Structural control is essential for further development of cellulosic materials. Here, we demonstrated the significance of the orientation and degree of polymerization in the integrated structure of cellulose microfibrils using sheets based on the hierarchical structure of wood. Non-cellulosic components were removed from wood blocks of a conifer by applying a two-step chemical treatment. Partially changing the treatment conditions generated cellulose blocks with varying degrees of polymerization while maintaining the anatomical structure. Cellulose sheets with oriented microfibrils were subsequently prepared by heat-pressing the blocks. Sheets with randomized appearance of orientation were also produced by disassembling tracheid alignment. These sheets were then subjected to structural evaluation and tensile tests. Comparison of both sheets showed that microfibril orientation mainly determined the modulus. As long as the orientation was maintained, the specific modulus was independent of the degree of polymerization. In contrast, the tensile strength of the oriented sheet varied with the degree of polymerization, indicating that it notably reflected the single fiber strength compared to the randomly oriented sheet. Hence, a highly oriented structure with unfragmented microfibrils is the determinant of a superior material. Consequently, the sheets in which these parameters are readily controlled can advance cellulose applications.

This study reports a new cellulosic material that maintains the original three-dimensional structure of bamboo and is produced by optimization of chemical treatments. Bamboo blocks were prepared from the current year culms of moso bamboo (Phyllostachys edulis) and subjected to three chemical treatments alone or in combination. Based on the color changes and Fourier transform infrared spectra, the combination of alkaline treatment with alcoholysis followed by Wise method was found to be an optimal treatment method. This serial treatment caused the blocks to become completely white and removed non-cellulosic components such as hemicellulose and lignin from the cell walls of the parenchyma as well as those of vascular bundles. This sample was named as “White-Colored Bamboo.” Extensive structural evaluations from anatomical- to nano- level were performed using X-ray computed tomography, X-ray diffraction, and transmission electron microscopy incorporated with the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation technique. These multiple observations showed that the white-colored bamboo maintained its inherent hierarchical structure, thus encouraging to produce functional biomaterials.

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