Unraveling the inhibition of bamboo node on dry shrinkage: insights from the specific vascular structure of bamboo node

Based on the vascular structure of bamboo node, studying the shrinkage behavior of bamboo at the vascular scale will be beneficial for further understanding the shrinkage behavior and providing a theoretical basis for preventing deformation and cracking of bamboo. The shrinkage behavior was different between internodes and nodes. This study analyzed the structure of bamboo node through sanding, scanning electron microscope, and micro computed tomography, as well as investigated the shrinkage differences between internodes and nodes in terms of changes in moisture content, vascular bundles and cracking through the target detection model and Python fitting technique. The results showed that only 6.4% axial vascular bundles in bamboo node underwent morphological enlargement and structural changes. Incomplete lignified fiber cells and small vessels appeared, vascular bundles bent towards the outside of the culm wall, and the culm wall thickness increased. Many radial and tangential horizontal vascular bundles appeared in bamboo node. These special structures affected the movement of water and dry shrinkage. The variation amplitude of the radius and radian in internodes was greater than that in nodes without diaphragm which was greater than that in nodes with diaphragm. The decrease in moisture content of nodes was faster than that of internodes. The diaphragm, tangential and radial horizontal vascular bundles limited the dry shrinkage. The cracking of internodes was similar to that of nodes without diaphragm, while the cracking of nodes with diaphragm had its own uniqueness.