Abstract: [Objective] Bamboo age is a key factor for logging and utilization of bamboo, and hence we focused on the fiber cell wall of different growth period. The characteristic and mechanical performance of fiber cell wall of moso bamboo aged 0.5 a, 4.5 a, and 10.5 a were investigated to find out the differences of characteristic and mechanical performance among immature, mature and overmature moso bamboo at nano-scale, which provided a new theoretical basis for the research of scientific logging, classification, modification and reorganization and rational utilization of bamboo in the future.[Method] The sections made by microtome and ultramicrotome were used to observe microstructure of the cross-section and then choose the precise area for nanoindentation experiments. Nanoindentation experiment combined with non-embedding method was used to investigate the mechanical properties of fiber cell wall, and the wide-angle X-ray scattering method with the Gaussian quasi legitimate calculation was applied to obtain the value of micrfibiril angle of moso bamboo.[Result] The observation of cross-section indicated that the parenchyma cells and vascular bundles were the main components of moso bamboo, and the vascular bundle was consisted of the vessel and thick walled fiber cells that surrounded the vessels. The mechanical properties of moso bamboo fiber exhibated significant differences among different growth period. The nanoindentation result showed that the mechanical properties of immature moso bamboo fiber cell wall were lower than those of mature and overimature moso bamboo. The value of elastic modulus and hardness were 10.7 GPa and 0.358 GPa, respectively. The mature moso bamboo showed the highest elastic modulus and hardness, 19.6 GPa and 0.489 GPa. The elastic modulus and hardness of overmature moso bamboo were 17.6 GPa and 0.445 GPa,respectively. The microfibril angle tests indicated that they were diverse among bamboos in different growth period. The mean microfibril angle of 0.5 a immature moso bamboo with 13.5° is higher than the others, and the 4.5 a mature moso bamboo with 8.43° is lowest, while the miscrofibril angle of 10.5 a overmature moso bamboo is 11.9°.[Conclusion] Based on the result it was concluded that the growth period have an influence on the fiber cell wall mechanical properties and microfibril angle of moso bamboo. The micromechanical properties showed apparent differences between the immature and mature moso bamboo, it was enhanced with bamboo age and achieved optimal micromechanical performances at mature, however, the reduced elastic modulus and hardness slightly decreased with bamboo age after the maturity. The angle between the microfibril arrangements and cell axis was least when the moso bamboo was mature, which account for its better mechanical properties. As a consequently, this study illustrates the micromechanical properties of the 4-5 years old moso bamboo was better than that of the immature and overmature moso bamboo at cell wall level.

Key words: Phyllostachys edulis, growth period, cell wall mechanical properties, microfibril angle