Structure of Cellulose−Soda Solutions at Low Temperatures

Calorimetry, small-angle X-ray scattering, and viscometry were used to study the structure of NaOH−water and cellulose−NaOH−water solutions in the range of 0−20% NaOH and 0−5% cellulose concentrations in the low-temperature region of −60 to 0 °C. Pure NaOH−water solutions show a pseudoeutectic behavior with three phases: free water that crystallizes and melts at a certain melting temperature which decreases with the increase of NaOH concentration; a NaOH hydrate that melts at −35 °C; water bound to hydrates that does not crystallize. The addition of cellulose does not change the amount of the free water. The cellulose chains are located in the hydrate region, one to two hydroxyl groups of the glucopyranose unit being bound to a soda hydrate.