Abstract
Bamboo is an anisotropic, hierarchical, and hygroscopic material. Moisture transport in bamboo is one of the most fundamental properties affecting almost all other physical and mechanical properties of the material. This study investigated the water vapor sorption behaviors of bamboo at various structural levels: cell walls, cells (with pits) and bamboo blocks. The specimens with two sorption directions, longitudinal (L) and transverse (T), were measured by saturated salt solution method and dynamic vapor sorption. The parallel exponential kinetics model was used to analyze the sorption kinetics. The results showed that at the cell wall level, the sorption rate and equilibrium moisture content (EMC) of cell wall in the L specimens were larger than those in the T specimens. The differences were probably caused by the looser cell wall layers in the L specimens. At the cellular scale, pits in the cell wall resulted in an enhanced sorption rate and EMC of the T specimens compared with the L specimens where the pits in the parenchyma cells were only distributed in the lateral walls but not in end walls. At the macro scale, the sorption rate and moisture content of bamboo blocks were largely controlled by the vessel cells. As a hierarchically-structured plant, bamboo performs the biological function of moisture transport at all these scales. This work helps improve the understanding of water transport behavior in bamboo, which may lead to better bamboo drying and impregnation processes.
Highlights
To investigate the bound-water sorption behavior of cell walls of bamboo in both longitudinal and transverse directions; To evaluate the effect of pits on water vapor sorption; and To investigate the water vapor sorption behavior of bulk bamboo in both longitudinal and transverse directions
The pits in parenchyma cells were only distributed in the lateral walls, not in the end walls (Fig. 4c)[29] and L specimens contained fewer pits than in T specimens along diffusion direction
Former being always higher than the latter, especially at high RH. All these results indicated that the existence of pits created more sorption spaces for w ater17. Siau[27,28] did not consider pits as an important factor for water sorption in wood, below the fiber saturation point
Summary
To investigate the bound-water sorption behavior of cell walls of bamboo in both longitudinal and transverse directions; To evaluate the effect of pits on water vapor sorption; and To investigate the water vapor sorption behavior of bulk bamboo in both longitudinal and transverse directions. The difference between L and T specimens is believed to be attributed again to the tightness of cell wall layers (Fig. 3c,f) and availability of hydroxyl groups to water molecules during the sorption process. This result was different from the result of 30 μm specimens where L specimens had a higher MC when only the bound-water sorption of cell wall substance was considered.
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