The dynamic viscoelastic properties of carboxymethylcellulose sodium salt (NaCMC) were measured isothermally as a function of relative humidity (r.h.). The dynamic modulus decreased with increasing r.h. and dropped markedly at about 70% r.h. In the tan 6 curve, a small peak appeared at about 20-30% r.h. and a large peak was observed at 80% r.h. To study the mechanism of these relaxations, the dynamic modulus was measured isothermally as a function of time at constant r.h. and the data were analysed in terms of the kinetics. Below about 70% r.h. bound water may be formed, having an activation energy of 15.0-15.6 kJ mol- 1. On the other hand, above 70% r.h., two types of mechanism may occur simultaneously: formation of bound water around hydrophilic groups with activation energy of 15.6 kJ mol- 1, and formation of free water with activation energy of 13.0kJmo1-1. Consequently, the tan 6 peak occurring at about 20-30% r.h. may be caused by the onset of local molecular motion of the hydrophilic groups, and the peak at about 80% r.h. by the onset ofmicro-Brownian motion of chain molecules plasticized with free water
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Dynamic viscoelastic properties of carboxymethylcellulose during isothermal water sorption / Shoichiro Yano // Polymer. – 1993. – Vol 34. – P. 2528-2532.
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