Investigation of the Scaling Law on Cellulose Solution Prepared at Low Temperature

Abstract

Cellulose was dissolved rapidly in a 9.5 wt % NaOH/4.5 wt % thiourea aqueous solution pre-cooled to -5 degrees C to prepare its concentrated solution, in which inclusion complexes (ICs) associated with cellulose, NaOH, thiourea, and water clusters were created. Physical gels could form in the cellulose solution at either high temperature or after long storage time, because of aggregation between the ICs. To clarify whether the Winter and Chambon theory could describe the gelation process of this complex system, we have investigated carefully the viscoelastic behavior of the cellulose solution with the advanced rheological expanded system (ARES). In the temperature range from 10 to 25 degrees C, we have successfully measured the loss tangent (tan delta) at the gel point according to the Winter and Chambon theory, showing the independence of tan delta on the frequency for the cellulose solution. The exponents of the scaling laws eta 0 proportional, variant epsilon-gamma and Ge proportional, variant epsilon z for the cellulose solution at 10 degrees C before and beyond the gel point were confirmed to be in agreement with the predicted values based on the percolation theory. The high sensitivity of the cellulose solution on temperature poses a limit for the application of the scaling law for the wide temperature range. The gel formed from the cellulose solution at 30 degrees C at long storage time could undergo a transition to a transparent liquid state after stirring at -5 degrees C. At the same time, the loss modulus (G' ') exceeds the storage modulus (G'), indicating a partially reversible sol-gel transition, as a result of the reconstruction of the hydrogen-bond networks between the solvent and cellulose.