Enhanced swelling ratio and water retention capacity for novel super-absorbent hydrogel

Super-absorbent hydrogels (SAH) have become the focus of attention due to their broadly applications in many areas like agriculture, wastewater treatment and hygienic products. Swelling ratio (SR), swelling rate and water retention capacity are the three most key parameters for SAHs. However, SR is commonly opposite to water retention capability. High SR usually means poor water retention capacity, and vice versa. High SR over 2000 g/g along with excellent water retention capacity for SAH is rarely reported so far. In this work, a novel SAH achieving high SR over 5500 g/g along with excellent water retention capability is obtained by co-polymerization of AA monomer and AM monomer. Particularly, water retention ratio (WRR) still remains over 60% after keeping the swollen hydrogel sample in the open air for 3 days at 298 K with humidity only around 40%, indicating its' excellent water retention capability. Furthermore, in 0.5–20 wt% urea water solution, SR is also high up to 1790–3210 g/g, implying its' excellent water absorbency in urea solution. Additionally, such SAH sample also shows good water absorbing behavior in salt solution including 0.9 wt% NaCl and 0.9 wt% KCl, and even this SAH sample displays excellent adsorption performance for removing methylene blue (MB) dye with the maximal adsorption capacity of 856 mg/g. This work open a new way to design and develop novel SAH with significantly improved swelling ratio and water retention capability for many potential applications.