In-situ synchrotron SAXS/WAXD analysis for tracking the change in multiscale structure of wood during macroscopic flexural deformation

Mechanical properties of wood are governed by its hierarchical organization across multiple length scales. This study hypothesizes that hierarchical structural changes in wood during macroscopic flexural deformation can be detected using in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) analysis in synchrotron radiation facility. The in-situ SAXS/WAXD experiments were conducted on water-saturated wood of Japanese larch (Larix kaempferi), with the specimen's length aligned along the tangential (T) direction. Flexural deformation was applied along the fiber direction of wood, inducing tensile and compressive strains in the T direction. SAXS profiles revealed expansion and densification of cellular structure under tensile and compressive strains, respectively. Fitting analysis using WoodSAS model (Penttilä et al., 2019) suggested that tensile and compression strains caused the increase and decrease in interfibrillar distance of cellulose microfibril (CMF), respectively. It was also suggested that the compressive strain reduced the smoothness of cell-lumen surface, whereas the tensile strain promoted the formation of microcracks. WAXD analysis showed that the lattice spacing and crystallite size of cellulose in the (200) plane remained unchanged under both tensile and compressive strains. These findings demonstrated that in-situ SAXS/WAXD analysis are effective for tracking multiscale structural changes in wood during macroscopic deformation.