Effect of the degree of saponification on the rheological and thermal properties of poly(vinyl alcohol) gels

The rheological and thermal properties of poly(vinyl alcohol) (PVA) gels prepared through freezing‐thawing cycles were studied, in order to clarify the relation between structure and functional properties. The breaking strength of PVA gels increases with increasing the degree of saponification (DS), i.e. the degree of deacetylation, while the breaking deformation decreases. The endothermic differential scanning calorimetry (DSC) peak accompanying the transition from gel to sol shifts to higher temperatures with increasing concentration and DS. The endothermic enthalpy as a function of concentration increases gradually up to 25 wt.‐%, then it increases rapidly for PVA with DS = 96,0,97,5 and 98,5 mol‐%. A sharp diffraction peak is observed in the X‐ray pattern for PVA gels with DS = 99,9 mol‐% but not for PVA gels with DS = 96,0 mol‐%. All results from rheology, DSC and X‐ray analysis show that only a slight increase in DS from 96,0 mol‐% to 97,5 mol‐% promotes the formation of ordered regions in PVA remarkably.