Impact of the natural structure of cortex and pith ring on water loss and deformation in bamboo processing

The function of the pith ring and cortex in biological and fluid exchanges with the surrounding environment implies a natural intelligence. Their ingenious structure enables bamboo to thrive and impacts its processing and utilization. As drying is an essential step in bamboo product manufacturing, in this study, the effects of the pith ring and cortex on the water loss, deformation, and cracking of bamboo at the macroscopic, tissue, and cellular levels were investigated. Our study revealed a previously unknown mechanism of bamboo drying deformation. The cortex significantly affected the rate of water loss, whereas the pith ring did not significantly reduce the drying rate. Three deformation mechanisms originating from the pith ring were identified: the cell structure and orientation, self-flattening during drying, and excellent bending performance in the chord direction. These pith ring characteristics led to a larger radius of the bamboo splits during drying. These findings expand our understanding of the natural intelligence of the inner and outer layers of bamboo and provide important insights into bamboo drying, deformation, cracking, bionics, and composite material manufacturing.