Contributions to the molecular origin of the dielectric relaxation processes in polysaccharides - the high temperature range

For ionic conducting glasses a concept of correlation of electrical conductivity with dielectric relaxation was developed. which was essential for understanding the relaxation processes found for this substance class. This paper describes on attempt to extend the concept for interpreting the so-called sigma-relaxation found in all systems of well dried polysaccharides in the solid state at high temperatures. For various cellulose-based materials. starches and other pure polysaccharides it was found that the activation energies of the dc-conductivity and the dielectric sigma-relaxations were well correlated and their values A ere nearly equal (95-110 kJ/mol) for, all substances, The shape and the intensity of this relaxation were nearly independent of temperature for one substance. In Cellulose derivatives this process can be only observed. if these have sufficient unsubstituted hydroxyl groups. Highly or pet-substituted celluloses show no separable sigma-relaxation. Two models are discussed for the interpretation of this relaxation process: the first one assumes a local diffusion process of hydrogen ions between high potential barriers in these disordered systems and the second one a conducting pathway through a badly conducting environment in the material, (C) 2003 Elsevier Science B.V. All rights reserved.