Influences of Intramolecular Cyclization on Structure and Cross-Linking Reaction Processes of PVA Hydrogels

Abstract

Poly(vinyl alcohol) (PVA) hydrogels were prepared in aqueous solutions at different concentrations using glutaraldehyde (GA) as cross-linker. The gel fraction, increase rate of gels, critical gel point, and swelling ratio were measured. Furthermore, the influences of intramolecular cyclization on the cross-linking processes and the structure of formed hydrogels were studied. The results show that the degree of intramolecular cyclization and the ratio of [−CHO]/[−OH] at critical gel point (rc) increase with the decrease of PVA concentration. The bulk gels do not form when PVA concentration is below 1.1 × 10-2 g/mL even at higher GA/PVA mixture ratio. In the concentration range of (2.20−12.3) × 10-2 g/mL, intramolecular cyclization fraction is basically not changed with gel fraction above the critical gel point. The way of gel growing is controlled by PVA concentration. In a certain range, the lower the PVA concentration is, the higher the increase rate of gels is. The equilibrium swelling ratio decreases with increasing PVA concentration. The structure of PVA hydrogels can be adjusted by changing the cross-linker or polymer concentrations.