Cryostructuring of polymeric systems. 36. Poly(vinyl alcohol) cryogels prepared from solutions of the polymer in water/low-molecular alcohol mixtures

Poly(vinyl alcohol) (PVA) cryogels are formed via freezing–storing frozen–thawing of concentrated solutions of the polymer. In this study the influence of the additives of the first four members of the series of aliphatic low-molecular alcohols to the initial aqueous PVA solution on the physicomechanical and thermal properties of the resulting cryogels has been explored. Addition of increasing amounts of methanol, ethanol and n-propanol were shown to cause a decrease in both the rigidity and the fusion temperature of the respective cryogels, and in the case of n-butanol additives the dependence of gel strength vs. alcohol concentration turned out to be bell-shaped. It was supposed that one of the basic reasons for such ‘deteriorative’ effects was the microcoagulation of PVA caused by growing concentration of the low-molecular alcohol in the unfrozen liquid microphase upon the ice crystallization. This assumption was confirmed in the optical microscopy experiments that revealed the formation of PVA microcoagulation zones entrapped in the macroporous cryogel bulk. Such an effect was previously unknown for PVA cryogels. The morphometric analysis (using specially developed algorithms) of the microscopic images of thin sections of such cryogels showed a sophisticated, without obvious direct correlations, pattern of properties–structure dependencies of such heterogeneous cryogels prepared from the solutions of the polymer in water/low-molecular alcohol mixtures.