A Study of Cryostructuring of Polymer Systems. 59. Effect of Cryogenic Treatment of Preliminarily Deformed Poly(vinyl alcohol) Cryogels on Their Physicochemical Properties

The influence of repeated cryogenic treatment (-20 degrees C for 12 h followed by defrosting at a heating rate of 0.03 degrees C/min) on poly(vinyl alcohol) cryogel (PVACG) samples occurring in a forcedly deformed state (bending, compression, torsion) has been investigated. It has been shown that this action on primary PVACG may be characterized as the secondary molding process, because the cryogel acquires and, further, retains a new geometric shape resultant from deformation. Therewith, the higher the deforming mechanical load, in particular compression force, the higher the rigidity of PVACG resulting from the secondary molding. The study of such cryogels by DSC and wide-angle X-ray scattering has revealed that the secondary molding increases the ordering of the structure of PVA microcrystallites, which have already being present in the nodes of the physical networks of primary cryogels and leads to the appearance of additional zones of microcrystallinity. On the whole, these formations fix the new geometry of the secondary PVACG samples.