Differential Scanning Calorimetric Studies on Chemically Cross-linked Sodium Carboxymethylcellulose Hydrogels.

Carboxymethylcellulose (CMC)-based polyurethane (PU) hydrogels were prepared from the solutions of CMC and hexamethylene diisocyanate (HDI). Water content [W_c = (mass of water) / (mass of dry sample)] of the obtained PU hydrogels was less than 3.0 g g^-1 and NCO/OH ratio was varied from 0.2 to 0.6 mol mol^-1. Phase transition behaviour of CMC-water systems and CMC-PU hydrogels was investigated in the temperature range from - 150 to 80°C by differential scanning calorimetry (DSC). From DSC heating curves, glass transition temperature (T_g), melting peak at low temperature side (T_ml), and melting peak at high temperature side (T_mh) were observed. The T_g minimum value increased with increasing NCO/OH ratio indicating that the molecular motion is restricted by cross-linking. From the enthalpy of melting, it was confirmed that there exist three kinds of water, non-freezing water, freezing bound water and freezing water respectively. [ABSTRACT FROM AUTHOR]