Masako Seki

Azelaic acid (AzA) impregnation is an effective method for improving the dimensional stability of wood; however, the related microstructural and mechanical changes in lignocellulose remain unclear. In this study, the microstructure and deformation behavior of AzA-esterified wood were investigated using an integrated approach combining thermal analysis, attenuated total reflection infrared (ATR-IR) spectroscopy, wide-angle X-ray diffraction (XRD), and compression testing. When heated below the melting point of AzA, unreacted AzA was observed on the wood surface and within the lumen. In contrast, heating above the melting point promoted diffusion of AzA into the cell wall and induced esterification, which progressed with increasing temperature. The maximum ester content was 1.08 mmol/g dry wood. Heat treatment at 120 °C or higher suggested the formation of cross-links between molecular chains. The relationship between nominal compressive stress (σ) and compression ratio (C) exhibited an inflection point at approximately 10 MPa, suggesting sliding behavior in the intercellular layer under low compressive loads. Furthermore, esterification-dependent differences in cellulose-derived molecular mobility and thermal decomposition behavior were observed.

Simulating large deformations of wood is difficult because the deformation of wood is complex, owing to the hierarchical structure of cells and annual rings. This study presents a finite element method (FEM) analysis that uses a lattice model to reproduce large wood deformations. The proposed lattice model comprises earlywood and latewood cells. The appropriate lattice geometry, considering the cell wall thickness and earlywood volume fraction, is investigated by comparing FEM analysis results with experimental results obtained via a lateral compression test. Consequently, the deformed shape and load–displacement (F–δ) diagram varied, depending on the annual ring tilt angle to the compression direction in the experiment. This anisotropy of the deformed shape was reproduced by the FEM analysis via a lattice model with an appropriate cell wall thickness and earlywood volume fraction. The F–δ diagram of the FEM was similar to that of the experiment.

In this study, we clarified the influence of lignin in wood on its plastic flow deformation due to shear sliding of wood cells. Wood samples were subjected to delignification, where the lignin structure gradually changed, and characterized for their chemical and physicochemical properties, and deformability by free compression testing. The delignified wood deformed by efficient stretching and maintained its cell structures at a lower pressure compared to the untreated wood. The deformability was evaluated from two viewpoints: the initial resistance to plastic flow and final stretchability. The deformability of the delignified and untreated wood increased with increasing compressive temperature, even though the changes in molecular motility associated with the glass transition of lignin contributed minimally to the improvement in deformability. In the early stages of delignification, the molecular mass of lignin in the compound middle lamella decreased, which reduced the initial resistance to plastic flow. However, during the early stages of delignification, the stretchability of delignified wood was scarcely affected by changes in lignin. As the amount of lignin was further reduced and delignification proceeded in the vicinity of the polysaccharides, the stretchability significantly improved. The correlation between chemical and physicochemical properties and plastic flow deformability presented in this paper will be helpful for low-energy and highly productive forming of solid-state wood.

With the aim of utilizing wood as a carbon cycle-oriented material, the improvement of hydrophobicity has been actively studied to solve manufacturing problems, such as dimensional stability and biodeterioration resistance. The introduction of benzyl group is a promising chemical modification for hydrophobizing wood. However, conventional benzylation methods are not suitable for industrial applications because they require high temperature and long reaction times. In this study, a novel method was developed for quickly benzylating the surface of block-shaped wood using an aqueous solution of tetra-n-butylphosphonium hydroxide as a pretreatment solvent and no heat. The color and shape of the benzylated wood was almost unchanged from that before the treatment. Analysis of the resulting chemical structure suggested that the developed method causes less damage to carbohydrates compared with the conventional method, which involves heating and stirring. The proposed method successfully imparted hydrophobicity and thermoplasticity to the benzylated wood surface. Furthermore, hydrophobicity of the benzylated wood was further improved by a simple heat treatment for only approximately 5 min. The water contact angle became ≥110° and remained almost unchanged even after 1 min after water dropping.

Converting wood waste into thermoplastic materials is an attractive means of increasing its utilization because complex three-dimensional molded products can easily be obtained by press molding wood with thermoplasticity. Chemical modification, especially esterification, is a promising method for imparting thermoplasticity to wood. In this study, we produced multiple propionylated wood specimens using several propionylation methods and elucidated the factors affecting the deformability of the wood. Regardless of the method, all of the propionylated wood samples showed deformability in the tangential direction. However, in the longitudinal direction, not only the degree of propionylation but also the propionylation method had a significant influence on the deformability. The flow in the tangential direction occurred under a relatively low pressure, whereas the flow in the longitudinal direction occurred under higher pressure. The chemical composition and motility of each sample were evaluated using solid-state NMR measurements. With some propionylation methods, decomposition of the cellulose main chain occurred during the reaction, which had a dominant effect on the deformability of the wood in the longitudinal direction. These results indicate that the deformability of wood can be controlled by the appropriate selection of a propionylation method and its treatment conditions.

Converting wood waste into thermoplastic materials is an attractive means of increasing its utilization. A promising method for imparting thermoplasticity to wood is chemical modification, in which the hydroxyl groups in wood are substituted with benzyl groups. In the common method, wood powder is first treated with a highly concentrated aqueous NaOH solution, and then reacted with a benzylation reagent by heating for a long time under stirring. In this study, a 50% aqueous tetra-n-butylphosphonium hydroxide solution was used for the pretreatment of wood powder. This modified alkaline treatment enhanced the efficiency of the subsequent benzylation reaction, which could be conducted without heating over a shorter time. The effects of various conditions on the efficiency of the benzylation reaction were evaluated. Both the alkali pretreatment and the subsequent benzylation required only ~5–10 min of stirring without heating to obtain benzylated wood with a similar degree of benzylation as that achieved by the common method. The chemical structure of the benzylated wood powder was characterized by Fourier-transform infrared and solid-state NMR spectroscopies, and its thermal softening characteristics were evaluated by thermomechanical analysis. Finally, a translucent film could be obtained by hot-pressing the benzylated wood powder.