Salt‐Resistant Superabsorbent Resin via Nonionic ACMO Comonomer Strategy: Synthesis and Performance

ACMO‐co‐AHPS superabsorbent resin was synthesized with acryloylmorpholine (ACMO) as nonionic monomer and 3‐allyloxy‐2‐hydroxy‐1‐propanesulfonic acid sodium salt (AHPS) as ionic monomer in aqueous solution by using potassium persulfate (KPS) as an initiator, and N‐N′ ‐methylene bis(acrylamide) (MBA) as a cross‐linking agent. FTIR confirmed that the synthesized product was the target compound. TGA demonstrated the excellent thermal stability of the resin, and it can be used at temperatures up to 300 °C. SEM revealed that the surface morphology of the superabsorbent resin presented the uneven and wavy structure with increased surface area, which is conducive to the infiltration of water molecules into the gel matrix. Reaction variables were systematically optimized using nine sets of orthogonal experiments to obtain superabsorbent resin with high swelling capacity, and the optimized conditions for the synthesized superabsorbent resin monomer molar ratio 1.95:1, reaction temperature 70 °C, initiator concentration 3.0 × 10 −3 mol/0.1 L and cross‐linking agent concentration 1.3 × 10 −3 mol/0.1 L, meanwhile, the maximum water absorbency was 319 ± 3 g/g in distilled water. The ACMO‐co‐AHPS resin maintained high water absorbency (>21 g/g) in saline solutions (up to 10 wt% NaCl, 5 wt% CaCl 2 /FeCl 3 ), demonstrating significantly improved salt resistance compared to conventional ionic SAPs. This is attributed to the nonionic ACMO monomer, which reduces the Donnan equilibrium effect by diluting the charge density of the polymer network. ACMO‐AHPS resin retains >65% of its distilled‐water absorbency in concentrated saline solutions (up to 10 wt% NaCl, 5 wt% CaCl 2 /FeCl 3 ). Its salt resistance stems from the non‐ionic ACMO mitigating charge screening and the robust hydration of sulfonate groups.