Characterization of the water state of hyaluronic acid and poly(vinyl alcohol) interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of hyaluronic acid and poly(vinyl alcohol) hydrogels were prepared, and the influence of water and the drying kinetics were investigated. The IPN hydrogels were characterized with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The glass-transition temperatures of the IPN hydrogels decreased with increasing water content. The bound water was the sum of the nonfreezing bound water and freezing bound water. From the DSC melting curves, the values of the total water and freezing bound water were evaluated for IPN hydrogels containing large amounts of water. At the same time, the bound water value was estimated with TGA. In the TGA curves, one-step and two-step weight losses, corresponding to free water and nonfreezing bound water, were observed. The bound water of the hydrophilic polymers broke the hydrogen bonding between the hydroxyl groups of the polymers. The swollen IPN hydrogels exhibited relatively high bound water contents (43.04-59.17%) by DSC and TGA. The bound water contents of the dry IPN hydrogel films were 10.2-15.29% by TGA. The drying reaction rate constant of the IPN hydrogel increased with increasing temperature. (C) 2004 Wiley Periodicals, Inc.