EFFECT OF CHEMICAL CROSS-LINKING UNDER ELONGATION ON SHAPE RESTORING OF POLY(VINYL ALCOHOL) HYDROGEL

An anisotropically swollen hydrogel of poly(vinyl alcohol) (PVA) was found to be able to restore an isotropic physical shape by restoring isotropic physical cross-links induced by anisotropically distributed chemical cross-links. The anisotropic chemical cross-links were introduced in the isotropic physical gel by cross-linking with glutaraldehyde under elongation. The physical gel was made from the PVA aqueous solution by repetitive freezing and thawing. The chemically cross-linked gel had kept its original shape and physical properties despite the chemical treatment under strain. However, by the heat treatment in boiling water, the gel changed its form anisotropically depending on the strain applied in the chemical treatment. The anisotropically swollen gel was deswollen in methanol and then reswollen in water. The reswollen gel took back its original isotropic shape, suggesting that the anisotropic chemical cross-links thus introduced in the gel have a memory effect on the restoration of isotropic physical cross-links.