| Bamboo fiber is the main structural unit of bamboo clum. The excellent mechanical properties of bamboo fiber are the base for fiber utilization. The systemic study on the mechanical property and its factors of bamboo fiber is not only benefit for further studying the mechanics of bamboo growth, but also the base theory and guide for selecting utilization of fibers and exploring advance materials.This paper systemically studied the influences of three main factors, namely microstructure, chemical components and moisture content, on the mechanical properties of bamboo fiber. In terms of microstructure, the effect of anatomy morphology and structure of cell wall on its mechanical properties was studied by using single fiber microtension technique. For chemical components, the mechanical properties of bamboo fiber with removing chemical components step by step were studied with single fiber microtension technique and in situ nanoindentation testing. For moisture content, the effect of moisture on the mechanical properties of single bamboo fiber and its cell wall was studied with single fiber microtension technique and in situ nanoindentation testing.The conclusions are as follows:(1) The aspect ratio of 12 kinds of Bamboo fibers are in the range from 122 to 165, with the ratio of wall to cavity are ranged from 4.20 to 7.50, which indicated that bamboo fibers are the cells with thick cell wall and high aspect ratio. Bamboo fiber has a special multilayered structure with alternating broad and narrow layers. Besides, there are only a few small pits in cell wall, and the microfibril angles(MFA) are small, the values ranges from 7.31 to 10.60°. However, relative crystallinity of bamboo cell walls are high, ranging from 67.26 to 75.22%. These results indicated that the structure of bamboo fiber is significantly different in different species.(2) The fracture of tensile testing is typical elasticity. The tensile modulus of single bamboo fiber ranges from 25.5 to 46.3 GPa, with the tensile strength from 1.13 to 1.93 GPa. The ratio of wall to cavity and MFA are the main factors affecting mechanical properties of bamboo fibers, which are negatively related with MOE while not related to tensile strength. In addition, MFA are positively related with elongation at break.(3) The MOE only changed a little with the extraction of lignin, but decreased sharply with the removal of hemicellulose, the values of MOE decreased by 51.43% under the freeze drying condition or 23.12% under the air drying condition. Meanwhile, the tensile strength of freeze dried samples decreased by 54.65%, whereas that of air dried samples almost did not change, because microfibrils reaggregated during the air drying process. The elongation at break of bamboo fiber decreased little with the extraction of lignin but increased significantly when the hemicellulose was removed, the value increased by 185.39% or 153.49% respectively for freeze dried samples or air dried samples.(4) During the maceration process, the indentation modulus just changed little, but hardness decreased 19.27% and 18% for freeze dried and air dried samples, respectively. With the removal of lignin, the indentation modulus increased a little, while decreased by 13.71% and 13.42% for freeze dried and air dried samples, respectively, when the hemicellulose was removed. The hardness of cell wall increased little for freeze dried samples, and increased by 22.73% for air dried samples when the matrix were removed.(5) Moisture influenced the mechanical properties of bamboo fiber significantly. Both tensile modulus and tensile strength decreased significantly by 26.66% and 22.17% with an increasing of moisture content from 4.58% to 21.52%. However, the elongation at break increased by 7.17% with increased moisture content. Both indentation modulus and hardness of cell wall decreased when the mositure content increased. When moisture content increased from 5.24% to 13.14%, indentation modulus decreased by 14.74%, while hardness decreased by 29.68%. |
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