Influence of Lignin On Plastic Flow Deformation of Wood

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.

Flow deformation characteristics of African blackwood, Dalbergia melanoxylon

African blackwood (ABW: Dalbergia melanoxylon) is a valuable tree in Tanzanian local community forests, and heartwood has been mainly utilized as an irreplaceable material in musical instruments, e.g., clarinet, oboe and piccolo. Since its use is generally for the production of musical instruments only, most of the harvested volume is wasted due to defects that would affect the quality of final products. Wood flow forming can transform bulk woods into materials in temperature/pressure-controlled mold via plastic flow deformation. The main object of this study was to evaluate the deformation characteristics of ABW heartwood in developing the potential of wasted ABW parts in terms of the effective material use. The deformation characteristics of heartwood were examined by free compression tests. Specimens were compressed along the radial direction at 120 °C, and air-dried heartwood was dramatically deformed in the tangential direction. The plastic flow deformation of ABW was amplified by the presence of both extractives and moisture. In particular, the ethanol/benzene (1:2, v/v) soluble extractives in heartwood may have contributed to flow deformation. The results of the dynamic mechanical analysis showed that the air-dried heartwood exhibited softening in a temperature range over 50 °C. The ethanol/benzene-soluble extractives contributed to the softening behavior. The clarified deformation characteristics of ABW can contribute to more efficient material use of local forests.