STUDY OF THE RHEOLOGICAL PROPERTIES OF HYDROGELS AND CRYOGELS OBTAINED USING THE AQUEOUS SOLUTIONS OF POLYVINYL ALCOHOL

The methods for producing cryogels and hydrogels from viscous aqueous solutions of polyvinyl alcohol (PVA) and their rheological properties are considered. Freezing an aqueous solution of polyvinyl alcohol, its exposure to negative temperature and subsequent thawing at a positive temperature lead to the formation of elastic cryogels. Chemical cross-linking of individual PVA molecules into spatial networks is accompanied by the transformation of aqueous solutions into hydrogels. Sodium tetraborate and glyoxal were used to structurise the polymer solutions. It has been determined that the interaction of these reagents with the functional groups of the polymer causes an increase in the viscosity of three-component systems “PVA - glyoxal - water” and “PVA - sodium tetraborate - water” with time. The kinetics of gel formation in the products of chemical reactions was investigated at different concentrations. It is shown that the viscosity of the studied systems increases with an increase in the concentrations of low-molecular reagents in both cases (PVA - glyoxal and PVA - sodium tetraborate). Hydrogels formed at a positive temperature were subjected to additional freezing-thawing cycle, cryogels were obtained, and their rheological properties were studied. The elastic properties of cryogels were determined to be more clearly pronounced than those of hydrogels. Hydrogels can be used as instantaneous gel-forming systems to protect from dangerous chemicals and to make waterproof barriers in hydraulic structures, as the elastic properties are enhanced after cryogenic exposure.