Thermal characterization by DSC and TGA analyses of PVA hydrogels with organic and sodium MMT

Polyvinyl alcohol (PVA) hydrogels were prepared by a cyclic freezing–thawing technique without any cross-linker agent, using PVA and Maghnite water dispersion with different ratios. The obtained results have shown a higher thermal stability of samples with sodium than with alkylammonium Maghnite. Furthermore, thermal stability was maximum at the lowest investigated Maghnite/PVA ratio, but higher than for the pure PVA at all the investigated compositions. DSC analysis has shown both a low crystal degree and a low heat capacity jump at the glass transition temperature for samples with high Maghnite content. This phase does not seem to depend on the kind of cations, sodium or alkylammonium into the gallery of the clay.