Evaluation of Changes in Fine Structures of Regenerated Cellulose Due to Thermal Molecular Motion in Solvents

摘要

We intended to evaluate quantitatively the relaxation behavior of chain orientation along fiber axis in specific amorphous regions of regenerated cellulose through refractive index measurement in solvents. The regenerated cellulose fiber that was represented by aggregates of spherical primary particles of ca 15 nm was employed as a well-defined regenerated cellulose sample. Temperature-dependence of birefringence Δn in hydrophilic or hydrophobic solvents was mainly measured by the freezing method. In hydrophilic solvents, the micro-Brownian motion of chain segments in amorphous regions was activated by diffusion of the solvent into the region related to each absorption. The relaxation of the chain orientation was accelerated by this diffusion. The relaxation was observed as an abrupt fall of Δn. It is possible to ascertain the region into which solvent molecules can diffuse from the temperature at which this relaxation arises. The degree of chain orientation within specific amorphous regions can be evaluated from the amount of relaxation of Δn. Thermal expansion anisotropy caused by the chain orientation could be evaluated quantitatively from the temperature-dependence of Δn (δΔn / δT) in the temperature range where relaxation did not take place. In the case of regenerated cellulose, ethylene glycol is the optimal solvent for evaluation of the relaxation behavior and the value of δΔn / δT.