Dissolution and Precipitation of Oligomeric Cellulose in Lithium Hydroxide Solutions

The dissolution and precipitation processes for oligomeric cellulose with degree of polymerization 15 in lithium hydroxide/water solution were studied. A phase diagram of dissolution was mapped based on mole ratios between cellulose anhydrous glucose units, lithium hydroxide ions and water. The solution showed lower critical solution temperature (LCST) behavior or precipitation upon heating up to 90°C. The precipitates redissolve after cooling to near 0°C. The LCST behavior and large temperature hysteresis is attributed to hydrogen bond formation between cellulose and hydrated ions. The precipitates from lithium hydroxide were found to be cellulose in the type II crystal form but the intensity ratio between (200) and (110) peaks was reversed, which differs from the precipitates from sodium hydroxide solutions.