Study On The Mechanical Poperties Of Fiber Cells Of Moso Bamboo

As the constitute substance or reinforcement of materials, the mechanical properties and variation of natural bamboo fibers are known little. In this study, the nanoindentation technique, the single fiber tension technique , the fiber bundle tension technique and conventional mechanical test were used to study systemly the mechanical properties of fibers of Moso bamboo (Phyllostachys edulis) at the subcellular, cell, tissue and macroscopic scale for the first time. The various factors affecting the mechanical properties were analysed. The influence of age factor on the mechanical properties of bamboo fiber was emphatically considered. The mechanical properties of fiber cell wall and single fiber of Moso bamboo and Masson pine (Pinus massoniana) were compared firstly. In order to reveal the structure design and excellent mechanical properties of bamboo, so as to choose bamboo fibers more scientifically and rationally, to design and develop the products with high properties and high value-added, to promote the continuous update of production process. Meanwhile, that would provide quantifiable objective and indexes for the gene modified and oriented cultivation of bamboo, enriching and improving the development of wood science of China, and would be very important for the theoretics and practice.The main research results were as follows:1. The longitudinal mechanical properties of fibers of Moso bamboo on the cell wall level(1)The study results of using nanoindentation showed that, in different positions of the vascular bundle, the longitudinal modulus of elasticity of cell wall of bamboo fiber were similar, the value were fluctuated at the middle line of 21 or 22 GPa. However, near the edge of the vascular bundle, the longitudinal modulus of elasticity of cell wall were relative small, which was about 15.61 GPa, and the values were very instable. The range of hardness of cell wall of bamboo fiber was from 0.4665 to 0.5603 GPa, and the measurement results showed a decreasing tendency from the center to edge of the vascular bundle.(2) The longitudinal modulus of elasticity of cell wall were comparable in value for the bamboo fibers with the age of 1, 2, 6 and 8 months. For the 1 month cell wall, the average value of modulus of elasticity reached to 21.51 GPa, which corresponded to those of 18 months. An increasing trend of cell wall hardness were found with different age, and the value ranged from 0.4673 to 0.6022 GPa, and the difference was significant at 0.01 level.2. The longitudinal mechanical properties of fibers of Moso bamboo on the cell level(3)Single fiber tension test proved that the load-displacement curves of air dried bamboo single fiber were nearly perfect line at room temperature, which had no significant yield and slippage, presenting a typical brittle fracture. The fracture surfaces of single fibers were divided into multilevel off-layer fracture and transverse break. The two kinds of fracture were all be found among different age, but the former were more ordinary.(4)For the bamboo fibers of 0.5, 1.5, 2.5, 4.5, 6.5, 8.5 years old, the tensile strength and modulus of elasticity of longitudinal changed little, the average values of which were 1543.77 MPa and 33.86 GPa, respectively, and the average break strain changed very small, between 3.63% and 5.74%, with an average value of 4.85%.(5)The longitudinal mechanical properties of cell wall of bamboo fibers achieved to optimization in the years old of 6 months.3. Comparetion of mechanical properties of fiber cell and cell wall of Moso bamboo and Masson pine(6)The average tensile strength and modulus of elasticity of bamboo single fibers were one and a half bigger than that of Masson pine single fibers. The bamboo fibers showed better strength, higher elasticity and bigger deformation performance. The break strain of bamboo fibers were bigger than those of pine, and the multilevel off-layer fracture were conmmon in bamboo fibers, however, for pine, irregular brush fracture was usually found in the juvenile wood, and transverse fracture was usually found in the mature wood. The modulus of elasticity and hardness of secondary cell wall of bamboo fibers were superior to those of pine fibers, the difference between them reached to 10%. The differences of mechanical properties between them were correlated highly to the microfibril angle and cell wall structure.4. The longitudinal mechanical properties of fiber bundles of Moso bamboo(7)The load-displacement curves of fiber bundles were similar to those of single fibers, all of them were linear brittle fracture. For bamboo fiber bundles, the average tensile strength was 461.03 MPa, the average modulus of elasticity was 37.74 GPa, both coefficient variation of them were all about 25%, the the average break strain was 1.27%.5. Correlation of bamboo fibers and the macroscopic mechanical properties(8)The distribution of stress-strain curves of thin slices were very scattered, and the fracture was brittle. On radial direction of bamboo, the mechanical properties was different, which was biggest in the outer part of bamboo, this difference were highly correlated with the gradient distribution of bamboo fibers content. In the outer part of bamboo, the fracture of thin slices was longitudinal splittary, in the middle part, the fracture showed uneven splitting feature, in the inner part, the fracture presented relative smooth, transverse feature.(9)The average tensile strength and modulus of elasticity of thin slices accounted for about one third of fiber bundles. The average tensile strength and break strain of fiber bundles were about 26.19% and 29.83% of fibers, respectively, while the average modulus of elasticity were roughly equal. According to the tested data of thin slices and the mixed law, the calculated tensile strength and modulus of elasticity of fiber bundles were 651.506 MPa and 52.0185 GPa, respectively, both of them were higher than the tested value, and 16.956 MPa and 0.8685 GPa for parenchyma.(10)The fibers or fiber bundles with high strength are the better reinforcement substance for bamboo, and the ground tissue constituted by parenchyma can absorb, transmit, uniform load, both of them make the mechanical properties of bamboo excellent. Bamboo is natural fiber composites of excellent designed.