Improvement in the water-absorbing properties of superabsorbent polymers (acrylic acid-co-acrylamide) in supercritical CO2

Superabsorbent resins prepared by ultraviolet radiation-inducing polymerization techniques with acrylic acid/acrylamide were treated with supercritical carbon dioxide (SC-CO2). The water-absorbing properties of the treated resins were greatly improved. The water-absorbing properties of resins treated with SC-CO2 in the pressure range of 10-35 MPa and the temperature range of 40-60degreesC were studied. The effects of the treatment time and depressurizing speed of CO2 after treatment were also examined. Obviously, different results were found for particles of different sizes. Smaller particles were more efficient under the same treatment conditions. Samples were tested with differential scanning calorimetry. The results showed that the plasticizing effect of CO2 reduced the glass-transition temperature of the polymer, and it was proposed that the plasticization effect might have led to polymer chain redistribution and better flexibility. Minor changes in the surface morphology of the particles were observed with scanning electron microscopy. The extraction of the unpolymerized monomers by SC-CO2 was also studied. (C) 2002 Wiley Periodicals, Inc.