A simple method to obtain a physically crosslinked poly(vinyl alcohol) (PVA) hydrogel is reported. In this technique, the PVA solution in pure water was simply cast at room temperature without using any additional chemical. The gelation proceeded during the dehydration after casting the PVA solution into a mold. After the completion of gelation, the swelling ratio of the gel in its equilibrium was measured whenever the solvent water was repeatedly exchanged. The weight gradually decreased due to the elution of non-crosslinked polymers into the solvent, and became constant after sufficient water exchange. The measurements using a Fourier Transform infrared spectroscopy and an X-ray diffraction suggested that the crosslinks due to hydrogen bonds and microcrystals were formed during the dehydration process of the PVA solution. We concluded that the sample obtained by the present method is a physically crosslinked polymer network, insoluble in water, i.e., a swollen gel in water.

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Poly(vinyl alcohol) cast gels (PVA cast gels) were prepared at different gelation temperatures, T gel , and the swelling ratio and mechanical properties were characterized by the equilibrium weight measurement, a uniaxial loading test, a tearing force measurement, and a cyclic compression test at room temperature. The results showed that the swelling ratio decreased and both the breaking stress and the tearing energy increased with an increase in T gel . The compression deformation energy of 50% reduction of its original size increased monotonically, while the hysteresis loss was not affected by T gel . To understand these macroscopic properties, the network structures of the samples were examined by X-ray diffraction and Fourier transform infrared measurements. As a result, the size of the microcrystallites increased with an increase in T gel and the average distance between the microcrystallites also increased. These results suggested that the structures of PVA networks, crosslinked by the microcrystallites, have essential roles in determining the mechanical properties of PVA cast gels. The macroscopic mechanical properties are discussed on the basis of the size, number, and distribution of microcrystallites as crosslinkers and the homogeneity of amorphous PVA networks, which were determined at gelation. Experimental procedure Sample preparationPVA powder was kindly supplied by Kuraray Co., Ltd. (cat. no. PVA117), and was used without further purification. The

We report the swelling behavior of chemically crosslinked polyvinyl alcohol (PVA) gels with different degrees of hydrolysis in water, several organic solvents, and their mixed solvents. The gels were dried after gelation and were put into their respective solvents. The gel volume in pure water decreased with increasing temperatures, and the total changes increased with decreasing degrees of hydrolysis. The swelling ratio depends on the solvent and its concentration. In the cases of mixed solvents of methanol–water, ethanol–water, and acetone–water, the gels shrank continuously with increasing concentrations of solvents and reached the collapsed state in the pure organic solvent. In the case of dimethyl sulfoxide (DMSO), on the other hand, the gels shrunk, swelled, and finally reached the swollen state in pure DMSO. Results of measurements using Fourier Transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) suggested that crosslinks and microcrystallites were formed due to hydrogen bonds during the drying process after gelation. The hydrogen bonds were partly destroyed in a rich solvent, but the residual hydrogen bonds had an essential role in determining the swelling behavior in a poor solvent. The swelling behavior and the possible phase transition of the present system are discussed in terms of the solubility of polymers with different degrees of hydrolysis in given mixed solvents and in terms of the formation and destruction of physical crosslinks in the chemical PVA gels. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1978–1986, 2010

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We report the swelling ratio and network structure of a poly(vinyl alcohol) (PVA) gel chemically crosslinked by glutaraldehyde with different degrees of crosslinks. Microcrystallites were formed in a chemical PVA gel during a drying process and were confirmed by X-Ray diffraction (XRD) measurements and Fourier transform infrared (FTIR) spectroscopy. The formation of microcrystallites in the dried gels was suppressed by increasing the degrees of chemical crosslinks. When the dried samples were immersed in pure water at 25 C, the swelling ratio depended on the degree of chemical crosslinks resulting from the destruction of physical crosslinks by microcrystallites. On the other hand, when the dried samples were immersed in a poor solvent of a mixture of dimethyl sulfoxide and water at 8 C, the gels did not swell and stayed in the collapsed state. Starting from the collapsed state, the equilibrium swelling ratios were measured while the temperature was increased to 90 C and then decreased to 8 C. As a result, irreversible swelling behaviors were observed for all gels with different degrees of crosslinks, which were attributed to the destruction of microcrystallites. The swelling behavior is discussed in terms of the formation and destruction of additional physical crosslinks in the chemical PVA gels. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: [96][97][98][99][100][101][102] 2011