Contribution to dissolution state of cellulose in aqueous amine oxide characterized by optical and rheological methods

The dissolution of cellulose in aqueous amine oxides to isotropic, completely solvated crosslinked solutions is a multiple stage process in microscopic, submicroscopic and molecular ranges. In a suspension of cellulose, water and NMMO at 85°C and with decreasing water content the cellulose undergoes a growing swelling accompanied by an increased flexibility of the chain leading to a heterogeneous phase for the 1,5 hydrate (81,3 % NMMO) to an irreversible transfer of cellulose I into cellulose II and for the 1,2 hydrate (84,4 % NMMO) to a homogeneous, partly solvated gel phase. Discrete inhomogeneities with equivalent spherical diameters greater than 0,5 µm and a concentration greater than 1 µl/l can be analyzed by microscopy and laser diffraction. Rheological parameters and in particular recording of deformation graphs and calculating relaxation time spectra were proven to be efficient for characterization of the solvation occurring during dissolution.