Abstract
Heat capacities (Cp) of carboxymethylcellulose (CMC) and CMC-water systems were measured by differential scanning calorimetry (DSC). Molecular weight (Mw) of CMC ranged from 1.7×104 to 3.8×105, and degree of substitution (DS) ranged from 0.6 to 1.7. Cp's of CMC in the dry state were 1.2 to 1.5 J/g·°C in the glassy region, regardless of Mw and DS. Glass transition temperature (Tg) of CMC in the dry state was maintained at around 135°C, regardless of Mw (DS=1.4), and Tg slightly increased with increasing DS. Tg of CMC decreased from ca. 135°C to -85°C on addition of 0.2 to 0.5 (g/g) of water (water content, Wc= mass of water/mass of dry sample). Water molecules in the above systems are categorized into nonfreezing water which is calculated by subtraction of the mass of freezing water from the total mass of water. It was found that Cp's at the glassy state markedly decreased in the presence of nonfreezing water. The minimum Cp value (ca. 0.5-1.4 J/g·°C) was found at around Wc = 0.3. The above facts suggest that CMC molecules take more stable states in the presence of nonfreezing water.
