Investigation on metastable solution of cellulose dissolved in NaOH/urea aqueous system at low temperature.

Our previous work has demonstrated that the cellulose solution dissolved in 7 wt % NaOH/12 wt % urea aqueous system precooled to -12 °C was metastable. It is worth noting that light scattering investigation on the cellulose solution at metastable state is difficult. In the present paper, the solution properties and dynamic behaviors of cellulose dissolved in the NaOH/urea aqueous solution were investigated by means of dynamic light scattering (DLS), to confirm the influence factors of the DLS measurement. The DLS results revealed that, after the dispersion of cellulose in NaOH/urea at low temperature, the single cellulose inclusion complexes (ICs) coexisted with minor IC aggregates even in very dilute solution. With increasing cellulose concentration or system temperature or prolonging storage time, the IC aggregation increased, as a result of the occurrence of the imperfect urea shell and the reconstruction of the hydrogen bonds between cellulose chains. The cellulose solution was relatively stable at low concentration and low storage temperature and for short storage time. In this case, the single cellulose inclusion complexes were the predominant species, and coexisted with minor IC aggregates, which was better to be used to measure the cellulose solution with DLS.