the dynamic properties of branches and their bases, as well as their support mechanisms, the present study examined the temperature dependence of the dynamic viscoelasticity of Japanese cypress samples saturated with water to clarify the responses in different regions, and identified factors influencing the characteristics. In the bases of the branches: E′ sharply decreased at approximately room temperature and significantly decreased at around 20 and 60 °C; a peak and shoulder peak of E″ or tan δ were noted at around 20 °C, and there was another peak of tan δ at around 60–80 °C; and mechanical relaxation was noted at around 20 °C and 60–80 °C. On the other hand, in some regions, including the trunks, branches, and their bases, mechanical relaxation was only noted on the high-temperature side. However, boiling treatment with about 12 % weight loss inhibited mechanical relaxation, and there were decreases in E′, E″, and tan δ at approximately room temperature. The bases of the branches of Japanese cypress are considered to develop its elasticity and viscosity to tolerate external stress by accumulating an extract, which enhances the strength of lignin.     

Acetylation of wood in combination with polysiloxanes to improve water-related and mechanical properties of wood

Scots pine sapwood was acetylated with ethyltriacetoxysilane using acetic acid as a solvent and sulfuric acid as a catalyst. A weight percent gain (WPG) of 14 % and cell wall bulking of 7 % were obtained after 5 h of reaction time. Pine specimens were acetylated with acetic anhydride in the presence of 1 % ethyltriacetoxysilane, dihydroxy-functional siloxane, acetoxy-functional siloxane, amino-functional siloxane and non-functional siloxane, respectively. Acetoxy-functional siloxane induced the greatest reduction in water uptake with a water repellent effectiveness after 24 h of up to 62 % as compared to acetylated wood. WPG and cell wall bulking increased compared to solely acetylated wood with increasing concentrations of acetoxy-functional siloxane in acetic anhydride; anti-shrink efficiency, however, did not increase. Fungal resistance of pine sapwood and beech as well as mechanical strength properties did not change when 20 % acetoxy-functional siloxane was added to acetic anhydride compared to solely acetylated specimens.     

Interaction between glycerin and wood at various temperatures from stress relaxation approach

In order to understand the reason why glycerin pre-treatment can accelerate the deformation fixation of compressed wood, the interaction between glycerin and wood at various temperatures was investigated in this study from stress relaxation approach. The compression stress relaxation curves of poplar (Populus cathayana Rehd.) samples impregnated with glycerin were measured at temperatures ranging from 25 to 180°C, together with the curves of oven-dry wood at temperatures between 100 and 180°C for comparison. The activation energy was calculated according to the Eyring’s absolute rate reaction theory. The results showed that temperature had very obvious effect on stress relaxation for both glycerin-treated wood (GTW) and oven-dry wood. The stress released very fast at higher temperatures. Glycerin showed an accelerating effect on stress relaxation. At temperatures exceeding 120°C, a complete relaxation of the stress could be expected. While for untreated wood, it cannot be reached until 160°C. By calculating the apparent activation energy (ΔE) of GTW at different temperatures, it is clear that two mechanisms are responsible for different temperature ranges. From 40 to 100°C, ΔE is only 8.24 kJ/mol, which corresponds to the hydrogen bonds formed between wood and glycerin molecules; from 120 to 180°C, ΔE reached 81.38 kJ/mol, which corresponds to the degradation of hemicelluloses or lignin, and during this process, new cross-linking would happen.     

Optimization study for preparation of activated carbon from Acacia mangium wood using phosphoric acid

A study on the preparation of activated carbon from Acacia mangium wood was conducted, and the operating factors, such as activating agent concentration, activation temperature and activation time, were optimized using response surface methodology. In order to determine the effects of the operating factors namely H₃PO₄ concentration (6.48–48.5 %), activation temperature (364–1,036 °C) and activation time (19–146 min) on the characteristics of activated carbon, a three-level rotatable central composite design was used. The second-order mathematical model was proposed by regression analysis of the experimental data gathered from 20 batch runs. The optimum H₃PO₄ concentration, activation temperature and activation time were found to be 40 %, 900 °C and 45 min, respectively. At optimum conditions of the operating factors, the percent yield and surface area were 20.3 % and 1,767 m²/g, respectively. The activated carbon was found to be largely composed of mesopores. About 95 % of the total surface area was attributed to mesopores.     

Effects of preheating temperatures on the formation of sandwich compression and density distribution in the compressed wood

Sandwich compression of wood that can control the density and position of compressed layer(s) in the compressed wood provides a promising pathway for full valorization of low-density plantation wood. This study aims at investigating the effects of preheating temperatures (60–210 °C) on sandwich compression of wood, with respect to density distribution, position and thickness of the compressed layer(s). Poplar (Populus tomentosa) lumbers with moisture content below 10.0% were first soaked in water for 2 h and stored in a sealed plastic bag for 18 h, the surface-wetted lumbers were preheated on hot plates at 60–210 °C and further compressed from 25 to 20 cm under 6.0 MPa at the same temperature on the radial direction. The compressed lumbers were characterized in terms of density distribution, position and thickness of compressed layer(s). It was found that depending on preheating temperatures, sandwich compressed wood with three structural modes, namely, surface compressed wood, internal compressed wood and central compressed wood can be formed. Density of the compressed layer(s) in wood increased gradually as a result of the elevated preheating temperatures. Higher preheating temperatures gave rise to bigger distance between compressed layer(s) and the surface, and preheating temperature elevation from 90 to 120 °C contributed to a maximal distance increase of 2.71 mm. In addition, higher preheating temperatures resulted in bigger thickness of compressed layer(s) over 60–150 °C and temperature elevation from 120 to 150 °C lead to the layers integration from two into one. Further temperature elevation over 150 °C reduced the thickness of the compressed layer in wood. SEM scanning suggested that cell wall bucking rather than cell wall crack occurred in compressed layer(s) and transition layer(s).     

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

Possible altitude and temperature limits on pine wilt disease: the reproduction of vector sawyer beetles (Monochamus alternatus), survival of causal nematode (Bursaphelenchus xylophilus), and occurrence of damage caused by the disease

Pine wilt disease is caused by the pine wood nematode [Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle]. In East Asia, an important vector of the nematode is Monochamus alternatus Hope. We determined the tolerance and reproductive ability of sawyer beetles and the nematode to altitude and temperature at elevations between 850 and 1,450 m on Mt. Fuji in Japan. The number of emergent adults decreased markedly along the altitudinal gradient, but the beetle could still reproduce at 1,050 m (8.2 °C annual mean temperature). Beetles with a 2-year life cycle increased rapidly in number with increasing altitude. The pine wood nematode survived through winter at all altitudes tested (850–1,450 m). The beetle population decreased between 950 (9.1 °C) and 1,150 m (8.3 °C). Therefore, the beetle population seems to be stable at 850 m (10.2 °C) and lower altitudes (higher temperatures) but cannot be maintained from 950 (9.1 °C) to 1,150 m (8.3 °C) without constant immigration of beetles from lower altitudes. The beetles could not reproduce at altitudes above 1,150 m (lower than 8.2 °C). From the mean and effective cumulative temperatures, we concluded that the beetle (and its population) can endure temperatures lower than those previously reported. Pine wilt disease also occurred at lower temperatures and higher altitudes than expected. We have summarized the principal strategies for controlling the disease at high altitudes based on these results.     

Curing kinetics study of melamine–urea–formaldehyde resin/liquefied wood

The objective of this research was to investigate the effect of liquefied wood (LW) on the cure kinetics and network properties of melamine–urea–formaldehyde (MUF) resins by differential scanning calorimetry. The MUF/LW compounds exhibited two distinct cross-linking processes. It can be assumed that there did not appear to be a coreaction of the MUF with the LW. The overall apparent activation energies (E _a) of the curing reactions were calculated using the Kissinger equation. An nth-order kinetic model was used to describe the cross-linking of MUF/LW compounds, of various compositions, cured at different heating rates. The E _a values for the cross-linking process of the MUF/LW compounds predominantly tended to be approximately 80 and 71 kJ mol^?1 for MUF and LW, respectively. The apparent reaction orders of the MUF cross-linking process of the MUF/LW compounds were in the range 1–2, whereas the n values of the LW were approximately unity or less, which hints to there being a more complex mechanism of this process.     

Provenance variation in growth and wood properties of juvenile Cyclocarya paliurus

Cyclocarya paliurus is a highly valued and multiple function tree species. There has been increasing interest in planting and managing C. paliurus for timber production and medical use owing to loss of harvestable acreage. Seed from six provenances was collected from the main natural range of this species. Significant variation in growth and wood properties was measured among the six provenances at age 7 years. Provenance mean height and DBH varied significantly from 730–991 and 6.7–10.0 cm, whereas provenance means of wood basic density and crystallinity ranged from 463–554 kg m^?3 and 51.4–74.1 %, respectively. Mean provenance microfibril angle (MFA) at breast height ranged from 18.1° to 23.2°, while MFA at breast height varied from 11.0° to 34.5° among growth rings which showed a consistent pith-to-bark trend of declining angles. There was no significant relationship of growth rate with latitude or longitude of seed sources, however, provenances from low latitude and longitude grew faster at the trial site. Wood quality was significantly related to latitude of seed sources, showing a positive correlation for both wood basic density and wood crystallinity, but a highly negative association with MFA. Significant correlations between wood properties measured indicated that there exists a great opportunity to improve wood quality of C. paliurus through selection of juvenile trees with low MFA.     

Dynamic viscoelastic properties of wood acetylated with acetic anhydride solution of glucose pentaacetate

 Spruce wood specimens were acetylated with acetic anhydride (AA) solutions of glucose pentaacetate (GPA), and their viscoelastic properties along the radial direction were compared to those of the untreated and the normally acetylated specimens at various relative humidities and temperatures. Higher concentrations of the GPA/AA solution resulted in more swelling of wood when GPA was introducted into the wood cell wall. At room temperature the dynamic Young's modulus (E′) of the acetylated wood was enhanced by 10% with the introduction of GPA, whereas its mechanical loss tangent (tan δ) remained almost unchanged. These changes were interpreted to be an antiplasticizing effect of the bulky GPA molecules in the wood cell wall. On heating in the absence of moisture, the GPA-acetylated wood exhibited a marked drop in E′ and a clear tan δ peak above 150°C, whereas the E′ and tan δ of the untreated wood were relatively stable up to 200°C. The tan δ peak of the GPA-acetylated wood shifted to lower temperatures with increasing GPA content, and there was no tan δ peak due to the melting of GPA itself. Thus the marked thermal softening of the GPA-acetylated wood was attributed to the softening of wood components plasticized with GPA. Received: March 29, 2002 / Accepted: May 21, 2002 Correspondence to:E. Obataya     

Moisture-dependent orthotropic viscoelastic properties of Chinese fir wood in low temperature environment

The influence of moisture content (MC) on the orthotropic viscoelasticity of Chinese fir wood (Cunninghamia lanceolata [Lamb.] Hook.) has been examined in low temperature environment. Storage modulus E′ and loss modulus E″ of wood with six different levels of MC ranging from 0.6 to 22.0% were determined from ??120 to 40 °C and at multi-frequency range of 0.5, 1, 2, 5, and 10 Hz using a TA instruments^® Dynamic Mechanical Analyzer (DMA 2980). The results showed that a distinct moisture dependency is exhibited by the orthotropic viscoelastic behaviour of Chinese fir wood. With the exception of some apparent activation energy (ΔE) for β-relaxation process, the E′ decreased and the E″ peak temperatures moved towards lower temperature and the ΔE for α-relaxation process became lower with MC increasing in all orthotropic directions, whereby individual decline of E′ and the E″ peak temperatures were affected by MC to different degrees. Besides, a little E″ peak at around 0 °C was only seen in L direction, which could be attributed to the melting of frozen water. Furthermore, the dynamic viscoelastic behavior of wood is also dependent on the measurement frequency. The findings suggest that the orthotropic structure and moisture content have an important influence on the viscoelastic performance in low temperature environment.