A Study of Cryostructuring of Polymer Systems. 51. The Combined Influence of Porous Cellulose-Containing Dispersed Fillers and Salting-Out Electrolytes on the Physicochemical Properties of Composite Poly(vinyl alcohol) Cryogels

Abstract

Composite poly(vinyl alcohol) (PVA) cryogels comprising dispersed porous cellulose-containing fillers (microcrystalline cellulose, wood sawdust) and salting-out electrolytes (Na2SO4, NaF) have been prepared by freezing at –20°C, incubation in the frozen state for 12 h, and defrosting at a rate of 0.03°C/min. The influence of the chemical nature and concentration of the soluble additives and fillers on the rheological behavior of initial suspensions, as well as the morphology of macropores and physicochemical and thermophysical properties of corresponding composite cryogels, has been studied. Viscometric studies have shown that, because of the salting-out action of the electrolytes, the viscosity of PVA solutions decreases due to the compaction of macromolecular coils. However, in the case of filler suspensions, the viscosity increases owing to the enhancement of the adhesion interactions between the discrete and continuous phases, thereby affecting the rigidity and heat endurance of filled cryogels resulting from the freezing–defrosting of such suspensions. The most pronounced increase in the compression elasticity modulus and heat endurance of the composites takes place upon the combined incorporation of a porous filler and a salting-out electrolyte into the cryogel matrix. The microstructure of both unfilled and filled cryogels has been studied by scanning electron microscopy. Substantial changes have been revealed in the macroporous morphology of these objects upon the incorporation of a porous dispersed cellulose-containing filler or a salting-out electrolyte separately and, especially, upon their combined incorporation into the matrix of the PVA cryogel.