Superabsorbent Sulfonated Polyacrylamide/Aluminum Nitrate Hydrogel: Swelling, Mechanical, Thermal and Structural Properties

A hydrogel was prepared with high swelling capacity and a stable three-dimensional structure under environmental conditions. The methodology in this study involved the design and construction of a three-dimensional network for a superabsorbent hydrogel using hydrolyzed sulfonated polyacrylamide as polymer and nonahydrate aluminum nitrate as crosslinker. Further methodology involved data analysis to achieve a hydrogel optimized by response surface methodology. The optimum hydrogel in terms of three responses (i.e., gelation time, syneresis and swelling) was identified by designing a series of experiments. The chemistry and morphology of optimal superabsorbent hydrogel was determined by bottle tests (swelling and syneresis), rheology, energy dispersive spectroscopy (EDS), and thermogravimetric analysis (TGA). The results of this study demonstrated its polymer concentration of 40,000 ppm and crosslinker concentration of 6 wt% for preparation of optimum hydrogel. The syneresis of the optimum hydrogel was more than 180 days and it swelled to 2800-times of its initial dry weight; its elastic modulus was 15240 Pa with thermal stability by 325°C. The highest swelling rate (4000-times of the dry weight) was observed for a hydrogel with a polyacrylamide concentration of 20000 ppm and a weight ratio of 6 wt% of crosslinker to polymer. An undesirable syneresis time of less than 10 days was obtained. Moreover, the main factor in controlling the gelation time and syneresis was the weight ratio of crosslinker to polymer, while for controlling the swelling capacity it was found to be polymer concentration.