Changing essential characteristics of Poly(vinylalcohol) cryogels by thermal treatments.

JIMENA SOLEDAD GONZALEZ; VERA ALEJANDRA ALVAREZ

Congreso; European Polymer Congress EPF2011, And XII Congress Of The Specialized Group Of Polymers GEP; 2011

The crosslinking method, based onfreeze and then thaw (F/T) solution of Poly vinylalcohol (PVA) several times, results in the formation ofcrystallites that serve as physical crosslinks making athree-dimensional network  that become thematerial insoluble in water. PVA molecules areaggregated during ice formation and hydrogen bondingis established between molecular chains. By increasethe number of F/T cycles, residual free molecular chainsare successively included in linking zones. On theother hand, the glass transition temperature (Tg) of thesekind of materials sharply decreases with the watercontent.Heat treatments above the Tg  as well as repeatedF/T cycles, are also used to achieve the same resultsmainly by increasing the amount of crystals of thepolymer, which act as a physical crosslinkers of thenetwork. When PVA films are annealed at constanttemperature (between Tg and the melting temperature;Tm), the macromolecular chains have enough mobilityto align themselves and fold to form crystals. It iswell known that the increasing in the polymercrystallinity degree (Xcr), results in a more resistantmaterial .The aim of this work was to investigate the effect of theannealing temperature over the structural and swellingcharacteristics of the PVA hydrogels obtained by F/Ttechnique.