On the viscoelastic properties of poly(vinyl alcohol) and chemically crosslinked poly(vinyl alcohol)

Poly(vinyl alcohol)(PVA) films chemically crosslinked with glutaraldehyde(G A) in the presence of HCl were prepared by casting from aqueous solutions. The PVA and PVA gels were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis ( DMA); their swelling characteristics and tensile strength were also determi ned. The DSC results for the gels displayed depressions of the melting and crystallization temperatures, as well as a decrease of the heat of fusion, when compared to those of PVA free of crosslinker. The DMA analysis reveale d that: (1) The glass transition temperature of the wet PVA was lower than that of the dry one, indicating that the water had a plasticizing effect. ( 2) The gels had a lower glass transition temperature than PVA. (3) The glas s transition temperature of the wet gels increased with increasing crosslin k density. Possible explanations are provided for these observations. Where as the thermogravimetric curves of PVA exhibited a single degradation peak, two degradation peaks were detected for the crosslinked PVA. The wet PVA a nd PVA gels displayed lower tensile strengths and higher elongations than t he dried ones. (C) 2001 John Wiley & Sons, Inc.