Sodium tungstate as green cross-linker to improve water absorbency of superabsorbent polymer

Superabsorbent polymers (SAPs) are attracting more research interests in many fields mainly due to its distinguished water-absorbing performance. Among all the factors that severely affecting water absorption of SAPs, cross-linkers play a non-negligible role in shaping the stable cross-linked networks of SAPs. As for cross-linking agents, previous studies have focused on the chemical cross-linker as well as functional nanoparticle cross-linker. Though their corresponding SAPs can achieve high water uptake capacity, the sustainable development of such SAPs was still limited by the natural defects of these cross-linkers. Herein, we reported small-molecule sodium tungstate (STD) as one novel cross-linker to optimize water-holding capabilities of SAPs. STD shows a high affinity to polymeric chains mainly via multiple hydrogen bonding interactions. The resultant poly(acrylic acid)/STD SAP exhibited a satisfactory water-absorbing capacities with swelling ratios of 7527 g/g in distilled water, 95 g/g in 0.9 wt% NaCl solution and 2210 g/g in 3 wt% urea solution, respectively. In addition, such high water absorbency was achieved within SAP system just made up of a sole polymer and a sole cross-linker, implying that STD can be used as novel cross-linker to promote the green development of SAPs.