Quantitative characterization of bamboo cortex structure based on X-ray microtomography

Bamboo is a natural fiber composite with layered structure. Millions of years of evolution have endowed bamboo with the most effective structure in nature. The ingenious microstructure provides bamboo with excellent mechanical properties. Bamboo culm is composed of the cortex, a middle layer, and a pith ring. The cortex refers to the area starting from the periphery of the culm wall to the vascular bundles. The present study obtained the two-dimensional (2D) microstructure of bamboo cortex cells by optical microscopy and characterized the three-dimensional (3D) structure through high-resolution X-ray microtomography (µCT). The 2D anatomical parameters of cortex cells were measured to verify the reliability of cortical cell classification in 3D models. Based on the analysis, the bamboo cortex cells were classified into four layers: epidermis layer, hypodermis layer, transitional layer, and parenchyma layer. The total volume of the reconstructed area of interest in μCT was 7.85 × 10⁶ µm³, in which the total pore volume of bamboo cortex was 2.84 × 10⁶ µm³, the average pore volume of bamboo cortex was about 1.54 × 10³ µm³. Thus the porosity was 36.1%, and the relative density was 0.639. Studies on bamboo anatomical structure, especially three-dimensional digital characterization, will enrich the bamboo microstructure database. Besides, the three-dimensional structure of the bamboo cortex revealed in this study can provide a reference for optimizing composite material hierarchy and biomimetic design.