Abstract:

Objective: Studying the hygroscopic behavior and clarifying of the mechanism of water adsorption in Calamus simplicifolius cane are important to provide the theoretical guidance for solving the quality problem caused by water adsorption and desorption in processing and utilization of rattan. Method: In this study, the dynamic vapor sorption apparatus was used to measure the water adsorption behavior of cane. The equilibrium moisture content (EMC) data were nonlinearly fitted by Hailwood-Horrobin (H-H) model, Guggenheim-Anderson-deBoer (GAB) model, Halsey model, Henderson model, Oswin model, and Smith model, and the fitting effects were also evaluated. The optimal fitting models were used to analyze the changes of EMC, monolayer and polylayer water adsorption during sorption processes. Result: The sorption isotherms of C. simplicifolius cane exhibited a sigmoidal shape, belonged to the second category of moisture adsorption isotherms and had the characteristics of multi-molecular layer adsorption. Similar to wood and bamboo, C. simplicifolius cane existed hygroscopic hysteresis, its hysteresis coefficient reached 0.8 at relative humidity (RH) of 80%, which was earlier than that of wood (RH=95%). Among the 6 models, H-H model and GAB model had the highest data fitting degree, with R² both over 0.99. In the H-H model, the parameter W₁, which means the apparent molecular mass of the dry rattan per sorption sites, was significantly less than that of wood and bamboo. In the hygroscopic stage, the adsorption was mainly monolayer water adsorption, and the value was 6.80% at RH < 60%. The water accessible specific surface area (S) and monolayer water adsorption (W₀) in the hygroscopic stage of rattan estimated by GAB model were 293 m²·g^-1 and 7.67%, respectively, which were greater than those of wood and bamboo. The reason might be that the fiber cell wall of rattan was thinner, the cell lumen was larger, the spaces between adjacent parenchyma cells were larger, and the cellulose crystallinity was smaller as well. The fiber saturation point values of rattan were also determined using the GAB and H-H models, which were 20.28% and 18.67%, respectively. Conclusion: The H-H and GAB models could be used to describe the water adsorption isothermal curve of rattan, and provided good fits with the experimental data. The chemical constituent contents, anatomical structure and the cellulose crystallinity were the important factors affecting the adsorption water content of the monolayer, which might result in the adsorption water content of rattan slightly higher than that of bamboo and the effective specific surface area of the cell wall adsorption larger than that of bamboo.

Key words: Calamus simplicifolius cane, water adsorption characteristics, isothermal adsorption model, monolayer water adsorption, polylayer water adsorption