Establishment of the method for preparing cellulose materials “colorless woods” derived from hardwoods with various densities and anatomical structures

Abstract This research reports novel cellulosic materials named “colorless hardwoods”, which have no lignin and almost no hemicellulose, derived from three wood species with different anatomical structures: Fagus crenata (diffuse-porous), Paulownia tomentosa (semi-ring-porous), and Zelkova serrata (ring-porous). To create these colorless hardwoods, we have employed alcoholysis and the Wise treatment, recognized as delignification methods for softwood and bamboo. The process of alcoholysis was carefully optimized based on the progress of the decolorization and the delignification of wood samples. After the optimization of the alcoholysis, the Wise treatment was applied, leading to the successful removal of non-cellulosic components from each of the three hardwood types. The preservation of the wood's morphology has been confirmed by confocal laser scanning microscopy, which showed no alteration in the woody anatomical structure in terms of cell wall shape and cell arrangement. Moreover, X-ray diffraction analyses indicated the retention of microfibril angles and the crystalline structure of cellulose within the cell wall. These results conclusively demonstrate that colorless hardwoods maintain the original hierarchical structure of their respective wood species and differ significantly from typical pulp and cellulose nanofibers in terms of suprastructure. This advancement in wood-based cellulosic materials opens new avenues for application, highlighting their potential for diverse and sustainable uses.