In this study, we apply mechanical

In this study, we apply mechanical compression along the radial (parallel to the fiber growth) direction to compress the delignified bamboo into a dense structure with approximately a 70% reduction in thickness (Figure 2D and Figure S2D: Supporting Information). The lack of conspicuous pits and the fully collapsed parenchyma cells in the densified bamboo (Figure 2E,F and Figure S1E,F: Supporting Information) sug- gest the hierarchical structure was fully compressed. As a result of this compressed structure, hydrogen bonding should be enhanced among the aligned fibers that are formed after the mechanical compression process, which makes the com- pressed bamboo stronger. The effectiveness of the lignin and hemicellulose removal after chemical treatment is shown in Figure 2G. After the delignification process, the densified bamboo sample was mainly composed of cellulose with littlehemicellulose or lignin content. Fourier-transform infrared spectroscopy (FT-IR) analysis of the natural and densified bamboo show that the functional groups of bamboo assigned to hemicellulose (CO stretching vibration) and lignin (G-lignin and CO stretching vibration)[31] are partially removed with a total weight loss of 39.3% as a result of the delignification process (Figure 2H and Figure S2: Supporting Information). The small-angle X-ray scattering (SAXS) pattern of the densified bamboo (Figure 2I) indicates the remaining cellulose fibers are well-aligned, which greatly facilitates the formation of hydrogen bonds and van der Waals forces among the neigh- boring cellulose molecular chains.[32] The fully compressed structure also results in an increase in density from 0.80 to1.35 g cm3 (Figure 2J). Considering the density of densifiedbamboo is close to that of bamboo fibers (1.45 g cm3),[33] we assume the compressed fiber in the densified bamboo sample with no lumen and little defects.