Abstract
The thermal properties of the poly(vinyl alcohol) pseudo-gel obtained by freezing have been investigated by differential scanning calorimetry in the temperature range 200–390 K. Determination of the enthalpies of melting and crystallization of the water contained within pseudo-gel allowed the classification of three different states of water viz. non-freezing, restrained and free water. It was also demonstrated by thermogravimetry that the water of pseudo-gel evaporated in three steps in the temperature range 340–420 K. The amount of non-freezing water was found to be constant, while those of restrained and free water were shown to depend on the thermal histories produced during the freezing. The size of ice crystals which formed in the gel was affected by the rate of freezing and it necessarily controlled the number of pseudo-crosslinks formed between poly(vinyl alcohol) molecules. A good relationship was observed between the amount of restrained water and the thermal stability of the gel.
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