Rheological and DSC changes in poly(vinyl alcohol) gels induced by immersion in water

Abstract

Abstract Poly(vinyl alcohol) (PVA) gels were prepared by freezing and thawing aqueous solutions at temperatures from −20 to 15°C. The temperature was varied periodically by use of a computer. The endothermic DSC peak was observed for the PVA gels at about 60°C for five specimens of different degrees of saponification (DS). Another endothermic peak was also observed in the range 67–80°C, and this peak shifted to higher temperature with increasing DS. These endothermic peaks shifted to lower temperature on immersion of the PVA gels in water. The dynamic Young's modulus E ′ at room temperature was also decreased by immersion of PVA gels in water; E ′ decreased monotonically with increasing temperature for PVA gels without immersion in water, while it increased up to a certain temperature and then decreased with increasing temperature for PVA gels in water. The X‐ray diffraction showed a characteristic crystalline pattern for PVA gels of higher DS, and this peak was intensified by stretching the gel.