Construction and water absorption capacity of a 3D network-structure starch-g-poly(sodium acrylate)/PVP Semi-Interpenetrating-Network superabsorbent resin

A new semi-interpenetrating network superabsorbent resin (semi-IPN SAR), starch-g-poly (sodium acrylate)/PVP, with a three-dimensional (3D) network structure constructed from a starch-g-poly(sodium acrylate) (starch-g-PNaA) network and linear poly(vinylpyrrololidone) (PVP) was synthesized by a free-radical solution polymerization method in the presence of initiator ammonium persulfate (APS) and crosslinker N,N′-methylene-bis-acrylamide (MBA). The synthesis conditions were systematically investigated. The optimum synthesis mass ratio of PVP, starch, APS, and MBA to AA was 20, 30, 1.25, and 0.15%, respectively, the neutralization degree of acrylic acid was 80%, and the reaction temperature was 60°C. Furthermore, the semi-IPN SAR was characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and three-dimensional X-ray diffraction microscopy (3D-XRDM). FTIR and TGA results agreed that PNaA had been grafted onto the starch macromolecular chains and the starch-g-PNaA network was penetrated by linear PVP polymers by a hydrogen binding action. Moreover, the surface morphology of the resin exhibited apparent wrinkling due to the introduction of PVP. The 3D-XRDM result further proved that the resin was provided with a three-dimensional network structure. The introduction of PVP and the formation of the semi-IPN structure greatly enhanced the water absorbency of the resin. The water and saline absorbency of the optimized material was improved to 2017.8 g/g distilled water and 89.7 g/g NaCl aqueous solution (0.9 wt%), respectively. Furthermore, kinetic analysis agreed that the pseudo-second-order kinetic model was fitted to describe a whole adsorption process, which indicated the adsorption process was not controlled by diffusion steps.