Comparative Study Of Vascular Bundles In Culm And Leaf Sheath Of Trachycarpus Fortunei

Culm and leaf sheath of Trachycarpus fortunei are its main components,it is also the main body of processing and utilization.However,there are few relatively studies on the anatomical structure and mechanical characteristics of culm and leaf sheath.Trachycarpus fortunei culm can be regarded as a two phase composite material consisting of vascular bundles(fibers)as reinforcing phase and parenchyma cells as matrix phases.Vascular bundle is the main load-bearing unit of its structure and properties,and is also the preferred part of its processing and utilization.In view of this,this paper takes culm and leaf sheath of Trachycarpus fortunei as the research object,and explores the anatomical structure and chemical composition of the two by means of various microscopic and chemical methods.The macroscopic and microscopic mechanical properties of culm and leaf sheath were studied by means of compression parallel to the grain,tension parallel to the grain,and nanoindentation;on this basis,the influence of the factors such as anatomical structure and chemical composition on its mechanical properties is analyzed,which provides data support for the high value utilization of culm and leaf sheath of Trachycarpus fortunei.The main conclusions of this paper are as follows:(1)Culm of Trachycarpus fortunei is similar to bamboo,it is a two component composite structure composed of vascular bundle and parenchyma cells.The vascular bundles contain fiber and porous phase.The porous phase of the tube and sieve tube is surrounded by the fiber sheath.The vascular bundles in culm are changed in a radial direction.Near the edge,the vascular bundle is large in size,flat in shape,smaller in the middle dimension,and tends to circle in the transverse section,near the middle,the vascular bundle is smaller in size,the transverse section tends to circle.The porous phase of brown filament is distributed in the vascular bundles,and there are no fibrous sheaths around the two sides of the airfoil.The diameter of vascular bundles of leaf sheath is generally larger than that of culm.(2)Chemical composition analysis:1.The content of the alcohol benzene extractive extract of culm,holocellulose,ethanol cellulose nitrate,α-cellulose,acid-insoluble lignin and ash content are 1.03-5.46%,64.42-66.63%,26.97-31.18%,29.74-35.68%,17.53-24.80%and 1.72-2.97%,respectively,and the leaf sheath is 1.45-1.75%,64.03-66.00%,32.04-33.48%,34.30-35.45%,36.,respectively.41-38.33%,1.12-3.92%.The higher lignin content than the leaf sheath compared to the culm.(3)The tensile modulus and tensile strength of inner leaf sheath are 3.26 GPa and 121.38 MPa respectively,while the tensile modulus and tensile strength of middle and outer leaf sheath are 2.42 GPa,7629 MPa and 2.64 GPa and 78.31 MPa,respectively.The tensile modulus of the inner leaf sheath can be approximated as the tensile modulus of the pure fiber sheath of the leaf sheath.The volume fraction of fibrous sheath of culm has a good linear correlation with the compressive elastic modulus,so the elastic modulus of the culm fibrous sheath can be calculated by the mixing law,the compression modulus of the parenchyma cells in the culm was 0.31 GPa by compression mechanics,and the modulus of pure fiber sheath in culm should be 2.74 GPa by using the mixing law.(4)The vascular bundle area and area occupation ratio of fibrous sheath in vascular bundle of culm are less than the leaf sheath.The average lengths of fibers in culm and leaf sheath were 1260.63μm and 710.89μm respectively,and the diameters of fibers were 42and 12.77 m respectively;there are a small number of three wall layers in the fiber of culm,while the fiber in leaf sheath is almost all two wall layers,filament size of fiber surface of culm fiber is less than leaf sheath fiber,the mean values are:20.53 nm and 41.32 nm,respectively(5)The mechanical properties of fiber cell wall in leaf sheath were better than that of culm fiber cell wall.The compressive modulus and hardness of fiber cell wall in leaf sheath and culm were 9.68 GPa,62.45 MPa and 8.37 GPa,43.33 MPa respectively,and leaf sheath was 15.7%and 44.4%higher than culm,respectively.(6)The compression mechanics experiment of culm and the anatomy of culm show that the volume fraction of stem fiber sheath has a good linear correlation with its compression modulus,and its correlation is y=0.0206x+0.3604,R~2=0.9522,meanwhile,there is a good linear correlation between fiber sheath volume fraction and tensile modulus of leaf sheath,and the correlation is y=0.0322x+0.0632,R~2=0.7261.Meanwhile,the cellulose content of the stem has a good linear correlation with the compression modulus of elasticity,and its R~2 is 0.9249.