| The measurement of the tensile properties of single plant fibers at the cellular level is one of front technology of wood science at the present. This technology is considered to be an international problem as the small size of single fiber. The investigation of mechanical properties of the single wood and bamboo fibers is a method to make the study of mechanical properties of biomass materials into deepening and enhance the study to the cell level from the macro level which making the study of macro-mechanical properties and its impact factors of materials at micro level come true. It is important to master the essence origin of mechanical properties of wood and bamboo. Meeting the urgent need of the mechanical properties data of the wood and bamboo fibers who as a reinforcement in the fiber-based polymer composite; Providing a scientific basis for the selective use of the fiber;guiding the design and improvement of manufacturing process of product and promoting the optimization of the product performance; Providing the quantifiable targets and indicators for the genetic improvement of the wood properties. So, the study is very important in practical and theoretical.The investigation of the mechanical properties of the single fibers is an inaugurated research in china. This paper presented a detailed technique to tensile the single fiber. And then, the fracture load,cross area,tensile strength,MOE and the elongation at break of the single bamboo fiber in different age (2,4,6 years old),the juvenile wood (the 5th rings) and the mature wood (the 25th rings) of the latewood of the Chinese fir fibers are investigated in this paper. The mechanical properties of different plant (Bamboo,Chinese fir,Ramie,Kenaf) single fibers and the sensitivity to humidity of the different fibers (Bamboo, Chinese fir, Ramie, Kevlar)at different environment humidity (40%, 70%, 90%) are also investigated in this paper. Finally, the mechanical properties of different treatment kenaf single fibers are investigated in this paper as well.Results were summarized as follows:1,The tensile properties of the single bamboo and Chinese fir fibers (1) The microfibril angle(MFA) of the 2,4,6 years bamboo are less the same with 9.91°,9.61°,9.76°,respectively. The MFA of 2years is slightly larger than the 4,6 years and the 4,6 years are almost the same. The MFA of the juvenile wood and mature wood of the Chinese fir is significantly different with 15.21°,34.88°,respectively.(2) The average value of tensile strength,tensile modulus and elongation for the 2,4,6 years bamboo fiber was 1590MPa,1710MPa,1755MPa;23.6GPa,27.1GPa,26.4GPa;7.2%,7.0%,7.0%,respectively. The mechanical properties of single fibers was increased with age, but reach a stable after 4 years later, the 4 years and 6 years fiber are very similar in the tensile strength, or in the elastic modulus and elongation.(3) The mechanical properties of the single juvenile wood and mature wood of the Chinese fir fibers were vary greatly , they were more than twice difference in tensile strength and MOE with 558MPa,1258MPa,8.5GPa,19.9GPa, respectively, the elongation at break also had a difference of 50% with9.9%, 6.6%, respectively. The single mature wood fiber showed a linear behavior presented to failure, but the load-deflection curve of juvenile wood fiber testing showed a clear plastic yielding stage. It was related to the MFA and the pits.(4) The bamboo fiber is more suitable than Chinese fir fiber for using as reinforcement in composite materials as its better performance than Chinese fir fiber in tensile strength,MOE and some other aspects.2,A comparison of tensile properties of different single cellulosic fibers(1) The average and largest tensile strength of the bamboo fiber were 1710MPa,2708MPa respectively. It was the maximum among the Chinese fir,ramie and kenaf fiber which about the same in tensile strength. The ramie fiber had the largest elongation of 8.9% and the best flexibility, while the kenaf had the lowest elongation of 3.2% that lower than the other three fibers significantly, but the kenaf had the largest MOE with the average of 30.8GPa and the largest of 42.3GPa which higher than the other three fibers significantly and the best rigidity.(2) The fracture mode of bamboo,Chinese fir,ramie and kenaf fiber was different. The fracture shape of most bamboo,Chinese fir,ramie fiber presented oblique tooth profile and the fracture surface was rough. It showed obvious ductile fracture performance which lead to the large tensile elongation. The Chinese fir fiber generally broken in the pits concentrated regions or where there was some defect. The fracture shape of kenaf fiber was smoother than the other three fibers and showed strong brittle fracture characteristics. It was in agreement with the lower elongation of the fiber.(3) The bamboo,Chinese fir,ramie and kenaf fiber showed their own characteristics in the fiber morphology,tensile strength,elongation,MOE and fracture mode which will help us to utilize these valuable resources more rationally and effectively.3,Effect of moisture on the tensile properties of single fibers(1) The sensitivity of mechanical properties to humidity was various with different kind of fibers. Among the fibers(Including Chinese fir,bamboo,ramie and Kevlar fiber) investigated, ramie fiber shows the most sensitive to the humidity, while Kevlar fiber was almost no induction to the humidity.(2) The MOE of bamboo,Chinese fir,ramie was increased in the ambient humidity of 70% but declined in the ambient humidity of 90% as compared with the fiber in the ambient humidity of 40%. While, as one of the man-made fiber, Kevlar fiber has homogeneous structure and steady performance which lead to the fiber no induction to humidity.4,The mechanical properties of the different treatment kenaf single fibers(1) The isolation temperature has a great effect on mechanical properties of the kenaf fiber. The mechanical properties of the kenaf fiber isolated at 110℃are better than the isolated at 160℃. Their average tensile strength,MOE,elongation,cross area were 1051MPa,810MPa, 23.6GPa,13.5GPa, 4.5%,5.6%, 187μm2,141μm2, respectively.(2) There is almost no difference in mechanical properties and a slight change in fiber morphology between the nano-modified at 100℃and 160℃kenaf fibers. Their average tensile strength,MOE,elongation,cross area were 1001MPa,1032MPa, 14.7GPa,14.6GPa, 6.6%,6.9%; 150μm2,124μm2, respectively.
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