CINÉTICA DE ABSORCIÓN Y TRANSPORTE DEL AGUA EN HIDROGELES SINTETIZADOS A PARTIR DE ACRILAMIDA Y ANHÍDRIDO MALEICO

Transport of water molecules towards the interior of the hydrogels during swelling is of significant importance in different fields of science and engineering, such as medicine, environment and agriculture. By using definitions given by Crank and Karadag et al. the mechanism of water penetration into the interior hydrogels prepared from acrylamide (AAm), maleic anhydride (AnhM) and N,N'methylenebisacrylamide (NNMBA) was studied. It was established that swelling index (H) and initial swelling speed (Vi) of the AAm/AnhM hydrogels with 1% NNMBA increased significantly from 27 to 676 and from 0.0331 to 0.3294 min -1 , respectively, when AnhM content in the initial reaction mixture was increased from 0 to 20%. It is postulated that this occurs due to the increasing presence of -COOH groups provided by the hydrolysis of AnhM. The H measurements as a function of the fraction of -COOH moieties in the different initial polymerization mixtures studied, clearly showed that their incorporation was effective and that the swelling behavior resulting from water/amide groups (-CONH2) interactions in the hydrogel of poly (AAm) deviates from the observed trend on the hydrogels of poly (AAm-co-AnhM), where the water/amide groups (-CONH2) and water/carboxyl groups (-COOH) interactions take place simultaneously. Obtained experimental values of the diffusional exponent (n) are above 0.5, implicating, according to Fick's second law, that water transport mechanism exhibits an anomalous behavior which emerge from the contribution of two concurrent processes: a diffusional process simultaneously accompanied by the viscoelastic relaxation of the polymer chains. Additionally, for these systems it was demonstrated by using the combined equation of Peppas and Sahlin that water diffusional process contributes predominantly upon the relaxation process of the polymer chains in the early stages of swelling.