Novel approach to highly porous superabsorbent hydrogels: synergistic effect of porogens on porosity and swelling rate

Abstract

Abstract A novel practical strategy for preparing highly porous superabsorbent hydrogels (HPSHs) was invented. HPSHs were quantitatively prepared through an optimized rapid convenient solution polymerization of partially neutralized acrylic acid in the presence of a crosslinking agent under normal atmospheric conditions. Acetone and sodium bicarbonate were used as porosity generators (porogens) during the polymerization process to create highly porous structures. Time and sequence of addition of the porogens, as well as the gelation time of the polymerization, were recognized to affect the efficiency of the porogens. Sodium bicarbonate produced the more porous hydrogels with a higher rate of swelling. In comparison with a hydrogel prepared under porogen‐free conditions (control), acetone and sodium bicarbonate enhanced the swelling rate as high as 43–55% and 111–131% of the control, respectively. When both the porogens were used consecutively in the process, a remarkable synergistic effect was observed in the swelling rate of the products. Nearly all the two‐porogen processes resulted in foamy products from the polymerization system. With the single‐porogen systems, however, the foam formation stage was observed only in a part of the total process time. The apparent volume of the as‐synthesized foamy products prepared from the two‐porogen system was more than that of the single‐porogen systems by up to fourfolds. Morphological studies using scanning electron microscopy (SEM) showed that the two‐porogen systems created highly porous structures. The density of all the HPSHs synthesized was about 1.5 g cm −3 and no distinct differences were observed in their equilibrium swelling. These superabsorbent hydrogels exhibited a very high rate of swelling, so that their swelling time was measured to be less than one minute. Copyright © 2003 Society of Chemical Industry