Relaxation phenomenon and swelling behavior of regenerated cellulose fibers affected by water.

Regenerated cellulose fibers are extremely sensitive to water; particularly, the mechanical properties are greatly affected by water. We examined the effect of water on regenerated cellulose fibers in respect of the relaxation phenomenon and swelling behavior. The peaks and shoulder of mechanical loss tangent δ were observed at room temperature and water regains of 56-78%. At the same time, the storage modulus markedly decreased around these water regains. Small angle X-ray scattering showed the maxima and shoulders in the wet state, which suggested that water decreased the density of the amorphous region and made space for the movement of polymer segments. It is possible that the glass transition temperatures of 510-550 K shift to room temperature at specific water regains. It is reasonable to suppose that water can penetrate into the amorphous region, loosening the interactions between cellulose molecules and widening the region, and in consequence decreasing the glass transition temperature.