POLY(VINYL ALCOHOL)-POLY(SODIUM ACRYLATE) COMPOSITE HYDROGELS .1. KINETICS OF SWELLING AND DEHYDRATION

摘要

Incorporation of sodium polyacrylate (NaPAA) in poly(vinyl alcohol) (PVA) gels as small, uniformly distributed precipitates greatly accelerates their volume expansion during swelling in water to form hydrogels. In addition to the usual water absorption, the swelling process includes dissolution of the precipitates that leads to a locally high osmotic pressure that in turn causes a further increase in water penetration and volume expansion. During swelling, soluble NaPAA is released into the water phase with a high initial release rate that then decreases continuously. The release can be described by an exponential decay function with a power dependent rate coefficient. Because the diffusion of NaPAA through the PVA walls is too slow to account for this release rate, a morphology of a closed cell foamlike structure with interconnecting channels is proposed. An aqueous solution of NaPAA seems to diffuse out of the hydrogel through these channels. (C) 1995 John Wiley & Sons, Inc. [References: 23]