Moisture migration mechanism of round bamboo in the radial direction during drying

Round bamboo exhibits a hierarchical gradient wall structure and contains closed bamboo cavities, creating a complex pathway for radial moisture migration. In this project work, round bamboo was dried at different temperatures (60, 75 and 90 °C), and the radial moisture content distribution and moisture migration pathway in the drying process were elucidated using the X-ray method, micromorphology and theoretical calculations. The porosity and average aperture of the inner bamboo internode were 38.92 % and 14.98 nm respectively, which were higher than those of the outer (23.17 % and 13.83 nm). The moisture diffusion coefficient at the bamboo diaphragm was about 1/4 that of the bamboo internode. The radial moisture content distribution in fresh round bamboo exhibited an asymmetric distribution, with higher levels in the middle and lower levels on both sides. During the drying process, moisture primarily migrated through the outer surface under the moisture gradient, with a small amount entering the bamboo cavity through the inner surface by temperature action. The moisture entering the bamboo cavity eventually migrated slowly through the diaphragm.