Dynamic Mechanical Absorptions Observed for Regenerated Cellulose Solids in the Temperature Range from 280 to 600 K

Abstract

An attempt was made to establish the mechanism of the dynamic mechanical absorption phenomena of regenerated cellulose solids observed in the temperature range between 280 and 600 K at a frequency of 110 Hz. For the purpose, isochronal dynamic viscoelasticities of regenerated cellulose fibers and membranes were measured by dynamic modulus, loss modulus, and dynamic loss tangent in air at a heating rate of 12 K min−1 or in various kinds of liquid medium at 3 K min−1. Three absorption peaks, α1, α2, and αH2O, and one absorption shoulder, αsh, were observed near 573, 513, 303, and 393 K, respectively. The content of water absorbed in the sample was closely related to the appearance of the αH2O absorption which was due to the cooperative motion of polymer segment and absorbed water molecules. The dependence of the viscoelasticity on temperature and frequency revealed that the α2 absorption consisted of two αa absorptions, α2,1 and α2,2, whose apparent activation energies were 289 and 209 kJmol−1, respectively. All of the α1, α2,1, α2,2, and αsh absorptions originated from the micro-Brownian motion of polymer segments in the amorphous region. The temperatures of these four absorptions were dominated by the segmental environment such as the density of intermolecular hydrogen bonding.