Hygroscopic swelling of moso bamboo cells

Bamboo is a natural cellulosic material which is strongly reactive to water. Its hygroscopic behavior affects almost all other physical and mechanical properties of bamboo. This study investigated the hygroscopic swelling of moso bamboo (Phyllostachys edulis) cells in response to changes in environmental humidity using a confocal laser scanning microscope. The swelling strains of fiber, vessel and parenchyma cells were obtained and compared. The interactions between adjacent cells were also analyzed. The results demonstrated that the swelling strain of the cell walls increased with relative humidity, and was independent of its location and orientation, but dependent on the cell type. The absolute swelling of fiber cells was highest among all cells because of dominantly high fiber wall thickness. In contrast, the relative swelling of fiber cells was lowest due to constraint of adjacent fibers. Fiber cells governed the deformation and movement of other cell lumens. The difference between tangential and radial swelling of bamboo was insignificant compared to that of wood, possibly due to the similar microfibril angle in both directions, the circular cell shape and the random embedment of vascular bundles.