Masakazu Nishida

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.

Reactions of bifunctional perfluoroarylsilanes, p- and m-C₆F₄(SiMe₃)₂ as well as o-BrC₆F₄SiMe₃, with substituted perfluoroarenes having electron-withdrawing groups were investigated using NMR and density functional theory calculation techniques. The C–F bond in perfluoroarenes was activated by the para-position of an electron-withdrawing group, such as CF₃, C₆F₅, CN, and NO₂. The reaction of C₆F₄(SiMe₃)₂ mainly occurred at the para-position of the perfluoroarenes and also occurred at the ortho-position of C₆F₅CN and C₆F₅NO₂. Two equivalent reactions of perfluoroarenes with bifunctional p- and m-C₆F₄(SiMe₃)₂ provided disubstituted perfluoroarenes, along with a small amount of protonated monosubstituted perfluoroarenes. The reaction of o-BrC₆F₄SiMe₃ with the CF₃- and CN-substituted pentafluorobenzenes provided unexpected coupling products between C–Br and C–F bonds, in addition to the coupling products between C–SiMe₃ and C–F bonds.