Dynamic viscoelastic behavior of natural cellulose fibers caused by water and the related swelling phenomenon

Recently, the relaxation behaviors of regenerated cellulose fibers induced by water have been studied. These explorations suggest that the glass transition temperatures of 513–552 K in a dry state are shifted to room temperature by interaction with water. This water-induced behavior may also occur in the transitions of natural cellulose fiber. In this study, the peaks of tan δ for natural cellulose fibers with water regains of 38–39% were observed; however, decreases in the elastic modulus of natural cellulose fibers were not marked when compared with regenerated cellulose fibers. These findings suggest that the molecular motions of natural cellulose fibers are less influenced by the presence of water. Small-angle X-ray scattering showed shoulders in the wet state, with increasing water regain accompanied by increased long periods of cotton and ramie. This implies that water reduced the density of the amorphous region, widening spaces between cellulose molecules, and created sufficient space for micro-Brownian motion in the cellulose main chains.