The role of node and internode microstructure on the longitudinal fluid transport in bamboo

Understanding bamboo permeability is essential for optimizing pressure-based preservative treatments and improving the durability of bamboo-based construction materials. Bamboo has a complex pore structure and contains diaphragms (nodes) along its length, which are thought to influence fluid transport. Vascular bundles (VBs) are largely continuous through internodal regions; however, at the nodes, shifts in VB orientation occur, along with the presence of horizontal bundles. In this study, air permeability and water sorptivity of bamboo nodes and internodes were measured to assess the impact of these microstructural variations on fluid transport. A reconstructed 3D model confirmed the expected structural complexity at the node, yet most VBs maintained longitudinal continuity. Fibre volume fraction between node and internode showed low variability, ranging from 33.9% to 44.5%, and VB percentage exhibited a slight reduction at the node. Although air permeability coefficients were marginally lower in node regions (k₁ = 1.00 to 5.42 × 10^{− 12} m² and k₂ = 0.76 to 9.85 × 10^{− 8} m), influenced by this minor reduction in VB percentage, these differences were not statistically significant compared to internodes (k₁ = 2.16 to 12.99 × 10^{− 12} m² and k₂ = 2.23 to 54.53 × 10^{− 8} m). Capillary water absorption and contact angle measurements were consistent between regions in the longitudinal direction and revealed much higher absorption longitudinally compared to radial and tangential directions. Overall, these findings indicate that nodes have only a minor influence on longitudinal transport, and confirm that bamboo permeability is highly anisotropic, with longitudinal coefficients that are several orders of magnitude higher than those in the radial and tangential directions.