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Superabsorbent polymers are hydrophilic networks that can absorb and retain huge amounts of water or aqueous solutions. They are currently used in many areas including hygienic and bio-related uses (particularly in disposable diapers), agricultural uses (e.g., water reserving in soil, soil conditioning, and controlled release of agrochemicals), pharmaceutical dosage forms, separation technology, fibers/textiles, waterswelling rubbers, soft actuators/valves, electrical, construction, packaging, artificial snow, sludge/coal dewatering, fire-extinguishing gels, etc. Addition of clays and organo-modified clays into superabsorbent formulation has funded new generations of these hydrogels, i.e., superabsorbent hydrogel composites (SHCs) and superabsorbent hydrogel nanocomposites (SHNCs). New superabsorbent hydrogels are cheaper in price, and possess superior mechanical properties than non-composite counterparts. This review introduces the SHC and SHNC polymers with the focus on different minerals and humic additives, synthetic methods, the hydrogel characteristics and their applications. POLYM. COMPOS., 32:277-289, 2011. ª

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Summary: Novel porous hydrogel composites with very high swelling capacity and enhanced rate of water absorption were synthesized in aqueous media at room temperature under normal atmospheric conditions. The porosity was induced through either foaming conducted in the course of polymerization or non‐solvent dewatering of the as‐synthesized gels. Kaolin was incorporated as an inorganic component in the polymerization process. The foaming technique was used to form porosity using three systems of different porogens (porosity generators), i.e. sodium bicarbonate, acetone and their combination. The as‐synthesized gels were dried through oven drying and non‐solvent dewatering. Morphology and swelling rate of the superabsorbent hydrogel composites (SHCs) were studied versus either the porogen system or the drying method. It was found that the simultaneous polymerization‐foaming technique had great influence on the improvement of porosity, morphology of the porous structure and the rate of water absorption. It was also shown that the drying procedure had remarkable influence on preserving the preformed porosity. Methanol as a dewatering solvent produced SHCs with higher porosity and swelling rate in comparison with the porosity of the hydrogels dewatered in acetone. Our invented methodology including simultaneous polymerization and foam formation using dual‐porogen system and the subsequent methanol‐dewatering approach was found to be the most efficient, highly practical, and cost‐effective route for preparing improved superabsorbing hydrogel materials.

A new cost‐effective approach to enhance gel strength of superabsorbent hydrogels was invented. Superabsorbent hydrogel composites (SHCs) were prepared through an optimized rapid solution polymerization of concentrated partially neutralized acrylic acid in the presence of a crosslinking agent under normal atmospheric conditions. Kaolin was used as an inorganic component in the polymerization process to strengthen the hydrogel products. FT‐IR spectroscopy was used to confirm grafting of acrylic chains on to the surface of kaolin particles. Morphology of the products was studied by scanning electron microscopy (SEM). Compared with the kaolin‐free hydrogel (control), kaolin caused a reduced equilibrium swelling and swelling rate as low as 17–31% and 19–29%, respectively. Kaolin, however, resulted in enhanced gel strength as high as 21–35% compared to the control. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study thermal properties of the composites. The SHCs exhibited higher thermal stability than the control. Meanwhile, changes in certain thermal transitions reconfirmed the chemical interaction of the acrylic chain with kaolin. These thermostabilized strengthened superabsorbent hydrogels may be considered as good candidates for agricultural application to retain more water under soil pressure. Copyright © 2003 John Wiley & Sons, Ltd.

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