Salt effects on formation of microcrystallites in poly(vinyl alcohol) gels prepared by cast-drying method

The preparation method of poly(vinyl alcohol) (PVA) gels by a simple cast-drying technique using salt solutions was reported in the present investigation. The effects of the salt concentration on the macro- and microscopic properties were examined in detail, and the relationships between macroscopic properties, such as swelling ratio, mechanical strength, and the network microstructure were presented. It was found that the swelling ratio of PVA cast gel increased largely by adding a small amount of salt, and decreased rapidly, hereafter it increased with increasing the salt concentration above 2% (mass fraction). The changes in the breaking stress and strain corresponded to the changes in the swelling ratio. The macroscopic properties were found to be correlated with the microcrystallites and hydrogen bonds, which were characterized by the measurements using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR).