Molecular interpretation of the main relaxations found in dielectric spectra of cellulose - experimental arguments

In dielectric spectra of cellulose two relaxation processes dominate in the low temperature range (-120 degreesC-0 degreesC). For application of the dielectric method as a diagnostic tool, these relaxations must be assigned to molecular motions of the polymeric system. This paper summarizes and discusses all experimental facts found by dielectric spectroscopy, which can help to solve this interpretation problem. It is necessary to include two other relaxation processes in this discussion: the beta(wet)-relaxation found in all wet materials and the gamma-relaxation evidently found in all derivatives. The main result of our investigations is that the dominant process in the dielectric spectra at low temperatures (called beta-relaxation) is the segmental motion of the chain and not methylol side-group reorientation. Additionally, for the first time, the dielectric spectra of Valonia (and also of bacterial cellulose) clearly indicate that the methylol side-group relaxation is represented in the dielectric spectra of pure polysaccharides. This gamma-process is only masked by the beta-process for the most pure celluloses. For low molecular weight saccharides and derivatives of cellulose both processes are simultaneously found in the dielectric spectra. For the first time a correlation is presented between the intensity of the local motion mode (beta-relaxation) and the degree of crystallinity for various cellulosic materials.