Structure of windmill palm (Trachycarpus fortunei) culm and its compressive properties

Abstract

Windmill palm (Trachycarpus fortunei (Hook.) H. Wendl.) is a typical vascular plant containing parenchyma cells and vascular bundles. The study of palm vascular bundles and their mechanical properties is of primary importance for a better understanding of the mechanical properties of the culm of windmill palm. Various microscopic techniques were used to observe and quantify the variation in vascular bundles along the radial direction, and micromechanical testing machines were used for the determination of mechanical properties of windmill palm culm blocks and pure parenchyma cells. It was observed that the proportional area of vascular tissue and parenchyma cells increased markedly with the decrease in the proportional area of fibrous sheaths and the number density of vascular bundles along the radial direction. The same trend was also observed for the shape of the vascular bundles changing from oval to round. From the inner to the outer layers, the value of the apparent Young’s modulus and compressive strength continuously increased with increase in fibrous sheath volume fraction, varying from 0.54 to 1.07 GPa, and 26.83 to 69.33 MPa, respectively. The theoretical average value of the compressive Young’s modulus of the fibrous sheath was 2.74 GPa, which is similar to that of the windmill palm leaf sheath fiber. These results provide a better understanding of the compressive performance of windmill palm culm associated with its hierarchical structure.