Dielectric spectroscopy and relaxation phenomena of moistened and dry polysaccharides



The effect of hydration on the dielectric constant equation image and loss factor tan δ of viscose hydrocellulose, hydroxypropyl cellulose, and dextran was studied in a wide range of temperatures and frequencies. The results obtained reveal that (1) whereas hydration shows little effect on the variation with temperature of both equation image and tan δ of hydrocellulose, the presence of adsorbed water significantly modifies the dielectric behavior of the other two samples; (2) only one relaxation denoted as γ-process is observed in the case of hydrocellulose sample irrespective of its moisture content; (3) two absorption peaks are recorded with moistened hydroxypropyl cellulose and dextran specimens, one below room temperature denoted as β-process and a dispersion loss at high temperature; and (4) after drying of these samples, the dispersion loss peak disappears, the β-peak diminishes, and the γ-peak, which is hidden behind the sizable β-peak, is observed and that, although with increasing frequency, the former peak disappears, the intensity of the latter one increases. The analysis of these results in view of the chemical and the fine structure of the test samples as well as the calculated activation energy indicates that the γ- and β-relaxations recorded are of different natures. The satisfactory interpretation given clarifies to a great extent the contradictions reported in the literature concerning the relaxation phenomena in polysaccharides. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 571–582, 2005