Structure and properties of PVA/PEO hydrogel prepared by freezing/thawing method

Abstract

Poly(vinyl alcohol) (PVA)/poly(ethylene oxide) (PEO) hydrogel with various PVA/PEO compositions was prepared by freezing/thawing method. The effect of PEO content on the structure and property of the gel was investigated. The molecular chains of PEO with relatively high crystalline and molecular weight may limit the movement of PVA chains, resulting in the increase in glass transition temperature ( T g ) of PVA and enhancement of the mechanical properties of PVA hydrogel. With increasing content of PEO, the equilibrium swelling ratio of PVA/PEO hydrogel films increased, resulting in the formation of porous structure with increasing pore size and capillary water absorption capacity. However, the swelling rate constant k decreased, because the formed loose network decreased the osmotic pressure, which weakened the driving force to absorb water. Most of the water in PVA hydrogel was in the form of free water and freezing bound water, and relatively less water was in the form of nonfreezing bound water. With increasing content of PEO, the free water content was remarkably increased and the weight ratio of freezing and nonfreezing bound water to dry gel weight increased, indicating that the interaction between PVA/PEO molecules and water molecules was enhanced.