DYNAMIC VISCOELASTICITY AND STRUCTURAL-CHANGES OF REGENERATED CELLULOSE DURING WATER SORPTION

The dynamic viscoelasticity of regenerated cellulose was studied as a function of relative humidity (r. h. ). At 50 and 80 degree C the dynamic modulus E prime decreased rapidly at about 70-80% r. h. and a steplike change in E prime was observed at 50-60% r. h. Simultaneously, a peak in tan delta appeared at about 90-95% r. h. and a shoulder was observed at about 50-60% r. h. From the X-ray analysis and nuclear magnetic resonance study, the steplike change in E prime and the shoulder in tan delta at about 50-60% r. h. may be caused by crystal growth accompanied by molecular rearrangement due to sorbed water. The significant drop of E prime and the tan delta peak at 90-95% r. h. may be due to the onset of micro-Brownian motion in the plasticized chain molecules.