Synthesis and swelling properties of pH-sensitive semi-IPN superabsorbent hydrogels based on sodium alginate-g-poly(sodium acrylate) and polyvinylpyrrolidone

A pH-sensitive semi-interpenetrating polymer network (semi-IPN) superabsorbent hydrogel composed of sodium alginate-g-poly(sodium acrylate) (NaAlg-g-PNaA) network and linear polyvinylpyrrolidone (PVP) was prepared by free-radical solution polymerization in the presence of initiator ammonium persulfate (APS) and crosslinker N,N-methylene-bis-acrylamide (MBA). FTIR results revealed that PNaA had been grafted onto NaAlg macromolecular chains and PVP was penetrated throughout the NaAlg-g-PNaA network by a hydrogen binding action. The surface morphologies of the hydrogels were improved due to the incorporation of PVP as shown by SEM observation. The introduction of PVP and the formation of semi-IPN structure greatly improved the water absorption and swelling rate of the hydrogel. The hydrogel possesses remarkable sensitivity to external pH stimulus and shows reversible On–Off switching swelling characteristic. An intriguing time-dependent swelling behavior of the semi-IPN hydrogel was observed in multi-valence saline and cationic surfactant solutions, but the similar time-dependent behaviors are resulting from two distinct mechanisms.