State of water in chitosan–PVA hydrogel

The bound water fraction ( X BW ) of a newly‐ developed pH‐sensitive, biodegradable chitosan‐polyvinyl alcohol (PVA) hydrogel crosslinked with glutaraldehyde (GA) was investigated as a function of the chitosan/PVA molar ratio, GA concentration ( C GA ), and ionization state. Differential scanning calorimetry (DSC) was used to determine the X BW of the initial hydrogel, and of the hydrogel equilibrated in pH 3 and pH 7 buffers. Changes in X BW during swelling and shrinking of hydrogel were also investigated. In the initial state of hydrogel, X BW increased with increasing PVA concentration ( C PVA ), without being significantly affected by C GA . In the buffer‐equilibrated hydrogels, X BW decreased with increasing C PVA and decreasing C GA . The amount of bound water based on dry mass ( C BW ) was substantially higher when the hydrogel was in the ionized (swollen) state compared to its unionized counterpart. This may be due to the association of a large quantity of water molecules with NH 3 + groups of chitosan when the gel swelled in the acidic environment. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3227–3232, 2006