We investigated the mechanical prop

We investigated the mechanical properties of the bamboo after the delignification and hot-compression treatments. Figure 3A,D shows photographs of the natural and densified bamboo samples after tensile testing, respectively. The fracture property of bamboo depends on the fracture initiates: the matrix region and fiber region.[34] Figure S3A–C (Supporting Informa- tion) shows the SEM photographs of the fracture surface of nat- ural bamboo. Shear stress arises when the load is transferred across the interface of the fiber and parenchymatous cells (matrix) because of their different mechanical properties. Then the crack usually generated in the weaker region with abun- dant parenchyma cells (matrix) propagated along the fibers and widen up until fibers are stretched out from the matrix and the parenchyma cells is broken. Different from the brittle fracture of the natural bamboo, the densified bamboo displays cracked sclerenchyma fibers in its fractured surface. The densified bamboo is composed of dense fibers and collapsed parenchym- atous cell walls. When under axial tensile load, the microcrack is initiated in the weakest point. With the increased loading, the densely packed fibers in the densified bamboo play an impor- tant role in carrying load bridging and inhibited crack opening. Under higher tensile load, the specimen did not fail as a whole and the remaining unbroken fiber bundles could still sustain the tensile load (Figure S3D–F, Supporting Information). The corresponding tensile stress–strain curves are shown in Figure 3B. The natural bamboo showed linear deformation before tensile failure with a tensile strength of 298 MPa. Mean- while, the densified bamboo initially exhibited linear behavior but became nonlinear once the stress exceeded the linear limit. Additionally, a significantly higher tensile strength of 770 MPa was obtained, which is 258% of that of natural bamboo. The densified bamboo also exhibited a 310% enhancement in the tensile modulus (Figure 3C).