Interaction between -OH groups of methylcellulose and solvent in NaOH/urea aqueous system at low temperature

To clarify the interaction between the -OH groups of cellulose and NaOH/urea in aqueous solutions, methylcellulose (MC) was used as solute to study its solution properties at low temperature. Dynamic light scattering, C-13 NMR spectroscopy, differential scanning calorimetry, and transmission electron microscopy (TEM) were used to characterize the MC macromolecular size and intermolecular interactions between MC and solvent molecules. The results revealed that MC existed mainly as individual molecules in the NaOH/urea aqueous solution prepared by freeze-thawing process, whereas aggregates occurred in the MC solution prepared at room temperature. DLS further confirmed that MC existed mainly as individual flexible chains in the solution treated at low temperature. TEM images showed the sphere-like coil appearance of the MC macromolecules in the solution prepared at low temperature. Therefore, the strong interaction between -OH groups of MC and solvent occurred at low temperature, leading to the formation of the imperfect inclusion complex through hydrogen bonding network between MC, NaOH, urea and water.