Interpenetrating polymer network (IPN) hydrogels composed of poly(vinyl alcohol) (PVA) and chitosan were prepared by UV irradiation. The characteristics of IPN hydrogels were investigated by swelling experiments, Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). IPN hydrogels exhibited a relatively high swelling ratio in the range of 210-350% at 35 degreesC. The swelling ratio of PVA/chitosan IPN hydrogels depended on pH and temperature. DSC was used for the quantitative determination of the amounts of freezing and non-freezing water. Free water contents in IPN1, IPN2 and IPN3 were 62.0, 69.6 and 72.3% in pure water, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.