Investigation of water uptake behavior and mechanical properties of superporous hydrogels

The present study describes the water uptake behavior and mechanical properties of superporous hydrogels prepared through rapid copolymerization of acrylamide and acrylic acid in the presence of NaHCO3 used as porogen. The formation of pores has been confirmed by SEM analysis. The increase in concentration of porogen from 23.8 x 10(-2) mM to 71.4 x 10(-2) mM caused enhancement in the equilibrium water uptake from 1068 +/- 48 to 8087 +/- 112 percent. Likewise, the variation in crosslinker content from 64.8 x 10(-3) mM to 194.5 x 10(-3) mM caused the percent water uptake to decrease from 9237 +/- 123 to 2758 +/- 61 in distilled water. For 9.71 mM of acrylic acid the equilibrium water uptake was found to be maximum (i.e., 10733 +/- 168) and it decreased above and below this optimum value. The gelation time varied appreciably with crosslinker and monomer acid concentrations in the gelation mixture. The water uptake of superporous gel decreased sharply when an equilibrated sample was put in NiCl2 solutions of different concentrations. However, NaCl was not found to be effective in reducing the water uptake. The gels, prepared with different amounts of crosslinker, showed different percent water retention capacity under varying loads. Surprisingly, gels prepared by adding 40 and 60 mg of NaHCO3 (porogen) showed nearly the same retention capacity. The gels swollen in gastric fluid of pH1.2 showed higher values of ultimate compressive strength. However, the gels, swollen in distilled water, had poor mechanical strength. Finally, the porosity, and pore volume were also determined for various samples and their buoyancy test was also performed.