Study On The Cell Wall Structure And Property During The Growth Of Moso Bamboo

The cell wall of bamboo is major component of bamboo cell and its polylamellate structure and chemical composition play an important role in its mechanical properties.The variation of cell wall structure and performance in bamboo growing process was studied,it helps to reveal the inner mechanism of cell wall formation and provides theoretical support for pulp and paper making,biomass fuel conversion,preparation of bamboo carbon nano-materials,and the improvement of bamboo material.This study took moso bamboo(Phyllostachys edulis)at the different growth period as research subject,and studied the changes of cell wall structure,lignin distribution and performance in the process of forming secondary wall at the nanometer scale.The anatomy characteristics of fiber,parenchyma,and vessel elements were measured by biological anatomy,and the change of microfibril angle(MFA)was tested by X-ray diffractometer.The variation of cell wall layer,thickness and microfibril orientation of each wall layer in submicron scale was investigated by means of various high resolution electron microscope.The micro region distribution of lignin was observed in situ by a variety of spectral means,and the lignin content and composition unit of different micro regions were compared quantitatively.The modulus and hardness of the secondary wall of fiber were obtained by using situ imaging nanoindentation technique.The main conclusions are as follows:(1)The main anatomical features of Moso bamboo were significantly influenced by the age of stem.The types of vascular bundle are mainly open and semi-open,and the density of vascular bundle is between 117.49 and 171.19.The fiber length,wall thickness and wall cavity ratio were 1.66-2.37 mm,13.40-15.16 ?m,120-180,respectively,and the parenchyma cell thickness was 2.49-11.24 ?m,the radial diameter of the vessels cavity was greater than that in tangential.With the age of bamboo,the ratio of vascular bundle diameter between tangential and radial,the lumen diameter of fiber and parenchyma cell were gradually decreased.The densityof vascular bundle,the thickness of cell wall and ratio of cell wall to cavity in fiber and parenchyma cell were increased.There was a sharp decline for microfibril angle from 10 days to six months,that of 1 to 5 years was stable at about 8.8°.(2)The secondary cell wall of fiber presents polylamellate structure with alternating broad and narrow lamellae.The lamellae number showed an increasing trend with bamboo age,and the deposition rate of secondary wall of vessels elements in the entire process was always lower than that of the fiber and parenchyma cell.Cell wall thickening is due to the lamellae number of cell wall lamellae increase and the widening between lamellae.In the fiber cell wall,the width of the compound middle lamellae was between 80-120 nm,and the thickness of the primary wall is between50-80 nm.The narrow lamellae of fiber was 100-400 nm,and the broad lamellae of fiber is 0.3-5 ?m.The broadest lamellae of fiber was generally found in the second to third broad lamellae of the secondary wall.In the parenchyma cell wall,the width of narrow lamellae in secondary wall was 200-300 nm,the width of broad lamellae was200-900 nm,and the differences in each layer of thick wall were not as significant.In addition,the thickness of secondary wall in vessels was between 200 and 800 nm.(3)The microfibril direction of secondary wall in narrow layer of fiber cells was nearly perpendicular to the cell axial,the microfibril angle in the adjacent layers was30-50°,the angle between cell cavity and fiber cells spindle was 40-50°,microfibril angle in thick layer of secondary wall was arranged between 50-60° with the cell axial,and the microfibril angle of each wall in vessels were spirally arranged.(4)The lignin content increases with the bamboo age.The vessel elements began to be lignified before fiber and parenchyma.In same fibrous sheath,the fibers near the vessel lignified first,and then toward the periphery of the vascular bundle.The lignin mainly accumulated on the cell corner(CC)and compound middle lamella(CML)and then moved toward the secondary wall(SW).The content of lignin components in different growth stages was different,the absorbance size of G lignin in different types of cells during the same period showed: fiber > parenchyma > vessel.The absorbance size of G lignin and hydroxycinnamic acid in different types of cells during different period showed: CC>CML>SW.(5)The elastic modulus(MOE)and hardness of fiber cell wall increased with bamboo age,and its range are 8.54-28.06 GPa and 0.425-0.895 GPa,respectively.Thechange of elastic modulus between the F ? and F ? area of the same bamboo fiber is lesser,the edge area of fiber sheath was reducing greatly,hardness from vascular bundle center to the periphery was significantly reduced.In different positions of the secondary wall of fiber cells,the variation of elastic modulus was greater than hardness,which decreased by 3-10 GPa in the adjacent cell cavity and the intercellular layer region.The Results of this study will be support theoretical basis in field of pulp and paper,biomass conversion,carbon-based nano material and modification.