Comparison of the molecular dynamics of celluloses and related polysaccharides in wet and dried states by means of dielectric spectroscopy

Abstract

The dielectric relaxation spectra of polysaccharides are already affected very specifically by small amounts of water. The measured samples of cellulose, starch and dextran behave differently in the wet and in the dried state comparing their low temperature dielectric spectra: The positions of the secondary relaxation in the frequency scale, which are due to the local chain mobility, shift in a specific manner between wet and dried state for every substance. In general, we can say that drying strongly decreases the relaxation strength for all samples. The dielectric spectra of the wet polysaccharides (2 to 12% w/w water content) show an additional relaxation process (βwet‐relaxation) in the room temperature range (0°C to 60°C) which vanishes after an intensive drying procedure. The experimental results were fitted by using the Havriliak‐Negami‐equation for each individual relaxation process. This evaluation leads to a number of physical parameters for the polymer dynamics given in the paper. The results could be explained by the differences in the interaction of the several polysaccharides with water caused by their distinct glycosidic linked backbones and their different supramolecular structures.

Influence of hydrogen bonds on glass transition and dielectric relaxations of cellulose

“…Measurements on others polysaccharides as starch and dextran confirm this results [22]. A β wet relaxation mode can be observed in all wet polysaccharides in the room temperature range (0-60°C) [22][23][24][25][26][27]. This mode is not observed anymore after drying the sample [22][23][24][25][26][27].…”

“…The γ process is more cooperative in wet celluloses than in dry celluloses [25]. Measurements on others polysaccharides as starch and dextran confirm this results [22]. A β wet relaxation mode can be observed in all wet polysaccharides in the room temperature range (0-60°C) [22][23][24][25][26][27].…”

“…A β wet relaxation mode can be observed in all wet polysaccharides in the room temperature range (0-60°C) [22][23][24][25][26][27]. This mode is not observed anymore after drying the sample [22][23][24][25][26][27]. The hydration influence of polysaccharides on their dielectric properties can be interpreted by several hypotheses: one the one hand, the OH-groups of glucosidic units form hydrogen bonds with water molecules.…”

“…Dielectric dynamic spectroscopy (DDS) has been already used on polysaccharides like cellulose and its derivatives [22][23][24][25][26][27][28][29]. Four dielectric relaxations modes are usually observed γ, β, β wet and α, in the order of increasing temperatures [22][23][24][25][26][27][28][29].…”

“…Four dielectric relaxations modes are usually observed γ, β, β wet and α, in the order of increasing temperatures [22][23][24][25][26][27][28][29]. The dielectric properties of cellulose have been also investigated by combined DDS/TSC [28].…”