Mechanical properties of bamboo fiber cell walls during the culm development by nanoindentation

• For bamboo fiber cell walls, age had no significant effect on NI modulus, while NI hardness did increase.
• The NI modulus changed very little in different locations of 1-month-old vascular bundle, but hardness decreased significantly.
• These results may provide mechanical evidence for bamboo growth, lignin deposition, and utilization of fibers.

Bamboo fibers have excellent mechanical properties, and as such are a popular raw material in papermaking, textile, and various high-tech industries. In this study, the longitudinal mechanical properties of Moso bamboo (Phyllostachys Heterocycla Var. Pubescens) fiber cell walls during development were systematically investigated via nano-indentation technique at the sub-cellular level. Several influencing factors were also analyzed, particularly the effects of different locations within the vascular bundle and age. The results showed that the longitudinal nano-indentationmodulus (NI modulus) of the 1-month-old bamboo fiber cell walls was relatively high and changed very little in different locations of the vascular bundle, only fluctuating near 22 GPa, while that at the interface between fibers and parenchyma cells (i.e., the edge of the vascular bundle) was smaller and less stable (15.61 GPa on average); nano-indentation hardness (NI hardness) decreased from the center of the vascular bundle to the outside, ranging between 0.4665 and 0.5603 GPa. Age had no significant effect on NI modulus from 1 month to 36 months, while NI hardness did increase with age (p < 0.05), showing mean values of 0.5452–0.6142 GPa across the samples. Our observations of longitudinal NI modulus and hardness were mainly affected by the microfibril angles and lignin content, respectively. These results may provide mechanical evidence for bamboo growth and lignin deposition, and also provide a scientific basis for the successful utilization of bamboo fibers.