Viscoelastic and structural properties of poly(vinyl alcohol)/poly(vinylpyrrolidone) hydrogels

Abstract

Physical hydrogels were obtained by freezing/thawing of aqueous solutions of 15% poly(vinyl alcohol) (PVA)/poly(vinylpyrrolidone) (PVP) mixtures with different ratios between the polymers. The rheological behavior was investigated after different numbers of freezing/thawing cycles at 37 °C. An aging effect, which depends on PVP content into the polymer mixture, was evidenced as an increase of the viscoelastic moduli in time. Swelling measurements demonstrated that the hydrogels containing up to 10% PVP show a higher stability in water. Scanning electron microscopy images of the hydrogels reveal a three-dimensional structure with the pores size depending on the ratio between the two polymers. X-ray powder diffraction evidenced that the addition of PVP determines a decrease of the crystallinity of PVA gels obtained by repeated freezing/thawing cycles. Small-angle X-ray scattering measurements indicated that the maximum diameter of the scattering objects reaches a minimum value for 10% PVP in the polymers mixture.