Poly (vinyl alcohol) (PVA) reacts with borate ions to give a thermoreversible gel. In this work, gel films (PVA-G) were successfully prepared by drying this gel or by soaking PVA films (PVA-O; crosslink-free PVA films) in a solution containing borate ions. On the other hand, the crosslinks formed in PVA-G can be removed by soaking PVA-G in an acid solution. The mechanical properties and structure of PVA-G were investigated by means of dynamic viscoelastic, wide angle X-ray diffraction, hot water resistance and thermogravimetric measurements, and were compared with those of PVA-O.
The results of dynamic viscoelastic measurements show that PVA-G retains a high value in storage modulus up to ca. 200°C which are different from PVA-O. In addition, there appeared a mechanical dispersion around ca. 220°C. Wide angle X-ray diffraction patterns show that the crystallite size of PVA-G is smaller than PVA-O. The characteristic behaviors in viscoelasticity are explained by the presence of crosslinks and/or crystallite size. Hot water resistance of PVA-G was also found to be improved by the introduction of crosslinks.
