Hydraulic permeability of water in poly(vinyl alcohol) membranes as a function of the degree of hydration

Poly(vinyl alcohol) membranes were prepared by solution cast and subsequent annealing. The degree of crystallinity of the membranes at the dry state was not affected by the annealing, whereas the degree of hydration H was markedly changed. This made us assume a double network structure. Hydraulic permeability of water, K w , in PVA membranes was measured to discuss the relation between H and the permeability. K w increased with increasing H with increasing slope. The linear relation between the reduced permeability K w / H and 1/ H , expected from a free volume theory, was not obtained in the PVA membranes. This nonlinearity of the relation was confirmed also in various hydrogels reported by other authors. We found that a linear relation between H and logarithm of K w / H , as expected from the Ogston's relation, is achieved in PVA and many other hydrogel membranes with H from 0.4 to 0.9. Under a given degree of hydration, the activation energy of permeation of PVA membrane was larger than that of cellulose, owing to the large amount of bound water in PVA membrane.