Study On Embrittlement Process Of Phyllostachys Edulis And The Change Of Properties From Cell-bongding Interfaces

Bamboo material has the characteristics of the growth rapidly and the earlier recession.Explore the embrittlement of the material process and the change of the micro mechanical properties and chemical composition during the recession of bamboo material is of great significance to reveal the reason of the recession of bamboo material,clear the recession period of the bamboo material,promote the efficient utilization of bamboo and promote the development of bamboo resources.It helps to deepen our awareness cell-bonding interfaces,provides a theoretical reference for the full utilization and improvement of the cell-bonding interfaces.This study took moso bamboo(Ph.edulis)of the growth rapidly and the most widely distribution in China at different growth period as research subject,and focused on the embrittlement process of bamboo material,explored the influence of impact toughness,the change of the properties and chemical compositions of cell-binding interfaces during the recession of bamboo material.According to JG/T 199--2007"Test Method for Physical and Mechanical Properties of Bamboo for Construction",the impact toughness of bamboo material was tested,the crack propagation and brittle fracture of samples after impact were statistically analyzed,and the fracture morphology was analyzed.The elastic modulus and hardness of tissue cell-bonding interfaces and fiber cells bonding interfaces were obtained by using situ imaging nanoindentation.The microdistribution of lignin was observed by laser confocal raman microscopy,and the content,structural units and retrograde of lignin at different cell-bonding interfaces were quantitatively compared.The main results are as follows:(1)Bamboo bad obvious embrittlement process.The impact toughness of bamboo first increased and then decreased with the increase of bamboo age.The impact toughness of 6-year old bamboo reached the maximum,respectively were:111.64k J/m~2(chordal direction)、74.75k J/m~2(chordal direction)and 146.42k J/m~2(chordal direction).The impact toughness of 8-10 years old bamboo decreased the fastest and embrittlement was obvious.The impact toughness of bamboo in different directions was obviously different,which was as follow:from bamboo yellow to bamboo green direction>from bamboo green to bamboo yellow direction>from bamboo green to bamboo yellow direction.(2)With the increase of bamboo age,the mechanical properties of interface and the impact properties of bamboo had a similar trend.At 6 years of age,The elastic modulus and hardness of interface between parenchyma and fiber sheath reached the maximum,which respectively were 15.92 GPa and 0.52 GPa.The elastic modulus and hardness of interface between fibrocells in the fibrous sheath were 13.21 GPa and 0.56 GPa,respectively.The elastic modulus and hardness of interface of 8-10 years old bamboo decreased obviously.The mechanical properties of interface between parenchyma cells and fibrous sheath were less different than those of interface between fibrous cells and fibrous cells in fibrous sheath.(3)With the embrittlement of the material,the chemical composition of interface of different bamboo ages also changed.The contents of lignin and p-hydroxycinnamic acid decreased with the increase of bamboo age.At the same cell-interface,the relative concentration of G and H lignin was significantly higher than that of S lignin.The relative contents of G、H and S lignin were as follows:parenchyma cell-bonding interface>tissue cell-boning interface>fiber cell-bonding interface.The concentration of lignin in the interface on the yellow side of bamboo was lower than that of interface on the green side and the middle part of bamboo wall.With the increase of bamboo age,the characteristic peak signals of the three lignin structural units at the interface of bamboo cells fluctuated to a certain degree,mainly concentrated in the 6-10 years old bamboo,indicating that the lignin structure changed in the material embrittlement process.To sum up,the change of cell-bonding interface performance of moso bamboo affectted the change of moso bamboo performance to a certain extent,to make the material of moso bamboo decline.