Mitsuhiko Tanahashi

Compressive-molding of wood by high-pressure steam-treatment : Part 1. Development of compressively molded squares from thinnings

We attempted to compressive-mold logs of sugi (Cryptomeria japonica D.Don) to squares, and to permanently fix the transformed shape. The transformation and fixation were successively conducted under high-temperature saturated steam atmosphere by a newly designed apparatus which was a combined pressure vessel and a press machine. The results are summarized as follows: (1) The logs were successively softened by steaming at 150°C, compressively molded to square, and fixed the transformed shape by steaming at 200°C in this apparatus. (2) The shape of square fixed by high-pressure steam-treatment did not recover to original log shape by water-soaking and boiling. The result shows that the high-pressure steaming is effective for permanent fixation of the transformed shape. (3) The condition for sufficient fixation of the compressive transformation was steaming at 220°C for 3min when a 15 cm of diameter and 10cm of length sugi-thinning was used as a specimen. (4) Inner stress within a compressed wood was gradually reduced during steaming and. finally, the stress was removed completely.

Compressive-molding of wood by high-pressure steam-treatment : Part 2. Mechanism of permanent fixation

Permanent fixation of the compressively transformed shape of Harigiri (Kalopanax pictus Nakai) specimens was attempted by steaming them, compressively transforming their shapes, and processing them with high-pressure steam again. Also, the mechanism of the shape fixation was examined. The results are summarized as follows: (1) Compressively transformed Harigiri specimens, after being processed with high-pressure steam, did not recover to their original shape with heat and moisture, thus achieving permanent fixation of compressed shape. (2) The conditions under which the fixed specimens would not recover to their original shape were found to be steaming with saturated steam at 200°C for 4min or longer or at 180°C for 8min or longer, within the scope of the current experiment. (3) Hemicellulose and lignin do not affect the fixation of compressive transformation. (4) The fixation of compressive transformation is caused by a structural change of cellulose. (5) The mechanism of fixation of compressive transformation is supposed to be that the inner stress is released because the paracrystalline region of cellulose, which is distorted by compressive transformation, is partially hydrolyzed. Further, steam-rearrangement of hydrolyzed constituent into crystalline region occurs, keeping the transformed shape intact.

Substituent effects of 3,5-disubstituted p-coumaryl alcohols on their oxidation using horseradish peroxidase–H2O2 as the oxidant

The consumption rates of three monolignols (p-coumaryl, coniferyl, and sinapyl alcohols) and eight analogues using horseradish peroxidase (HRP)–H2O2 as an oxidant were measured and compared with the anodic peak potentials thereof measured with cyclic voltammetry. 3-Monosubstituted p-coumaryl alcohols, i.e., 3-methoxy-, 3-ethoxy-, 3-n-propoxy-, and 3-n-butoxy-p-coumaryl alcohols, had faster reaction rates than p-coumaryl alcohol. This is most probably due to the electron-donating effect of alkoxyl groups. However, the reaction rates gradually decreased with an increase in the molecular weight of the alkoxyl groups. Furthermore, t-butoxyl group, which is a very bulky substituent, caused an extreme reduction in the reaction rate, even though its electron-donating effect was almost the same as that of other alkoxyl groups. The reaction rates of 3,5-disubstituted p-coumaryl alcohols, especially 3,5-dimethyl-p-coumaryl alcohol, were very low compared with 3-monosubstituted p-coumaryl alcohols. These results suggest that there are three main factors of hindrance during the approach of monolignols to the active site of HRP. First, from the results of 3-monoalkoxy-p-coumaryl alcohols, it was suggested that the volume of substituents could decrease their oxidation rates. Second, from the results of 3,5-disubstituted p-coumaryl alcohols, it was suggested that local steric hindrance by the amino residues quite near the heme decreased the oxidation rates. Third, from the results of the substrates with hydrophobic substituents at their 3,5-positions, we suggested that hydrophilicity near heme would decrease their oxidation rates.

Chemical degradation methods for characterization of lignins

Publisher Summary Lignins are complex aromatic polymers that are generally classified into three major groups based on their structural monomer units. The monomeric phenylpropane units in lignins are connected by both ether and carbon- carbon linkages. Arylglycerol-β-aryl ether is the most abundant interphenylpropane linkage (45%) in lignins, followed by phenylcoumaran (14%), diarylpropane (15%), resinol (13%), biphenyl (25%), and diphenyl ether (5%). Thus, it is important for the characterization of lignins to determine the ratio of guaiacyl, syringyl, and p-hydroxyphenyl units with these lignin substructures. Compared to acidolysis, thioacidolysis gives less complex mixtures of monomers. The monomer yields in thioacidolysis from lignin are higher than in acidolysis. This increased yield is particularly evident for hardwood lignins. Therefore, thioacidolysis gives more reliable monomeric composition of hydrolyzable structures of lignin.

Effect of adding steam-exploded wood flour to thermoplastic polymer/wood composite

The effect of steam-exploded wood flour (SE) added to wood flour/plastic composite was examined using SE from beech, Japanese cedar, and red meranti and three kinds of thermoplastic polymer: polymethylmethacrylate, polyvinyl chloride, and polystyrene. Addition of SE increased the fracture strength and water resistance of the composite board to an extent dependent on the polymer species and the composition of wood/SE/polymer. However, water resistance decreased with the increasing proportion of SE when SE meranti was added. Effects of the wood species of SE on the properties of resulting board were small. An increased moisture content of wood flour or SE (or both) increased the variation of board performance.

Comparative Study on Mild Depolymerization of Lignin Model Dehydrogenation Polymers and Milled Wood Lignin

Abstract Dehydrogenation polymers (DHPs) of coniferyl alcohol prepared in three different ways (bulk, end-wise and membrane) and spruce (Picea mariana) milled wood lignin (MWL) were depolymerized with dry hydrogen iodide. The amounts of the only monomeric product, 1,3-diiodo-1-(4-hydroxy-3-methoxyphenyl)propane and oligomeric products resulted from this procedure were compared. All DHPs differ noticeably from MWL in their structural organization, the bulk one being the best approximation. Yields of the diiodide were high in all cases (end-wise DHP: 45%, membrane DHP: 55%, MWL and bulk DHP: 20%). Molecular mass distributions of higher molecular mass products were similar in all the cases except end-wise DHP which demonstrated lesser degree of polymerization of high molecular mass fraction.

Transition state leading to β-O′ quinonemethide intermediate of p -coumaryl alcohol analyzed by semi-empirical molecular orbital calculation

The radical coupling reaction leading to the β-0′ quinonemethide intermediate of p-coumaryl alcohol was analyzed by semi-empirical molecular orbital calculation with MOPAC2002. By analyzing the radical monomer in a one-electron oxidation, the spin density of the unpaired electron at the 4-oxygen was less than half of the values at the C1, C3, C5, and Cβ positions. By analyzing the transition state during the radical coupling reaction, the activation enthalpy was evaluated as 9.76 kcal/mol, which corresponds to the activation energies for the propagation of common vinyl polymers. From the analysis of atomic interactions in the transition state, it was found that the activation enthalpy was largely composed of a high coulombic repulsion between Cβ of the first monomer and the phenolic oxygen of the second monomer. After passing the transition state, the two radical monomers formed a metastable quinone-methide intermediate. The optimum conformation of the quinonemethide intermediate was formed from the meta-stable conformation through a second transition state with a small energy barrier.

Application of the DFRC (Derivatization Followed by Reductive Cleavage) Method to Dilignols

Abstract The DFRC method was applied to dimeric model compounds of lignin; dehydrodiconiferyl alcohol, syringaresinol, pinoresinol, syringylglycerol‐β‐sinapyl ether, and guiacylglycerol‐β‐coniferyl ether. Dehydrodiconiferyl alcohol yielded no coniferyl alcohol, but syringaresinol and pinoresinol gave small amounts of corresponding p‐hydroxycinnamyl alcohol. In the case of syringaresinol, an acetylated bromo dihydro‐(Compound 1, 23%) and tetrahydronaphthalene (Compound 2, 52%) were obtained after acetyl bromide treatment, the first step in the DFRC method. Further, a small amount of sinapyl alcohol diacetate was obtained from compounds 1 and 2 by zinc and successive acetylation treatments. Compound 2 yielded a larger amount of sinapyl alcohol than compound 1. We thank Dr. Shingo Kawai, Shizuoka University, for giving us guiacylglycerol‐β‐guiacyl ether. We also thank Dr. Siaw Onwona‐Agyeman, Gifu University, for helping in the preparation of this manuscript. Finally, we thank the staff of the Division of Instrumental Analysis, Life Science Research Center, Gifu University, for their help in 1H‐NMR, 13C‐NMR, and GC‐MS analysis.