2.8 Drying behavior and kinetics of cellulose nanofiber filament prepared by flow-focusing methods
- Masato Kamogawa
- “Flow-focusing” spinning method by using micro-fluid channel can fabricate highly aligned cellulose nanofiber (CNF) filament, with excellent mechanical properties. The spinning method consists of the wet-filament formation process in the channel and followed by its drying process. Generally, drying conditions affect structure and property of cellulose-based materials. Recent study reported that tensile properties of the filaments tend to decline by increasing the drying temperatures in the range of 20 °C to 105 °C. However, the drying behavior of filaments is still unclear. The aim of this study is to investigate the drying behavior of wet-state filaments and quantitatively characterize its dependence on drying temperature. As one aspect of the drying behavior, the dimensional change of filaments during room temperature drying was observed. The observation indicated that the dimensional change almost finished at 20 minutes. At the initial state, water droplets were formed, and their shrinkage may be delayed compared to narrow regions. Local shrinking rate analysis suggests a possible water transport from the droplets to narrower regions during the intermediate stage of drying. Furthermore, the time-dependent moisture ratio was monitored during drying process to quantitatively characterize the drying behavior. At room temperature, more than 40 minutes were required to reach the equilibrium moisture ratio, and the drying process was accelerated as the temperature increased in the range of 20 - 105 ºC. Over this temperature range, the drying rate decreased with decreasing the moisture ratio, suggesting that internal water diffusion controls the overall drying rate.