The Mechanism of Improvement of Physical Properties of Moso Bamboo (Phyllostachys pubescens) with Increasing Age I. Relationship between modulus of elasticity in bending and cell wall thickness and/or percentage of cell walls

The purpose of this study is to elucidate the factors related to improvement of the physical properties of bamboo as a material with increasing age. Moso bamboo (Phyllostachys pubescens) at various times (40 days similar to 9 years) since shooting were used for test samples in the green condition. The modulus of elasticity in bending (MOE) when loaded on the endodermis or the epidermis side was determined. In addition, at each endodermis and epidermis side, the thickness of parenchyma and fibrous cell walls and the percentages of cell walls of parenchyma and vascular bundles were measured. Results obtained are as follows. The MOE of bamboo is affected not only by the density of the entire woody substance but also by the types of cells in which the cell wall thickness increases, that is, parenchyma cells or fibrous cells, and by their radial location, that is, endodermis side or epidermis side. The MOE obtained by endodermis-side loading is greatly affected by the thickness of parenchyma cells and the percentages of cell walls of parenchyma, and the MOE obtained by epidermis-side loading is greatly affected by the thickness of fibrous cells and the percentages of cell walls of vascular bundles.