Preparation and characterization of superabsorbent polymers (SAPs) surface-crosslinked with polycations

Abstract

For the application of superabsorbent polymer (SAP) particles in personal hygiene products such as disposable diapers, the SAP surface is additionally crosslinked to minimize gel blocking and enhance absorbency under external pressure. Physically surface-crosslinked poly(acrylic acid)(PAA)-based SAP microspheres were prepared using polycations (branched polyethylene imine (bPEI) and polyamidoamine (PAMAM)). Compared with chemical crosslinking, which requires a high temperature and prolonged reaction, physical crosslinking via electrostatic interaction between the polycations and negatively charged PAA chains was achieved within 20 min at room temperature. The polycation-crosslinked SAP particles had a rougher surface and lower water absorption capacity. The thickness of the physically crosslinked surface, visualized using fluorescence labeled polycations, increased with increasing polycation concentration and reaction time, eventually reaching saturation. PAMAM produced mechanically stronger and thicker surface-crosslinking than bPEI, owing to its lower molecular weight. Micro-CT analysis of the collective swelling behavior of a gel bed packed with the SAP particles confirmed that the shapes of the SAP particles crosslinked with polycations were better maintained during swelling and there was a greater void fraction in the packed gel bed than with the use of bare SAP particles, which might minimize gel blocking and improve the permeability of fluid through gel bed.